Effects of mammillary body and mediodorsal thalamic lesions on elevated plus maze exploration.

This study investigates the effects of lesioning the mamillary bodies (MB) or the dorsomedian nucleus (MD) of the thalamus on exploration of an elevated plus maze in mice. Exploration of 'open' and 'enclosed' arms of the maze has been used to evaluate anxiety in rodents. Normal rodents visit the enclosed arms more often than the open ones (innate agoraphobia). As operationally defined, the less the activity in the open arms, the more anxious is the subject. MB-lesioned mice entered the open alleys more often, and spent more time in them, than did controls, whereas the opposite was observed in MD-damaged subjects. It is suggested that, in mice given this task, MB lesions decrease anxiety and that MD lesions increase anxiety.