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Laurencin C, Lancelot S, Merida I, Costes N, Redouté J, Le Bars D, Boulinguez P, Ballanger B. Distribution of α 2-Adrenergic Receptors in the Living Human Brain Using [ 11C]yohimbine PET. Biomolecules 2023; 13:biom13050843. [PMID: 37238713 DOI: 10.3390/biom13050843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Revised: 05/12/2023] [Accepted: 05/12/2023] [Indexed: 05/28/2023] Open
Abstract
The neurofunctional basis of the noradrenergic (NA) system and its associated disorders is still very incomplete because in vivo imaging tools in humans have been missing up to now. Here, for the first time, we use [11C]yohimbine in a large sample of subjects (46 healthy volunteers, 23 females, 23 males; aged 20-50) to perform direct quantification of regional alpha 2 adrenergic receptors' (α2-ARs) availability in the living human brain. The global map shows the highest [11C]yohimbine binding in the hippocampus, the occipital lobe, the cingulate gyrus, and the frontal lobe. Moderate binding was found in the parietal lobe, thalamus, parahippocampus, insula, and temporal lobe. Low levels of binding were found in the basal ganglia, the amygdala, the cerebellum, and the raphe nucleus. Parcellation of the brain into anatomical subregions revealed important variations in [11C]yohimbine binding within most structures. Strong heterogeneity was found in the occipital lobe, the frontal lobe, and the basal ganglia, with substantial gender effects. Mapping the distribution of α2-ARs in the living human brain may prove useful not only for understanding the role of the NA system in many brain functions, but also for understanding neurodegenerative diseases in which altered NA transmission with specific loss of α2-ARs is suspected.
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Affiliation(s)
- Chloé Laurencin
- Université de Lyon, 69622 Lyon, France
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France
- INSERM U1028, Lyon Neuroscience Research Center (CRNL), 69000 Lyon, France
- CNRS UMR5292, Lyon Neuroscience Research Center (CRNL), 69000 Lyon, France
- Hôpital Neurologique Pierre Wertheimer, Service de Neurologie C, Centre Expert Parkinson, Hospices Civils de Lyon, 69677 Bron, France
| | - Sophie Lancelot
- Université de Lyon, 69622 Lyon, France
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France
- INSERM U1028, Lyon Neuroscience Research Center (CRNL), 69000 Lyon, France
- CNRS UMR5292, Lyon Neuroscience Research Center (CRNL), 69000 Lyon, France
- CERMEP-Imagerie du Vivant, 69500 Bron, France
- Hospices Civils de Lyon, 69677 Bron, France
| | - Inès Merida
- CERMEP-Imagerie du Vivant, 69500 Bron, France
| | | | | | - Didier Le Bars
- CERMEP-Imagerie du Vivant, 69500 Bron, France
- Hospices Civils de Lyon, 69677 Bron, France
| | - Philippe Boulinguez
- Université de Lyon, 69622 Lyon, France
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France
- INSERM U1028, Lyon Neuroscience Research Center (CRNL), 69000 Lyon, France
- CNRS UMR5292, Lyon Neuroscience Research Center (CRNL), 69000 Lyon, France
| | - Bénédicte Ballanger
- Université de Lyon, 69622 Lyon, France
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France
- INSERM U1028, Lyon Neuroscience Research Center (CRNL), 69000 Lyon, France
- CNRS UMR5292, Lyon Neuroscience Research Center (CRNL), 69000 Lyon, France
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Harada R, Furumoto S, Kudo Y, Yanai K, Villemagne VL, Okamura N. Imaging of Reactive Astrogliosis by Positron Emission Tomography. Front Neurosci 2022; 16:807435. [PMID: 35210989 PMCID: PMC8862631 DOI: 10.3389/fnins.2022.807435] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 01/14/2022] [Indexed: 11/13/2022] Open
Abstract
Many neurodegenerative diseases are neuropathologically characterized by neuronal loss, gliosis, and the deposition of misfolded proteins such as β-amyloid (Aβ) plaques and tau tangles in Alzheimer’s disease (AD). In postmortem AD brains, reactive astrocytes and activated microglia are observed surrounding Aβ plaques and tau tangles. These activated glial cells secrete pro-inflammatory cytokines and reactive oxygen species, which may contribute to neurodegeneration. Therefore, in vivo imaging of glial response by positron emission tomography (PET) combined with Aβ and tau PET would provide new insights to better understand the disease process, as well as aid in the differential diagnosis, and monitoring glial response disease-specific therapeutics. There are two promising targets proposed for imaging reactive astrogliosis: monoamine oxidase-B (MAO-B) and imidazoline2 binding site (I2BS), which are predominantly expressed in the mitochondrial membranes of astrocytes and are upregulated in various neurodegenerative conditions. PET tracers targeting these two MAO-B and I2BS have been evaluated in humans. [18F]THK-5351, which was originally designed to target tau aggregates in AD, showed high affinity for MAO-B and clearly visualized reactive astrocytes in progressive supranuclear palsy (PSP). However, the lack of selectivity of [18F]THK-5351 binding to both MAO-B and tau, severely limits its clinical utility as a biomarker. Recently, [18F]SMBT-1 was developed as a selective and reversible MAO-B PET tracer via compound optimization of [18F]THK-5351. In this review, we summarize the strategy underlying molecular imaging of reactive astrogliosis and clinical studies using MAO-B and I2BS PET tracers.
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Affiliation(s)
- Ryuichi Harada
- Department of Pharmacology, Tohoku University Graduate School of Medicine, Sendai, Japan
- *Correspondence: Ryuichi Harada,
| | - Shozo Furumoto
- Cyclotron and Radioisotope Center, Tohoku University, Sendai, Japan
| | - Yukitsuka Kudo
- Department of New Therapeutics Innovation for Alzheimer’s and Dementia, Institute of Development and Aging, Tohoku University, Sendai, Japan
| | - Kazuhiko Yanai
- Department of Pharmacology, Tohoku University Graduate School of Medicine, Sendai, Japan
| | - Victor L. Villemagne
- Department of Molecular Imaging and Therapy, Austin Health, Melbourne, VIC, Australia
- Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, United States
| | - Nobuyuki Okamura
- Division of Pharmacology, Faculty of Medicine, Tohoku Medical and Pharmaceutical University, Sendai, Japan
- Nobuyuki Okamura,
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Astroglial tracer BU99008 detects multiple binding sites in Alzheimer's disease brain. Mol Psychiatry 2021; 26:5833-5847. [PMID: 33888872 PMCID: PMC8758481 DOI: 10.1038/s41380-021-01101-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 03/17/2021] [Accepted: 04/01/2021] [Indexed: 12/15/2022]
Abstract
With reactive astrogliosis being established as one of the hallmarks of Alzheimer's disease (AD), there is high interest in developing novel positron emission tomography (PET) tracers to detect early astrocyte reactivity. BU99008, a novel astrocytic PET ligand targeting imidazoline-2 binding sites (I2BS) on astrocytes, might be a suitable candidate. Here we demonstrate for the first time that BU99008 could visualise reactive astrogliosis in postmortem AD brains and propose a multiple binding site [Super-high-affinity (SH), High-affinity (HA) and Low-affinity (LA)] model for BU99008, I2BS specific ligands (2-BFI and BU224) and deprenyl in AD and control (CN) brains. The proportion (%) and affinities of these sites varied significantly between the BU99008, 2-BFI, BU224 and deprenyl in AD and CN brains. Regional binding studies demonstrated significantly higher 3H-BU99008 binding in AD brain regions compared to CN. Comparative autoradiography studies reinforced these findings, showing higher specific binding for 3H-BU99008 than 3H-Deprenyl in sporadic AD brain compared to CN, implying that they might have different targets. The data clearly shows that BU99008 could detect I2BS expressing reactive astrocytes with good selectivity and specificity and hence be a potential attractive clinical astrocytic PET tracer for gaining further insight into the role of reactive astrogliosis in AD.
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Wilson H, Dervenoulas G, Pagano G, Tyacke RJ, Polychronis S, Myers J, Gunn RN, Rabiner EA, Nutt D, Politis M. Imidazoline 2 binding sites reflecting astroglia pathology in Parkinson's disease: an in vivo11C-BU99008 PET study. Brain 2019; 142:3116-3128. [PMID: 31504212 DOI: 10.1093/brain/awz260] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2019] [Revised: 06/06/2019] [Accepted: 07/04/2019] [Indexed: 12/11/2022] Open
Abstract
Astroglia are multifunctional cells that regulate neuroinflammation and maintain homeostasis within the brain. Astroglial α-synuclein-positive cytoplasmic accumulations have been shown post-mortem in patients with Parkinson's disease and therefore astroglia may play an important role in the initiation and progression of Parkinson's disease. Imidazoline 2 binding sites are expressed on activated astroglia in the cortex, hippocampus, basal ganglia and brainstem; therefore, by measuring imidazoline 2 binding site levels we can indirectly evaluate astrogliosis in patients with Parkinson's disease. Here, we aimed to evaluate the role of astroglia activation in vivo in patients with Parkinson's disease using 11C-BU99008 PET, a novel radioligand with high specificity and selectivity for imidazoline 2 binding sites. Twenty-two patients with Parkinson's disease and 14 healthy control subjects underwent 3 T MRI and a 120-min 11C-BU99008 PET scan with volume of distribution (VT) estimated using a two-tissue compartmental model with a metabolite corrected arterial plasma input function. Parkinson's disease patients were stratified into early (n = 8) and moderate/advanced (n = 14) groups according to disease stage. In early Parkinson's disease, increased 11C-BU99008 VT uptake was observed in frontal (P = 0.022), temporal (P = 0.02), parietal (P = 0.026) and occipital (P = 0.047) cortical regions compared with healthy controls. The greatest 11C-BU99008 VT increase in patients with early Parkinson's disease was observed in the brainstem (52%; P = 0.018). In patients with moderate/advanced Parkinson's disease, loss of 11C-BU99008 VT was observed across frontal (P = 0.002), temporal (P < 0.001), parietal (P = 0.039), occipital (P = 0.024), and insula (P < 0.001) cortices; and in the subcortical regions of caudate (P < 0.001), putamen (P < 0.001) and thalamus (P < 0.001); and in the brainstem (P = 0.018) compared with healthy controls. In patients with Parkinson's disease, loss of 11C-BU99008 VT in cortical regions, striatum, thalamus and brainstem correlated with longer disease duration (P < 0.05) and higher disease burden scores, measured with Movement Disorder Society Unified Parkinson's Disease Rating Scale (P < 0.05). In the subgroup of patients with moderate/advanced Parkinson's disease, loss of 11C-BU99008 VT in the frontal (r = 0.79; P = 0.001), temporal (r = 0.74; P = 0.002) and parietal (r = 0.89; P < 0.001) cortex correlated with global cognitive impairment. This study demonstrates in vivo the role of astroglia in the initiation and progression of Parkinson's disease. Reactive astroglia observed early in Parkinson's disease could reflect a neuroprotective compensatory mechanisms and pro-inflammatory upregulation in response to α-synuclein accumulation. However, as the disease progresses and significant neurodegeneration occurs, astroglia lose their reactive function and such loss in the cortex has clinical relevance in the development of cognitive impairment.
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Affiliation(s)
- Heather Wilson
- Neurodegeneration Imaging Group, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK
| | - George Dervenoulas
- Neurodegeneration Imaging Group, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK
| | - Gennaro Pagano
- Neurodegeneration Imaging Group, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK
| | - Robin J Tyacke
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, UK
| | - Sotirios Polychronis
- Neurodegeneration Imaging Group, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK
| | - Jim Myers
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, UK
| | - Roger N Gunn
- Division of Brain Sciences, Department of Medicine, Imperial College London, London, UK
- Invicro LLC, Centre for Imaging Sciences, Hammersmith Hospital, London, UK
| | - Eugenii A Rabiner
- Invicro LLC, Centre for Imaging Sciences, Hammersmith Hospital, London, UK
- Centre for Neuroimaging Sciences, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK
| | - David Nutt
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, UK
| | - Marios Politis
- Neurodegeneration Imaging Group, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK
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Molecular Imaging in Huntington's Disease. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2018; 142:289-333. [PMID: 30409256 DOI: 10.1016/bs.irn.2018.08.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Huntington's disease (HD) is a rare monogenic neurodegenerative disorder caused by a trinucleotide CAG repeat expansion in the huntingtin gene resulting in the formation of intranuclear inclusions of mutated huntingtin. The accumulation of mutated huntingtin leads to loss of GABAergic medium spiny neurons (MSNs); subsequently resulting in the development of chorea, cognitive dysfunction and psychiatric symptoms. Premanifest HD gene expansion carriers, provide a unique cohort to examine very early molecular changes, occurring before the development of overt symptoms, to elucidate disease pathophysiology and identify reliable biomarkers of HD progression. Positron emission tomography (PET) is a non-invasive molecular imaging technique allowing the evaluation of specific molecular targets in vivo. Selective PET radioligands provide invaluable tools to investigate the role of the dopaminergic system, brain metabolism, microglial activation, phosphodiesterase 10A, and cannabinoid, GABA, adenosine and opioid receptors in HD. PET has been employed to monitor disease progression aiming to identify a reliable biomarker to predict phenoconversion from premanifest to manifest HD.
