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Zhang X, Liu Y, Hong X, Li X, Meshul CK, Moore C, Yang Y, Han Y, Li WG, Qi X, Lou H, Duan S, Xu TL, Tong X. NG2 glia-derived GABA release tunes inhibitory synapses and contributes to stress-induced anxiety. Nat Commun 2021; 12:5740. [PMID: 34593806 PMCID: PMC8484468 DOI: 10.1038/s41467-021-25956-y] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Accepted: 09/09/2021] [Indexed: 11/08/2022] Open
Abstract
NG2 glia, also known as oligodendrocyte precursor cells (OPCs), play an important role in proliferation and give rise to myelinating oligodendrocytes during early brain development. In contrast to other glial cell types, the most intriguing aspect of NG2 glia is their ability to directly sense synaptic inputs from neurons. However, whether this synaptic interaction is bidirectional or unidirectional, or its physiological relevance has not yet been clarified. Here, we report that NG2 glia form synaptic complexes with hippocampal interneurons and that selective photostimulation of NG2 glia (expressing channelrhodopsin-2) functionally drives GABA release and enhances inhibitory synaptic transmission onto proximal interneurons in a microcircuit. The mechanism involves GAD67 biosynthesis and VAMP-2 containing vesicular exocytosis. Further, behavioral assays demonstrate that NG2 glia photoactivation triggers anxiety-like behavior in vivo and contributes to chronic social defeat stress.
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Affiliation(s)
- Xiao Zhang
- Center for Brain Science, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Yao Liu
- Center for Brain Science, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Xiaoqi Hong
- Center for Brain Science, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Xia Li
- Institute of Special Environmental Medicine, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Charles K Meshul
- Research Services, VA Medical Center, Portland, OR, USA
- Department of Behavioral Neuroscience and Pathology, Oregon Health & Science University, Portland, OR, USA
| | - Cynthia Moore
- Research Services, VA Medical Center, Portland, OR, USA
| | - Yabing Yang
- Center for Brain Science, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Yanfei Han
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Wei-Guang Li
- Center for Brain Science, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Xin Qi
- Center for Brain Science, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Huifang Lou
- Department of Neurobiology, Key Laboratory of Medical Neurobiology of Ministry of Health of China, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Shumin Duan
- Department of Neurobiology, Key Laboratory of Medical Neurobiology of Ministry of Health of China, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Tian-Le Xu
- Center for Brain Science, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Xiaoping Tong
- Center for Brain Science, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
- Shanghai Research Center for Brain Science and Brain-Inspired Intelligence, Shanghai, China.
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Elliott JE, De Luche SE, Churchill MJ, Moore C, Cohen AS, Meshul CK, Lim MM. Dietary therapy restores glutamatergic input to orexin/hypocretin neurons after traumatic brain injury in mice. Sleep 2018; 41:4791165. [PMID: 29315422 PMCID: PMC6454530 DOI: 10.1093/sleep/zsx212] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 10/27/2017] [Indexed: 02/06/2023] Open
Abstract
Study Objectives In previous work, dietary branched-chain amino acid (BCAA) supplementation, precursors to de novo glutamate and γ-aminobutyric acid (GABA) synthesis, restored impaired sleep-wake regulation and orexin neuronal activity following traumatic brain injury (TBI) in mice. TBI was speculated to reduce orexin neuronal activity through decreased regional excitatory (glutamate) and/or increased inhibitory (GABA) input. Therefore, we hypothesized that TBI would decrease synaptic glutamate and/or increase synaptic GABA in nerve terminals contacting orexin neurons, and BCAA supplementation would restore TBI-induced changes in synaptic glutamate and/or GABA. Methods Brain tissue was processed for orexin pre-embed diaminobenzidine labeling and glutamate or GABA postembed immunogold labeling. The density of glutamate and GABA immunogold within presynaptic nerve terminals contacting orexin-positive lateral hypothalamic neurons was quantified using electron microscopy in three groups of mice (n = 8 per group): Sham/noninjured controls, TBI without BCAA supplementation, and TBI with BCAA supplementation (given for 5 days, 48 hr post-TBI). Glutamate and GABA were also quantified within the cortical penumbral region (layer VIb) adjacent to the TBI lesion. Results In the hypothalamus and cortex, TBI decreased relative glutamate density in presynaptic terminals making axodendritic contacts. However, BCAA supplementation only restored relative glutamate density within presynaptic terminals contacting orexin-positive hypothalamic neurons. BCAA supplementation did not change relative glutamate density in presynaptic terminals making axosomatic contacts, or relative GABA density in presynaptic terminals making axosomatic or axodendritic contacts, within either the hypothalamus or cortex. Conclusions These results suggest TBI compromises orexin neuron function via decreased glutamate density and highlight BCAA supplementation as a potential therapy to restore glutamate density to orexin neurons.
