Diurnal drinking of rats with limbic system lesions maintained in an open vivarium

The diurnal patterning of drinking of rats maintained in an open colony room was measured immediately following — and four weeks after — surgery. Drinking behavior was measured in operated control rats, or animals who had received lesions of the septum, dorsal hippocampus, habenula or combined destruction of habenula and medial-dorsal hippocampus (including part of the subiculum). Two daily measurements of water intake during weeks one and four postsurgery were made just after the lights came on in the morning and 12 hr later, just before the lights went off. All animals drank most of their water during the dark hours. However, despite the strong entraining cues available in any open colony room, rats with lesions of the dorsal hippocampus in the present experiment drank more in the light than any of the other groups. Rats with septal lesions did not drink more water per 24 hr than control animals during the first postsurgical week, but did so during the fourth week postsurgery. Lesions restricted to either the dorsal hippocampus or habenula did not alter the total amount of fluid consumed, but combined lesions involving both medial-dorsal hippocampus and habenula elevated water intake above that of all other groups both immediately after surgery and four weeks later. These results suggest that further behavioral fractionation of the limbic system may be possible. The importance of environmental isolation in the examination of circadian rhythms is inferred.