Nitric oxide modulates blood pressure through NMDA receptors in the rostral ventrolateral medulla of conscious rats.

Abstract

The rostral ventrolateral medulla (RVLM) is an important site of cardiovascular control related to the tonic excitation and regulating the sympathetic vasomotor tone through local presympathetic neurons. Nitric oxide (NO) has been implicated in the modulation of neurotransmission by several areas of the central nervous system including the RVLM. However the path ways driving NO affects and the correlation between NO and glutamate-induced mechanisms are not well established. Here, we investigate the influence of NO on the cardiovascular response evoked by the activation of NMDA and non-NMDA glutamatergic receptors in the RVL Minconscious rats. For that, we examined the influence of acute inhibition of the NO production with in the RVLM, by injecting the nonselective constitutive NOS inhibitor, L-NAME, on responses evoked by the microinjection of excitatory aminoacids L-glutamate, NMDA or AMPA agonists into RVLM. Our results show that the injection of L-glutamate, NMDA or AMPA agonists in to RVLM, unilaterally, induced a marked increase in the mean arterial pressure (MAP). Pretreament with L-NAME reduced the hypertensive response evoked by the glutamate injection, and also abolished the pressor response induced by the injection of NMDA in to the RVLM. However, block ng the NO synthesis did not alter the response produced by the injection of AMPA agonist. These data provide evidence that the glutamatergic neuro transmission with in the RVLM depend son excitatory effects exerted by NO on NMDA receptors, and that this mechanism might be essential to regulate systemic blood pressure.