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Affiliation(s)
- Jonathan E Elliott
- VA Portland Health Care System, Portland, OR
- Department of Neurology, Oregon Health and Science University, Portland, OR
| | | | | | - Cindy Moore
- VA Portland Health Care System, Portland, OR
| | - Akiva S Cohen
- Department of Anesthesiology and Critical Care Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Anesthesiology, Joseph Stokes Research Institute, Children’s Hospital of Philadelphia, Philadelphia, PA
| | - Charles K Meshul
- VA Portland Health Care System, Portland, OR
- Department of Behavioral Neuroscience and Pathology, Oregon Health and Science University, Portland, OR
| | - Miranda M Lim
- VA Portland Health Care System, Portland, OR
- Department of Neurology, Oregon Health and Science University, Portland, OR
- Department of Medicine and Behavioral Neuroscience, Oregon Institute of Occupational Health Sciences, Oregon Health and Science University, Portland, OR
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van den Brink WJ, Palic S, Köhler I, de Lange ECM. Access to the CNS: Biomarker Strategies for Dopaminergic Treatments. Pharm Res 2018; 35:64. [PMID: 29450650 PMCID: PMC5814527 DOI: 10.1007/s11095-017-2333-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 12/18/2017] [Indexed: 12/26/2022]
Abstract
Despite substantial research carried out over the last decades, it remains difficult to understand the wide range of pharmacological effects of dopaminergic agents. The dopaminergic system is involved in several neurological disorders, such as Parkinson's disease and schizophrenia. This complex system features multiple pathways implicated in emotion and cognition, psychomotor functions and endocrine control through activation of G protein-coupled dopamine receptors. This review focuses on the system-wide effects of dopaminergic agents on the multiple biochemical and endocrine pathways, in particular the biomarkers (i.e., indicators of a pharmacological process) that reflect these effects. Dopaminergic treatments developed over the last decades were found to be associated with numerous biochemical pathways in the brain, including the norepinephrine and the kynurenine pathway. Additionally, they have shown to affect peripheral systems, for example the hypothalamus-pituitary-adrenal (HPA) axis. Dopaminergic agents thus have a complex and broad pharmacological profile, rendering drug development challenging. Considering the complex system-wide pharmacological profile of dopaminergic agents, this review underlines the needs for systems pharmacology studies that include: i) proteomics and metabolomics analysis; ii) longitudinal data evaluation and mathematical modeling; iii) pharmacokinetics-based interpretation of drug effects; iv) simultaneous biomarker evaluation in the brain, the cerebrospinal fluid (CSF) and plasma; and v) specific attention to condition-dependent (e.g., disease) pharmacology. Such approach is considered essential to increase our understanding of central nervous system (CNS) drug effects and substantially improve CNS drug development.
