Involvement of the ipsilateral rostral ventrolateral medulla in the pressor response to l-glutamate microinjection into the nucleus tractus solitarii of awake rats

Abstract

Microinjection of l-glutamate into the lateral commissural nucleus tractus solitarii (NTS) of unanesthetized rats evokes increases in mean arterial pressure (MAP) and a bradycardia. In a previous study we verified that this increase in MAP is mediated sympathetically because prazosin (iv) blocks this response. The aim of the present study was to evaluate the role of the rostral ventrolateral medulla (RVLM) in the pressor response produced by l-glutamate microinjected into the NTS of unanesthetized rats. l-Glutamate was microinjected into the NTS before and 15 and 90 min after microinjection of kynurenic acid into the ipsilateral RVLM. Pressor (+24±3 vs. +6±3 mm Hg) and bradycardic (−101±10 vs. −3±12 bpm) responses to l-glutamate microinjected into the NTS ( n=8) were almost abolished 15 min after microinjection of kynurenic acid into the RVLM when compared with control responses. Both pressor (+23±6 mm Hg) and bradycardic (−93±16 bpm) responses to l-glutamate into the NTS returned to control values 90 min after microinjection of kynurenic acid into the RVLM. These data indicate that the pressor response to l-glutamate into the NTS is essentially dependent on the ipsilateral RVLM and also that this sympatho-excitatory response is mediated by excitatory amino acid receptors in RVLM neurons.