Electrophysiology of ganglionic transmission in the sympathetic nervous system

The sympathetic nervous system contributes to the regulation and control of a great number of body functions. A considerable fraction of preganglionic fibers are constantly discharging nerve impulses, and this tonic activity is responsible for a number of sustained bodily conditions. These tonic sympathetic discharges are of central origin and may be decreased by inhibition or augmented by excitation of the central neural mechanisms in control of the relevant preganglionic neurons. Certain other sympathetic paths become active only when special conditions lead to excitation of their central connections. The effect of the activity of preganglionic fibers on the different target organs, however, does not depend entirely on central regulatory influences. The sympathetic ganglia play a significant role processing and integrating the information arriving from the central nervous system and controlling the output to the target organs. In this context, the different potentials described above constitute the basis for the integrative process to occur. We now have substantial information about the basic biophysical events associated with different electrical events in the sympathetic ganglia. Very little is known, however, about how they operate in an integrative manner to control specific functions. The control of sympathetic responses during surgical stimulation is an important goal of general anesthesia. General anesthetics may operate to produce this effect at both central and peripheral levels. The sympathetic ganglion as a peripheral synapse, with basic integrative properties similar to the complex central nervous system, is a model still not sufficiently exploited to understand mechanisms by which general anesthetics control sympathetic response. The relevance of the findings described above in a variety of clinical situations, such as stress, hypertension, exercise, and anesthesia, remains to be studied.