Abstract
Recent findings have shown that dendritically released dopamine (DA) plays an important modulatory role in the substantia nigra pars reticulata (SNr). It is therefore possible that the loss of DA observed in Parkinson's disease (PD) could hold important consequences for nigral function. Previously, we have shown that activation of presynaptically localized group II metabotropic glutamate receptors (mGluRs) inhibits excitatory transmission at the subthalamic nucleus (STN)-SNr synapse and that activation of presynaptically localized group III mGluRs decreases excitatory and inhibitory transmission in the SNr. To test the hypothesis that nigral DA can modulate mGluR function in the SNr, we performed whole-cell patch-clamp recordings from γ-aminobutyric acidergic SNr neurons in slices obtained from rats that were acutely reserpinized. In slices obtained from reserpinized animals, the effect of group II mGluR activation by the selective agonist (+)-2-aminobicyclo[3·1·0]-hexane-2,6-dicarboxylate monohydrate (LY354740) (100 nM), but not group III mGluR activation [l-(+)-2-amino-4-phosphonobutyric acid, L-AP4, 500 μM], at STN-SNr synapses is significantly decreased. This effect could be mimicked in control slices by prior bath application of haloperidol (20 μM) andR-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH23390) (20 μM) but not sulpiride (50 μM). Furthermore, application of dopamine (100 μM) and (±)-6-chloro-7,8-dyhydroxy-3allyl-1-phenyl-2,3,4,5-tetra-hydro-1H-benzazepine (SKF82958) (1 μM) but not quinpirole (10 μM) could rescue the group II mGluR effect in reserpinized slices. The effect of group III mGluR activation (L-AP4, 100 μM) on inhibitory synaptic transmission was also significantly reduced in slices from reserpine-treated animals. This effect was mimicked by haloperidol (20 μM), SCH23390 (20 μM), and sulpiride (50 μM) in control slices. Thus, in a Parkinsonian state, the loss of nigral DA may add to the overall pathophysiological changes in basal ganglia output.
Footnotes
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This work was supported by grants from the National Institutes of Health, the National Institute of Neurological Disorders and Stroke, the National Parkinson's Foundation, the Tourette's Syndrome Association, National Alliance for Research on Schizophrenia and Depression, and the U.S. Army Medical Research and Material Command.
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DOI: 10.1124/jpet.102.033266
- Abbreviations:
- BG
- basal ganglia
- DA
- dopamine
- GABA
- γ-aminobutyric acid
- SNr
- substantia nigra pars reticulata
- STN
- subthalamic nucleus
- SNc
- substantia nigra pars compacta
- PD
- Parkinson's disease
- mGluR
- metabotropic glutamate receptor
- ACSF
- artificial cerebrospinal fluid
- IPSC
- inhibitory postsynaptic current
- EPSC
- excitatory postsynaptic current
- ANOVA
- analysis of variance
- PK
- protein kinase
- LY354740
- (+)-2-aminobicyclo[3·1·0]-hexane-2,6-dicarboxylate monohydrate
- SCH23390 hydrochloride
- R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine
- SKF82958
- (±)-6-chloro-7,8-dyhydroxy-3allyl-1-phenyl-2,3,4,5-tetra-hydro-1H-benzazepine
- L-AP4
- l-(+)-2-amino-4-phosphonobutyric acid
- Received February 6, 2002.
- Accepted April 5, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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