Changes in regional vascular resistance in response to microinjection of L-glutamate into different antero-posterior coordinates of the RVLM in awakerats

Changes in mean arterial pressure (MAP) and in regional vascular resistance (PVR, hindquarter, mesenteric and renal) induced by microinjection of L-gl utamate into three different antero-posterior coordinates of the rostral ve ntrolateral medulla (RVLM) [1200-1600 mu m (n=10), 1601-2000 mu m (n=12) an d 2001-2500 mu m (n=6) rostral to the obex] were investigated in unanesthet ized rats. Guide cannulas directed towards the RVLM were implanted 4 days p rior to the experiments. Doppler probes were implanted around the superior mesenteric, inferior abdominal aorta and left renal arteries and a catheter was inserted into the femoral artery and vein 1 day prior to the experimen ts. insertion of the injector into the RVLM produced an increase in baselin e MAP, which was back to control levels 2 min later, when L-glutamate was m icroinjected. Microinjection of L-glutamate (1 nmol/30 nl) into the three a ntero-posterior coordinates of the RVLM produced an increase in MAP associa ted with a similar increase in hindquarter, mesenteric and renal vascular r esistance, which were back to control 1 min later. Saline into the RVLM pro duced negligible effects on MAP and RVR. These findings suggest that the sy mpathetic vasomotor neurons involved in the regulation of the regional vasc ular resistance in rats are not topographically distributed in the antero-p osterior coordinates of the RVLM. However, the experimental methods used to evaluate the topographic distribution of sympatho-vasomotor neurons in the RVLM and the measurement of the regional blood flow may not be precise eno ugh to detect any possible differences. (C) 2000 Elsevier Science B.V. All rights reserved.