Properties of the synaptic transmission of the newly formed cortico-rubral synapses after lesion of the nucleus interpositus of the cerebellum.

1. Properties of synaptic transmission during and after repetitive activation of the newly formed cortico-rubral were examined in the red nucleus neurons (RN) of cats after lesions of the nucleus interpositus of the cerebellum (chronic cats) as well as in normal ones. 2. A prominent facilitation of the amplitude of cortico-rubral unitary EPSPs was observed in both normal and chronic cats when a stimulus to the cerebral peduncle (CP) was preceded by another stimulus by 2-50 msec. 3. Time course of the facilitation shows that it attains maximum at the interval of about 3 msec and decays approximately exponentially lasting for 50 msec or more. 4. When three successive stimuli of identical intensity were applied to CP, the degree of facilitation was more prominent than that for double shock. 5. There was a positive correlation between the time to peak of the cortico-rubral EPSPs and their maximum value of facilitation. 6. The posttetanic potentiation of the cortico-rubral EPSPs was observed after tetanic stimulation to CP in chronic and normal cats. It lasts for a few minutes in both cases.