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Affiliation(s)
- Willem Johan van den Brink
- Division of Systems Biomedicine and Pharmacology, Leiden Academic Centre for Drug Research, Leiden University, Einsteinweg 55, 2333 CC, Leiden, The Netherlands
| | - Semra Palic
- Division of Systems Biomedicine and Pharmacology, Leiden Academic Centre for Drug Research, Leiden University, Einsteinweg 55, 2333 CC, Leiden, The Netherlands
| | - Isabelle Köhler
- Division of Systems Biomedicine and Pharmacology, Leiden Academic Centre for Drug Research, Leiden University, Einsteinweg 55, 2333 CC, Leiden, The Netherlands
| | - Elizabeth Cunera Maria de Lange
- Division of Systems Biomedicine and Pharmacology, Leiden Academic Centre for Drug Research, Leiden University, Einsteinweg 55, 2333 CC, Leiden, The Netherlands.
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Jimenez VA, Helms CM, Cornea A, Meshul CK, Grant KA. An ultrastructural analysis of the effects of ethanol self-administration on the hypothalamic paraventricular nucleus in rhesus macaques. Front Cell Neurosci 2015; 9:260. [PMID: 26236193 PMCID: PMC4500925 DOI: 10.3389/fncel.2015.00260] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 06/23/2015] [Indexed: 01/29/2023] Open
Abstract
A bidirectional relationship between stress and ethanol exists whereby stressful events are comorbid with problematic ethanol use and prolonged ethanol exposure results in adaptations of the physiological stress response. Endocrine response to stress is initiated in the hypothalamic paraventricular nucleus (PVN) with the synthesis and release of corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP). Alterations in CRH and AVP following long-term ethanol exposure in rodents is well demonstrated, however little is known about the response to ethanol in primates or the mechanisms of adaptation. We hypothesized that long-term ethanol self-administration in nonhuman primates would lead to ultrastructural changes in the PVN underlying adaptation to chronic ethanol. Double-label immunogold electron microscopy (EM) was used to measure presynaptic gamma-aminobutyric acid (GABA) and glutamate density within synaptic terminals contacting CRH- and AVP-immunoreactive dendrites. Additionally, pituitary-adrenal hormones (ACTH, cortisol, DHEA-s and aldosterone) under two conditions (low and mild stress) were compared before and after self-administration. All hormones were elevated in response to the mild stressor independent of ethanol consumption. The presynaptic glutamate density in recurrent (i.e., intra-hypothalamic) CRH terminals was highly related to ethanol intake, and may be a permissive factor in increased drinking due to stress. Conversely, glutamate density within recurrent AVP terminals showed a trend-level increase following ethanol, but was not related to average daily consumption. Glutamate density in non-recurrent AVP terminals was related to aldosterone under the low stress condition while GABAergic density in this terminal population was related to water consumption. The results reveal distinct populations of presynaptic terminals whose glutamatergic or GABAergic density were uniquely related to water and ethanol consumption and circulating hormones.
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Affiliation(s)
- Vanessa A Jimenez
- Behavioral Neuroscience, Oregon Health and Science University Portland, OR, USA ; Division of Neuroscience, Oregon National Primate Research Center Beaverton, OR, USA
| | - Christa M Helms
- Division of Neuroscience, Oregon National Primate Research Center Beaverton, OR, USA
| | - Anda Cornea
- Division of Neuroscience, Oregon National Primate Research Center Beaverton, OR, USA
| | - Charles K Meshul
- Behavioral Neuroscience, Oregon Health and Science University Portland, OR, USA ; Research Services, Veterans Affairs Medical Center Portland, OR, USA
| | - Kathleen A Grant
- Behavioral Neuroscience, Oregon Health and Science University Portland, OR, USA ; Division of Neuroscience, Oregon National Primate Research Center Beaverton, OR, USA
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Collins-Praino LE, Podurgiel SJ, Kovner R, Randall PA, Salamone JD. Extracellular GABA in globus pallidus increases during the induction of oral tremor by haloperidol but not by muscarinic receptor stimulation. Behav Brain Res 2012; 234:129-35. [DOI: 10.1016/j.bbr.2012.06.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 06/07/2012] [Accepted: 06/12/2012] [Indexed: 11/28/2022]
