Excitatory amino acid receptors in the parallel fibre pathway in rat cerebellar slices.

The grease-gap technique was used on young rat cerebellar slices to study the synaptic pharmacology of the parallel fibre pathway. Electrical stimulation of the parallel fibres produced a characteristic response in Purkinje cells: a sharp negative (N) potential, representing the population action potential and underlying parallel fibre EPSP, followed by a slow positive (P) wave, the population inhibitory postsynaptic potential (IPSP). In the presence of 1.2 mM Mg2+, D-2-amino-5-phosphonovalerate (APV, 30 microM) had no effect but both potentials could be inhibited by 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline (CNQX, 10 microM). Removal of Mg2+ had no effect on the N-potential but enhanced the P-wave in an APV-sensitive fashion, particularly when CNQX was present. The results provide further evidence that glutamate is the parallel fibre transmitter and suggest that its acts only on non-NMDA (non-N-methyl-D-aspartate) receptors at synapses with Purkinje cells but on both NMDA and non-NMDA receptors at synapses with inhibitory interneurones. At the latter synapses, the NMDA system is likely to be brought into operation in an activity-dependent manner.