Septal neurons respond to activation of baro- and chemoreceptors in the rat.

Because it has recently been shown that selective activation of neuronal perikarya in the septal area elicits arterial depressor responses, it seems reasonable to expect that information from receptors in the cardiovascular system may be related to the septum. This possibility was investigated by searching for single units in the medial and lateral septal nuclei responding to activation of baroreceptors, elicited either by electrical stimulation of the aortic depressor nerve (ADN) or by systemic injection of phenylephrine (PE), or responding to activation of chemoreceptors, elicited by intracarotid injection of sodium cyanide. Fifty-four male Wistar rats weighing 300-400 g were anesthetized with urethan (1.4 g/kg ip) or alpha-chloralose-urethan (35 and 400 mg/kg ip, respectively) and allowed to breathe spontaneously. One-third of spontaneously firing units tested responded to ADN stimulation; these 93 units were divided into two groups according to their response patterns; 62 (67%) showed an increase and 31 (33%) a decrease in their discharge. Of 35 units tested, 6 responded to intravenous injection of PE. The majority of the units (48 of 60) affected by chemoreceptor activation were excited, and the remaining 12 were inhibited. These experiments suggest that sensory information from cardiovascular receptors may play an important role in the control of the circulation by the septum.