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 sp lanchnic and lumbar sympathetic nerve discharge and on the discharges of barosensitive neurons of the rostral ventrolateral medulla (RVLM) w ere studied in halothane-anesthetized rats. Electrical stimulation (20 Hz, 1 ms, 100 mu A, 10 s) of the MPFC produced depressor responses an d sympathoinhibitory responses (reduced discharge of the splanchnic sy mpathetic nerve). Microinjection of glutamate (10 nmol/100 nl) into th e 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 sympathe tic nerve discharge. A clear sympathoinhibitory phase with an onset la tency 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 barosen sitive neurons tested. RVLM neurons were never excited by MPFC stimula tion. These results Indicate that the MPFC contains neurons that form part of a central sympathoinhibitory pathway.