Septal hyperreactivity: a comparison of lesions within and adjacent to the septum.

Following large septal lesions, male hooded rats were tested for reactivity 2, 7, and 14 days postoperatively. The results showed that lesions which destroyed the septal nuclei bilaterally caused a significant increase in reactivity above that of an operated control group. A similar increase in reactivity was produced by lesions which damaged the bed nucleus of the stria terminalis as well as the septum. A significantly greater level of reactivity was produced when the lesion destroyed the septum and in addition the area ventral to the anterior septum, including parts of the diagonal band of Broca and the accumbens nucleus. A second experiment examined the effectiveness of more restricted lesions ventral to the septum on reactivity. Ventral lesions which destroyed primarily the bed nucleus of the stria terminalis caused a small but significant increase in reactivity. With lesions ventral to the anterior septum the increase in reactivity was significantly larger. The increase in reactivity produced by the anterior-ventral lesions was also larger than that produced by lesions of the septum but it was not as great as that produced by combined lesions of the septum and the anterior-ventral area. These results suggest that several areas contribute to the hyperreactivity that is usually attributed to septal lesions.