Crossed Reflexes of Cutaneous Origin1j2

PERL, EDWARD R. (State U. New York Coll. Med., Syracuse, N. Y.) Crossed rejexes of cutaneous origin. Am. J. Physiol. 188(3) : 609-615. 1957.Changes in excitability of spinal motorneurons produced by a volley of impulses in cutaneous nerves of the contralateral hindleg were studied in cats acutely made spinal or decerebrate. Motorneuron excitability was determined by measuring changes in electrical activity recorded from ventral roots or muscle nerves. Depending upon the size of fibers fired, at least two different effects were produced by synchronous impulses in crossed cutaneous nerves. When the cutaneous nerve activity was confined to the low threshold, rapidly conducting fibers, 14-6 g in diameter, crossed knee and ankle flexor motorneurons were facilitated after a central latency of some 3 msec., and on occasion discharged. In several instances crossed extensor motorneurons were depressed during the course of flexor facilitation. When the cutaneous nerve activity involved the smaller (6-2 p) myelinated fibers as well, prolonged inhibition of the crossed flexor motorneurons followed the initial facilitation and the crossed extensor motorneurons were facilitated, after a delay of 6-30 msec., for periods up to 300 msec. UCH OF THE RECENT WORK on the M functional organization of the spinal cord has been devoted to the relation between activity of a specific sense organ or its afferent fiber and the subsequent change in ipsilateral motorneuron activity. Information of a similar type on the afferents capable of provoking the bilateral or crossed responses, known to occur in spinal animals, would make it possible to better understand the manner in which they and the ipsilateral reflexes are tied into integrated patterns. In preliminary experiments, undertaken with this objective in mind, it was noted that a single shock to a peripheral nerve containing cutaneous fibers evoked a discharge in contralateral ventral roots which was short in latency (5 msec.) and brief in duration (S-IO msec.). These features were in contrast to properties of the one well known crossed reflex of cutaneous origin, the Received for publication August I, 1956. l Preliminary reports of this material were presented to the Annual Meetings of the American Physiological Society, April 11-15, 1955 and April 16-20, 1956. 2 This investigation was supported in part by a research grant, B676, from the National Institute of Neurological Diseases and Blindness. crossed extensor response. The crossed extensor reflex is characteristically long in latency (20 msec. or more), slow to develop, and of long duration when evoked by single shocks or repetitive stimuli (I, 2). This paper presents an analysis of the short-latency crossed activity. Experiments were designed to determine the motorneurons contributing to the discharge, the afferent fibers evoking it, and the distinction of these afferent fibers from those responsible for crossed extension. The ventral root discharge itself was studied by recording the electrical activity from ventral roots or muscle nerves discharged in response to a volley of impulses in a contralateral nerve; however, a more useful tool proved to be the effects produced by an aff erent volley in a contralateral nerve on the electrical signs of an ipsilateral reflex.