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

Abstract

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 γ- d- glutamylglycine (γ-DGG) effectively antagonized the excitation of Purkinje cells by parallel fibre stimulation in a dose-dependent manner. Both kynurenate and γ-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.