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Brown NK, Roche JK, Farmer CB, Roberts RC. Evidence for upregulation of excitatory synaptic transmission in the substantia nigra in Schizophrenia: a postmortem ultrastructural study. J Neural Transm (Vienna) 2023; 130:561-573. [PMID: 36735096 DOI: 10.1007/s00702-023-02593-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Accepted: 01/14/2023] [Indexed: 02/04/2023]
Abstract
The dopamine hypothesis of schizophrenia suggests that psychotic symptoms originate from dysregulation of dopaminergic activity, which may be controlled by upstream innervation. We hypothesized that we would find anatomical evidence for the hyperexcitability seen in the SN. We examined and quantified synaptic morphology, which correlates with function, in the postmortem substantia nigra (SN) from 15 schizophrenia and 12 normal subjects. Synapses were counted using stereological techniques and classified based on the morphology of the post-synaptic density (PSD) and the presence or absence of a presynaptic density. The density and proportion of excitatory synapses was higher in the schizophrenia group than in controls, while the proportion (but not density) of inhibitory synapses was lower. We also detected in the schizophrenia group an increase in density of synapses with a PSD of intermediate thickness, which may represent excitatory synapses. The density of synapses with presynaptic densities was similar in both groups. The density of synapses with mixed morphologies was higher in the schizophrenia group than in controls. The human SN contains atypical synaptic morphology. We found an excess amount and proportion of excitatory synapses in the SN in schizophrenia that could result in hyperactivity and drive the psychotic symptoms of schizophrenia. The sources of afferent excitatory inputs to the SN arise from the subthalamic nucleus, the pedunculopontine nucleus, and the ventral tegmental area (VTA), areas that could be the source of excess excitation. Synapses with mixed morphologies may represent inputs from the VTA, which release multiple transmitters.
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Affiliation(s)
- Nicole K Brown
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Sparks Center 835C, 1720 2nd Avenue South, Birmingham, AL, 35294, USA
| | - Joy K Roche
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Sparks Center 835C, 1720 2nd Avenue South, Birmingham, AL, 35294, USA
| | - Charlene B Farmer
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Sparks Center 835C, 1720 2nd Avenue South, Birmingham, AL, 35294, USA
| | - Rosalinda C Roberts
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Sparks Center 835C, 1720 2nd Avenue South, Birmingham, AL, 35294, USA.
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Mabry SJ, McCollum LA, Farmer CB, Bloom ES, Roberts RC. Evidence for altered excitatory and inhibitory tone in the post-mortem substantia nigra in schizophrenia. World J Biol Psychiatry 2020; 21:339-356. [PMID: 31062628 PMCID: PMC6891153 DOI: 10.1080/15622975.2019.1615638] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 03/21/2019] [Accepted: 05/02/2019] [Indexed: 12/14/2022]
Abstract
Objectives: The substantia nigra (SN) receives glutamatergic and GABAergic inputs that regulate dopaminergic neuronal activity. Imaging studies have shown hyperactivity of the SN in schizophrenia (SZ) patients. We examined neurochemically defined inputs to the SN, synaptic density, and neuromelanin content that might contribute to or reflect this hyperexcitability.Methods: Glutamatergic axon terminals were identified by the immunohistochemical localisation of vGLUT1 and vGLUT2; GABA inputs were identified by the immunohistochemical localisation of GAD67. Neuromelanin granules are visible in unstained sections and thus were assessed in unstained sections. Optical densitometry was measured to assess the density of vGLUT1, vGLUT2 or GAD67 immunolabelled axon terminals and neuromelanin granules. Electron microscopy was used to quantify synaptic and mitochondrial density.Results: Compared to controls, SZ subjects had nonsignificant trends toward a decrease in vGLUT1, and an increase in both vGLUT2 and GAD67. vGLUT1 was negatively correlated with GAD67 in normal controls (NCs) and positively correlated in SZ subjects. A correlation of coefficient analysis showed a significant difference between the negative correlation in NCs and the positive correlation in SZ subjects. Frequency histograms showed the distribution of neuromelanin density was different in SZ subjects compared to NCs. Synaptic density data showed a decrease in inhibitory synapses in SZ subjects. Mitochondrial density was normal in SZ subjects.Conclusions: Synaptic density alterations and the lack of a positive correlation between GAD67 and vGLUT1 could contribute to hyperactivity in the SN.
