Cerebral vasoconstrictive response produced by chemical stimulation of the caudal ventrolateral medullary depressor area is mediated via the rostral ventrolateral medullary pressor area and the cervical sympathetic nerves

Abstract

It was investigated that the cerebral blood flow (CBF) decrease response elicited by chemical stimulation of the caudal ventrolateral medullary depressor area (VLDA) is mediated via the rostral ventrolateral medullary pressor area (VLPA) and the cervical sympathetic nerve. The CBF was determined by radiolabeled microsphere technique in urethane (1.1–1.5 g · kg –1, i.p.) anesthetized Wistar rats. (i) Microinjection of l-glutamate (1.7 nmol) into the VLDA produced a significant ( P < 0.01) decrease in CBF from 64 ± 9 (mean ± SEM) to 48 ± 9 ml · min −1 · (100 g) −1 and a significant ( P < 0.01) increase in cerebrovascular resistance (CVR) from 1.7 ± 0.2 to 2.4 ± 0.4 mmHg per [ml · min −1 · (100 g) −1] in the cerebral cortex ipsilateral to the stimulated VLDA side ( n = 9). (ii) After cervical sympathectomy, l-glutamate was unilaterally microinjected into the VLDA. The CBF and CVR did not change significantly ( n = 10). (iii) After depression of the VLPA neurons with muscimol (GABA agonist), l-glutamate was unilaterally microinjected into the VLDA. The CBF and CVR did not change significantly ( n = 14). These results suggest that the pathway from the VLDA to control cerebral vessels may be mediated via the VLPA and the cervical sympathetic nerves.