Neural mechanisms of autonomic responses elicited by somatic sensory stimulation.

All evidence introduced here indicates that, in anesthetized animals in which emotional factors have been eliminated, somatic afferent nerve stimulation can regulate various visceral functions by responses that are reflex in nature. One conclusion emerging from the evidence presented is that the effects of somatic afferent stimulation are dependent upon the particular organs and on the spinal afferent segments. When the central nervous system is intact, the responses are sometimes general, as seen in cerebral cortical blood flow, heart rate, and adrenal medullary hormonal secretion and splenic immune function, whereas sometimes they have a strong segmental organization, as seen in gastric motility and urinary vesical contractility (Fig. 8). Needless to say, in the spinalized preparation all responses are strongly segmental. The contribution of the sympathetic and parasympathetic efferent nerves to the somato-visceral reflexes depends on the organs. It is difficult for us to state specifically or to generalize upon which autonomic component, the sympathetic or parasympathetic, will dominate as the efferent path in these reflexes, because this depends on the individual organ, the site being stimulated, and the nature or mode of the stimulation. The somatically-induced reflex responses of autonomic, hormonal and immune functions demonstrated in anesthetized animals, as have been discussed herein, appear to function even during conscious states. We need further studies to evaluate the physiological meaning of these somato-autonomic reflex responses. The analysis of neural mechanisms of these reflex responses seems to be very important for clinical application to regulate visceral function by physical treatment.