To elucidate the role of serotonin in the onset of puberty, the effects of both systemic and in-ovarian bursa administration of serotonin on the neuroendocrine mechanism that modulates the onset of puberty, follicular development and first ovulation were evaluated. Two experiments were carried out. For the first, 25 or 37.5 mg kg–1 of bodyweight of serotonin creatinine sulfate was administered by a subcutaneous route to 30-day-old female rats. In the second experiment, serotonin creatinine sulfate was administered directly into the ovarian bursa of 34-day-old female rats. Systemic administration of 25 or 37.5 mg kg–1 of serotonin creatinine sulfate induced a delay in the ages of vaginal opening and first vaginal oestrus, a decrease in the number of ovulating animals, and serum concentrations of FSH, LH, oestradiol and progesterone. An increase in the number of Class 3 (>500 μm) and atretic follicles was observed in the ovaries of these animals. The administration of serotonin creatinine sulfate in the ovarian bursa did not modify the onset of puberty and ovulation, but a reduced serum concentration of oestradiol was observed. Our results suggest that serotonin acts on the components of the hypothalamus–hypophysis–ovary axis by modulating follicular development, ovarian functions and the onset of puberty.

The innervation reaching the ovaries by the ovarian pedicle participates in regulating the response of ovarian follicles to gonadotrophins. The aim of our study was to analyse the effects of mechanical manipulation of the ovarian pedicle on spontaneous and induced ovulation performed in the peripubertal period. 32-day old rats subjected to mechanical manipulation were injected with 8 U of pregnant mare's serum gonadotrophin (PMSG), 10 U of human chorionic gonadotrophin (hCG) or 8 U of PMSG, followed 56 h later by 10 U hCG. The treatments were given immediately after surgery, and the rats killed on the day of first vaginal oestrus. In those animals subjected to unilateral or bilateral mechanical stimulation of the ovarian pedicle, the ovulation rate and number of ova shed were similar to those of the control group, when the injection of PMSG or hCG was performed immediately after pedicle manipulation. When both gonadotrophins were administered, the total number of ova shed was significantly higher than in the control or sham operated groups (left stimulation 17.3 +/- 0.7, right stimulation 17.6 +/- 0.5, bilateral stimulation 17.5 +/- 0.4 vs control 9.6 +/- 0.2, sham operated 11.9 +/- 1.3, P < 0.05). These results suggest that the innervation reaching the ovary via the ovarian pedicle regulates, in a stimulatory way, the effects of gonadotrophin, resulting in ovulation. Med Sci Res 27:561-564 (C) 1999 Lippincott Williams & Wilkins.

We have measured variations in catecholamine (norepinephrine (NA) and dopamine (DA)) and indolamine (serotonin (5-HT)) concentrations and the neural activity in these systems in the female rat hypothalamus at birth and every 2 days thereafter until the first vaginal oestrous. The concentrations of NA, 5-HT and their metabolites increased progressively from birth to days 14 and 16. Noradrenergic activity in the hypothalamus reached its highest point two days after birth to a level which was significantly greater than at any other time studied. The activity of 5-HT neurones showed three peaks, on days 2, 16 and 30. Significant variations in DA and DOPAC were seen between days 26 to the time of the first vaginal oestrous. Dopamine neural activity did not change significantly during the time period studied but showed a striking increase on the day of first vaginal oestrous. The daily variations in activity in the monoaminergic systems in the hypothalamus of the female rat throughout prepubertal development are probably linked to several physiological events. These include the control of feeding, temperature, the secretion of other pituitary hormones and water metabolism. Med Sci Res 27:7-12 (C) 1999 Lippincott Williams & Wilkins.