Presynaptic glycine receptors on GABAergic terminals facilitate discharge of dopaminergic neurons in ventral tegmental area.
GABA-mediated postsynaptic currents (IPSCs) were recorded from dopaminergic (DA) neurons of the ventral tegmental area (VTA) of rats, in acute brain slices, and from enzymatically or mechanically dissociated neurons. In young rats (3-10 d of age), where GABA is excitatory, glycine (1-3 microm) and taurine (10-30 microm) increased the amplitude of evoked IPSCs (eIPSCs) and the frequency of spontaneous IPSCs (sIPSCs) but had minimal postsynaptic effects. Strychnine (1 microm) blocked the action of glycine; when applied alone, it reduced the amplitude of eIPSCs and the frequency of sIPSCs, indicating a tonic facilitation of GABAergic excitation by some endogenous glycine agonist(s). In medium containing no Ca2+, or with Cd2+ or tetrodotoxin added, the amplitude and especially the frequency of sIPSCs greatly diminished. In many cells, glycine had no effect on remaining miniature IPSCs, suggesting a preterminal site of glycine receptors (GlyRs). Fura-2 fluorescent imaging showed a glycine-induced increase of [Ca2+] in nerve terminals (on DA neurons), which was suppressed by strychnine or 3 microm omega-conotoxin MVIIA. Therefore, the presynaptic GlyR-mediated facilitation of GABAergic transmission seems to be mediated by N- and/or P/Q-type Ca2+ channels. In older rats (22-30 d of age), where GABA causes inhibition, the effect of strychnine on GABAergic IPSCs was reversed to facilitation, indicating a tonic glycinergic inhibition of GABA release. Furthermore, glycine (1-3 microm) reduced the amplitude of eIPSCs and the frequency of sIPSCs. Hence, the overall effect of the presynaptic action of glycine is to enhance the firing of DA cells, both in very young and older rats.
Ye
Jiang-Hong
JH
Department of Anesthesiology, New Jersey Medical School, Newark, New Jersey 07103-2714, USA. ye@umdnj.edu
Wang
Fushun
F
Krnjevic
Kresimir
K
Wang
Weizhen
W
Xiong
Zhi-Gang
ZG
Zhang
Jingli
J
D000367:Age Factors; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002469:Cell Separation; D004298:Dopamine / Q000378:metabolism*; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D018684:Glycine Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018009:Receptors, Glycine / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013654:Taurine / Q000378:metabolism / Q000494:pharmacology; D017557:Ventral Tegmental Area / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002121:Calcium Channel Blockers; D018684:Glycine Agents; D018009:Receptors, Glycine; D013654:Taurine; D005680:gamma-Aminobutyric Acid; D002118:Calcium; D004298:Dopamine