Pharmacologic independence of subfornical organ receptors mediating drinking.
In rats with chronically implanted cannulae in the subfornical organ (SFO), the relationship between cholinergic- and angiotensin (AII)-induced drinking was investigated pharmacologically. All substances were injected via SFO cannulae which did not rupture ventricular ependyma. Pretreatment with low doses of the muscarinic antagonist atropine abolished carbachol-induced drinking, while nicotinic antagonists had no effect. Nonetheless, pretreatment with much larger doses of atropine had no effect on AII-induced drinking. Similarly, relatively small doses of the AII antagonist, saralasin, blocked AII-induced drinking, yet a much larger dose of saralasin had no effect on carbachol-induced drinking. The receptors mediating cholinergic- and AII-induced drinking therefore cannot be in series and must be in parallel. A hypothesis is proposed to account for this independence and for the significance of the SFO cholinergic innervation.
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003650:Decamethonium Compounds / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004326:Drinking / Q000187:drug effects*; D006584:Hexamethonium Compounds / Q000494:pharmacology; D008297:Male; D009490:Neurosecretory Systems / Q000187:drug effects*; D051381:Rats; D011950:Receptors, Cholinergic / Q000187:drug effects*; D011976:Receptors, Muscarinic / Q000187:drug effects; D012504:Saralasin / Q000494:pharmacology; D013356:Subfornical Organ / Q000187:drug effects*
D003650:Decamethonium Compounds; D006584:Hexamethonium Compounds; D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic; D000804:Angiotensin II; D001285:Atropine; D002217:Carbachol; D012504:Saralasin