Does tolerance develop to the anxiolytic effects of septal lesions?

Previous studies have shown that septal lesions produce anxiolytic-like effects in tests of rat "anxiety" (i.e., septal lesions increase open-arm exploration in the elevated plus-maze test and decrease burying in the shock-probe burying test). The present experiment examined whether "tolerance" develops to the anxiolytic effects of septal lesions, in a manner similar to that of anxiolytic drugs. Accordingly, septal- and sham-lesioned rats were repeatedly tested in the elevated plus-maze. As in previous studies using anxiolytic drugs, septal lesions produced a clear anxiolytic effect on the first test day, but this effect virtually disappeared by the third test day. Although these findings suggest "tolerance" had developed to the anxiolytic effects of septal lesions, these same rats showed clear evidence of anxiolysis when they were subsequently tested in the shock-probe burying paradigm. A second experiment showed that these basic effects did not depend critically 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.