title: Glycine blocks long-term potentiation of GABAergic synapses in the ventral tegmental area.
abstract: The mesocorticolimbic dopamine system, originating in the ventral tegmental area (VTA) is normally constrained by GABA-mediated synaptic inhibition. Accumulating evidence indicates that long-term potentiation of GABAergic synapses (LTPGABA) in VTA dopamine neurons plays an important role in the actions of drugs of abuse, including ethanol. We previously showed that a single infusion of glycine into the VTA of rats strongly reduces ethanol intake for 24h. In the current study, we examined the effect of glycine on the electrophysiological activities of putative dopamine VTA neurons in midbrain slices from ethanol-naïve rats. We report here that a 15-min exposure to 10 μM glycine prevented trains of high-frequency stimulation (HFS) from producing LTPGABA, which was rescued by the glycine receptor (GlyR) antagonist strychnine. Glycine also concentration-dependently decreased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs). By contrast, glycine pretreatment did not prevent potentiation of inhibitory postsynaptic currents (IPSCs) during a continuous exposure to the nitric oxide (NO) donor, SNAP (S-nitroso-N-acetylpenicillamine), or a brief exposure to 10 μM glycine and 10 μM NMDA (N-methyl-D-aspartate), an agonist of NMDA-type glutamate receptors. Thus, the blockade of LTPGABA by glycine is probably resulted from suppressing glutamate release by activating the GlyRs on the glutamatergic terminals. This effect of glycine may contribute to the reduction in ethanol intake induced by intra-VTA glycine observed in vivo.
authors.affiliation: Department of Anesthesiology, Pharmacology and Physiology, Rutgers, The State University of New Jersey, New Jersey Medical School, Newark, NJ, USA; Department of Physiology, Mudanjiang Medical University, Mudanjiang, China. Electronic address: md-guan@163.com.
authors.forename: Y-Z
authors.initials: YZ
authors.lastname: Guan
authors.affiliation: Department of Anesthesiology, Pharmacology and Physiology, Rutgers, The State University of New Jersey, New Jersey Medical School, Newark, NJ, USA. Electronic address: ye@njms.rutgers.edu.
authors.forename: J-H
authors.initials: JH
authors.lastname: Ye
mesh_terms: D000818:Animals; D004298:Dopamine / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005998:Glycine / Q000494:pharmacology*; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects; D017774:Long-Term Potentiation / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000187:drug effects* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D017557:Ventral Tegmental Area / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D005680:gamma-Aminobutyric Acid; D005998:Glycine; D004298:Dopamine
keywords: EPSCs; GABA; long-term potentiation; mesolimbic system; synaptic plasticity