SYNAPTIC TRANSMISSION BETWEEN RAT INFERIOR OLIVARY NEURONS AND CEREBELLAR PURKINJE-CELLS IN CULTURE

Monosynaptic excitatory connections between rat inferior olivary neurons and cerebellar Purkinje cells were studied in culture. Cerebellar cells were dissociated and cultured with small pieces of tissue excised from inferior olivary region. Stimulation of inferior olivary neurons elicited and all-or-none response, which resembled a climbing fiber response, in a whole-cell current-clamped Purkinje cell. Under a voltage-clamp condition of a Purkinje cell, large excitatory postsynaptic current (EPSC) was recorded. The inward EPSC recorded at -50 mV decreased in amplitude as the membrane potential was set more positive and reversed to the outward current around -10 mV. The amplitude of the EPSC changed linearly with the membrane potential between -90 and 10 mV, both in Mg2+-free and Mg2+-containing solutions. The EPSC was suppressed with excitatory amino acid antagonist kynurenate or γ-D-glutamylglycine (DGG) at 1 mM. Specific N-methyl-D-aspartate (NMDA) antagonist, DL-2-amino-5-phosphonovalerate (APV), little affected the EPSC at 0.2 mM. The results indicate that the functional synapses were formed between inferior olivary neurons and cerebellar Purkinje cells in culture and suggest that the major postsynaptic receptors at the synapse are excitatory amino acid receptors of non-NMDA type.