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6
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Tyacke RJ, Myers JFM, Venkataraman A, Mick I, Turton S, Passchier J, Husbands SM, Rabiner EA, Gunn RN, Murphy PS, Parker CA, Nutt DJ. Evaluation of 11C-BU99008, a PET Ligand for the Imidazoline 2 Binding Site in Human Brain. J Nucl Med 2018; 59:1597-1602. [PMID: 29523627 DOI: 10.2967/jnumed.118.208009] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Accepted: 02/21/2018] [Indexed: 11/16/2022] Open
Abstract
The imidazoline2 binding site (I2BS) is thought to be expressed in glia and implicated in the regulation of glial fibrillary acidic protein. A PET ligand for this target would be important for the investigation of neurodegenerative and neuroinflammatory diseases. 11C-BU99008 has previously been identified as a putative PET radioligand. Here, we present the first in vivo characterization of this PET radioligand in humans and assess its test-retest reproducibility. Methods: Fourteen healthy male volunteers underwent dynamic PET imaging with 11C-BU99008 and arterial sampling. Six subjects were used in a test-retest assessment, and 8 were used in a pharmacologic evaluation, undergoing a second or third heterologous competition scan with the mixed I2BS/α2-adrenoceptor drug idazoxan (n = 8; 20, 40, 60, and 80 mg) and the mixed irreversible monoamine oxidase type A/B inhibitor isocarboxazid (n = 4; 50 mg). Regional time-activity data were generated from arterial plasma input functions corrected for metabolites using the most appropriate model to derive the outcome measure VT (regional distribution volume). All image processing and kinetic analyses were performed in MIAKAT. Results: Brain uptake of 11C-BU99008 was good, with reversible kinetics and a heterogeneous distribution consistent with known I2BS expression. Model selection criteria indicated that the 2-tissue-compartment model was preferred. VT estimates were high in the striatum (105 ± 21 mL⋅cm-3), medium in the cingulate cortex (62 ± 10 mL⋅cm-3), and low in the cerebellum (41 ± 7 mL⋅cm-3). Test-retest reliability was reasonable. The uptake was dose-dependently reduced throughout the brain by pretreatment with idazoxan, with an average block across all regions of about 60% (VT, ∼30 mL⋅cm-3) at the highest dose (80 mg). The median effective dose for idazoxan was 28 mg. Uptake was not blocked by pretreatment with the monoamine oxidase inhibitor isocarboxazid. Conclusion:11C-BU99008 in human PET studies demonstrates good brain delivery, reversible kinetics, heterogeneous distribution, specific binding signal consistent with I2BS distribution, and good test-retest reliability.
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Affiliation(s)
- Robin J Tyacke
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, London, United Kingdom
| | - Jim F M Myers
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, London, United Kingdom
| | - Ashwin Venkataraman
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, London, United Kingdom
| | - Inge Mick
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, London, United Kingdom
| | - Samuel Turton
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, London, United Kingdom
| | - Jan Passchier
- Imanova Limited, Imperial College London, London, United Kingdom
| | - Stephen M Husbands
- Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
| | | | - Roger N Gunn
- Imanova Limited, Imperial College London, London, United Kingdom
- Restorative Neurosciences, Imperial College London, London, United Kingdom; and
| | - Philip S Murphy
- Experimental Medicine Imaging, GlaxoSmithKline Research and Development Limited, Stevenage, United Kingdom
| | - Christine A Parker
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, London, United Kingdom
- Experimental Medicine Imaging, GlaxoSmithKline Research and Development Limited, Stevenage, United Kingdom
| | - David J Nutt
- Neuropsychopharmacology Unit, Centre for Academic Psychiatry, Division of Brain Sciences, Imperial College London, London, United Kingdom
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Parker CA, Nabulsi N, Holden D, Lin SF, Cass T, Labaree D, Kealey S, Gee AD, Husbands SM, Quelch D, Carson RE, Nutt DJ, Huang Y, Tyacke RJ. Evaluation of 11C-BU99008, a PET ligand for the imidazoline2 binding sites in rhesus brain. J Nucl Med 2014; 55:838-44. [PMID: 24711648 DOI: 10.2967/jnumed.113.131854] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
UNLABELLED The development of a PET radioligand selective for I2-imidazoline binding sites (I2BS) would enable, for the first time, specific, measurable in vivo imaging of this target protein, along with assessment of alterations in expression patterns of this protein in disease pathophysiology. METHODS BU99008 was identified as the most promising I2BS radioligand candidate and radiolabeled with (11)C via methylation. The in vivo binding properties of (11)C-BU99008 were assessed in rhesus monkeys to determine brain penetration, brain distribution, binding specificity and selectivity (via the use of the unlabeled blockers), and the most appropriate kinetic model for analyzing data generated with this PET radioligand. RESULTS (11)C-BU99008 was demonstrated to readily enter the brain, resulting in a heterogeneous distribution (globus pallidus > cortical regions > cerebellum) consistent with the reported regional I2BS densities as determined by human tissue section autoradiography and preclinical in vivo PET studies in the pig. In vivo competition studies revealed that (11)C-BU99008 displayed reversible kinetics specific for the I2BS. The multilinear analysis (MA1) model was the most appropriate analysis method for this PET radioligand in this species. The selective I2BS blocker BU224 was shown to cause a saturable, dose-dependent decrease in (11)C-BU99008 binding in all regions of the brain assessed, further demonstrating the heterogeneous distribution of I2BS protein in the rhesus brain and binding specificity for this radioligand. CONCLUSION These data demonstrate that (11)C-BU99008 represents a specific and selective PET radioligand for imaging and quantifying the I2BS, in vivo, in the rhesus monkey. Further work is under way to translate the use of (11)C-BU99008 to the clinic.
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Affiliation(s)
- Christine A Parker
- Centre for Neuropsychopharmacology, Hammersmith Hospital, Imperial College London, United Kingdom
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Semenova S, Markou A. The alpha2 adrenergic receptor antagonist idazoxan, but not the serotonin-2A receptor antagonist M100907, partially attenuated reward deficits associated with nicotine, but not amphetamine, withdrawal in rats. Eur Neuropsychopharmacol 2010; 20:731-46. [PMID: 20627663 PMCID: PMC3545706 DOI: 10.1016/j.euroneuro.2010.05.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Revised: 04/01/2010] [Accepted: 05/04/2010] [Indexed: 11/27/2022]
Abstract
Based on phenomenological similarities between anhedonia (reward deficits) associated with drug withdrawal and the negative symptoms of schizophrenia, we showed previously that the atypical antipsychotic clozapine attenuated reward deficits associated with psychostimulant withdrawal. Antagonism of alpha(2) adrenergic and 5-HT(2A) receptors may contribute to these effects of clozapine. We investigated here whether blockade of alpha(2) or 5-HT(2A) receptors by idazoxan and M100907, respectively, would reverse anhedonic aspects of psychostimulant withdrawal. Idazoxan treatment facilitated recovery from spontaneous nicotine, but not amphetamine, withdrawal by attenuating reward deficits and increase the number of somatic signs. Thus, alpha(2) adrenoceptor blockade may have beneficial effects against nicotine withdrawal and may be involved in the effects of clozapine previously observed. M100907 worsened the anhedonia associated with nicotine and amphetamine withdrawal, suggesting that monotherapy with M100907 may exacerbate the expression of the negative symptoms of schizophrenia or nicotine withdrawal symptoms in people, including schizophrenia patients, attempting to quit smoking.
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Affiliation(s)
- Svetlana Semenova
- Department of Psychiatry, School of Medicine, University of California San Diego, 9500 Gilman Drive, M/C 0603, La Jolla, CA 92093-0603, USA.
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Smith DF, Marthi K, Munk OL, Cumming P, Hansen SB, Jakobsen S. PET neuroimaging of [11C]mirtazapine enantiomers in pigs. Eur Neuropsychopharmacol 2006; 16:350-7. [PMID: 16361085 DOI: 10.1016/j.euroneuro.2005.10.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Revised: 09/16/2005] [Accepted: 10/20/2005] [Indexed: 10/25/2022]
Abstract
Previously, we used positron emission tomography (PET) for studying the pharmacokinetics of rac-[11C]mirtazapine in living brain. Our findings showed that rac-[11C]mirtazapine has suitable properties for PET neuroimaging. However, separate studies of enantiomers are typically required for characterizing the pharmacokinetics of a racemic drug. Therefore, we have determined the whole-body distribution and brain pharmacokinetics of S- and R-[11C]mirtazapine in pigs. The enantiomers of [11C]mirtazapine produced similar effective doses of radioactivity in most body organs, except for the brain, in which the dose was approximately 40% higher after injection of S-[11C]mirtazapine than the antipode. Kinetic analyses of dynamic brain PET recordings showed that values for regional accumulation of compound (k3) were significantly higher for S-[11C]mirtazapine than for the antipode, while the values for clearance of compounds from tissue to circulation (k2) were consistently lower for S-[11C]mirtazapine than for the R-form. No reliable difference occurred in the rate of metabolism of S- and R-[11C]mirtazapine in the bloodstream of the pigs. The present findings indicate that enantioselective processes affect the cerebral pharmacokinetics of rac-mirtazapine.
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Affiliation(s)
- Donald F Smith
- Center for Basic Psychiatric Research, Psychiatric Hospital of Aarhus University, 8240 Risskov, Denmark.
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10
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SCHAMBRA UB, MACKENSEN GB, STAFFORD-SMITH M, HAINES DE, SCHWINN DA. Neuron specific alpha-adrenergic receptor expression in human cerebellum: implications for emerging cerebellar roles in neurologic disease. Neuroscience 2006; 135:507-23. [PMID: 16112482 PMCID: PMC2277099 DOI: 10.1016/j.neuroscience.2005.06.021] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2004] [Revised: 06/06/2005] [Accepted: 06/15/2005] [Indexed: 12/13/2022]
Abstract
Recent data suggest novel functional roles for cerebellar involvement in a number of neurologic diseases. Function of cerebellar neurons is known to be modulated by norepinephrine and adrenergic receptors. The distribution of adrenergic receptor subtypes has been described in experimental animals, but corroboration of such studies in the human cerebellum, necessary for drug treatment, is still lacking. In the present work we studied cell-specific localizations of alpha1 adrenergic receptor subtype mRNA (alpha 1a, alpha 1b, alpha 1d), and alpha2 adrenergic receptor subtype mRNA (alpha 2a, alpha 2b, alpha 2c) by in situ hybridization on cryostat sections of human cerebellum (cortical layers and dentate nucleus). We observed unique neuron-specific alpha1 adrenergic receptor and alpha2 adrenergic receptor subtype distribution in human cerebellum. The cerebellar cortex expresses mRNA encoding all six alpha adrenergic receptor subtypes, whereas dentate nucleus neurons express all subtype mRNAs, except alpha 2a adrenergic receptor mRNA. All Purkinje cells label strongly for alpha 2a and alpha 2b adrenergic receptor mRNA. Additionally, Purkinje cells of the anterior lobe vermis (lobules I to V) and uvula/tonsil (lobules IX/HIX) express alpha 1a and alpha 2c subtypes, and Purkinje cells in the ansiform lobule (lobule HVII) and uvula/tonsil express alpha 1b and alpha 2c adrenergic receptor subtypes. Basket cells show a strong signal for alpha 1a, moderate signal for alpha 2a and light label for alpha 2b adrenergic receptor mRNA. In stellate cells, besides a strong label of alpha 2a adrenergic receptor mRNA in all and moderate label of alpha 2b message in select stellate cells, the inner stellate cells are also moderately positive for alpha 1b adrenergic receptor mRNA. Granule and Golgi cells express high levels of alpha 2a and alpha 2b adrenergic receptor mRNAs. These data contribute new information regarding specific location of adrenergic receptor subtypes in human cerebellar neurons. We discuss our observations in terms of possible modulatory roles of adrenergic receptor subtypes in cerebellar neurons responding to sensory and autonomic input signals, and review species differences in cerebellar adrenergic receptor expression.
