Studies of pineal and hypothalamic 5-HT in the ferret

Using a highly sensitive and specific radioenzymatic assay for serotonin (5-HT) in conjunction with a simple reliable technique for removal of small areas of hypothalamus, 5-HT levels have been determined at three time points in several areas of the anterior hypothalamus and the pineal of ovariectomized ferrets housed in long or short day photoperiod. The rhythm seen in all areas of anterior hypothalamus and the pineal was similar in both photoperiods. The data conflict with a previous report from this laboratory; possible reasons for this discrepancy are discussed. These findings do not support the hypothesis that a differential daily hypothalamic 5-HT rhythm is a key component in the neuroendocrine control of seasonal breeding in the ferret.