Comparison of fos-like immunoreactivity induced in rat brain by central injection of angiotensin II and carbachol.

Rats were given intracerebroventricular injections of either angiotensin II (ANG II) or the cholinomimetic carbachol. Some rats received cotreatment with ANG II antagonists selective for either angiotensin receptor AT1 (losartan) or AT2 (PD-123319, CGP-42112A). One hour later, the rats were killed and the brains processed for immunocytochemical detection of Fos-like immunoreactivity (FLI). ANG II treatment induced strong FLI in the anterior subfornical organ (SFO), median preoptic nucleus (MnPO), organum vasculosum laminae terminalis (OVLT), and supraoptic and paraventricular hypothalamic nuclei (SON, PVH). The AT1 antagonist abolished FLI in all regions normally stimulated by ANG II. The AT2 antagonist PD-123319 reduced FLI in SON and PVH, but CGP-42112A was less effective. Carbachol induced strong FLI in SON, PVH, and MnPO and only moderate FLI in SFO and OVLT. The AT1 antagonist prevented carbachol-induced FLI in the MnPO only. The distributions of FLI are compared between these central dipsogens and with that previously reported after peripheral infusion of ANG II, and their implications for mapping central thirst pathways are discussed.