Handling from weaning to adulthood does not prevent hyperdefensiveness induced by septal, medial accumbens, or medial hypothalamic lesions

Weanling male hooded rats were handled or not handled for 10 min each day, 5 days/week, for 6 weeks. At the end of this time all animals received one of the following: a septal lesion, a medial accumbens lesion, a medial hypothalamic lesion, or a sham lesion. The animals were tested for defensiveness toward the experimenter on Days 3, 7, and 14 postoperatively. All behavioral testing was done blind. Each of the three lesions increased defensiveness toward the experimenter. However, with each lesion, there was no difference in the defensiveness scores of preoperatively handled and nonhandled animals at any of the postoperative test sessions while those of animals with medial hypothalamic lesions did not. These results are consistent with observations that hyperdefensiveness occurs in human subjects following tumors in each of these brain areas in spite of their familiarity with the situation in which they are observed. They contrast with observations that mouse killing induced by septal lesions is readily prevented by preoperative exposure to a mouse.