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Affiliation(s)
- Samuel J. Mabry
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 1720 7 Ave. South, Birmingham AL, 35294
| | - Lesley A. McCollum
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 1720 7 Ave. South, Birmingham AL, 35294
| | - Charlene B. Farmer
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 1720 7 Ave. South, Birmingham AL, 35294
| | - Emma S. Bloom
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 1720 7 Ave. South, Birmingham AL, 35294
| | - Rosalinda C. Roberts
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 1720 7 Ave. South, Birmingham AL, 35294
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Vitale F, Capozzo A, Mazzone P, Scarnati E. Neurophysiology of the pedunculopontine tegmental nucleus. Neurobiol Dis 2019. [DOI: 10.1016/j.nbd.2018.03.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Schoonover KE, Queern SL, Lapi SE, Roberts RC. Impaired copper transport in schizophrenia results in a copper-deficient brain state: A new side to the dysbindin story. World J Biol Psychiatry 2018; 21:13-28. [PMID: 30230404 PMCID: PMC6424639 DOI: 10.1080/15622975.2018.1523562] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Objectives: Several schizophrenia brain regions exhibit decreased dysbindin. Dysbindin modulates copper transport crucial for myelination, monoamine metabolism and cellular homeostasis. Schizophrenia patients (SZP) exhibit increased plasma copper, while copper-decreasing agents produce schizophrenia-like behavioural and pathological abnormalities. Therefore, we sought to determine dysbindin and copper transporter protein expression and copper content in SZP.Methods: We studied the copper-rich substantia nigra (SN) using Western blot and inductively-coupled plasma mass spectrometry. We characterised specific protein domains of copper transporters ATP7A, CTR1, ATP7B and dysbindin isoforms 1 A and 1B/C in SZP (n = 15) and matched controls (n = 11), and SN copper content in SZP (n = 14) and matched controls (n = 11). As a preliminary investigation, we compared medicated (ON; n = 11) versus unmedicated SZP (OFF; n = 4).Results: SZP exhibited increased C terminus, but not N terminus, ATP7A. SZP expressed less transmembrane CTR1 and dysbindin 1B/C than controls. ON exhibited increased C terminus ATP7A protein versus controls. OFF exhibited less N terminus ATP7A protein than controls and ON, suggesting medication-induced rescue of the ATP7A N terminus. SZP exhibited less SN copper content than controls.Conclusions: These results provide the first evidence of disrupted copper transport in schizophrenia SN that appears to result in a copper-deficient state. Furthermore, copper homeostasis may be modulated by specific dysbindin isoforms and antipsychotic treatment.
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Affiliation(s)
- Kirsten E. Schoonover
- Department of Psychology and Behavioral Neuroscience, University of Alabama at Birmingham
| | - Stacy L. Queern
- Department of Radiology, University of Alabama at Birmingham,Department of Chemistry, Washington University in St. Louis
| | - Suzanne E. Lapi
- Department of Radiology, University of Alabama at Birmingham,Department of Chemistry, Washington University in St. Louis
| | - Rosalinda C. Roberts
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham
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Yetnikoff L, Lavezzi HN, Reichard RA, Zahm DS. An update on the connections of the ventral mesencephalic dopaminergic complex. Neuroscience 2014; 282:23-48. [PMID: 24735820 DOI: 10.1016/j.neuroscience.2014.04.010] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Revised: 04/03/2014] [Accepted: 04/04/2014] [Indexed: 12/21/2022]
Abstract
This review covers the intrinsic organization and afferent and efferent connections of the midbrain dopaminergic complex, comprising the substantia nigra, ventral tegmental area and retrorubral field, which house, respectively, the A9, A10 and A8 groups of nigrostriatal, mesolimbic and mesocortical dopaminergic neurons. In addition, A10dc (dorsal, caudal) and A10rv (rostroventral) extensions into, respectively, the ventrolateral periaqueductal gray and supramammillary nucleus are discussed. Associated intrinsic and extrinsic connections of the midbrain dopaminergic complex that utilize gamma-aminobutyric acid (GABA), glutamate and neuropeptides and various co-expressed combinations of these compounds are considered in conjunction with the dopamine-containing systems. A framework is provided for understanding the organization of massive afferent systems descending and ascending to the midbrain dopaminergic complex from the telencephalon and brainstem, respectively. Within the context of this framework, the basal ganglia direct and indirect output pathways are treated in some detail. Findings from rodent brain are briefly compared with those from primates, including humans. Recent literature is emphasized, including traditional experimental neuroanatomical and modern gene transfer and optogenetic studies. An attempt was made to provide sufficient background and cite a representative sampling of earlier primary papers and reviews so that people new to the field may find this to be a relatively comprehensive treatment of the subject.
