RECEPTOR SUBTYPES INVOLVED IN RESPONSES OF PURKINJE-CELL TO EXOGENOUS EXCITATORY AMINO-ACIDS AND LOCAL ELECTRICAL-STIMULATION IN CEREBELLAR SLICES IN THE RAT

The effects of the NMDA receptor antagonist, 2-amino-5-phosphonovalerate (APV) and non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on responses of Purkinje cells to exogenous excitatory amino acids and to electrical stimulation of the parallel fibres, were investigated in slices of the cerebellum of the rat. Glutamate, aspartate, kainate and quisqualate all induced excitation of Purkinje cells. Responses to kainate and quisqualate were blocked by CNQX (10-mu-M) but not by APV (10-mu-M). N-Methyl-D-aspartate induced biphasic excitatory-inhibitory responses, both components of which were blocked by APV but not by CNQX. The inhibitory component was less sensitive to blockade by APV but was totally blocked by bicuculline, the GABA(A) receptor antagonist. Parallel fibre stimulation most commonly induced inhibition of Purkinje cells, with or without preceding excitation. This inhibition was blocked by APV and excitatory responses were often revealed. A less commonly-observed predominately excitatory response was blocked by CNQX but not by APV and inhibition tended to be revealed. These data suggest that parallel fibre-Purkinje cell synapses possess non-NMDA postsynaptic receptors, while the parallel fibre-inhibitory interneurone synapses possess functional NMDA receptors.