Modulation of gastric and arterial pressure by nucleus tractus solitarius in rat

By using L-glutamate as a physiological tool to selectively stimulate neurons in specific subnuclear regions of the nucleus tractus solitarius (NTS), we have sought to differentiate those regions that modulate cardiovascular activity from those that modulate gastric activity. Microinjections of L-glutamate (300 pmol/25 nl) into the dorsomedial NTS of alpha-chloralose-anesthetized rats elicited dose-dependent falls in arterial pressure (AP) of 37.5 +/- 7.7 Torr from a base line of 130 +/- 5.8 Torr and gastric pressure (GP) of 0.8 +/- 0.1 cmH2O and inhibited the usual 5-6 waves/min phasic activity. Microinjection into the ventromedial NTS did not affect AP but transiently lowered GP by 1.6 +/- 0.2 cmH2O and eliminated phasic waves. The GP changes were vagally mediated. Microinjections into the area postrema or the hypoglossal nucleus elicited neither AP nor GP changes. Microinjections in other NTS areas at the same rostral-caudal level did not alter GP consistently. This study suggests that local stimulation of neurons in a specific region of the NTS elicits vagally mediated alterations of tonic GP and phasic activity and that AP and GP can be influenced independently in the medial NTS region.