BRACHIO-RUBRAL AND RUBRO-BRACHIAL ACTIVITY IN CAT

The main cerebellar efferent pathway, the brachium conjunctivum, has one group of fibers which has properties similar to group A fibers of peripheral nerve. The largest fibers are about 8 μ and have a velocity of 50 m/sec. The fiber activity was recorded in the medial part of the tectum and tegmentum of the contralateral midbrain. Postsynaptic activity was distinctly recorded in all parts of the red nucleus. Intracellular recordings of rubral neurons showed that only excitatory postsynaptic potentials could be recorded following brachium activity. The synaptic delay was about 0.5 msec. The synaptic system is a secure one capable of high frequency transmissions and does develop potentiation. Anesthesia noticeably affects rubral spontaneous discharge, afterpotentials and responsiveness cycles. Muscle paralysis following gallamine triethiodide administration decreased the RN 'spontaneous' firing. Adjustable implanted recording electrodes in red nucleus of awake animals showed different patterns of neuronal firing and slow potentials with rest, passive and active movements. The brachio-rubral synaptic system is under the control of the cerebellum and some activity from RN does feed back directly via a few BC fibers and possibly indirectly by inferior olive and lateral reticular nucleus to the contralateral cerebellum. © 1969.