LATERAL AND MEDIAL SEPTAL-LESIONS REDUCE ANXIETY IN THE PLUS-MAZE ANDPROBE-BURYING TESTS

Previous studies have shown that septal lesions produce anxiolytic-lik e effects in rat models of ''anxiety'' (i.e., septal lesions, like anx iolytic drugs, increase rats' open-arm exploration in the elevated plu s-maze test and decrease rats' burying behavior in the shock-probe bur ying test). Although these anxiolytic effects occur after lesions to p osterior (but not anterior) regions of the septum, their anatomical sp ecificity has not been clearly defined with respect to classical subdi visions of the septum, such as the medial and lateral nuclei. Thus, in Experiment 1, we compared the effects of lateral or medial septal les ions on rats' anxiety reactions in the elevated plus-maze and shock-pr obe burying tests. Contrary to the ''anxiogenic'' effects of septal le sions recently found in a ''conflict'' model of anxiety, we found that both lateral and medial septal lesions produced equivalent anxiolytic effects in the plus-maze and shock-probe tests. In Experiment 2, we f ound similar anxiolytic effects whenever lesions included septal areas just anterior to the fornix (i.e., the lateral septum) but not when s eptal lesions were restricted to areas just posterior to the fornix (i .e., the septofimbrial and triangular septal nuclei). Taken together w ith our previous results, these data suggest that classical subdivisio ns of the septum bounded rostrally by the genu of the corpus callosum and caudally by the fornix play an exclusively excitatory role in the control of anxiety, as expressed in the plus-maze and shock-probe bury ing models.