Effect of serotonin and progesterone on induced ovulation in immature rats

Effects of systemic administration or intrabursal injection of serotonin on puberty, first ovulation and follicular development in rats

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.

Neurobiological mechanisms of the onset of puberty in primates

An increase in pulsatile release of LHRH is essential for the onset of puberty. However, the mechanism controlling the pubertal increase in LHRH release is still unclear. In primates the LHRH neurosecretory system is already active during the neonatal period but subsequently enters a dormant state in the juvenile/prepubertal period. Neither gonadal steroid hormones nor the absence of facilitatory neuronal inputs to LHRH neurons is responsible for the low levels of LHRH release before the onset of puberty in primates. Recent studies suggest that during the prepubertal period an inhibitory neuronal system suppresses LHRH release and that during the subsequent maturation of the hypothalamus this prepubertal inhibition is removed, allowing the adult pattern of pulsatile LHRH release. In fact, y-aminobutyric acid (GABA) appears to be an inhibitory neurotransmitter responsible for restricting LHRH release before the onset of puberty in female rhesus monkeys. In addition, it appears that the reduction in tonic GABA inhibition allows an increase in the release of glutamate as well as other neurotransmitters, which contributes to the increase in pubertal LHRH release. In this review, developmental changes in several neurotransmitter systems controlling pulsatile LHRH release are extensively reviewed.

The effect of adrenal glands on ovulation in Japanese quail (Coturnix coturnix japonica)

Adrenal involvement in ovulation has been demonstrated for several mammalian species and has recently come under scrutiny in birds. Complete adrenalectomy causes severe system imbalances; therefore, it was decided to evaluate the effect of unilateral adrenalectomy on ovulation in coturnix. Since no mortality occurred among 59 hens recovering from anesthesia following hemiadrenalectomy, systemic imbalances appeared to be tolerable. Hen-day egg production of adrenalectomized hens was significantly (P greater than .05) lower than that of sham operated and unoperated controls. Adrenalectomized birds exhibited their lowest rate of lay (18.7%) on the second day following treatment. The amount of time that hemiadrenalectomy preceded oviposition on the day of treatment influenced the occurrence of an ovulation. When adrenalectomy occurred 5 to 7.5 hr prior to oviposition, 86.7% of the birds failed to ovulate that day, compared with 27.8% of controls. This difference was highly significant. When adrenalectomy occurred less than 2.5 hr prior to oviposition, 92.3% of the birds ovulated on that day, but failed to ovulate on the next day. Subsequent to the period of adrenal insufficiency, hens resumed normal egg production. It was concluded that the adrenals directly influence daily ovulations in Coturnix, exerting an effect on hormonal events leading to ovulation.

Modification of the 5-hydroxytryptophan-induced head-twitch response by exogenous endocrine agents

Estrogens both alone and in combination with progestagens, gonadotrophins, gonadotrophin-releasing factor, corticosteroids, and corticotrophin antagonise the head-twitch response produced by 5-hydroxytryptophan in mice. In contrast, a potentiation was seen following thyroid hormones, thyrotrophin, and thyrotrophin-releasing hormone. Pre-treatment with androgens had no significant effect. Possible mechanisms for these interactions are discussed.