Abstract
Female, virgin rats studied to determine areas within the limbic system that respond to gonadal steroids. Under ether anesthesia bipolar electrodes were stereotaxically placed in the lateral septum, dorsal hippocampus, medial amygdala and parietal cortex. Following cutaneous injections of novacain, animals were injected with tubocurare and respirated artificially. Intraperitoneal (IP) injections of estradiolโ17B and progesterone in propylene glycol were given and the electrical activity of the limbic structures was recorded and a frequency analysis made. Those areas which responded to systemic treatment were implanted with the same gonadal steroids using a recording cannulaโelectrode. The parietal cortex and medial amygdala showed no significant change in electrical activity that was consistent throughout the experiment. The dorsal hippocampus responded to IP injections of both estradiolโ17B and progesterone in diestrous and estrous rats, but did not respond to direct stimulation with the gonadal steroids. The electrical activity of the hippocampus increased within 30 minutes when the septum was stimulated directly with either progesterone or estradiolโ17B. The lateral septum responded to injections of both estradiolโ17B and progesterone in diestrous and estrous animals. Following direct implantation of either gonadal steroid into the lateral septum, there was an immediate increase in the activity of the septum. The lateral septum appears to be a site within the limbic system that is able to respond to both estrogen and progesterone.