The glutamate receptor subtype mediating parallel fibre-Purkinje cell transmission in rabbit cerebellar cortex

Responses of Purkinje cells to parallel fibre stimulation and to ionophoretically applied glutamate agonists, L-glutamate, L-aspartate, quisqualate, kainate and N-methyl-D-aspartate (NMDA), were extracellularly recorded in a superficial folium of the dorsal paraflocculus of high-decerebrate rabbits. NMDA caused an inhibition of simple spike discharge from Purkinje cells. 2-Amino-5-phosphonovalerate (APV), a selective NMDA receptor antagonist, effectively antagonized this inhibition. However, APV did not antagonize the excitation of Purkinje cells caused by quisqualate or parallel fibre stimulation. By contrast, both kynurenate and gamma-D-glutamylglycine (gamma-DGG) effectively antagonized the excitation of Purkinje cells by parallel fibre stimulation in a dose-dependent manner. Both kynurenate and gamma-DGG also antagonized the excitation of Purkinje cells caused by quisqualate, L-glutamate, L-aspartate or kainate. However, the antagonism was more prominent to L-aspartate and kainate than to quisqualate and L-glutamate. Quisqualate response was antagonized to an extent comparable with the response to parallel fibre stimulation. These results indicate that the receptor for the neurotransmitter at parallel fibre-Purkinje cell synapses is of quisqualate-specific type. The present data are consistent with the evidence that L-glutamate is the endogenous transmitter at these synapses.