Abstract
To test the hypothesis that the mesencephalic ventral tegmental area (VTA) plays a role in autonomic control of the cardiovascular system, we examined the cardiovascular effects of electrical stimulation of the mesencephalic ventral areas in anesthetized, paralyzed cats and rats. Electrical stimulation of the VTA for 30 s (100-μA current intensity; 40-50-Hz pulse frequency; 0.5-1-ms pulse duration) increased femoral blood flow by 130-162% in anesthetized cats and rats, whereas the identical stimulation of the substantial nigra (SN) failed to increase femoral blood flow. Electrical stimulation of the VTA also increased the arterial blood pressure and heart rate in anesthetized rats, but did not alter them in anesthetized cats. Accordingly, femoral vascular conductance was increased by 102-134% in both cats and rats. Atropine methyl nitrate (0.1 mg/kg) injected intravenously in the cats markedly attenuated the increases in femoral blood flow and vascular conductance. VTA stimulation was able to produce substantial increases in femoral blood flow and vascular conductance following a decerebration procedure performed at the premammillary and precollicular level in the cats, although their responses tended to attenuate to 55-69% of the control before the decerebration. Thus, it is likely that electrical stimulation of the VTA, but not the SN, is capable of evoking skeletal muscle vasodilatation, particularly via a sympathetically mediated cholinergic mechanism in the cat, and that the ascending projection from the VTA to the forebrain may not be responsible for the muscle vasodilatation.