VESTIBULAR AND MUSCLE NERVE CONNECTIONS TO PYRAMIDAL TRACT NEURONS OF CAT

Abstract

Weak electrical stimulation (frequency. 12-15/-minute) of the left vestibular nerve of chloralose-anesthetized cats, paralyzed with gallamine triethiodide, evoked discharges (latency: 18-22 mseconds) recorded bilaterally from the bulbar pyramids. These discharges were attenuated by sub-hypnotic doses of pentobarbital and by asphyxia but remained unaffected by cerebellectomy, C1 spinal cord transection and bilateral destruction of the cortical vestibular receiving areas. Group II/III muscle afferent volleys, but not Group I volleys, provoked discharges of pyramidal tract neurons. Cervicothoracic and lumbosacral motoneuron discharges (laterncies exceeding 15 msecond) were sometimes evoked by vestibular nerve stimulation in non-strychninized cats. These discharges were probably channelled via the reticulospinal, not the pyramidal, system. It was concluded that the vestibular, not Group I muscle afferent, input influences motor cortex excitability.