Effects of Asphyxia and Repetitive Stimulation on Intramedullary Afferent Fibers

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Abstract
Effects of asphyxia and of repetitive stimulation on intramedullary projections of the afferent fibers were studied in spinal cords of cats anesthetized with Nembutal. The spinal cord focal potential, elicited by dorsal root stimulation and recorded from the cord, and the antidromically conducted response of afferent fibers produced by intraspinal needle electrode stimulation and recorded from the dorsal roots, were used as indices of afferent fiber activity. The focal potential and the antidromic response from terminal presynaptic fibers disappeared with 5–6 minutes of asphyxiation. Antidromic responses from preterminal regions were less susceptible to asphyxial block. Asphyxia impaired the ability of both types of responses to follow high frequencies of stimulation. The focal potential and the antidromic responses were observed to follow similar orders of high frequency stimulation. Double pulse stimulation of intramedullary fibers demonstrated a longer refractory period of terminal regions with progressive decrease of refractoriness in more dorsally located regions. A gradient of sensitivity to asphyxia and a postresponse recovery gradient exist along the intramedullary fibers.

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