Chapter 29. Modulations of autonomic functions by somatic nociceptive inputs

Abstract

This chapter discusses the modulations of autonomic functions by somatic nociceptive inputs. A great deal of basic research on somato-autonomic reflex regulation of visceral function has been carried out in anesthetized animals, particularly cats and rats. These animal models have been useful in revealing the underlying neural mechanisms in the absence of emotional influences. Because of the limitations of anesthesia, most of these studies have necessarily addressed acute effects. Nonetheless, it is apparent that somatic stimulation is capable of causing widespread and, at times, profound visceral responses, both in the short and long term. The most consistent and potent reflexes are induced by noxious stimulation or the activation of unmyelinated afferent fibers. Somato-autonomic reflexes can be sub-divided into A- and C-reflexes, which are elicited by stimulation of myelinated (A) and unmyelinated (C) afferent fibers, respectively, in somatic nerves. As many unmyelinated afferent fibers serve polymodal receptors, autonomic C-reflexes provide an interesting tool for studying the characteristics of somatic nociceptors.