Lateral and medial septal lesions reduce anxiety in the plus-maze and probe-burying tests

Previous studies have shown that septal lesions produce anxiolytic-like effects in rat models of "anxiety" (i.e., septal lesions, like anxiolytic drugs, increase rats' open-arm exploration in the elevated plus-maze test and decrease rats' burying behavior in the shock-probe burying test). Although these anxiolytic effects occur after lesions to posterior (but not anterior) regions of the septum, their anatomical specificity has not been clearly defined with respect to classical subdivisions of the septum, such as the medial and lateral nuclei. Thus, in Experiment 1, we compared the effects of lateral or medial septal lesions on rats' anxiety reactions in the elevated plus-maze and shock-probe burying tests. Contrary to the "anxiogenic" effects of septal lesions 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 found similar anxiolytic effects whenever lesions included septal areas just anterior to the fornix (i.e., the lateral septum) but not when septal lesions were restricted to areas just posterior to the fornix (i.e., the septofimbrial and triangular septal nuclei). Taken together with our previous results, these data suggest that classical subdivisions 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 burying models.