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Walker RH, Moore C, Davies G, Dirling LB, Koch RJ, Meshul CK. Effects of subthalamic nucleus lesions and stimulation upon corticostriatal afferents in the 6-hydroxydopamine-lesioned rat. PLoS One 2012; 7:e32919. [PMID: 22427909 PMCID: PMC3299711 DOI: 10.1371/journal.pone.0032919] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2011] [Accepted: 02/06/2012] [Indexed: 12/27/2022] Open
Abstract
Abnormalities of striatal glutamate neurotransmission may play a role in the pathophysiology of Parkinson's disease and may respond to neurosurgical interventions, specifically stimulation or lesioning of the subthalamic nucleus (STN). The major glutamatergic afferent pathways to the striatum are from the cortex and thalamus, and are thus likely to be sources of striatal neuronally-released glutamate. Corticostriatal terminals can be distinguished within the striatum at the electron microscopic level as their synaptic vesicles contain the vesicular glutamate transporter, VGLUT1. The majority of terminals which are immunolabeled for glutamate but are not VGLUT1 positive are likely to be thalamostriatal afferents. We compared the effects of short term, high frequency, STN stimulation and lesioning in 6-hydroxydopamine (6OHDA)-lesioned rats upon striatal terminals immunolabeled for both presynaptic glutamate and VGLUT1. 6OHDA lesions resulted in a small but significant increase in the proportions of VGLUT1-labeled terminals making synapses on dendritic shafts rather than spines. STN stimulation for one hour, but not STN lesions, increased the proportion of synapses upon spines. The density of presynaptic glutamate immuno-gold labeling was unchanged in both VGLUT1-labeled and -unlabeled terminals in 6OHDA-lesioned rats compared to controls. Rats with 6OHDA lesions+STN stimulation showed a decrease in nerve terminal glutamate immuno-gold labeling in both VGLUT1-labeled and -unlabeled terminals. STN lesions resulted in a significant decrease in the density of presynaptic immuno-gold-labeled glutamate only in VGLUT1-labeled terminals. STN interventions may achieve at least part of their therapeutic effect in PD by normalizing the location of corticostriatal glutamatergic terminals and by altering striatal glutamatergic neurotransmission.
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Affiliation(s)
- Ruth H Walker
- Department of Neurology, James J Peters Veterans Affairs Medical Center, Bronx, New York, United States of America.
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Ferraro L, O'Connor WT, Beggiato S, Tomasini MC, Fuxe K, Tanganelli S, Antonelli T. Striatal NTS1 , dopamine D2 and NMDA receptor regulation of pallidal GABA and glutamate release--a dual-probe microdialysis study in the intranigral 6-hydroxydopamine unilaterally lesioned rat. Eur J Neurosci 2011; 35:207-20. [PMID: 22211865 DOI: 10.1111/j.1460-9568.2011.07949.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The current microdialysis study elucidates a functional interaction between the striatal neurotensin NTS(1) receptor and the striatal dopamine D(2) and N-methyl-d-aspartic acid (NMDA) receptors in the regulation of striatopallidal gamma-aminobutyric acid (GABA) and glutamate levels after an ipsilateral intranigral 6-hydroxydopamine-induced lesion of the ascending dopamine pathways to the striatum. Lateral globus pallidus GABA levels were higher in the lesioned group while no change was observed in striatal GABA and glutamate levels. The 6-hydroxydopamine-induced lesion did not alter the ability of intrastriatal NT (10 nm) to counteract the decrease in pallidal GABA and glutamate levels induced by the dopamine D(2) -like receptor agonist quinpirole (10 μm). A more pronounced increase in the intrastriatal NMDA- (10 μm) induced increase in pallidal GABA levels was observed in the lesioned group while it attenuated the increase in striatal glutamate levels and amplified the increase in pallidal glutamate levels compared with that observed in the controls. NT enhanced the NMDA-induced increase in pallidal GABA and glutamate and striatal glutamate levels; these effects were counteracted by the NTS(1) antagonist SR48692 (100 nm) in both groups. These findings demonstrate an inhibitory striatal dopamine D(2) and an excitatory striatal NMDA receptor regulation of striatopallidal GABA transmission in both groups. These actions are modulated by NT via antagonistic NTS(1) /D(2) and facilitatory NTS(1) /NMDA receptor-receptor interactions, leading to enhanced glutamate drive of the striatopallidal GABA neurons associated with motor inhibition, effects which all are counteracted by SR48692. Thus, NTS(1) antagonists in combination with conventional treatments may provide a novel therapeutic strategy in Parkinson's disease.