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Affiliation(s)
- U. B. SCHAMBRA
- Department of Anatomy and Cell Biology, Quillen College of Medicine, East Tennessee State University, Box 70582, Johnson City, TN 37614-0582, USA
- *Corresponding author. Tel: +1-423-439-2014; fax: +1-423-439-2017. E-mail address: (U. B. Schambra)
| | - G. B. MACKENSEN
- Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA
| | - M. STAFFORD-SMITH
- Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA
| | - D. E. HAINES
- Department of Anatomy, University of Mississippi Medical Center, Jackson, MS 39216, USA
| | - D. A. SCHWINN
- Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA
- Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA
- Department of Pharmacology/Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA
- *Corresponding author. Tel: +1-423-439-2014; fax: +1-423-439-2017. E-mail address: (U. B. Schambra)
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11
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Smith DF, Dyve S, Minuzzi L, Jakobsen S, Munk OL, Marthi K, Cumming P. Inhibition of [11C]mirtazapine binding by α2-adrenoceptor antagonists studied by positron emission tomography in living porcine brain. Synapse 2006; 59:463-71. [PMID: 16565964 DOI: 10.1002/syn.20262] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We have developed [(11)C]mirtazapine as a ligand for PET studies of antidepressant binding in living brain. However, previous studies have determined neither optimal methods for quantification of [(11)C]mirtazapine binding nor the pharmacological identity of this binding. To obtain that information, we have now mapped the distribution volume (V(d)) of [(11)C]mirtazapine relative to the arterial input in the brain of three pigs, in a baseline condition and after pretreatment with excess cold mirtazapine (3 mg/kg). Baseline V(d) ranged from 6 ml/ml in cerebellum to 18 ml/ml in frontal cortex, with some evidence for a small self-displaceable binding component in the cerebellum. Regional binding potentials (pBs) obtained by a constrained two-compartment model, using the V(d) observation in cerebellum, were consistently higher than pBs obtained by other arterial input or reference tissue methods. We found that adequate quantification of pB was obtained using the simplified reference tissue method. Concomitant PET studies with [(15)O]-water indicated that mirtazapine challenge increased CBF uniformly in cerebellum and other brain regions, supporting the use of this reference tissue for calculation of [(11)C]mirtazapine pB. Displacement by mirtazapine was complete in the cerebral cortex, but only 50% in diencephalon, suggesting the presence of multiple binding sites of differing affinities in that tissue. Competition studies with yohimbine and RX 821002 showed decreases in [(11)C]mirtazapine pB throughout the forebrain; use of the multireceptor version of the Michaelis-Menten equation indicated that 42% of [(11)C]mirtazapine binding in cortical regions is displaceable by yohimbine. Thus, PET studies confirm that [(11)C]mirtazapine affects alpha(2)-adrenoceptor binding sites in living brain.
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Affiliation(s)
- Donald F Smith
- Center for Basic Psychiatric Research, Psychiatric Hospital of Aarhus University, DK-8240 Risskov, Denmark.
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12
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Anderson NJ, Lupo PA, Nutt DJ, Hudson AL, Robinson ESJ. Characterisation of imidazoline I2 binding sites in pig brain. Eur J Pharmacol 2005; 519:68-74. [PMID: 16109401 DOI: 10.1016/j.ejphar.2005.06.042] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2005] [Accepted: 06/28/2005] [Indexed: 11/29/2022]
Abstract
The imidazoline I2 binding sites in the central nervous system have previously been described in several different species including rat, mouse, rabbit and frog. The present study has investigated the imidazoline I2 binding site, and its relationship to the monoamine oxidase isoforms, in pig whole brain and compared the results obtained with data from other species. Results from saturation binding studies revealed that the imidazoline I2-selective ligand, [3H]2BFI (2-(2-benzofuranyl)-2-imidazoline) labelled a single saturable population of sites with a KD=6.6 nM and Bmax=771.7 fmol/mg protein. The pharmacological characterisation of the sites was similar to that previously reported with a rank order of potency for the imidazoline I2 ligands of 2BFI>BU224>Idazoxan>BU226. Displacement by the imidazoline I1 ligands was low affinity and the monoamine oxidase inhibitors displaced with micromolar affinity. The majority of compounds displaced the binding in a monophasic manner, however, displacement by the putative endogenous ligand, harmane was biphasic. The relative populations of the two monoamine oxidase isoforms revealed a 10 fold greater expression of monoamine oxidase B relative to monoamine oxidase A. These data confirm the presence of imidazoline I2 binding sites in pig brain and show that their pharmacology is characteristic of that seen in other species. The proportion of monoamine oxidase A and B expressed in the pig brain is similar to that seen in the human brain therefore, given the association between imidazoline I2 binding sites and monoamine oxidase, the pig may provide a more useful model for human imidazoline I2 binding sites than other species such as the rat.
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Affiliation(s)
- Neil J Anderson
- Department of Pharmacology, School of Medical Sciences, University Walk, Clifton, Bristol BS8 1TD, UK
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13
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Raasch W, Schäfer U, Chun J, Dominiak P. Biological significance of agmatine, an endogenous ligand at imidazoline binding sites. Br J Pharmacol 2001; 133:755-80. [PMID: 11454649 PMCID: PMC1572857 DOI: 10.1038/sj.bjp.0704153] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Affiliation(s)
- W Raasch
- Institute of Experimental and Clinical Pharmacology and Toxicology, Medical University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany.
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14
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Dossin O, Moulédous L, Baudry X, Tafani JA, Mazarguil H, Zajac JM. Characterization of a new radioiodinated probe for the alpha2C adrenoceptor in the mouse brain. Neurochem Int 2000; 36:7-18. [PMID: 10566954 DOI: 10.1016/s0197-0186(99)00102-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
[125I]17alpha-hydroxy-20alpha-yohimban-16beta-(N-4-p6 hydroxyphenethyl)carboxamide or [125I]rauwolscine-OHPC, a new radioiodinated probe derived from rauwolscine was synthesized and its binding characteristics investigated on sections of the mouse caudate putamen. [125I]rauwolscine-OHPC binding was saturable and revealed interaction with a single class of binding sites (KD= 0.171 nM, Bmax = 3082 pCi/mg of tissue). The kinetically derived affinity was in close agreement with the affinity evaluated by saturation experiments: k(-1)/k(+1)(0.0403 min(-1)/114 10(6) M(-1) min(-1))=0.35 nM. Competition studies revealed interaction with one single class of binding sites for each of the twelve compounds tested. The rank of potency suggested an interaction with alpha2 adrenoceptors (atipamezole > or = RX 821002 > yohimbine > (-)epinephrine). Moreover, the good affinity of [125I] rauwolscine-OHPC binding sites for spiroxatrine, yohimbine, WB 4101, the relatively good affinity for prazosin (Ki =37.4 nM) and the affinity ratio prazosin/oxymetazoline (37.4/43.4=0.86) were consistent with an alpha2C selective labelling of [125I]rauwolscine-OHPC. The distribution of [125I]rauwolscine-OHPC binding sites in mouse brain was characterized by autoradiography. The density of binding sites was high in the islands of Calleja, accumbens nucleus, caudate putamen and olfactory tubercles, moderate in the hippocampus, amygdala and anterodorsal nucleus of the thalamus. These findings demonstrated that [125I]rauwolscine-OHPC is a useful radioiodinated probe to label alpha2C adrenoceptors in mouse brain.
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Affiliation(s)
- O Dossin
- Institut de Pharmacologie et de Biologie Structurale, CNRS UPR 9062, Toulouse, France
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15
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16
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Abstract
Major depression, opioid addiction, neurodegenerative diseases, and glial tumors are associated with disturbances of imidazoline receptors (IR) in the human brain. In depression, the level of a 45-kD IR protein (putative I1-IR) is increased in the brain of suicide victims (51%) and in platelets of depressed patients (40%). The density of platelet I1-IR ([125I]-p-iodoclonidine binding) is also increased in depression (135%). The 29/30-kD IR protein (putative I2B-IR) is downregulated (19%) in suicide victims in parallel with a reduction (40%) in the density of I2B-IR ([3H]idazoxan binding). Antidepressant drugs induce downregulation of 45-kD IR protein and I1-sites in platelets of depressed patients and upregulation of I2-sites in rat brain. The densities of I2B-IR and the related 29/30-kD IR protein are decreased (39% and 28%) in the brain of heroin addicts. The density of I2B-IR is increased in Alzheimer's disease (63%) and decreased in Huntington's disease (56%). Brain I2B-IR is not altered in Parkinson's disease. The level of I2-IR in glial tumors is increased (two-fivefold) in parallel with the abundance of the related 29/30-kD IR protein (39%), whereas the level of 45-kD IR protein is decreased (39%). The possible functional relevance of these findings in the context of the pathogenesis of these disorders remains to be elucidated.
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Affiliation(s)
- J A García-Sevilla
- Institute of Neurobiology Ramón y Cajal/CSIC, Department of Biology, University of the Balearic Islands, Palma de Mallorca, Spain
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17
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Hosseini AR, Jackman GP, King PR, Louis WJ, Gundlach AL. Pharmacology and subcellular distribution of [3H]rilmenidine binding sites in rat brain. JOURNAL OF THE AUTONOMIC NERVOUS SYSTEM 1998; 72:129-36. [PMID: 9851561 DOI: 10.1016/s0165-1838(98)00097-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
We have previously reported that in rat brain membranes, [3H]rilmenidine, in addition to labelling alpha2-adrenoceptors and the I2B-subtype of imidazoline receptor binding site (I2B-RBS), may label an additional I-RBS population, distinct from previously classified I1-RBS and I2-RBS. In this study, using crude or fractionated rat brain membranes we examined the possible association of [3H]rilmenidine-labelled I-RBS with the A- and B-isoforms of monoamine oxidase (MAO) by studying the inhibition of [3H]rilmenidine binding by a number of MAO inhibitors; and comparing the maximal binding density (Bmax) and subcellular distribution of [3H]rilmenidine binding sites with that of MAO-A and MAO-B catalytic sites labelled by [3H]RO41-1049 and [3H]RO19-6327 and 12-RBS labelled by [3H]2-BFI. Inhibition of [3H]rilmenidine binding by all MAO inhibitors tested produced very shallow curves (slope 0.29-0.56). Clorgyline and moclobemide (selective MAO-A inhibitors) displayed moderate affinities (60-140 nM), while pargyline (non-selective MAO-inhibitor), RO41-1049 (selective MAO-A inhibitor) and RO19-6327 (selective MAO-B inhibitor) exhibited very low affinities (> 2 microM) for 50-75% of [3H]rilmenidine-labelled I-RBS in crude brain membranes and even lower affinity for the remaining binding. Under identical buffer conditions, the Bmax of [3H]rilmenidine-labelled I-RBS (1.45+/-0.14 pmol/mg protein) was considerably lower than those of MAO-A (13.10+/-0.15 pmol/mg) and MAO-B (10.35+/-0.50 pmol/mg) sites. These results suggest that [3H]rilmenidine does not interact directly with the active catalytic site of either MAO enzyme and could at best only associate with a subpopulation of MAO molecules. Binding studies on five fractions of rat cortex homogenates-nuclear (N), heavy (M) and light (L) mitochondrial, microsomal non-mitochondrial (P), and soluble cytosolic (S) fractions-revealed that 45% of total [3H]rilmenidine binding was present in the P fraction cf. 20 and 23% in the M and L fractions, in contrast to [3H]RO19-6327 and [3H]2-BFI which bound 11-13% in the P fraction and 36-38% and 35-44% in the M and L fractions, respectively. Binding of all ligands in the N fraction was 6-15% of total. These studies reveal that [3H]rilmenidine-labelled I-RBS, unlike the I2-RBS, are not predominantly associated with mitochondrial fractions containing the MAO enzymes (and cytochrome oxidase activity), but appear to be distributed in both the mitochondrial and plasma membrane fractions in rat cerebral cortex.
