EVOKED CENTRAL NERVOUS SYSTEM ACTIVITY RELATING TO PERIPHERAL UNMYELINATED OR ‘C’ FIBERS IN CAT

Abstract

In unanesthetized cats, immobilized with gallamine triethiodide (4 mg/kg), evoked activity in the region of the nucleus medullae oblongatae centralis, subnucleus ventralis and the nucleus interfascicularis hypoglossi of the caudal medulla oblongata was related to repetitive stimulation of unmyelinated or "C" fibers in peripheral nerve. The thresholds of various components of the peripheral nerve action potential were delineated. Repetitive stimuli above gamma delta threshold were necessary to elicit the prolonged succession of spikes characteristic of the medullary response. Trains of stimuli applied to the peripheral nerve at intensities greater than "C" threshold increased the duration of the medullary response. Following blocking of all but the unmyelinated fibers in the monitored peripheral nerve action potential, a delayed medullary response was recorded.