Carbachol-induced drinking at ventricular and subfornical organ sites of application

Carbamylcholine chloride (carbachol) applied to the cerebral ventricle of the rat in the region of the interventricular foramen produced drinking behavior. This contrasts with prior reports and arguments concerning the lack of involvement of the ventricular system in carbachol-induced drinking. Furthermore, the subfornical organ was implicated as one site of action of carbachol-induced drinking on the basis of the following results: (1) Injection of carbachol into the ventricle, but not in intact fornix fibers, reliably produced drinking; (2) direct application of carbachol to the subfornical organ produced drinking; (3) latency to drink was immediate and dose required to produce drinking was less for subfornical organ placements than for ventricular placements; (4) although application to fornix did not produce drinking, if demyelination of fornix fibers between the probe tip and the subfornical organ was present, drinking was observed. It was concluded that (a) drinking can be elicited by carbachol applied to the ventricle, thereby supporting the ventricular hypothesis; (b) the subfornical organ, situated below the fornical commissure in the interventricular foramen, is one site of action of carbachol-induced drinking.