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Affiliation(s)
- A R Hosseini
- The University of Melbourne, Department of Medicine, Austin and Repatriation Medical Centre, Heidelberg, Victoria, Australia
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18
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Otake K, Ruggiero DA, Regunathan S, Wang H, Milner TA, Reis DJ. Regional localization of agmatine in the rat brain: an immunocytochemical study. Brain Res 1998; 787:1-14. [PMID: 9518530 DOI: 10.1016/s0006-8993(97)01200-6] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The distribution of agmatine (decarboxylated arginine) was mapped in the central nervous system (CNS) in the rat. Agmatine-like immunoreactivity was identified by light microscopy, exclusively in the cytoplasm of neuronal perikarya. Immunoreactive neurons were present in the cerebral cortex, predominantly within laminae VI and V and, to a lesser extent, III and mainly in retrosplenial, cingulate, primary somatosensory and auditory cortices, and the subiculum. In the lower brainstem, immunoreactivity was selectively localized to visceral relay nuclei: the nucleus tractus solitarii and pontine parabrachial complex, and periventricular areas including the laterodorsal nucleus, locus coeruleus and dorsal raphe. In the midbrain, immunolabeled cells were concentrated in the ventral tegmental area and periaqueductal gray. In the forebrain, subcortical neurons were labeled predominantly in the preoptic area, amygdala, septum, bed nucleus of the stria terminalis, midline thalamus, and the hypothalamus. Ultrastructural analysis of layer V of the somatosensory cortex demonstrated agmatine-immunoreactivity in neurons, primarily in large dense-core vesicles located in the cytoplasm. Agmatine immunoreactivity was also affiliated with endoplasmic reticulum and the plasmalemma. Cortical neurons and the subiculum were labeled in animals not administered the axonal transport inhibitor, colchicine; thus, may normally contain higher concentrations of the amine than other brain regions. The central distribution of agmatine is consistent with the hypothesis that the amine may be a novel neurotransmitter of neurons involved in behavioral and visceral control.
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Affiliation(s)
- K Otake
- Division of Neurobiology, Department of Neurology and Neuroscience, Cornell University Medical College, 411 East 69th Street, New York, NY 10021, USA
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19
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Ruggiero DA, Regunathan S, Wang H, Milner TA, Reis DJ. Immunocytochemical localization of an imidazoline receptor protein in the central nervous system. Brain Res 1998; 780:270-93. [PMID: 9507161 DOI: 10.1016/s0006-8993(97)01203-1] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Imidazoline (I) receptors have been implicated in the regulation of arterial blood pressure and behavior although their distribution in the central nervous system (CNS) remains in question. Presumptive I- receptor sites were detected in the rat central nervous system with a polyclonal antibody to an imidazoline receptor protein (IRP) with binding characteristics of the native receptor. IRP-like immunoreactivity (LI) was detected in neurons and glia by light and electron microscopy. Spinal cord: processes were heavily labeled in superficial laminae I and II of the dorsal horn, lateral-cervical and -spinal nuclei and sympathetic cell column. Medulla: label was concentrated in the area postrema, rostral, subpostremal and central subnuclei of nucleus tractus solitarii, spinal trigeminal nucleus caudalis, and inferior olivary subnuclei. Visceromotor neurons in the dorsal vagal and ambigual nuclei were surrounded by high concentrations of immunoreactive processes. In reticular formation, label was light, though predominant in the intermediate reticular zone and ventrolateral medulla. Pons: label was detected in the neuropil of the periventricular gray, concentrated in the dorsal- and external-lateral subnuclei of lateral parabrachial nucleus, and present intracellularly in the mesencephalic trigeminal nucleus. Midbrain: IRP-LI was most heavily concentrated in the interpeduncular nucleus, nuclei interfascicularis and rostral-linearis, the subcommissural organ, central gray, and in glia surrounding the cerebral aqueduct. Diencephalon: high densities were detected in the medial habenular nucleus, nucleus paraventricularis thalami, other midline-intralaminar thalamic nuclei, the supramammillary and mediobasal hypothalamic nuclei. In the median eminence, immunolabeled processes were restricted to the lamina interna and lateral subependymal zone. Telencephalon: IRP-LI was concentrated in the central amygdaloid nucleus, bed nucleus of stria terminalis and globus pallidus, followed by moderate labeling of the medial amygdaloid nucleus, amygdalostriatal zone and caudoputamen, the hilus of the dentate gyrus, and stratum lacunosum-moleculare of field CA1 of Ammon's horn. The subfornical organ and organum vasculosum lamina terminalis were filled with diffuse granular immunoreactivity. Ultrastructural studies identified IRP-LI within glia and neurons including presynaptic processes. I-receptor(s) localize to a highly restricted network of neurons in the CNS and circumventricular regions lying outside of the blood-brain barrier. Putative imidazoline receptors have a unique distribution pattern, show partial overlap with alpha 2 adrenoreceptors and are heavily represented in sensory processing centers and the visceral nervous system.
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Affiliation(s)
- D A Ruggiero
- Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021, USA
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20
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Uhlén S, Lindblom J, Johnson A, Wikberg JE. Autoradiographic studies of central alpha 2A- and alpha 2C-adrenoceptors in the rat using [3H]MK912 and subtype-selective drugs. Brain Res 1997; 770:261-6. [PMID: 9372228 DOI: 10.1016/s0006-8993(97)00860-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In the present study we examined the distribution of alpha 2A- and alpha 2C-adrenoceptors in tissue slices from the rat cervical spinal cord and from brain slices collected at the level of the striatum. To differentiate between alpha 2A- and alpha 2C-adrenoceptors, the slices were incubated with [3H]MK912 in the presence of graded concentrations of the alpha 2A-selective drug, BRL44408, or the alpha 2C-selective drug, spiroxatrine. Computer analysis of the autoradiograms indicated that 0.4 nM [3H]MK912 plus 185 nM BRL44408 selectively labeled alpha 2C-adrenoceptors, while 0.4 nM [3H]MK912 plus 220 nM spiroxatrine selectively labeled alpha 2A-adrenoceptors. Using this approach, alpha 2C-adrenoceptors were detected in the striatum, while alpha 2A-adrenoceptors predominated in the cortical layers 1-4, the spinal cord distal dorsal horn, the septum and the endopiriform nucleus.
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Affiliation(s)
- S Uhlén
- Department of Pharmaceutical Biosciences, Uppsala University, Sweden.
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21
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Heider M, Schliebs R, Rossner S, Bigl V. Basal forebrain cholinergic immunolesion by 192IgG-saporin: evidence for a presynaptic location of subpopulations of alpha 2- and beta-adrenergic as well as 5-HT2A receptors on cortical cholinergic terminals. Neurochem Res 1997; 22:957-66. [PMID: 9239751 DOI: 10.1023/a:1022418708293] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
To study whether the changes in cortical noradrenergic and serotonergic mechanisms observed in patients with Alzheimer's disease are the consequence of reduced cortical cholinergic activity, a novel colinergic immunotoxin (conjugate of the monoclonal antibody 192IgG against the lower affinity nerve growth factor receptor with the cytotoxic protein saporin, 192IgG-saporin) was used to produce a specific and selective loss of cholinergic cells in rat basal forebrain nuclei. To correlate the responses to cholinergic immunolesion in cholinoceptive cortical target regions with cholinergic hypoactivity, quantitative receptor autoradiography to measure adrenoceptors and 5-hydroxytryptamine (5-HT) receptor subtypes, and histochemistry to estimate acetylcholinesterase activity, were performed in adjacent brain sections. alpha 1-adrenoceptor and 5-HT1A receptor binding were not affected by cholinergic immunolesion in any of the cortical and hippocampal regions studied. However, cholinergic immunolesion resulted in significantly reduced alpha 2- and beta-adrenoceptor as well as 5-HT2A receptor binding in a number of cortical and hippocampal regions displaying a reduced activity of acetylcholinesterase, already detectable seven days after a single injection of 192IgG-saporin and persisting up to three months post lesion without any significant recovery. The data suggest that at least a subpopulation of alpha 2- and beta-adrenoceptor as well 5-HT2A receptor subtype is present on cortical and hippocampal cholinergic terminals originating in the basal forebrain. The lesion-induced receptor changes suggest that the alterations in cortical 5-HT2 receptor binding observed in patients with Alzheimer's disease might be secondary to cholinergic deficits.
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MESH Headings
- 8-Hydroxy-2-(di-n-propylamino)tetralin/metabolism
- Acetylcholinesterase/metabolism
- Animals
- Antibodies, Monoclonal/pharmacology
- Autoradiography
- Cerebral Cortex/enzymology
- Cerebral Cortex/metabolism
- Cholinergic Fibers/drug effects
- Cholinergic Fibers/metabolism
- Dihydroalprenolol/metabolism
- Immunotoxins/pharmacology
- Isotope Labeling
- Ketanserin/metabolism
- Male
- N-Glycosyl Hydrolases
- Prazosin/metabolism
- Presynaptic Terminals/drug effects
- Presynaptic Terminals/metabolism
- Prosencephalon/drug effects
- Prosencephalon/immunology
- Prosencephalon/metabolism
- Radioligand Assay
- Rats
- Rats, Wistar
- Receptor, Serotonin, 5-HT2A
- Receptors, Adrenergic, alpha/drug effects
- Receptors, Adrenergic, alpha/metabolism
- Receptors, Adrenergic, alpha-1/metabolism
- Receptors, Adrenergic, alpha-2/metabolism
- Receptors, Adrenergic, beta/drug effects
- Receptors, Adrenergic, beta/metabolism
- Receptors, Presynaptic/drug effects
- Receptors, Presynaptic/metabolism
- Receptors, Serotonin/drug effects
- Receptors, Serotonin/metabolism
- Receptors, Serotonin, 5-HT1
- Ribosome Inactivating Proteins, Type 1
- Saporins
- Tritium
- Yohimbine/metabolism
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Affiliation(s)
- M Heider
- Paul Flechsig Institute for Brain Research, University Leipzig, Germany
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22
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El-Mas MM, Abdel-Rahman AA. Aortic barodenervation up-regulates alpha2-adrenoceptors in the nucleus tractus solitarius and rostral ventrolateral medulla: an autoradiographic study. Neuroscience 1997; 79:581-90. [PMID: 9200741 DOI: 10.1016/s0306-4522(96)00648-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Earlier findings have shown that alpha2-adrenoceptors in the nucleus tractus solitarius and rostral ventrolateral medulla modulate baroreflexes. The present study investigated whether attenuation of baroreflexes induced by surgical interruption of aortic baroafferents is related to an alteration of alpha2-adrenoceptor binding in these regions of the brainstem. In vitro autoradiography was utilized to assess the density and binding dissociation constant (affinity) of alpha2-adrenoceptors in the rostral ventrolateral medulla and in the middle and rostral portions of the nucleus tractus solitarius of aortic-barodenervated and sham-operated rats. Compared to sham operation, aortic barodenervation caused an acute rise in mean arterial pressure and heart rate and a significant reduction in baroreflex sensitivity. Two days later, mean arterial pressure and heart rate of conscious aortic-barodenervated rats subsided to sham-operated levels, whereas the baroreflex sensitivity remained significantly (P<0.05) reduced when measured by phenylephrine (0.55+/-0.08 vs 1.26+/-0.07 ms/mmHg) or nitroprusside (0.43+/-0.06 vs 1.01+/-0.09ms/mmHg). Examination of brainstem coronal sections obtained from separate groups of rats 48 h after surgery and preincubated with [3H]rauwolscine (0.5-16 nM) revealed that labeling of alpha2 binding sites was saturable and of high affinity. Scatchard analysis of the saturation isotherms obtained from the three brain areas of sham-operated rats showed an uneven distribution of alpha2 binding sites; the rostral nucleus tractus solitarius exhibited the highest density and lowest affinity. Aortic barodenervation caused region-dependent changes in the binding activity of alpha2-adrenoceptors. These changes comprised significant (P<0.05) increases in the density of alpha2-adrenoceptors in the middle nucleus tractus solitarius (436+/-60 vs 240+/-50 fmol/mg protein) and rostral ventrolateral medulla (350+/-67 vs 194+/-35 fmol/mg protein) compared with sham-operated rats; no significant changes occurred in the rostral nucleus tractus solitarius. The affinity of alpha2 binding sites was not changed by aortic barodenervation in any of the three brain regions. These findings suggest that attenuation of baroreflexes produced by aortic barodenervation coincides with up-regulation of alpha2-adrenoceptors in brainstem areas that play critical roles in the control of cardiovascular functions.
