Brain serotoninergic stimulation reduces the water intake induced by systemic and central beta-adrenergic...

1. This study was undertaken to determine if the stimulation of central serotoninergic receptors affects the thirst-inducing action of systemically or intracerebroventricularly (icv) injected isoproterenol. 2. Male Wistar rats weighing 220-300 g were used in groups of 10-14 animals each. Normally hydrated rats implanted with a delay cannula into the third ventricle were injected icv with the 5HT1C/5HT2 agonist MK212 (50 nmol/2 microliters) prior to administration of isoproterenol sc (330 micrograms/kg body weight) or icv (10 and 25 and 50 micrograms/2 microliters). 3. Icv injections of MK212 reduced the water intake induced by isoproterenol injected systemically (56%) and by the two lowest doses of isoproterenol injected icv (76 and 86%, respectively). 4. The results suggest that the central serotoninergic system modulates the central beta-adrenergic system involved in water intake. 5. Taken together with previous results showing that the activation of 5HT1C/5HT2 receptors promotes a reduction of the dipsogenic response evoked by water deprivation or by icv injection of angiotensin II or carbachol, the present data suggest that the central serotoninergic system plays a ubiquitous role in the modulation of water intake behavior.