Central serotonergic modulation of drinking behavior induced by angiotensin II and carbachol in normally hydrated rats: effect of intracerebroventricular injection of MK-212.

The objective of the present study was to evaluate the role of the central serotonergic (5-HT) system in the modulation of drinking behavior induced by angiotensin II (Ang II) and carbachol. Male Wistar rats implanted with a delay cannula in the 3rd ventricle were injected with the 5-HT1C/5-HT2 agonist 6-chloro-2-[1-piperazinyl]-pyrazine (MK-212) (50 nmol/2 microliters) before receiving an intracerebroventricular (icv) injection of Ang II or carbachol (100 ng/2 microliters). MK-212 induced a significant reduction in the drinking response evoked by Ang II or carbachol which was more marked in the case of the cholinergic agonist. The results obtained suggest that thirst and water intake produced by angiotensinergic or cholinergic activation are modulated by the action of 5-HT, possibly at the level of the periventricular hypothalamus.