Suppression of spontaneous ovulation by interruption of dorsal input of hypothalamus at various timings during rat estrous cycle

To clarify the role of the extrahypothalamic input to the preoptic area (POA)-medial basal hypothalamus (MBH) on spontaneous ovulation, the dorsal cut of the POA-MBH was performed on various days and ova were counted in female rats. An anterior half-circle cut (anterior dorsal cut; ADC) was performed at the dorsal of the POA on the day of proestrus. As a result, ovulation was seen on the day of estrus when ADC was performed in the evening (18:00-19:30 h) but did not occur when performed in the morning (10:00-11:30 h). Furthermore, the suppressive effect of ADC was observed, even when cut was performed in the evening 2-5 days before estrus. These results suggest that the dorsal input to the POA-MBH plays an important role in ovulation-triggering mechanisms. In addition, about 7 days after the ADC, regular estrous cycle and normal ovulation were seen. Furthermore, destruction of the medial or bilateral lateral septum was done in the morning of proestrus, to investigate the role of gonadotropin-releasing hormone (GnRH) neurons in these areas. Lesions in the septal area had no effect, suggesting that the inhibitory effect on ovulation of the ADC is not due to interruption of the fibers of the septum including GnRH neurons.