The subfornical organ and carbachol-induced drinking

The initial report of Routtenberg and Simpson³² indicated that exogenous carbamylcholine chloride (carbachol) applied directly to 3rd ventricle or subfornical organ elicited drinking behavior. The possibility that subfornical organ was the site of action of the carbachol was more thoroughly investigated in this study. The time course and total water consumed as a function of dose of carbochol directly applied to subfornical organ, 3rd ventricle, or lateral hypothalamus was compared. Latency until drinking was significantly shorter and amount of water consumed following carbachol application was significantly greater following subfornical organ applications, relative to either of the other two loci. It was also demonstrated that total ablation of subfornical organ greatly drinking elicited following ventricular carbachol application. This effect was not observed following lesions in tissue adjacent to subfornical organ. Localized destruction of subfornical organ produced partial adipsia on the first day following lesioning, and this effect was not observed following localized lesions in adjacent tissue. This depression in water intake was transient, however; on subsequent days water intake of subfornical organ-ablated animals did not differ from controls. These results are discussed in relation to previous research on carbachol-induced drinking. A role of the subfornical organ in the regulation of water intake was suggested and supported by available information on the physiological and morphological characteristics of this structure.