Convergence of Cutaneous Afferent Impulses on Units of the Pontine Defecation Reflex Center in the Dog
The convergence of cutaneous afferents was studied in 168 pontine reticular units. The units responded to afferent stimulation of rectal branches of the contralateral pelvic nerve of the dog, and were, therefore, regarded as candidate cells for the pontine defecation reflex center. About one third of the candidate units responded to cutaneous stroking, although most responded to cutaneous stimulation in the noxious range. The candidate units activated by both stroking and noxious stimulation were 21 of 65 units tested. Three units were excited by stroking although not by the noxious stimulation. Twenty-two of the 54 candidate units of which the spontaneous discharges were inhibited by afferent stimulation of the contralateral rectal branches were excited by the noxious stimulation. Most candidate units responded to cutaneous stimulation of two or more of the seven body parts tested. Latency of the responses to tapping and electrical stimulation of both hindlegs did not significantly differ from that of responses to the hunting stimulation. These results confirm that the pontine defecation reflex center mediates the effects of cutaneous stimulation on outflow of the rectal branch and on colonic motility.