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Affiliation(s)
- Luca Ferraro
- Department of Clinical and Experimental Medicine, Pharmacology Section and LTTA Centre, University of Ferrara, Via Fossato di Mortara 17-19, 44100 Ferrara, Italy.
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Darvesh AS, Carroll RT, Geldenhuys WJ, Gudelsky GA, Klein J, Meshul CK, Van der Schyf CJ. In vivo brain microdialysis: advances in neuropsychopharmacology and drug discovery. Expert Opin Drug Discov 2011; 6:109-127. [PMID: 21532928 PMCID: PMC3083031 DOI: 10.1517/17460441.2011.547189] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
INTRODUCTION: Microdialysis is an important in vivo sampling technique, useful in the assay of extracellular tissue fluid. The technique has both pre-clinical and clinical applications but is most widely used in neuroscience. The in vivo microdialysis technique allows measurement of neurotransmitters such as acetycholine (ACh), the biogenic amines including dopamine (DA), norepinephrine (NE) and serotonin (5-HT), amino acids such as glutamate (Glu) and gamma aminobutyric acid (GABA), as well as the metabolites of the aforementioned neurotransmitters, and neuropeptides in neuronal extracellular fluid in discrete brain regions of laboratory animals such as rodents and non-human primates. AREAS COVERED: In this review we present a brief overview of the principles and procedures related to in vivo microdialysis and detail the use of this technique in the pre-clinical measurement of drugs designed to be used in the treatment of chemical addiction, neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD) and as well as psychiatric disorders such as attention-deficit/hyperactivity disorder (ADHD) and schizophrenia. This review offers insight into the tremendous utility and versatility of this technique in pursuing neuropharmacological investigations as well its significant potential in rational drug discovery. EXPERT OPINION: In vivo microdialysis is an extremely versatile technique, routinely used in the neuropharmacological investigation of drugs used for the treatment of neurological disorders. This technique has been a boon in the elucidation of the neurochemical profile and mechanism of action of several classes of drugs especially their effects on neurotransmitter systems. The exploitation and development of this technique for drug discovery in the near future will enable investigational new drug candidates to be rapidly moved into the clinical trial stages and to market thus providing new successful therapies for neurological diseases that are currently in demand.
