Stimulation of the ventral tegmental area enhances the effect of vasopressin on blood pressure in conscious rats

1 The mesolimbic dopamine system projects to a large number of forebrain ar eas and plays an important role in the regulation of locomotor activity, co gnition and reward. We previously found evidence for a functional interacti on between the mesolimbic dopamine system and circulating vasopressin and t he present study was performed to test the hypothesis that mesolimbic dopam ine stimulation modulates the cardiovascular effects of vasopressin. 2 Sprague-Dawley rats were stereotaxically implanted with a guide cannula i nto the region of origin of the mesolimbic system, the ventral tegmental ar ea, and instrumented with catheters into the abdominal aorta and jugular ve in. One week later, separate groups of conscious rats were injected intrave nously with 1, 3 or 10 ng kg(-1) of arginine-vasopressin or other vasopress or drugs before and after intra;ventral tegmental area injection of 10 nmol of neurotensin. 3 Intra-ventral tegmental area injections of neurotensin had no significant effect on mean arterial pressure and heart rate but significantly potentia ted the presser response to intravenous administration of vasopressin when compared to saline-injections. However, the vasopressin-induced bradycardia was unaffected. Intravenous pretreatment with raclopride blocked the abili ty of neurotensin, injected into the ventral tegmental area, to potentiate the vasopressin-induced presser response. Intra ventral tegmental area inje ctions of neurotensin had no effect on the presser response and bradycardia induced by intravenous angiotensin II or methoxamine. 4 In conclusion, these results suggest that the mesolimbic dopamine system, in addition to its well-known role in the regulation of behaviour, modulat es cardiovascular control by potentiating the effects of vasopressin on mea n arterial pressure.