Effects of septal lesion on lordosis response induced by estradiol in middle-aged and old female rats.

Long-Evans female rats were divided into three age groups: 10 young rats (5 months of age), 7 middle-aged rats (10-13 months of age) and 6 old rats (21-27 months of age). The rats were ovariectomized and immediately implanted subcutaneously with a silastic capsule filled with estradiol benzoate (E2). Lordosis response was compared in each animal before and after the septal lesion. Serum E2 levels were 197 +/- 27 pg/ml (mean +/- SEM), 192 +/- 81 pg/ml and 405 +/- 83 pg/ml in young, middle-aged and old rats respectively. When serum E2 levels were adjusted by analysis of covariance, LQ (lordosis quotient) was 42, 36 and 61 in young, middle-aged and old rats respectively before the septal lesion and 98, 68 and 88 respectively after the septal lesion. The extent of potentiation of lordosis after the septal lesion was less in middle-aged and old rats than young rats. These results indicate that an enhanced lordosis response in aged rats is partly due to high circulating E2 levels and partly due to disinhibition of the septal region on lordosis.