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Affiliation(s)
- M M El-Mas
- Department of Pharmacology, School of Medicine, East Carolina University, Greenville, NC 27858, U.S.A
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23
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Abstract
There is growing evidence that noradrenergic inputs to the prefrontal cortex (PFC) play an important role in regulating its function. This paper reviews the pharmacological control of noradrenaline (NA) release in this region, with particular reference to our studies using brain microdialysis, and also describes how NA levels are modulated by antidepressant and antipsychotic drugs. The suggestion that atypical antipsychotics such as clozapine and risperidone may produce clinical benefits by their ability to increase NA release is discussed. Finally, a new class of drugs, which show selectivity for imidazoline receptors is described. These compounds are shown to similarly increase extracellular NA in the PFC. Their potential utility as clinical treatments is discussed.
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Affiliation(s)
- D J Nutt
- Psychopharmacology Unit, School of Medical Sciences, University of Bristol, UK.
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24
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Wiest SA, Steinberg MI. Binding of [3H]2-(2-benzofuranyl)-2-imidazoline (BFI) to human brain: potentiation by tranylcypromine. Life Sci 1997; 60:605-15. [PMID: 9048963 DOI: 10.1016/s0024-3205(96)00639-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Recently, a new imidazoline (I2) ligand, [3H]2-(2-benzofuranyl)-2-imidazoline (BFI) was shown to be more selective for I2 vs alpha 2 binding in rodent brain. We characterized [3H]BFI binding in human brain cortex and lateral reticular nucleus (NRL). Membranes were incubated with [3H]BFI at 22 degrees C in 50 mM Tris, 1.5 mM EDTA at pH 7.5. Saturation experiments with [3H]BFI (0.5-80 nM) were analyzed using non-linear curve fitting. The NRL had 4X more binding sites than cortex with similar affinity (Bmax = 2085 +/- 732 and 471 +/- 41 fmol/mg protein; KD = 9.3 +/- 3.5 and 11.9 +/- 2.7 nM, respectively). In competition studies, cortical [3H]BFI binding was displaced in order of decreasing potency by clorgyline > BFI > or = cirazoline > idazoxan > or = guanabenz > clonidine > RX821002. The monoamine oxidase (MAO) inhibitor tranylcypromine (TCP) (1 nM-10 microM), markedly enhanced [3H]BFI binding in both NRL and cortex. Enhanced binding was maximal at 300 nM (12 X control) and returned to baseline at 30 microM. Potentiation was not seen with pargyline or clorgyline. TCP did not effect [3H]BFI binding in rat cortex, or [3H]idazoxan binding in human cortex and NRL. In human cortex, inhibition of MAO by preincubation with pargyline (10 micro M) abolished the TCP effect. Upon preincubation with TCP, the stimulation of [3H]BFI binding was dose-dependently related to a simultaneous inhibition of MAO. Thus, [3H]BFI labels a site in human NRL and cortex that appears similar to the previously described I2 site labeled by [3H]idazoxan. However, [3H]BFI binding is dramatically stimulated by TCP in human brain via a mechanism dependent on endogenous MAO activity.
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Affiliation(s)
- S A Wiest
- Lilly Research Laboratories, Eli Lilly and Company Indianapolis, IN 46285, USA
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25
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Gargalidis-Moudanos C, Pizzinat N, Javoy-Agid F, Remaury A, Parini A. I2-imidazoline binding sites and monoamine oxidase activity in human postmortem brain from patients with Parkinson's disease. Neurochem Int 1997; 30:31-6. [PMID: 9116585 DOI: 10.1016/s0197-0186(96)00035-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
I2-imidazoline binding site (I2BS) has been identified with a regulatory site located on a sub-population of monoamine oxidase (MAO)-A and -B. Previous studies showed a modification of MAO and I2BS in the elderly and in neurodegenerative processes such as Alzheimer's disease. In the present study, we studied the potential modification of I2 binding sites and monoamine oxidases in Parkinson's disease. Putamen and cerebral cortex were collected from 17 normal subjects (79 +/- 12 yr) and 16 patients (76 +/- 9 yr) affected by Parkinson's disease. In mitochondrial preparations, radioligand binding studies with [3H]idazoxan showed that putamen and frontal cortex express equivalent amount of I2BS. The density and affinity of I2BS were similar in normal subjects (putamen: Bmax = 207 +/- 58 fmol/mg of protein, Kd = 10.1 +/- 3.4 nM; cerebral cortex: Bmax = 193 +/- 54 fmol/mg of protein, Kd = 12.8 +/- 6.8 nM) and Parkinson's disease patients (putamen: Bmax = 193 +/- 60 fmol/mg of protein, Kd = 9.8 +/- 4.6 nM; cerebral cortex: Bmax = 199 +/- 49 fmol/mg of protein, Kd = 15.9 +/- 8.1 nM). The activity of total monoamine oxidase and monoamine oxidase B, measured by [14C]tyramine and [14C]phenylethylamine oxidation, respectively, were higher in putamen than in cerebral cortex. No differences have been detected in the enzyme activity between normal and pathological subjects. These data suggest that, although MAO and I2BS may play a role in the development of Parkinson's disease, they are not altered in the chronic phase of this disease.
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Grijalba B, Callado LF, Javier Meana J, García-Sevilla JA, Pazos A. Alpha 2-adrenoceptor subtypes in the human brain: a pharmacological delineation of [3H]RX-821002 binding to membranes and tissue sections. Eur J Pharmacol 1996; 310:83-93. [PMID: 8880071 DOI: 10.1016/0014-2999(96)00381-0] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In order to study the characterization and localization of [3H]RX-821002 (2-methoxy-idazoxan) binding to alpha 2-adrenoceptor subtypes in several regions of the human brain, we have carried out competition studies using both autoradiography and membrane binding assays. The alpha 2A-adrenoceptor subtype was found to be predominant in the different layers of the frontal cortex, cerebellum and hippocampal formation, while in the neostriatum it was the non-alpha 2A- (alpha 2B- and alpha 2C-) adrenoceptor subtype. In the frontal cortex, in addition to binding to the alpha 2A-adrenoceptor subtype, [3H]RX-821002 bound also to a small portion of alpha 2B- and alpha 2C-adrenoceptors in layer III, and to an unidentified binding site in the external layers. In the hippocampus, both alpha 2A- and non-alpha 2A- (alpha 2B- and alpha 2C-) adrenoceptors were labelled in the dentate gyrus and the CA1 field, together with 5-HT1A receptors. 5-HT1A receptors were labelled predominantly in the stratum pyramidale layer. These results, in addition to delineate the relative presence of alpha 2-adrenoceptor subtypes, indicate that caution is needed when analyzing RX 821002 binding to human brain tissue.
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Affiliation(s)
- B Grijalba
- Department of Physiology and Pharmacology, University of Cantabria, Santander, Spain
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27
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Reynolds GP, Boulton RM, Pearson SJ, Hudson AL, Nutt DJ. Imidazoline binding sites in Huntington's and Parkinson's disease putamen. Eur J Pharmacol 1996; 301:R19-21. [PMID: 8773473 DOI: 10.1016/0014-2999(96)00196-3] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Binding of [3H]2-(2-benzofuranyl)-2-imidazoline ([3H]BFI) to the imidazoline I2 receptor was determined in putamen taken post mortem from patients with two extrapyramidal motor disorders, Parkinson's and Huntington's diseases, and age-matched control subjects. No deficit of binding was apparent in Parkinson's disease, indicating that the receptors are not present on nigrostriatal terminals. A significant loss (by 56%) in imidazoline I2 receptor binding was observed in Huntington's disease, consistent with the receptors being sited on degenerating neurons.
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Affiliation(s)
- G P Reynolds
- Department of Biomedical Science, University of Sheffield, UK
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28
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el-Mas MM, Abdel-Rahman AA. Upregulation of imidazoline receptors in the medulla oblongata accounts for the enhanced hypotensive effect of clonidine in aortic barodenervated rats. Brain Res 1995; 691:195-204. [PMID: 8590053 DOI: 10.1016/0006-8993(95)00672-d] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The present study tested the hypothesis that an upregulation of the imidazoline receptor in the rostral ventrolateral medulla (RVLM) of aortic barodenervated (ABD) rats may account for the enhanced hypotensive effect of clonidine. In vitro autoradiographic radioligand binding studies were utilized to investigate the binding characteristics of imidazoline receptors in the RVLM and nucleus tractus solitarius (NTS), areas that play critical roles in cardiovascular regulation and elicitation of clonidine responses. ABD but not sham operation (SO) caused immediate and significant (P < 0.05) increases in mean arterial pressure (MAP) and heart rate (HR) and an impairment of the baroreflex-mediated HR response (baroreflex sensitivity, BRS). Two days after ABD, these parameters, except BRS, subsided to near-control (SO) levels. Intracisternal (i.c.) administration of clonidine (0.1 micrograms) elicited a 3-fold greater decrease in BP of conscious ABD compared with SO rats (-20.3 +/- 2.6 vs. -7.4 +/- 0.9 mmHg) thus demonstrating the ability of ABD to enhance centrally-mediated hypotensive responses. Autoradiographic visualization of brain sections obtained from separate groups of ABD and SO rats 48 h after surgery preincubated with [3H]idazoxan (2.5-3.5 nM) showed that [3H]idazoxan binding in RVLM, middle NTM (mNTS) and rostral NTS (rNTS) was saturable and of high affinity. Uneven distribution of imidazoline binding sites was evident since in control (SO) rats, Scatchard analysis of binding data revealed similar densities (Bmax) of [3H]idazoxan binding sites in the RVLM and mNTS versus significantly higher density in the rNTS. In ABD rats, the binding dissociation constant (Kd) was significantly decreased in both the RVLM (8.1 +/- 3.1 vs. 21.4 +/- 5.0 nM) and rNTS (12.3 +/- 1.3 vs. 18.6 +/- 3.1 nM) compared with SO rats while the Bmax was not affected. This finding suggests an increased receptor affinity in the RVLM and rNTS of barodenervated rats. The mNTS of ABD rats exhibited significant increases in the Bmax (861 +/- 96 vs. 570 +/- 87 fmol/mg protein) compared with values of SO rats but the receptor affinity was not affected. It is concluded that: (i) aortic baroreceptors exert a tonic inhibitory influence on central imidazoline receptor function; and (ii) the enhanced hypotensive effect of clonidine in conscious ABD rats may be accounted for by the increased affinity of the medullary imidazoline receptors particularly in the RVLM.
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Affiliation(s)
- M M el-Mas
- Department of Pharmacology, School of Medicine, East Carolina University, Greenville, NC, USA
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29
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Ruggiero DA, Regunathan S, Wang H, Milner TA, Reis DJ. Distribution of imidazoline receptor binding protein in the central nervous system. Ann N Y Acad Sci 1995; 763:208-21. [PMID: 7677332 DOI: 10.1111/j.1749-6632.1995.tb32408.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
I-receptors can be localized immunocytochemically in rat nervous system with polyclonal antibodies to an IRBP. I-receptors are cytoplasmic and detected in neuronal perikarya, processes, and glia. Labeled neuronal perikarya in the CNS are uncommon and localized to the mesencephalic trigeminal nucleus. I-receptors are heavily represented in primary sensory systems including: somatosensory systems (spinal and trigeminal) and visceral afferent systems (NTS), in central networks subserving autonomic regulation, neuroendocrine control and emotional behaviors, in circumventricular (neurohaemal) organs and in nonneuronal cells including astrocytes with regional densities paralleling neuronal innervation. The distributions of I-receptors and alpha 2-adrenergic receptors partially differ. I-receptors in the CNS appear to relate broadly to the visceral brain and its afferent inputs, particularly pain. Its functions may relate to regulation of integrative behaviors related to stress.
