Effects of Electrical Stimulation and of Direct Current and High Frequency Lesions of the Hypothalamus on Gonadotrophin Release and Puberty in Female Rats

The arcuate nucleus region of the hypothalamus of twenty-eight day old female rats was subjected to either electrical stimulation (AC), direct current (DC) lesions, high frequency (HF) lesions or to sham-procedures. Gonadotrophin levels were measured at various times after treatment. At 0-30 mn after treatment a significant rise in LH level was seen in AC, DC and HF rats, which rise was significantly higher in DC and HF rats than in AC rats. At 3 hours after treatment no differences in LH levels were found between the various groups ; FSH levels tended to be higher in stimulated and lesioned rats, but this reached significance for HF rats only. At 2 days after treatment LH as well as FSH levels were not different in experimental and control groups with the exception of lower FSH levels in the AC group. AC rats uniformly showed advancement of vaginal opening (VO), accompanied by (first) ovulation ; occurrence of these phenomena was much more variable in DC and HF rats. Measurements of gonadotrophin levels at 17 .00h on the day preceding the day of VO demonstrated peak levels of both LH and FSH in all control and AC rats. For DC and HF rats high levels of LH and FSH were encountered in those animals that had ovulated on the day of VO. It is concluded that in the immature rat hypothalamic lesions are effective via stimulation of gonadotrophin release. Advanced first ovulation in lesioned and stimulated rats is preceded by gonadotrophin surges comparable to those at spontaneous first ovulation, while, at least under experimental conditions, VO may occur without ovulatory gonadotrophin release and ovulation.