Crossing interaction of adrenergic, cholinergic, histaminergic and opioidergic systems on water intake in adult male rats

Several lines of evidence have indicated that many nuclei in the brain including preoptic nucleus, AV3V, subfornical organ, septal area and lateral hypothalamus are the targets of efferents from chemo-sensitive and pressure-sensitive systems. These areas may concern with regulation of fluid homeostasis. In the present study, intracerebroventricular injections were carried out in all experiments. After a 24 h deprivation of water, the volume of consumed water was measured for 1 h. Administration of pilocarpine (0.5-1 ?g/rat), prazocin (2 ?g/rat), histamine (40-80 ?g/rat) and naloxone (0.5-1 ?g/rat) increased, while scopolamine (5-10 ?g/rat), phenylepherine (30 ?g/rat), morphine (2.5 ?g/rat), pyrilamine (25-50 ?g/rat) and ranitidine (10-20 ?g/rat) decreased water intake in isolated rats. The activation of muscarinic cholinoceptors by pilocarpine attenuated the inhibitory effect induced by phenylepherine. Blockade of muscarinic cholinoceptors did not change the phenylepherine-induced response. Pretreatment of rats with prazocin decreased the pilocarpine-induced response. Pharmacological blockade of muscarinic cholinoceptors by scopolamine decreased the prazocin –induced effect on water intake. Blockade of histamine H1 and H2 receptors attenuated the histamine-induced response. Furthermore, pyrilamine, but not ranitidine, increased the inhibitory effect induced by morphine. Pharmacological blockade of H1 and H2 receptors decreased the naloxone-induced effect on water intake. It is concluded that the histaminergic system may have a close interaction with morphine and naloxone regarding drinking behavior. Also, muscarinic cholinoceptors and adrenoceptors may have an interactive effect in this respect.