Brain stem neurons governing the discharges of sympathetic nerves

Recent work from our laboratory revealed that the brain stem is inherently capable of generating a 2-6 cycles/s rhythm in sympathetic nerve discharge (SND) of the baroreceptor denervated cat. It is believed that this rhythm is representative of the fundamental organization of those brain stem networks responsible for the background discharges in sympathetic nerves. As a consequence, an attempt was made to identify brain stem neurons with activity patterns related to the 2-6 cycles/s rhythm in inferior cardiac SND of the baroreceptor denervated cat. Specifically, the relationships between the spontaneous discharges of single brain stem neurons and the inferior cardiac nerve were analyzed with the technique of spike-triggered averaging. Neurons whose discharges were synchronized either to the rising or falling phase of inferior cardiac SND were located in the classic pressor region of the lateral medullary reticular formation. These neurons may comprise or receive inputs from the oscillator responsible for the 2-6 cycles/s rhythm in SND. In addition, neurons which reset the 2-6 cycles/s rhythm were identified. These neurons may provide inputs to the 2-6 cycles/s oscillator in the brain stem.