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Affiliation(s)
- L Yetnikoff
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, 1402 S. Grand Boulevard, Saint Louis, MO 63104, United States.
| | - H N Lavezzi
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, 1402 S. Grand Boulevard, Saint Louis, MO 63104, United States
| | - R A Reichard
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, 1402 S. Grand Boulevard, Saint Louis, MO 63104, United States
| | - D S Zahm
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, 1402 S. Grand Boulevard, Saint Louis, MO 63104, United States.
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Pienaar IS, Elson JL, Racca C, Nelson G, Turnbull DM, Morris CM. Mitochondrial abnormality associates with type-specific neuronal loss and cell morphology changes in the pedunculopontine nucleus in Parkinson disease. THE AMERICAN JOURNAL OF PATHOLOGY 2013; 183:1826-1840. [PMID: 24099985 DOI: 10.1016/j.ajpath.2013.09.002] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2013] [Revised: 08/10/2013] [Accepted: 09/04/2013] [Indexed: 01/07/2023]
Abstract
Cholinergic neuronal loss in the pedunculopontine nucleus (PPN) associates with abnormal functions, including certain motor and nonmotor symptoms. This realization has led to low-frequency stimulation of the PPN for treating patients with Parkinson disease (PD) who are refractory to other treatment modalities. However, the molecular mechanisms underlying PPN neuronal loss and the therapeutic substrate for the clinical benefits following PPN stimulation remain poorly characterized, hampering progress toward designing more efficient therapies aimed at restoring the PPN's normal functions during progressive parkinsonism. Here, we investigated postmortem pathological changes in the PPN of PD cases. Our study detected a loss of neurons producing gamma-aminobutyric acid (GABA) as their output and glycinergic neurons, along with the pronounced loss of cholinergic neurons. These losses were accompanied by altered somatic cell size that affected the remaining neurons of all neuronal subtypes studied here. Because studies showed that mitochondrial dysfunction exists in sporadic PD and in PD animal models, we investigated whether altered mitochondrial composition exists in the PPN. A significant up-regulation of several mitochondrial proteins was seen in GABAergic and glycinergic neurons; however, cholinergic neurons indicated down-regulation of the same proteins. Our findings suggest an imbalance in the activity of key neuronal subgroups of the PPN in PD, potentially because of abnormal inhibitory activity and altered cholinergic outflow.
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Affiliation(s)
- Ilse S Pienaar
- Centre for NeuroInflammation and Neurodegeneration, Division of Brain Sciences, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, Hammersmith, United Kingdom.
