Is glycine an inhibitory synaptic transmitter in the substantia nigra?

Nigral tissue accumulated 14C-glycine by an energy-, temperature- and sodium-dependent mechanism; the transport process was inhibited by small neutral amino acids and had an apparent Km of 143 microM and Vmax of 787 nmol/g/min. Re-release of accumulated 14C-glycine was initially extremely rapid (40% in first 5 min) and subsequently accelerated by +40 mM K+ in a Ca2+-dependent manner. Intranigral kainate (0.25 microgram) lowered the levels of striatal DA (63%) and nigral GABA (25%) ipsilaterally, but not nigral glycine. Injections of glycine or strychnine (10--100 micrograms) into one SN induced slow ipsiversive or contraversive turning respectively. The evidence for glycine as a neurotransmitter in SN is discussed.