Synaptic formations and modulations of synaptic transmissions between identified cerebellar neurons in culture.

1. Synaptic formations between a rat cerebellar granule cell and a Purkinje cell, and also between an inferior-olivary neuron and a Purkinje cell have been accomplished in culture. 2. The synaptic transmission between an inferior-olivary neuron and a Purkinje cell was far much more potent than that between a granule cell and a Purkinje cell in the culture, and the former always induced in a Purkinje cell an action potential followed by prolonged depolarization, which resembled a climbing fiber response in vivo. 3. Synaptic potentiation was induced by repetitive stimulation (2 Hz, 20 sec) of a granule cell, and the synaptic depression was induced by repetitive conjunctive stimulation of both a granule cell and an inferior-olivary neuron as in a slice preparation. 4. When repetitive stimulation of both neurons were given while the postsynaptic Purkinje cell was voltage-clamped at -80 mV, not the depression but the potentiation took place. When repetitive stimulation of a granule cell was coupled with the postsynaptic strong depolarization induced by direct outward current injection, the depression took place. These two experiments indicate that the postsynaptic depolarization during activation of a presynaptic granule cell is both necessary and sufficient to induce the depression, and that the potentiation is induced without the postsynaptic depolarization. 5. The quantal analysis on the synaptic transmission, where fluctuations of amplitudes of synaptic currents in a Purkinje cell induced by a single granule cell were measured, indicated that the synaptic potentiation involves the enhancement of transmitter release from a presynaptic granule cell and that the depression involves changes of postsynaptic receptors on a Purkinje cell.