| | - Joanna L Elson
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom; Centre for Human Metabolomics, Biochemistry Division, North-West University, Potchefstroom, South Africa
| | - Claudia Racca
- Institute of Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Glyn Nelson
- Institute for Ageing and Health, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, United Kingdom
| | - Douglass M Turnbull
- Institute for Ageing and Health, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, United Kingdom; The Wellcome Trust Centre for Mitochondrial Research, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Christopher M Morris
- Institute of Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom; Institute for Ageing and Health, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, United Kingdom; Medical Toxicology Centre, Newcastle University, Newcastle upon Tyne, United Kingdom
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Garzón M, Pickel VM. Somatodendritic targeting of M5 muscarinic receptor in the rat ventral tegmental area: implications for mesolimbic dopamine transmission. J Comp Neurol 2013; 521:2927-46. [PMID: 23504804 PMCID: PMC4038040 DOI: 10.1002/cne.23323] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 01/29/2013] [Accepted: 02/26/2013] [Indexed: 11/10/2022]
Abstract
Muscarinic modulation of mesolimbic dopaminergic neurons in the ventral tegmental area (VTA) plays an important role in reward, potentially mediated through the M5 muscarinic acetylcholine receptor (M5R). However, the key sites for M5R-mediated control of dopamine neurons within this region are still unknown. To address this question we examined the electron microscopic immunocytochemical localization of antipeptide antisera against M5R and the plasmalemmal dopamine transporter (DAT) in single sections through the rat VTA. M5R was located mainly to VTA somatodendritic profiles (71%; n = 627), at least one-third (33.2%; n = 208) of which also contained DAT. The M5R immunoreactivity was distributed along cytoplasmic tubulovesicular endomembrane systems in somata and large dendrites, but was more often located at plasmalemmal sites in small dendrites, the majority of which did not express DAT. The M5R-immunoreactive dendrites received a balanced input from unlabeled terminals forming either asymmetric or symmetric synapses. Compared with dendrites, M5R was less often seen in axon terminals, comprising only 10.8% (n = 102) of the total M5R-labeled profiles. These terminals were usually presynaptic to unlabeled dendrites, suggesting that M5R activation can indirectly modulate non-DAT-containing dendrites through presynaptic mechanisms. Our results provide the first ultrastructural evidence that in the VTA, M5R has a subcellular location conducive to major involvement in postsynaptic signaling in many dendrites, only some of which express DAT. These findings suggest that cognitive and rewarding effects ascribed to muscarinic activation in the VTA can primarily be credited to M5R activation at postsynaptic plasma membranes distinct from dopamine transport.
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Affiliation(s)
- Miguel Garzón
- Department of Anatomy, Histology, and Neuroscience, Medical School, Universidad Autónoma de Madrid (UAM), Madrid, 28029, Spain.
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Garzón M, Duffy AM, Chan J, Lynch MK, Mackie K, Pickel VM. Dopamine D₂ and acetylcholine α7 nicotinic receptors have subcellular distributions favoring mediation of convergent signaling in the mouse ventral tegmental area. Neuroscience 2013; 252:126-43. [PMID: 23954803 DOI: 10.1016/j.neuroscience.2013.08.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Revised: 08/06/2013] [Accepted: 08/06/2013] [Indexed: 11/24/2022]
Abstract
Alpha7 nicotinic acetylcholine receptors (α7nAChRs) mediate nicotine-induced burst-firing of dopamine neurons in the ventral tegmental area (VTA), a limbic brain region critically involved in reward and in dopamine D2 receptor (D2R)-related cortical dysfunctions associated with psychosis. The known presence of α7nAChRs and Gi-coupled D2Rs in dopamine neurons of the VTA suggests that these receptors are targeted to at least some of the same neurons in this brain region. To test this hypothesis, we used electron microscopic immunolabeling of antisera against peptide sequences of α7nACh and D2 receptors in the mouse VTA. Dual D2R and α7nAChR labeling was seen in many of the same somata (co-localization over 97%) and dendrites (co-localization over 49%), where immunoreactivity for each of the receptors was localized to endomembranes as well as to non-synaptic or synaptic plasma membranes often near excitatory-type synapses. In comparison with somata and dendrites, many more small axons and axon terminals were separately labeled for each of the receptors. Thus, single-labeled axon terminals were predominant for both α7nAChR (57.9%) and D2R (89.0%). The majority of the immunolabeled axonal profiles contained D2R-immunoreactivity (81.6%) and formed either symmetric or asymmetric synapses consistent with involvement in the release of both inhibitory and excitatory transmitters. Of 160 D2R-labeled terminals, 81.2% were presynaptic to dendrites that expressed α7nAChR alone or together with the D2R. Numerous glial processes inclusive of those enveloping either excitatory- or inhibitory-type synapses also contained single labeling for D2R (n=152) and α7nAChR (n=561). These results suggest that classic antipsychotic drugs, all of which block the D2R, may facilitate α7nAChR-mediated burst-firing by elimination of D2R-dependent inhibition in neurons expressing both receptors as well as by indirect pre-synaptic and glial mechanisms.
