DOES TOLERANCE DEVELOP TO THE ANXIOLYTIC EFFECTS OF SEPTAL-LESIONS

Previous studies have shown that septal lesions produce anxiolytic-lik e effects in tests of rat ''anxiety'' (i.e., septal lesions increase o pen-arm exploration in the elevated plus-maze test and decrease buryin g in the shock-probe burying test). The present experiment examined wh ether ''tolerance'' develops to the anxiolytic effects of septal lesio ns, in a manner similar to that of anxiolytic drugs. Accordingly, sept al- and sham-lesioned rats were repeatedly tested in the elevated plus -maze. As in previous studies using anxiolytic drugs, septal lesions p roduced a clear anxiolytic effect on the first test day, but this effe ct virtually disappeared by the third test day. Although these finding s suggest ''tolerance'' had developed to the anxiolytic effects of sep tal lesions, these same rats showed clear evidence of anxiolysis when they were subsequently tested in the shock-probe burying paradigm. A s econd experiment showed that these basic effects did not depend critic ally on time since surgery. Thus, the diminution of anxiolysis induced by septal lesions in the elevated plus-maze is test-specific and does not reflect a general recovery of normal fear reactions.