Forebrain structures involved in ovulation and release of serum LH and FSH in proestrous rats

To investigate in detail the localization of the extrahythalamic neural structures indispensable for ovulation and serum gonadotropin release, small electrolytic lesions were produced in the forebrain under acute experimental conditions with a platinum electrode at 11.30–13.30 h on the day of proestrus. Blood sampling was performed using ether anesthesia on the afternoon of proestrus and the number of ova in the ampulla were verified with a microscope the next morning. Lesions in the diagonal band of Broca (DBB) or the supracommissural area inhibited spontaneous ovulation and proestrous surges of serum LH and FSH. On the other hand, full or partial ovulation occurred in animals with lesions outside the DBB-supracommissural area, including the medial septum (m-SEPT) and the subcommissural periventricular part of the medial preoptic area (MPO). In this experiment, the lesions which inhibited spontaneous ovulation were limited to the DBB including the supracommissural area. Electrochemical stimulation of the DBB in pentobarbital-blocked proestrous rats was effective in inducing ovulation and serum gonadotropin release. The stimulatory effects of DBB stimulation on the ovulatory response were interrupted by bilateral lesions in the mediobasal preotic area including the suprachiasmatic nucleus (SCH). The present study indicates that the DBB-supracommissural area is indispensable for acute ovulatory gonadotropin release, and that the DBB efferents for ovulation are conducted to the mediobasal hypothalamus (MBH) by way of the SCH-mediobasal MPO.