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Affiliation(s)
- D A Ruggiero
- Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021, USA
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30
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Nicholas AP, Pieribone V, Dagerlind A, Meister B, Elde R, Hökfelt T. In situ hybridization. A complementary method to radioligand-mediated autoradiography for localizing adrenergic, alpha-2 receptor-producing cells. Ann N Y Acad Sci 1995; 763:222-42. [PMID: 7677334 DOI: 10.1111/j.1749-6632.1995.tb32409.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- A P Nicholas
- Department of Histology and Neurobiology, Karolinska Institute, Stockholm, Sweden
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31
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Angel I, Le Rouzic M, Pimoule C, Graham D, Arbilla S. [3H]cirazoline as a tool for the characterization of imidazoline sites. Ann N Y Acad Sci 1995; 763:112-24. [PMID: 7677320 DOI: 10.1111/j.1749-6632.1995.tb32396.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Recent studies have shown that cirazoline, an alpha 1-adrenoceptor agonist, has greater affinity than do other imidazoline or guanidinium compounds at imidazoline recognition sites. In this report we used [3H]cirazoline as a probe to characterize imidazoline recognition sites present in membrane homogenates of rat brain and kidney as well as pancreatic beta HIT T15 cells. Specific binding of [3H]cirazoline to these various homogenates was saturable and reversible and was resolved into two classes of high affinity binding sites. Competition inhibition studies of [3H]cirazoline binding to these different membrane preparations were performed with alkaloid, phenylethylamine, imidazoline, and guanidinium compounds. Catecholamines and non-imidazoline adrenoceptor ligands such as epinephrine, benextramine, prazosin, propranolol, rauwolscine, or adrenoceptor ligands such as epinephrine, benextramine, prazosin, propranolol, rauwolscine, or yohimbine did not compete with [3H]cirazoline (Ki > 10 microM). Under our experimental conditions, only guanidinium and imidazoline derivatives had high affinities for [3H]cirazoline binding sites. Unlabeled cirazoline, clonidine, bromoxidine, idazoxan, and amiloride had the highest affinities with this respective rank order. These results suggest that [3H]cirazoline is a novel high affinity radioligand that specifically labels nonadrenergic imidazoline-guanidinium sites in the brain, kidney, and beta cells. Furthermore, the obtained rank order of inhibition suggests that [3H]cirazoline binding does not distinguish between I1 and I2 sites. In addition, we compared the specific binding of [3H]cirazoline with that of the alpha 2-adrenoceptor antagonist [3H]rauwolscine in chinese hamster ovary (CHO) cell lines stably expressing human alpha 2C2-, alpha 2C4-, and alpha 2C10-adrenoceptor subtypes. Using [3H]rauwolscine as a probe, each of these transfected cell lines expressed high levels for the three different alpha 2-adrenoceptor subtypes (Bmax values were between 2 and 7 pmol.mg-1 protein). In contrast, none of these cell lines displayed measurable imidazoline recognition sites. In summary, [3H]cirazoline is a novel high affinity radioligand that specifically labels imidazoline recognition sites without significant alpha- or beta-adrenoceptor binding. Furthermore, our results using alpha 2-adrenoceptor transfected cells confirm that the imidazoline recognition sites and each of the cloned alpha 2-adrenoceptor subtypes represent distinct macromolecular entities.
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Affiliation(s)
- I Angel
- Synthélabo Recherche, Rueil-Malmaison, France
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32
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Schmidt ME, Matochik JA, Risinger RC, Schouten JL, Zametkin AJ, Cohen RM, Potter WZ. Regional brain glucose metabolism after acute alpha 2-blockade by idazoxan. Clin Pharmacol Ther 1995; 57:684-95. [PMID: 7781269 DOI: 10.1016/0009-9236(95)90232-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
BACKGROUND Several classes of antidepressant drugs act on alpha 2-adrenergic receptors. Studies of patients with disorders responsive to treatment with these drugs report group differences in ex vivo measures of alpha 2-binding and in vivo responses mediated by alpha 2-receptors. Measurement of regional brain metabolic response to an alpha 2-antagonist may be a useful method for further definition of the role alpha 2-receptor regulation plays in the treatment of neuropsychiatric disorders. METHODS Regional brain glucose metabolism was measured before and after infusion with 200 micrograms/kg idazoxan with use of 18F-fluoro-2-deoxyglucose positron emission tomography in 13 healthy men. Arterial drug concentration, behavioral responses, and cardiovascular responses were also measured. RESULTS The absolute and normalized glucose metabolic rate significantly increased in primary visual cortex. Significant increases and decreases occurred in normalized metabolic rates in prefrontal cortical regions. Measurement of metabolic effects occurred during the peak cardiovascular response. CONCLUSIONS Our findings are consistent with regionally specific effects of alpha 2-blockade. This method may be useful for the study of alpha 2-receptor function in humans.
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Affiliation(s)
- M E Schmidt
- Section on Clinical Pharmacology, National Institute of Mental Health, Bethesda, MD 20892, USA
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33
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King PR, Gundlach AL, Louis WJ. Quantitative autoradiographic localization in rat brain of alpha 2-adrenergic and non-adrenergic I-receptor binding sites labelled by [3H]rilmenidine. Brain Res 1995; 675:264-78. [PMID: 7796138 DOI: 10.1016/0006-8993(95)00083-3] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
alpha 2A-Adrenergic receptor (AR) and non-adrenergic imidazoline receptor (I-R) binding sites have been previously characterized in rat cerebral cortex membranes using the N-substituted oxazoline, [3H]rilmenidine ([3H]Ril) [King, P.R. et al., Eur. J. Pharmacol., 218 (1992) 101-108]. In the present study, in vitro autoradiography was used to quantify the regional distribution of these receptors throughout the rat neuroaxis. The distribution and relative density (fmol/mg tissue) of I-Rs was examined in the presence of 1 microM adrenaline to block the adrenergic component of 40 nM [3H]Ril binding and non-specific binding was measured in the presence of another oxazoline, Bay a6781 (10 microM). Both alpha 2A-ARs and I-Rs were broadly, but heterogeneously, distributed. In forebrain, high levels of [3H]Ril-labelled alpha 2A-AR sites were observed in the anterior olfactory nucleus, the piriform, entorhinal and perirhinal cortices, lateral septum, bed nucleus of the stria terminalis, several thalamic nuclei, the amygdala and the arcuate, dorsomedial and posterior hypothalamic nuclei. In hindbrain, alpha 2A-AR sites were concentrated in locus coeruleus, lateral parabrachial nucleus, nucleus of the solitary tract and area postrema. I-R sites accounted for 50% or more of specific [3H]Ril binding (40 nM) in most cortical and hypothalamic nuclei, nucleus of the solitary tract, cranial motor nuclei and most spinal cord layers. The highest densities of I-Rs were found in the arcuate, dorsomedial and posterior hypothalamic nuclei, the locus coeruleus, the area postrema, the cranial motor nuclei and associated with spinal motor neurones. A very high concentration of I-Rs was also detected in the pineal gland. The distribution of alpha 2-AR sites determined resembled that reported with [3H]p-aminoclonidine which appears to specifically label alpha 2-ARs and not I1-R sites in rat brain sections, and [3H]methoxyidazoxan which is a selective alpha 2-AR antagonist. The regional and cellular distribution of I-R binding sites was unlike the distribution of putative I1-R sites labelled by [3H]clonidine in human brain, although comparable autoradiographic mapping studies in rat brain have not been done using this ligand. The regional and cellular distribution of [3H]-labelled I-R binding sites had both similarities and differences to that reported using the imidazoline ligand, [3H]idazoxan, with common labelling of areas such as area postrema, arcuate and interpeduncular nuclei and pineal gland with the two ligands, and differential relative binding levels ([3H]Ril > [3H]idazoxan) associated with hippocampal pyramidal cells and brainstem and spinal motor neurones.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- P R King
- University of Melbourne, Department of Medicine, Austin Repatriation Hospital, Heidelberg, Vic., Australia
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34
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Browne SE, Macrae IM. Differential patterns of local cerebral glucose utilisation associated with rilmenidine- or B-HT 933-induced hypotension. Brain Res 1994; 666:216-22. [PMID: 7882031 DOI: 10.1016/0006-8993(94)90775-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The anti-hypertensive drug, rilmenidine, has activity at both imidazoline-preferring receptors (IPRs) and alpha 2-adrenoceptors. However, available evidence suggests that its hypotensive effect is mediated via central IPRs. In the present study, the neuroanatomical regions involved in mediating the hypotensive response to rilmenidine were investigated using the [14C]2-deoxyglucose in vivo autoradiographic technique to map drug-induced changes in glucose utilisation within the CNS of conscious, spontaneously hypertensive rats (SHR). The cerebral metabolic effects of rilmenidine were compared with those of B-HT 933, a selective, alpha 2-adrenoceptor agonist with no selectivity for the IPR. Rilmenidine (1 mg/kg, s.c.) and B-HT 933 (2 mg/kg, s.c.) both elicited a moderate but significant hypotension (-24 +/- 2 and -18 +/- 5 mmHg, resp.) and bradycardia (-62 +/- 19.5 and -69 +/- 14 beats/min, resp.). [14C]2-deoxyglucose autoradiography, initiated after stabilisation of the drug-induced reduction in blood pressure, revealed significant reductions (P < 0.05) in local cerebral glucose utilisation (LCGU) in the intermediolateral cell column of the spinal cord, area postrema, ventrolateral medulla, nucleus tractus solitarius and cuneate nucleus of rilmenidine-treated rats. Rilmenidine did not significantly alter LCGU in a number of structures containing high densities of alpha 2-adrenoceptors such as nucleus accumbens, locus coeruleus, frontal cortex. No significant changes in glucose use were evident in any of the 26 CNS regions examined following B-HT 933 administration. These results provide evidence for the functional involvement of brainstem cardiovascular control centres in the central hypotensive effects of rilmenidine.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S E Browne
- Wellcome Surgical Institute, University of Glasgow, UK
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35
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Fulford AJ, Butler S, Heal DJ, Kendall DA, Marsden CA. Evidence for altered alpha 2-adrenoceptor function following isolation-rearing in the rat. Psychopharmacology (Berl) 1994; 116:183-90. [PMID: 7862947 DOI: 10.1007/bf02245061] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
This study investigated central alpha 2-adrenoceptor function in differentially reared rats. Rats reared from weaning were either housed singly or in groups of five. Measurements of spontaneous ambulatory activity at 4 weeks postweaning showed that isolates were more hyperactive on exposure to a novel environment than grouped rats. alpha 2-Adrenoceptors were investigated using alpha 2-adrenoceptor agonist-induced behaviours, [3H]-idazoxan binding and measurement of forskolin-stimulated cyclic AMP accumulation. Clonidine (0.001-1.0 mg/kg IP) induced mydriasis in both groups with no difference observed in the response between the isolation and group-reared animals. Clonidine (0.01-0.5 mg/kg IP) induced hypoactivity in both groups, with the effect significantly greater in the isolation-reared rats. Idazoxan markedly attenuated both responses, confirming their induction by alpha 2-adrenoceptor stimulation. Clonidine-induced hypoactivity and mydriasis are mediated by pre- and postsynaptic alpha 2-adrenoceptors, respectively; therefore the results suggest rats reared in isolation have enhanced presynaptic but unchanged postsynaptic alpha 2-adrenoceptor function. Saturation binding experiments using [3H]-idazoxan were undertaken to determine alpha 2-adrenoceptor number (Bmax) and affinity (Kd) in membranes prepared from the frontal cortex and hippocampus. Analysis of binding data revealed an increase in receptor number in the hippocampus of isolates. Cyclic AMP accumulation was measured in hippocampal slices from differentially reared rats. Isolation-rearing did not affect cyclic AMP accumulation in response to stimulation by forskolin (30 microM). However, the selective alpha 2-adrenoceptor agonist, UK14304, produced a significantly greater inhibition of cyclic AMP accumulation in slices from isolated rats, confirming changes in alpha 2-adrenoceptor function following isolation rearing.
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Affiliation(s)
- A J Fulford
- Department of Physiology and Pharmacology, Medical School, Queen's Medical Centre, Nottingham, UK
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Escribá PV, Sastre M, Wang H, Regunathan S, Reis DJ, García-Sevilla JA. Immunodetection of putative imidazoline receptor proteins in the human and rat brain and other tissues. Neurosci Lett 1994; 178:81-4. [PMID: 7816347 DOI: 10.1016/0304-3940(94)90295-x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A specific anti-imidazoline receptor (IR) protein antiserum was used to detect these putative receptors in brain and other tissues. In immunoblotting experiments, various brain areas and tissues expressed a double band of 29-30 kDa, and some of them bands of 47 and 66 kDa. The human medulla oblongata also showed bands of 44 and 50 kDa; and the rat adrenal medulla, bands of 58 and 86 kDa. Total immunoreactivity correlated with the density of IR binding sites in the various tissues. This is first evidence of heterogeneity of immunoreactive IRs in the mammalian brain.
