Electrical stimulation of afferent fibers of the tibial nerve in anaesthetiz ed rats evokes somato sympathetic reflexes which are recorded from efferent sym p athetic fibers such as branches of the inferior cardiac nerve or the renal nerve . The reflex sympathetic response consists of two components: A reflex, whi c h has a short latency (41±2 ms) and is elicited by stimulation of afferent myel inated fibers, and C reflex, which has a long latency (210±13 ms) and is a t tributed to unmyelinated afferent fibers. Generally speaking, the A and C ref lexes represent different somatic sensory inputs. Studies demonstrated that in anesthetized rats, the somato sympathetic A and C reflexes could be, respectively, modulated not only by several chemical agen ts involving neurotic transmission such as glutamate and nitric oxide, but al s o by sensory inputs from chemoreceptor or baroreceptor. Glutamate augmented, whi le nitric oxide inhibited the somato sympathetic A and C reflexes. Activatio n o f chemoreceptor augmented, while activation of baroreceptor inhibited the somato sympathetic A and C reflexes. In another study, an acupuncture needle (diam ete r 0.34 mm) was inserted into the hind limbs of the rat, dorsolaterally around th e area of acupoint: Huantiao (GB 30), at a depth of 4～5 mm and was twisted righ t and left ward twice every second during recording the somato sympathetic r efle xes. The study found that acupuncture inhibited both somato sympathetic A and C reflexes. These results suggest that the somato sympathetic reflexes may be an experimental model for study on acupuncture mechanism, because acupuncture, as a kind o f sensory input to the central nervous system, may has similar reflex pathways w hen it plays a therapeutic role in some target tissues and organs.
