Sympathetic nerve rhythm of brain stem origin

Abstract
The origin of the 2-6 cycle/s rhythm in sympathetic nerve discharge (SND) of the baroreceptor-denervated cat was determined. Whether the rhythm is inherent to the brain stem network responsible for basal SND or whether, as suggested by the work of Camerer it is dependent on the integrity of interconnections between the forebrain and brain stem was determined. A comparison was made of the frequency characteristics in SND before and after decerebration in the baroreceptor-denervated cat. Forms [2] of the rhythm were observed in the baroreceptor-denervated cat with an intact neuraxis: irregular and regular. The irregular form was characterized by variability in the frequency of sympathetic nerve slow wave occurrence in the 2-6 cycle/s band and was routinely observed under normocapnic conditions. A regular rhythm (i.e., constant inter-slow wave intervals) was observed during short periods of asphyxia. Significantly, these patterns were not affected by midcollicular decerebration. A 2-6 cycle/s rhythm could be synchronized to single shocks applied to cardiovascular reactive sites in the medulla and to afferents in the sciatic nerve in the baroreceptor-denervated and decerebrate cat. The rhythm is intrinsic to the brain stem.

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