Pharmacological evidence for GABA as the transmitter in granule cell inhibition in the olfactory bulb

Summary

The convulsants picrotoxin and bicuculline block the depressant action of microelectrophoretically administered GABA and strychnine selectively blocks the depressant action of glycine on olfactory bulb mitral cells. The amino acids,d,l-homocysteate (DLH), glutamate, and aspartate, which excite virtually all other central neurons, often inhibited mitral cells and this effect was blocked by Mg²⁺. The depression produced by excitant amino acids is reversed to excitation by picrotoxin and bicuculline. These results are consistent with the proposal that granule cell synaptic inhibition of mitral cells is mediated by GABA. The granule cell inhibition elicited physiologically, however, proved difficult to antagonize with convulsants, but in some cases a degree of antagonism could be demonstrated. The results suggest that GABA may be the inhibitory transmitter released by granule cells.