Rhythmogenesis in the sympathetic nervous system

This paper reviews work performed in our laboratory on the origin of the 2--6 cycles per second (c/s) rhythm in the discharges of preganglionic and postganglionic sympathetic nerves of the cat. It was demonstrated that the 2--6 c/s rhythm does not result as the simple consequence of the baroreceptor reflexes. Furthermore, the rhythm persisted in the baroreceptor-denervated cat after midcollicular decerebration, but not after high spinal transection. These observations indicate that brain stem networks are inherently capable of generating a 2--6 c/s rhythm in sympathetic nerve discharge (SND). Two forms of the rhythm were observed in the baroreceptor denervated and decerebrate cat--simple and complex. The complex form is characterized by variability of sympathetic nerve slow wave occurrence in the 2--6 c/s band. A model for the genesis of the complex form of the rhythm is presented. It is proposed that the brain stem sympathetic network is composed of a number of oscillators that are directly coupled and/or receive common inputs. Each oscillator primarily drives a separate group of preganglionic neurons. Moreover, the lead oscillator and thus the sequence of activation of the coupled oscillators changes from cycle to cycle. Shifts in the leading focus of brain stem activity (i.e., lead oscillator) presumably account for the complex rhythm in SND. The functional implications of this model are discussed.