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Affiliation(s)
- M Garzón
- Brain and Mind Research Institute, Weill Cornell Medical College, 407 East 61st Street, New York, NY 10065, USA; Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina UAM, Madrid 28029, Spain; Instituto de Investigación Hospital Universitario La Paz (IDIPAZ), Paseo de la Castellana 261, Madrid 28046, Spain
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Majkutewicz I, Cecot T, Jerzemowska G, Myślińska D, Plucińska K, Trojniar W, Wrona D. Lesion of the ventral tegmental area amplifies stimulation-induced Fos expression in the rat brain. Brain Res 2010; 1320:95-105. [PMID: 20079346 DOI: 10.1016/j.brainres.2010.01.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2009] [Revised: 12/31/2009] [Accepted: 01/05/2010] [Indexed: 11/17/2022]
Abstract
Unilateral lesions of the ventral tegmental area (VTA), the key structure of the mesolimbic system, facilitate behavioral responses induced by electrical stimulation of the VTA in the contralateral hemisphere. In search of the neuronal mechanism behind this phenomenon, Fos expression was used to measure neuronal activation of the target mesolimbic structures in rats subjected to unilateral electrocoagulation and simultaneously to contralateral electrical stimulation of the VTA (L/S group). These were compared to the level of mesolimbic activation after unilateral electrocoagulation of the VTA (L group), unilateral electrical stimulation of the VTA (S group) and bilateral electrode implantation into the VTA in the sham (Sh) group. We found that unilateral stimulation of the VTA alone increased the density of Fos containing neurons in the ipsilateral mesolimbic target structures: nucleus accumbens, lateral septum and amygdala in comparison with the sham group. However, unilateral lesion of the VTA was devoid of effect in non-stimulated (L) rats and it significantly amplified the stimulation-induced Fos-immunoreactivity (L/S vs S group). Stimulation of the VTA performed after contralateral lesion (L/S) evoked strong bilateral induction of Fos expression in the mesolimbic structures involved in motivation and reward (nucleus accumbens and lateral septum) and the processing of the reinforcing properties of olfactory stimuli (anterior cortical amygdaloid nucleus) in parallel with facilitation of behavioral function measured as shortened latency of eating or exploration. Our data suggest that VTA lesion sensitizes mesolimbic system to stimuli by suppressing an inhibitory influence of brain areas afferenting the VTA.