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Affiliation(s)
- P V Escribá
- Department of Fundamental Biology and Health Sciences, University of the Balearic Islands, Palma de Mallorca, Spain
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37
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Wallace DR, Muskardin DT, Zahniser NR. Pharmacological characterization of [3H]idazoxan, [3H]RX821002 and p-[125I]iodoclonidine binding to alpha 2-adrenoceptors in rat cerebral cortical membranes. Eur J Pharmacol 1994; 258:67-76. [PMID: 7925601 DOI: 10.1016/0014-2999(94)90058-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Binding characteristics of alpha 2-adrenoceptors in rat cerebral cortical membranes were compared using the antagonist radioligands [3H]idazoxan, [3H]2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline ([3H]RX821002), and the partial agonist radioligand [125I]2-[2,6-(dichloro-4-iodophenyl)imino]imidazoline ([125I]iodoclonidine). With [3H]RX821002 and alpha 2-adrenoceptor subtype-selective competitors, both alpha 2A/D- and alpha 2C-adrenoceptor subtypes were detected, suggesting rat cortical membranes contain approximately 90% alpha 2A/D-adrenoceptor subtype and 10% alpha 2C-adrenoceptor subtype. Only alpha 2A/D-adrenoceptors were detected with [3H]idazoxan and [125I]iodoclonidine. All three radioligands bound to a single high affinity site (Kd = 0.3-1.6 nM). However, the densities of sites labeled by [3H]idazoxan and [125I]iodoclonidine were 50% greater than the density labeled by [3H]RX821002, likely representing non-adrenoceptor binding sites. The density of [125I]iodoclonidine binding sites in glycylglycine buffer was similar to that labeled by [3H]RX821002. These results suggest that: (1) alpha 2A/D-adrenoceptors are the predominant subtype in rat cerebral cortex, (2) demonstrate that the small number of alpha 2C-adrenoceptors in this tissue can be detected using prazosin to displace [3H]RX821002 binding, and (3) non-adrenoceptor binding with [125I]iodoclonidine can be minimized with the use of glycylglycine buffer.
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Affiliation(s)
- D R Wallace
- Department of Pharmacology, University of Colorado Health Science Center, Denver
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38
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De Vos H, Bricca G, De Keyser J, De Backer JP, Bousquet P, Vauquelin G. Imidazoline receptors, non-adrenergic idazoxan binding sites and alpha 2-adrenoceptors in the human central nervous system. Neuroscience 1994; 59:589-98. [PMID: 8008210 DOI: 10.1016/0306-4522(94)90179-1] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Both [3H]clonidine and [3H]idazoxan bind to alpha 2 adrenoceptors. The former also labels imidazoline receptors, and the latter non-adrenergic idazoxan binding sites. In order to investigate whether the imidazoline receptors and non-adrenergic idazoxan binding sites are identical, we compared the binding characteristics of [3H]clonidine and [3H]idazoxan to these sites by radioligand binding experiments on ultra-thin slices and homogenates of human striatum. A good correlation was found between the effect of different ions on the binding characteristics of [3H]clonidine and [3H]idazoxan, and the affinities of most competing drugs. However, clonidine and rilmenidine displayed a 100- and 10-fold lower affinity, respectively, for the idazoxan binding sites than for the imidazoline receptors. Autoradiography with [3H]clonidine showed that high densities of imidazoline receptors were present in the striatum, pallidum, gyrus dentatus of the hippocampus, amygdala, and substantia nigra. Moderate densities were found throughout the cerebral cortex, thalamus and several brainstem nuclei including the nucleus olivarius inferior. Low densities were seen in the cerebellum, spinal cord and pituitary gland. As for the non-adrenergic sites labelled by [3H]idazoxan, the imidazoline receptors can be found in all major brain areas examined. However, there are some striking differences between the concentrations of imidazoline receptors and non-adrenergic idazoxan binding sites in certain brain regions. To reconcile distribution and pharmacologic data, we propose that imidazoline receptors and non-adrenergic idazoxan binding sites represent different proteins or protein complexes and that at least in the nucleus reticularis lateralis and the striatum, imidazoline receptors and non-adrenergic idazoxan binding sites may be physically associated. The regional distribution of alpha 2 adrenoceptors within the human CNS was determined by quantitative autoradiography with [3H]RX821002. The highest densities of alpha 2 adrenoceptors were found in the cerebral and cerebellar cortex, and certain regions in the medulla oblongata (floor of the IV ventricle, reticular formation, hypoglossal nucleus and nucleus olivarius inferior). No alpha 2 adrenoceptors were detected in the pituitary gland. There exists no relationship between the distribution pattern of imidazoline receptors and alpha 2 adrenoceptors, indicating that these binding sites are independent from each other.
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Affiliation(s)
- H De Vos
- Department of Protein Chemistry, Vrije Universiteit Brussel, St. Genesius-Rode, Belgium
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Ventura S, Pennefather JN. Alpha 2-adrenoceptor binding sites vary along the length of the male reproductive tract: a possible basis for the regional variation in response to field stimulation. Eur J Pharmacol 1994; 254:167-73. [PMID: 7911427 DOI: 10.1016/0014-2999(94)90384-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Field stimulation (60V, 1 ms, 10 Hz, 10 s) produced monophasic contractions of cauda epididymides that were enhanced by the noradrenaline uptake inhibitor, nisoxetine, but unaffected by the alpha 2-adrenoceptor antagonist, idazoxan. Similar stimulation of vas deferens produced biphasic contractions that in the presence of idazoxan were enhanced and became monophasic. Nisoxetine accentuated the separation of the two phases. Radioligand binding studies yielded dissociation constants (KD) for [3H]prazosin binding that were similar (0.1-0.2 nM) in membrane preparations of both halves of the vas deferens and in the cauda epididymis; maximum binding density (Bmax) was slightly lower in cauda epididymis (20 fmol/mg protein) than in vas deferens (approximately 50 fmol/mg protein). KD values for [3H]rauwolscine were similar in the two halves of the vas deferens but Bmax values were higher in the prostatic half of the tissue (39 fmol/mg protein) than in the epididymal half (22 fmol/mg protein). We were unable to detect specific binding of [3H]rauwolscine in cauda epididymis. Absence or masking of alpha 2-adrenoceptors in this tissue would explain our findings that alpha 2-adrenoceptor agonists and antagonists do not modulate the responses of the cauda epididymis to trains of field stimulation.
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MESH Headings
- Adrenergic alpha-Antagonists/pharmacology
- Animals
- Binding, Competitive/drug effects
- Dioxanes/pharmacology
- Electric Stimulation
- Epididymis/drug effects
- Epididymis/metabolism
- Epididymis/physiology
- Idazoxan
- In Vitro Techniques
- Male
- Membranes/drug effects
- Membranes/metabolism
- Muscle Contraction/drug effects
- Prazosin/pharmacokinetics
- Radioligand Assay
- Rats
- Receptors, Adrenergic, alpha-1/drug effects
- Receptors, Adrenergic, alpha-1/metabolism
- Receptors, Adrenergic, alpha-1/physiology
- Receptors, Adrenergic, alpha-2/drug effects
- Receptors, Adrenergic, alpha-2/metabolism
- Receptors, Adrenergic, alpha-2/physiology
- Vas Deferens/drug effects
- Vas Deferens/metabolism
- Vas Deferens/physiology
- Yohimbine/pharmacokinetics
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Affiliation(s)
- S Ventura
- Department of Pharmacology, Monash University, Clayton, Victoria, Australia
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41
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Miralles A, Ribas C, Olmos G, García-Sevilla JA. Differential effects of the alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline on brain alpha 2-adrenoceptors and I2-imidazoline sites in vitro and in vivo. J Neurochem 1993; 61:1602-10. [PMID: 8228980 DOI: 10.1111/j.1471-4159.1993.tb09793.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) is a peptide-coupling agent that is being used to inactivate irreversibly alpha 2-adrenoceptors and other receptors. The aim of the present study was to assess the in vitro and in vivo effects of EEDQ on the newly discovered brain I2-imidazoline sites, located mainly in mitochondria. Preincubation of rat cortical membranes with EEDQ (10(-8)-10(-5) M) markedly decreased (20-90%) the specific binding of the selective antagonist [3H]RX821002 to alpha 2-adrenoceptors without affecting that of [3H]idazoxan (in the presence of adrenaline) to I2-imidazoline sites. In EEDQ-pretreated membranes (10(-5) M, 30 min at 25 degrees C), the density of I2-imidazoline sites (Bmax = 80 +/- 4 fmol/mg of protein) was not different from that determined in untreated membranes in the presence of (10(-6) M (-)-adrenaline (Bmax = 83 +/- 4 fmol/mg of protein), and both densities were lower (24%, p < 0.05) than the total native density of [3H]idazoxan binding sites (Bmax = 107 +/- 6 fmol/mg of protein) (I2-imidazoline sites plus alpha 2-adrenoceptors). Treatment of rats with an optimal dose of EEDQ (1.6 mg/kg, i.p., for 2 h to 30 days) reduced maximally at 6 h (by 95 +/- 1%) the specific binding of [3H]-RX821002 to alpha 2-adrenoceptors, but also the binding of [3H]idazoxan to I2-imidazoline sites (by 44 +/- 5%). Pretreatment with yohimbine (10 mg/kg, i.p.) fully protected against EEDQ-induced alpha 2-adrenoceptor inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- A Miralles
- Department of Fundamental Biology and Health Sciences, University of the Balearic Islands, Palma de Mallorca, Spain
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42
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Meana JJ, Barturen F, Martin I, García-Sevilla JA. Evidence of increased non-adrenoceptor [3H]idazoxan binding sites in the frontal cortex of depressed suicide victims. Biol Psychiatry 1993; 34:498-501. [PMID: 8268335 DOI: 10.1016/0006-3223(93)90243-7] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- J J Meana
- Department of Pharmacology, University of the Basque Country Medical School Leioa, Bizkaia
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43
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Sastre M, García-Sevilla JA. Opposite age-dependent changes of alpha 2A-adrenoceptors and nonadrenoceptor [3H]idazoxan binding sites (I2-imidazoline sites) in the human brain: strong correlation of I2 with monoamine oxidase-B sites. J Neurochem 1993; 61:881-9. [PMID: 8395564 DOI: 10.1111/j.1471-4159.1993.tb03599.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
In the postmortem human brain (27 specimens of frontal cortex, Brodmann area 9), the specific binding of the antagonists [3H]RX 821002 (2-methoxyidazoxan) to alpha 2A-adrenoceptors and that of [3H]idazoxan to I2-imidazoline sites (a nonadrenoceptor mitochondrial site) were determined in parallel to study the effect of aging (range, 4-89 years) on both brain proteins. The density of alpha 2A-adrenoceptors and age were negatively correlated (r = -0.71; p < 0.001). In contrast, the density of I2-imidazoline sites was positively correlated with aging (r = 0.59; p < 0.005). The ratio of receptor densities (alpha 2A/I2) also showed a marked negative correlation with age (r = -0.76; p < 0.001). In an age-selected group (range, 10-89 years), the density of monoamine oxidase (MAO)-B sites labeled by [3H]Ro 19-6327 (lazabemide) also showed a positive correlation with age (r = 0.80; p < 0.005). In these subjects, the density of I2-imidazoline sites correlated well with the density of MAO-B sites (r = 0.70; p < 0.005). The ratio of the density of these sites (MAO-B/I2) did not correlate with the age of the subject at death (r = -0.15). In the human frontal cortex, idazoxan displayed very low affinity (Ki = 89 microM) against the binding of [3H]Ro 19-6327 to MAO-B, which discounted a direct interaction of [3H]idazoxan with the active center of the enzyme and indicated that the I2-imidazoline site cannot be identified with MAO-B.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Sastre
- Department of Fundamental Biology and Health Sciences, University of the Balearic Islands, Palma de Mallorca, Spain
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44
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Renouard A, Widdowson PS, Cordi A. [3H]-idazoxan binding to rabbit cerebral cortex recognises multiple imidazoline I2-type receptors: pharmacological characterization and relationship to monoamine oxidase. Br J Pharmacol 1993; 109:625-31. [PMID: 8102932 PMCID: PMC2175647 DOI: 10.1111/j.1476-5381.1993.tb13618.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
1. In rabbit cerebral cortical homogenates, saturation analysis of [3H]-idazoxan, an alpha 2-adrenoceptor antagonist, revealed high affinity binding to a single site with high density. Competition experiments demonstrated that the [3H]-idazoxan recognition site was insensitive to the catecholamines, adrenaline and noradrenaline and possessed a low affinity for the alpha 2- and alpha 1-adrenoceptor antagonists, rauwolscine, yohimbine and prazosin, suggesting that the site was not an adrenoceptor. Mapping [3H]-idazoxan binding sites in the forebrain of rabbits by autoradiography, showed high densities of I2 sites in the medial preoptic area and in the stria terminalis. Moderate binding was found in caudate nucleus, putamen, cerebral cortex and hippocampus. 2. The imidazolines cirazoline, naphazoline, guanabenz and BRL44408 along with amiloride, which is structurally related to the imidazolines, all had high affinity for the [3H]-idazoxan site, suggesting that the site was related to the I2 imidazoline-recognition site described by other groups. However, the imidazolines, clonidine and UK-14,304 and the structurally related rilmenidine all had a low affinity for the binding site, showing that [3H]-idazoxan was not binding to the I1 imidazoline-recognition site found in rat, bovine and human medulla oblongata. 3. Naphazoline, guanabenz, clonidine and amiloride competition studies had Hill slopes which were significantly different from unity (P < 0.01) and computer analysis showed that the [3H]-idazoxan binding data could be best fitted to a model which considers binding to two sites (P < 0.01). One site has a high affinity for idazoxan, cirazoline, naphazoline, guanabenz and amiloride and a moderate affinity for BRL44408 and clonidine (70% of binding) and the second site (30% of binding) has a high affinity for idazoxan and cirazoline, but a lower affinity for naphazoline, guanabenz, amiloride,BRL44408 and clonidine.4. Experiments using [3H]-RX821002, in contrast to [3H]-idazoxan, clearly demonstrated the presence ofa single type of alpha2-adrenoceptor in rabbit cortex with a pharmacological profile which is similar to the alpha2A-adrenoceptor possessing a high affinity for yohimbine, rauwolscine, BRL44408 and oxymetazoline,but a lower affinity for prazosin.5. The monoamine oxidase inhibitors, clorgyline, pargyline and deprenyl had at least a ten fold lower affinity at the rabbirt cortex I2 site as compared to their known affinity at monoamine oxidase suggesting that the I2 site is not related to the active site of the enzyme, monoamine oxidase. In addition, the peripheral benzodiazepine ligands, PK-11195 or Ro 5-4864 both had very low affinities at the I2 site in rabbit cortex suggesting that the [3H]-idazoxan binding was not to the peripheral benzodiazepine binding site.
