Forebrain angiotensin type 1 receptors and parabrachial serotonin in the control of NaCl and water intake.

This study investigated the roles of serotonin (5-HT) receptors in the lateral parabrachial nucleus (LPBN) and brain angiotensin type 1 (AT1) receptors in the intake of 0.3 M NaCl and water induced by angiotensin II (ANG II). Rats were implanted with stainless steel cannulas for injections into the subfornical organ (SFO) and into the LPBN. Bilateral LPBN pretreatment with the nonselective serotonergic 5-HT1/5-HT2 receptor antagonist methysergide (4 micrograms/200 nl) markedly enhanced 0.3 M NaCl intake induced by injections of ANG II (20 ng/200 nl) into the SFO. Pretreatment of the SFO with the AT1 receptor antagonist losartan (1 microgram/200 nl) blocked the intake of 0.3 M NaCl induced by ANG II in combination with LPBN methysergide injections. These results suggest that serotonergic mechanisms associated with the LPBN inhibit the expression of salt appetite induced by ANG II injections into the SFO. In addition, the results indicate that the enhanced NaCl intake generated by central administration of ANG II in the presence of LPBN 5-HT blockade is mediated by brain AT1 receptors.