Medullary sympathoexcitatory neurons are inhibited by activation of the medial prefrontal cortex in the rat

Electrical stimulation of the medial prefrontal cortex (MPFC) reduces arterial blood pressure. To investigate the mechanism of this response, the effects of electrical and chemical stimulation of the MPFC on splanchnic and lumbar sympathetic nerve discharge and on the discharges of barosensitive neurons of the rostral ventrolateral medulla (RVLM) were studied in halothane-anesthetized rats. Electrical stimulation (20 Hz, 1 ms, 100 mu A, 10 s) of the MPFC produced depressor responses and sympathoinhibitory responses (reduced discharge of the splanchnic sympathetic nerve). Microinjection of glutamate (10 nmol/100 nl) into the MPFC also reduced arterial blood pressure and sympathetic discharge. Electrical stimulation (0.5 Hz, 1-ms pulse pairs, 3-ms interval, 150-300 mu A) produced distinct patterns of splanchnic and lumbar sympathetic nerve discharge. A clear sympathoinhibitory phase with an onset latency of 146 +/- 14 ms was observed only in the case of the splanchnic sympathetic nerve activity. Electrical stimulation at depressor sites within the MPFC also inhibited the discharge of 10 of 21 RVLM barosensitive neurons tested. RVLM neurons were never excited by MPFC stimulation. These results Indicate that the MPFC contains neurons that form part of a central sympathoinhibitory pathway.