Neural activity changes correlated with central anticholinergic blockade of cholinergically-induced drinking

In the rat, microinjections of carbachol into the septal area elicited water ingestion and increased multiple unit activity at this site and also the noninjected lateral hypothalamus. Carbachol injection into the lateral hypothalamus also elicited water ingestion, but multiple unit activity did not increase in this structure, although it did in the noninjected septal area. If carbachol was injected into one of these sites and isotonic saline into the other (conditions comparable to those for which drinking has been previously demonstrated), increased multiple unit activity was still found. However, if carbachol was injected into one of these sites and atropine into the other (conditions comparable to those for which the blockade of drinking has been previously demonstrated), the increases in multiple unit activity were blocked. Carbachol-elicited drinking may result from neural activity changes similar to those recorded in this study, and atropine may inhibit carbachol-elicited drinking by inhibiting such neural firing changes.