Role of somatic afferents in autonomic system control of the intestinal motility.

(1) In anesthetized (chloralose-urethane) rats, strong mechanical stimuli which were applied to the abdominal skin always inhibited motility of the small intestine. This reflex is referred to as an 'inhibitory cutaneo-intestinal reflex'. Similar stimuli applied to the skin of the upper chest, neck, forepaws, or hindpaws, however, evoked the opposite effect, which is referred to as a 'facilitatory cutaneo-intestinal reflex'. (2) By recording the activity of efferent sympathetic nerves to the small intestine and by transecting intestinal sympathetic or parasympathetic nerves we found that the inhibitory cutaneo-intestinal reflex was largely due to an increase in intestinal sympathetic efferent activity, and that the facilitatory cutaneo-intestinal reflex was due to decrease in the intestinal sympathetic efferent nerve activity; both changes reflexly evoked. (3) The inhibitory cutaneo-intestinal reflex was shown to be a propriospinal reflex which was caused by excitation of group IV (unmyelinated) cutaneous afferent nerve fibers. On the other hand, the facilitatory cutaneo-intestinal reflex seemed to be mediated through supraspinal pathways, and was evoked by excitation of mainly group III (A-delta group) cutaneous afferent nerve fibers. (4) Interaction between the cutaneo-intestinal reflex and intestino-intestinal reflex was demonstrated. (5) The possibility of a dorsal root reflex contribution to cutaneo-intestinal reflex was eliminated. (6) Significance of the cutaneo-intestinal reflex in neural control of the gastro-intestinal tract was discussed.