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Affiliation(s)
- A Renouard
- Institut de Recherches Servier, Surenes, France
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45
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Fatima B, Hugues G, Giampiero B, Alain B, Pascal B, Dontenwill M. Polyclonal anti-idazoxan antibodies: characterization and purification. Eur J Pharmacol 1993; 246:45-51. [PMID: 8354342 DOI: 10.1016/0922-4106(93)90008-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Amino-idazoxan coupled to hemocyanine was used to raise anti-idazoxan antibodies in the rabbit. The antibodies were affinity purified with an amino-idazoxan affinity column. Binding studies with [3H]idazoxan showed a dissociation constant of 2.2 +/- 1.4 nM. The specificity spectrum of these antibodies indicates that the imidazoline part of idazoxan is more important for recognition than the benzodioxan ring as imidazoline substances (clonidine, cirazoline) are powerful competitors of [3H]idazoxan binding on the antibodies. Catecholamines or imidazoles were unable to displace [3H]idazoxan from the antibodies. These anti-idazoxan antibodies present specificity similarities with the imidazoline receptor as did our previously obtained anti-clonidine antibodies. Affinity-purified antibodies represent useful tools for studying the imidazoline receptors particularly with an anti-idiotypic approach.
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Affiliation(s)
- B Fatima
- Laboratoire de Pharmacologie Cardiovasculaire et Rénale, CNRS URA, Faculté de Médecine, Strasbourg, France
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46
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Van Liefde I, Vauquelin G, De Keyser J, De Backer JP, De Vos H. Alpha 2A adrenoceptors and non-adrenergic idazoxan binding sites in calf brain and retina are distinct from those in human brain. Neurochem Int 1993; 22:501-9. [PMID: 8387366 DOI: 10.1016/0197-0186(93)90046-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
alpha 2 Adrenoceptors in membrane preparations of human and calf frontal cortex and of calf retina can be labelled by the antagonists [3H]idazoxan, [3H]rauwolscine and [3H]RX 821002. Present and previous data indicate that [3H]idazoxan possesses the highest affinity for the alpha 2 adrenoceptors in the calf tissues, whereas [3H]rauwolscine displays the highest affinity for those in the human frontal cortex. Competition binding experiments with adrenergic and serotonergic drugs further support the notion that the alpha 2 adrenoceptors in calf frontal cortex and retina are similar, but distinct from the receptors in human frontal cortex. The alpha 2 adrenoceptors in the three investigated tissues display low affinity for the antagonist prazosin, which suggests that they all belong to the alpha 2A subclass. The competition binding curves of the alpha 2A adrenoceptor subtype-selective agonist oxymetazoline are shallow, but undergo a rightward shift and steepening in the presence of GTP. The shallow curves can therefore be attributed to the coupling of the alpha 2 adrenoceptors to G proteins. The different binding characteristics of the alpha 2A adrenoceptors from the investigated human and bovine tissues are likely to reflect species-related differences in protein structure. [3H]Idazoxan binds also to non-adrenergic sites in membrane preparations from the three tissues. However, the affinity of [3H]idazoxan for these sites in calf cortex and retina is appreciably lower than for those in human cortex. The species-related differences of the non-adrenergic idazoxan binding sites may be due to differences in protein structure or even to differences in gene-product.
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Affiliation(s)
- I Van Liefde
- Department of Protein Chemistry, Vrije Universiteit Brussel, St. Genesius-Rode, Belgium
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47
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Nicholas AP, Pieribone V, Hökfelt T. Distributions of mRNAs for alpha-2 adrenergic receptor subtypes in rat brain: an in situ hybridization study. J Comp Neurol 1993; 328:575-94. [PMID: 8381444 DOI: 10.1002/cne.903280409] [Citation(s) in RCA: 316] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Selective 35S-labeled oligonucleotide probes were designed to sequences of the rat alpha-2A (RG20), alpha-2B (RNG), and alpha-2C (RG10) adrenoreceptor mRNAs for use in in situ hybridization experiments on sections of unfixed rat brain, spinal cord and kidney. After hybridized sections were exposed to film or dipped in autoradiographic emulsion, specific and selective labeling patterns characteristic for each probe and region of the central nervous system were observed. Alpha-2A mRNA labeling was most pronounced in neurons in layer six of the cerebral cortex, hypothalamic paraventricular nucleus, reticular thalamic nucleus, pontine nuclei, locus coeruleus, vestibular nuclei, trapezoid nuclei, deep cerebellar nuclei, nucleus tractus solitarii, ventrolateral medullary reticular formation, and the intermediolateral cell column of the thoracic spinal cord. In some of these locations, the receptor mRNA, in all probability, is present in noradrenaline and perhaps adrenaline neurons. The alpha-2B probe, which primarily labels the kidney, gave only a very light signal in the thalamus in the central nervous system after extended exposure times. Alpha-2C mRNA labeling was primarily observed in the olfactory bulb, cerebral cortex, islands of Calleja, striatum, hippocampal formation, cerebellar cortex, and dorsal root ganglia. Labeling patterns disappeared when excess unlabeled probes were added to their respective radiolabeled probes, or when sense probes were employed. When a hybrid antisense probe homologous to all three alpha-2 probes was used, labeling patterns also disappeared. The present study therefore justifies the pharmacological subclassification of alpha-2 receptors by providing anatomical evidence for specific and selective cell groups in the rat central nervous system containing mRNA for three alpha-2 receptor subtypes.
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Affiliation(s)
- A P Nicholas
- Department of Histology and Neurobiology, Karolinska Institutet, Stockholm, Sweden
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48
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Bricca G, Greney H, Dontenwill-Kieffer M, Zhang J, Belcourt A, Bousquet P. Heterogeneity of the specific imidazoline binding of [3H]idazoxan in the human cerebral cortex. Neurochem Int 1993; 22:153-63. [PMID: 8439769 DOI: 10.1016/0197-0186(93)90008-s] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The aim of the present study was to verify whether [3H]idazoxan can be considered as a highly selective ligand for imidazoline preferring receptors (IPR). In human frontal cortex membrane preparations [3H]idazoxan at a low concentration (2 nM) only labelled imidazoline sensitive, catecholamine insensitive sites. Binding was of high affinity, saturable and stereospecific. The rank order of potency of different compounds able to inhibit this binding was cirazoline > (+/-)-idazoxan > guanoxan > (-)-idazoxan > tolazoline > UK-14304 > clonidine. Amiloride, imidazol-4-acetic acid and histamine had no significant affinity for IPR labelled by [3H]idazoxan. [3H]idazoxan bound to 2 different sites (KD1 = 1 nM and KD2 = 16.4 nM). Clonidine behaved as a non competitive, non allosteric inhibitor of [3H]idazoxan binding. Both [3H]idazoxan binding sites were equally affected by clonidine. In membrane preparations obtained from the Nucleus Reticularis Lateralis region (NRL) of the brainstem, [3H]idazoxan binding was similar to that in cortical membranes, particularly with regard to specificity and kinetics. However, in the NRL region binding sites were 4-5 times more numerous than in the frontal cortex. Non linear analyses of saturation data obtained with NRL membrane preparations were compatible with both a one site and a two sites model. No significant effects of 1 mM MgCl2 alone or with 100 microM Gpp(NH)p were observed on either [3H]idazoxan binding or the competition with clonidine or rilmenidine. As in the cortical membrane, clonidine was a non competitive inhibitor of [3H]idazoxan binding to membranes from the NRL region. In conclusion, we show that when a low concentration is used, [3H]idazoxan binding to human brain involves sites almost completely insensitive to catecholamines and specific for imidazolines or related compounds. This binding involves two distinct sites. We also report that [3H]idazoxan imidazoline binding sites are not coupled with a G protein. Because of the non competitive interaction between clonidine and [3H]idazoxan for the binding sites of the latter, we are unable to conclude that the binding sites of the two drugs are identical. However, the non competitive, non allosteric interaction suggests a complex model of multiple binding sites.
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Affiliation(s)
- G Bricca
- Laboratoire de Pharmacologie cardiovasculaire et rénale, CNRS URA589, Faculté de Médecine, Université Louis Pasteur, Strasbourg, France
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49
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Affiliation(s)
- J P Hieble
- Department of Pharmacology, Smith Kline Beecham Pharmaceuticals, King of Prussia, Pennsylvania
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50
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Flügge G, Jöhren O, Fuchs E. [3H]Rauwolscine binding sites in the brains of male tree shrews are related to social status. Brain Res 1992; 597:131-7. [PMID: 1335817 DOI: 10.1016/0006-8993(92)91514-f] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The aim of the present study was to investigate the influence of social status on central nervous alpha 2-adrenoceptors. Using the specific alpha 2-adrenoceptor antagonist [3H]rauwolscine, binding sites in the brains of dominant and subordinate male tree shrews were quantified by in vitro autoradiography. In 5 of the 14 brain structures investigated, subordinates had significantly lower numbers of binding sites than dominants. These structures were the solitary tract nucleus, the dorsal motor nucleus of the vagus, the periaqueductal gray, the perifornical region of the hypothalamus and the medial nucleus of the amygdala. These brain areas are all intimately involved in the regulation of autonomic functions and of emotional behavior. Also the affinities for [3H]rauwolscine differed between the groups. In 3 nuclei, the solitary tract nucleus, the periaqueductal gray and the medial nucleus of the amygdala, dominants had significantly higher Kd-values than subordinates. This demonstrates the presence of low affinity binding sites in dominants which do not exist in subordinates. It is suggested that the low number of [3H]rauwolscine binding sites in subordinates results from down-regulation of alpha 2-adrenoceptors by high levels of noradrenaline and/or adrenaline. The disappearance of low affinity [3H]rauwolscine binding sites may play an important role in the etiology of psychosocial stress.
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Affiliation(s)
- G Flügge
- German Primate Center, Göttingen
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