On the adequate stimulus for rectal mechanoreception and perception: a study in cat and humans

The adequate stimulus that is specific for both rectal mechanoreceptor exci tation and rectal perception is still undefined. Using a visual analogue sc ale, healthy male volunteer subjects rated the intensity of the non-noxious 'pressure' sensation evoked by slow balloon-induced distensions of the rec tum. lit a parallel study, the responses of spinal afferents originating fr om intramural mechanoreceptors of the rectum to the same stimulus were reco rded in decerebrate cats. Both receptor activity and sensation intensity we re linearly related to the diameter of the rectum, which is in turn a linea r function of the tangential length of the rectal wall. In contrast, both s aturated when expressed as a function of intrarectal pressure or rectal wal l tension. A is concluded that the perception associated with rectal disten sions in the non-noxious range is mediated by intramural mechanoreceptors t hat linearly encode tangential wall length, and that the underlying informa tion is linearly transmitted throughout the CNS.