ROLE OF THE ROSTRAL VENTROLATERAL MEDULLA IN THE PRESSOR-RESPONSE TO STIMULATION OF THE NUCLEUS-RAPHE-OBSCURUS

1. Electrical stimulation of the nucleus raphe obscurus (NRO) in ureth ane-anesthetized rats increases arterial blood pressure (BP) between 2 0 and 95 mmHg (mean, 61.14 +/- 6.57; N = 30). 2. Unilateral electrolyt ic destruction of the rostral ventrolateral medulla (RVLM) did not red uce BP or heart rate (HR) but significantly reduced the pressor respon se to NRO stimulation (control, DELTA 76.0 +/- 5.4 mmHg; after lesion, DELTA 26.0 +/- 13.9 mmHg; P<0.01, N = 5). 3. Bilateral destruction of the RVLM reduced basal BP (control, 104.1 +/- 11.4 mmHg; after lesion , 58.0 +/- 5.7 mmHg; P<0.01) and the pressor response to NRO stimulati on (control, DELTA 71.6 +/- 7.3; after lesion, DELTA 12.5 +/- 3.8 mmHg ; P<0.01, N = 6). 4. When topically applied to or microinjected into t he RVLM, pentobarbital sodium (200 nl/l mul, 10 nmol) decreased BP, HR and the pressor response to NRO stimulation (control, DELTA 56.2 +/-6 .7 mmHg; after pentobarbital, DELTA 11.2 +/- 3.1 mmHg; P<0.01, N = 13) . Similar effects were obtained when glycine (200 nl, 50 nmol) was mic roinjected into RVLM (control, DELTA 40.5 +/- 5.9 mmHg; after glycine, DELTA 18.1 +/- 4.9 mmHg; P<0.01, N = 6). 5. We conclude that RVLM is essential for the pressor response to NRO stimulation.