Differences in spontaneous ovulation in rats with unilateral lesion of the hypothalamus.

The effects of unilateral lesion of the anterior (AH), median (MH) or posterior hypothalamus (PH) performed on diestrus 1, on ovulation and estrous cycle were analyzed in virgin rats. Only rats showing two consecutive estrous cycles of the same length were used. The lesion of AH decreased the ovulation rate (number of ovulating/number of treated rats) (14/26 vs. 24/24 of sham-operated group, p less than 0.01, Chi-square test), and the number of released ova per rat (5.0 +/- 1.1 vs. 10.3 +/- 0.8, p less than 0.05). Meanwhile, for ovulating animals no differences in the number of ova shed were observed. Lesions of the MH or PH did not modify the ovulation rate nor the number of ova shed. The left ovary of rats with MH and PH lesions, however, shed less ova than the left ovary of the control group (MH: 4.1 +/- 0.5; PH: 3.9 +/- 0.6; control: 5.7 +/- 0.5, p less than 0.05). These results suggest that neural information arising from the AH, MH or PH plays different roles in the regulation of ovulation.

Differential effects of a unilateral hypothalamic lesion on ovulation and compensatory ovarian hypertrophy in hemiovariectomized adult rats.

The effects were analysed of a unilateral lesion in the anterior or medial hypothalamus made on the day of oestrus on right or left hemicastrated rats. On the day of oestrus after two consecutive oestrous cycles of the same length, the ovulation rate in rats with lesions in the anterior left hypothalamus was lower than in control hemicastrated animals (5/16 vs 18/20; P less than 0.01), and normal in those rats with lesions in the right side (14/18). None of the animals with lesions in the left side of the anterior hypothalamus and with the left ovary in situ ovulated (0/7), but 5/9 with the right ovary in situ did ovulate (P less than 0.05). Lesions on either side of the medial hypothalamus did not modify ovulation rate. Compensatory ovulation was reduced in those animals with lesions in the right anterior hypothalamus and with the right ovary in situ. Lesions in either side of the medial hypothalamus reduced compensatory ovulation. Lesions in the right side of the anterior and medial hypothalamus increased compensatory ovarian hypertrophy in the left ovary and decreased it in the right ovary. Lesions in the left side of the anterior hypothalamus increased compensatory ovarian hypertrophy in the left ovary only, whereas lesions in the left side of the medial hypothalamus reduced compensatory ovarian hypertrophy in the right ovary. The results suggest that the information arising in each side of the anterior and medial hypothalamus plays different roles in the ipsi-and contralateral ovary, when either the left or the right ovary is absent.