Metabotropic glutamate receptor subtypes involved in cardiovascular regulation in the rostral ventrolateral medulla of rats

We have previously reported that metabotropic glutamate receptors (mGluR) participate in cardiovascular regulation in the rostral ventrolateral medulla (RVLM) of rats. In the present study, we have tried to elucidate which subtype of mGluR contributes to cardiovascular responses elicited by L-glutamate in the RVLM. Adult male Wistar rats (348 ± 11 g, n = 21) were anesthetized and artificially ventilated. Microinjections of agonists and antagonists for each mGluR subtype were done into unilateral RVLM. Each of group I, II and III mGluR agonist (1 nmol/50 nl) produced significant increases in arterial pressure (18 ± 2, 9 ± 2 and 34 ± 3 mmHg, respectively) and heart rate (18 ± 4, 13 ± 3 and 33 ± 12 bpm, respectively). Microinjections of group I, II and III mGluR antagonists failed to inhibit the cardiovascular responses induced by subsequently injected agonists. However, group I antagonist [(RS)-1-aminoindan-1,5-dicarboxylic acid] elicited transient increases in arterial pressure and heart rate, followed by decreases in both variables (-19 ± 4 mmHg and -22 ± 4 bpm). These results suggest that all of three subtypes of mGluR participate in cardiovascular responses induced by L-glutamate, and group I mGluR may play an important role in the maintenance of arterial pressure. Copyright (C) 2000 Elsevier Science Inc.