Synaptic responses of red nucleus neurons in the alert cat to cortical and cerebellar inputs

Postsynaptic potentials of neurons of the red nucleus (RN), evoked to stimulation of the sensorimotor region of the cerebral cortex and cerebellar nucleus interpositus, were studied in chronic experiments on alert cats by means of an intracellular recording technique. Movements of the animals were restricted by rigid fixation (through a special device previously attached to the head) of the animal's head on the frame of the stereotaxic apparatus. Rubrospinal neurons were identified according to their antidromic activation in response to stimulation of the rubrospinal tract at the decussation level. A decrease in the critical level of depolarization necessary for spike generation was shown to be a characteristic peculiarity for mono- and polysynaptic reaction of the RN neurons in the alert animals. A rare possibility of recording separate EPSPs, the presence of burst discharges of rubrospinal neurons as well as a higher activity of RN interneurons was observed.