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Affiliation(s)
- Altaf S. Darvesh
- Pharmaceutical Sciences-Neurotherapeutics Focus Group, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, OH 44272, USA
- Psychiatry, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, OH 44272, USA
| | - Richard T. Carroll
- Pharmaceutical Sciences-Neurotherapeutics Focus Group, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, OH 44272, USA
| | - Werner J. Geldenhuys
- Pharmaceutical Sciences-Neurotherapeutics Focus Group, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, OH 44272, USA
| | - Gary A. Gudelsky
- Pharmaceutical Sciences, James L. Winkle College of Pharmacy, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Jochen Klein
- Chemistry, Biochemistry, Pharmacy, Johann Wolfgang Goethe University of Frankfurt, Frankfurt, D-60438, Germany
| | - Charles K. Meshul
- Behavioral Neuroscience, Pathology, School of Medicine, Oregon Health and Science University, Portland, OR 97239, USA
- Portland Veterans Affairs Research Center, Portland, OR 97239, USA
| | - Cornelis J. Van der Schyf
- Pharmaceutical Sciences-Neurotherapeutics Focus Group, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, OH 44272, USA
- Neurobiology, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, OH 44272, USA
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Fuchs H, Hauber W. Changes in extracellular dopamine in the rat globus pallidus induced by typical and atypical antipsychotic drugs. Neurochem Int 2004; 45:1029-38. [PMID: 15337302 DOI: 10.1016/j.neuint.2004.05.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2004] [Revised: 04/30/2004] [Accepted: 05/14/2004] [Indexed: 01/23/2023]
Abstract
Typical antipsychotic drugs with a high extrapyramidal motor side-effects liability markedly increase extracellular dopamine in the caudate-putamen, while atypical antipsychotic drugs with a low incidence of extrapyramidal motor side-effects have less pronounced stimulating actions on striatal dopamine. Therefore, it has been suggested that the extrapyramidal motor side-effects liability of antipsychotic drugs (APD) is correlated with their ability to increase extracellular dopamine in the caudate-putamen. The globus pallidus (GP) is another basal ganglia structure probably mediating extrapyramidal motor side-effects of typical antipsychotic drugs. Therefore, the present study sought to determine whether extracellular dopamine in the globus pallidus might be a further indicator to differentiate neurochemical actions of typical and atypical antipsychotic drugs. Using in vivo microdialysis we compared effects on pallidal dopamine induced by typical and atypical antipsychotic drugs in rats. Experiment I demonstrated that systemic administration of haloperidol (1 mg/kg; i.p.) and clozapine (20 mg/kg; i.p.) induced a significant pallidal dopamine release to about 160 and 180% of baseline, respectively. Experiment II revealed that reverse microdialysis of raclopride and clozapine using a cumulative dosing regimen did not stimulate extracellular dopamine in the globus pallidus if low (1microM) or intermediate (10 and 100 microM) concentrations were used. Only at a high concentration (1,000 microM), raclopride and clozapine induced a significant pallidal dopamine release to about 130 and 300% of baseline values, respectively. Thus, effects of typical and atypical antipsychotic drugs on pallidal dopamine were similar and thus, may not be related to their differential extrapyramidal motor side-effects liability. Furthermore, the finding that reverse microdialysis of raclopride over a wide range of concentrations did not stimulate pallidal dopamine concentrations tentatively suggests that pallidal dopamine release under basal conditions is not regulated by D2 autoreceptors.
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Affiliation(s)
- Holger Fuchs
- Abteilung Tierphysiologie, Biologisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany
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Abstract
The authors review the available literature on the preclinical and clinical studies involving GABAergic neurotransmission in mood disorders. Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter present almost exclusively in the central nervous system (CNS), distributed across almost all brain regions, and expressed in interneurons modulating local circuits. The role of GABAergic dysfunction in mood disorders was first proposed 20 years ago. Preclinical studies have suggested that GABA levels may be decreased in animal models of depression, and clinical studies reported low plasma and CSF GABA levels in mood disorder patients. Also, antidepressants, mood stabilizers, electroconvulsive therapy, and GABA agonists have been shown to reverse the depression-like behavior in animal models and to be effective in unipolar and bipolar patients by increasing brain GABAergic activity. The hypothesis of reduced GABAergic activity in mood disorders may complement the monoaminergic and serotonergic theories, proposing that the balance between multiple neurotransmitter systems may be altered in these disorders. However, low GABAergic cortical function may probably be a feature of a subset of mood disorder patients, representing a genetic susceptibility. In this paper, we discuss the status of GABAergic hypothesis of mood disorders and suggest possible directions for future preclinical and clinical research in this area.
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Affiliation(s)
- P Brambilla
- Biological Psychiatry Unit, IRCCS S Giovanni di Dio, Fatebenefratelli, Brescia, Italy.
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