SOMATIC SENSORY REPRESENTATION OF FORELIMB IN DORSAL ROOT FIBERS OF RACCOON, COATIMUNDI, AND CAT

Abstract

Evoked electrical activity of single fibers in dorsal roots C6 through T2 was investigated in 10 raccoons, 3 coatimundis, and 7 cats. Tungsten microelectrodes were used to record from a total of 1052 units activated by mechanical stimulation of cutaneous receptors, and 1159 units activated by mechanical stimulation of deep receptors in the forelimb region of these animals. Principal results were as follows: (a) A significantly greater proportion of forelimb, and especially forepaw, units were cutaneous, as opposed to deep, in origin in raccoons, than in either coatimundis or cats. (b) In all cases, the majority of cutaneous units were rapidly adapting, while the majority of deep units adapted slowly, (c) Reconstruction of dermatomes for the 5 roots investigated reveals serial overlap of input from distinct body regions. Thus, a single root may innervate all 5 digits, and a single digit may project afferents through 4 dorsal roots, (d) Cutaneous receptive field areas in raccoons and cats increased exponentially as a function of body locus, from the tip of the digits to the body midline.