Effects of specific dopamine lesions and dopamine receptor sensitivity on angiotensin II- and carbachol-induced thirst in rats

A study was made of the effects of manipulating brain dopaminergic activity upon drinking induced by intracerebroventricular administration of angiotensin II or carbachol. Non-specific lesions induced by injecting 6-hydroxydopamine (6-OHDA) into the cerebroventricles caused a significant reduction in angiotensin-induced thirst without affecting carbachol drinking. Specific 6-OHDA-induced lesions of the dopaminergic nigro-striatal pathway also attenuated the angiotensin-induced response, while unilateral lesions reduced and bilateral lesions almost completely abolished the effect. Again, the response to carbachol was unaffected. Chronic haloperidol treatment increased behavioural responses to the dopamine agonist apomorphine and significantly stimulated angiotensin-induced drinking without affecting response to carbachol. These studies provide support for the hypothesis that a dopaminergic event is involved in the angiotensin-induced thirst response and point to the need for a functioning dopaminergic nigro-striatal pathway for the full expression of this response.