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Affiliation(s)
- Irena Majkutewicz
- Department of Animal Physiology, University of Gdańsk, 24 Kładki St., 80-822 Gdańsk, Poland
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Subcortical Connections of the Basal Ganglia. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/b978-0-12-374767-9.00023-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
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Koprich JB, Johnston TH, Huot P, Fox SH, Brotchie JM. New insights into the organization of the basal ganglia. Curr Neurol Neurosci Rep 2009; 9:298-304. [DOI: 10.1007/s11910-009-0045-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Steiniger-Brach B, Kretschmer BD. Different function of pedunculopontine GABA and glutamate receptors in nucleus accumbens dopamine, pedunculopontine glutamate and operant discriminative behavior. Eur J Neurosci 2005; 22:1720-30. [PMID: 16197512 DOI: 10.1111/j.1460-9568.2005.04361.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The nucleus accumbens, as the main input structure of the ventral basal ganglia loop, is described as a limbic-motor interface. Dopamine input to nucleus accumbens modulates processing of concurrent glutamate input from limbic structures carrying motor and motivational information. There is evidence that these dopamine/glutamate interactions are fundamentally involved in response selection processes. However, the pedunculopontine tegmental nucleus (PPTg) in the brainstem is connected with limbic structures as well as dopaminergic midbrain areas, which also project to the nucleus accumbens. Furthermore, behavioral studies implicate the PPTg in complex, motivated behavior. Thus, the PPTg might be involved in motivated behavior by influencing response selection processes in the nucleus accumbens. In this study we used in vivo microdialysis in freely moving rats in order to inhibit (100, 200, 300 and 400 microm baclofen) or stimulate [5, 12.5, 25 or 50 micromalpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA)] the PPTg in animals that are performing an operant discrimination task for food reward. The behavioral consequences were correlated with dopamine and glutamate levels in nucleus accumbens and PPTg, respectively. PPTg inhibition by local GABAB receptors impaired the response rate and accuracy of performance in the operant discrimination task. PPTg stimulation by local AMPA receptors exclusively impaired the response rate. Both treatments blocked the performance-driven dopamine signal in nucleus accumbens, whereas glutamate in PPTg was enhanced after AMPA administration only. The data indicate that the PPTg functionally participates in a network of subcortical and cortical structures, which is responsible for the execution of motivated behavior and response selection processes.
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Abstract
Interactions between apparently separate dopaminergic and glutamatergic pathways figure prominently in the pathophysiology of Parkinson's Disease. So it is surprising that the ventral midbrain dopamine neurons, which give rise to the dopaminergic pathway, may themselves also be glutamatergic. We have addressed this idea in both rat and monkey brain and found that most ventral midbrain dopamine neurons exhibit glutamate immunoreactivity. We used postnatal cell culture to examine ventral midbrain dopamine neurons more closely. In vitro most dopamine neurons exhibit glutamate immunoreactivity, as well as immunoreactivity for phosphate-activated glutaminase, the enzyme principally responsible for the synthesis of neurotransmitter glutamate; inhibition of glutaminase reduces glutamate staining. In single cell microcultures, dopamine neurons make both dopaminergic and glutamatergic synaptic varicosities. Stimulation of individual dopamine neurons evokes a fast excitatory synaptic response mediated by glutamate; it also evokes dopamine release that inhibits the excitatory response via presynaptic D2 receptors. Thus, dopamine neurons appear to exert rapid synaptic actions via their glutamatergic synapses and slower modulatory actions via their dopaminergic synapses, including possibly inhibition of their own glutamatergic synapses. So, in the setting of dopamine neuron demise, there will be a loss of both dopaminergic and glutamatergic inputs to the striatum; furthermore, glutamate released by dopamine neurons may contribute to an excitotoxic cascade and the death of neighboring dopamine neurons.
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Affiliation(s)
- S Rayport
- Departments of Psychiatry, Anatomy and Cell Biology, and Center for Neurobiology and Behavior, Columbia University, 10032, New York, NY, USA
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Parent A, Sato F, Wu Y, Gauthier J, Lévesque M, Parent M. Organization of the basal ganglia: the importance of axonal collateralization. Trends Neurosci 2000; 23:S20-7. [PMID: 11052216 DOI: 10.1016/s1471-1931(00)00022-7] [Citation(s) in RCA: 208] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Recent neuroanatomical data obtained with single-axon or single-cell labeling procedures in both rodents and primates have revealed the presence of various types of projection neurons with profusely collateralized axons within each of the major components of the basal ganglia. Such findings call for a reappraisal of current concepts of the anatomical and functional organization of the basal ganglia,which play such a crucial role in the control of motor behavior. The basal ganglia now stand as a widely distributed neuronal network, whose elements are endowed with a highly patterned set of axon collaterals. The elucidation of this finely tuned network is needed to understand the complex spatiotemporal sequence of neural events that ensures the flow of cortical information through the basal ganglia.
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Affiliation(s)
- A Parent
- Centre de recherche Université Laval Robert-Giffard, Beauport, Québec, Canada
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