Effects of experimental bilateral cryptorchidism and castration on the plasma gonadotropins in male rats during sexual maturation

Kisspeptin neurons from mice to men: similarities and differences

The discovery that kisspeptin was critical for normal fertility in humans ushered in a new chapter in our understanding of the control of GnRH secretion. In this paper, we will review recent data on the similarities and differences across several mammalian species in the role of kisspeptin in reproductive neuroendocrinology. In all mammals examined to date, there is strong evidence that kisspeptin plays a key role in the onset of puberty and is necessary for both tonic and surge secretion of GnRH in adults, although kisspeptin-independent systems are also apparent in these studies. Similarly, two groups of kisspeptin neurons, one in the arcuate nucleus (ARC) and the other more rostrally, have been identified in all mammals, although the latter is concentrated in a limited area in rodents and more scattered in other species. Estrogen has divergent actions on kisspeptin expression in these two regions across these species, stimulating it the latter and inhibiting expression in the former. There is also strong evidence that the rostral population participates in the GnRH surge, whereas the ARC population contributes to steroid-negative feedback. There may be species differences in the role of these two populations in puberty, with the ARC cells important in rats, sheep, and monkeys, whereas both have been implicated in mice. ARC kisspeptin neurons also appear to participate in the GnRH surge in sheep and guinea pigs, whereas the data on this possibility in rodents are contradictory. Similarly, both populations are sexually dimorphic in sheep and humans, whereas most data in rodents indicate that this occurs only in the rostral population. The functional consequences of these species differences remain to be fully elucidated but are likely to have significance for understanding normal neuroendocrine control of reproduction as well as for use of kisspeptin agonists/antagonists as a therapeutic tool.

Sex differences in the regulation of Kiss1/NKB neurons in juvenile mice: implications for the timing of puberty

In mammals, puberty onset typically occurs earlier in females than in males, but the explanation for sexual differentiation in the tempo of pubertal development is unknown. Puberty in both sexes is a brain-dependent phenomenon and involves alterations in the sensitivity of neuronal circuits to gonadal steroid feedback as well as gonadal hormone-independent changes in neuronal circuitry. Kisspeptin, encoded by the Kiss1 gene, plays an essential but ill-defined role in pubertal maturation. Neurokinin B (NKB) is coexpressed with Kiss1 in the arcuate nucleus (ARC) and is also important for puberty. We tested whether sex differences in the timing of pubertal development are attributable to sexual differentiation of gonadal hormone-independent mechanisms regulating hypothalamic Kiss1/NKB gene expression. We found that, in juvenile females, gonadotropin secretion and expression of Kiss1 and NKB in the ARC increased immediately following ovariectomy, suggesting that prepubertal females have negligible gonadal hormone-independent restraint on their reproductive axis. In contrast, in similarly aged juvenile males, no changes occurred in LH levels or Kiss1 or NKB expression following castration, suggesting that gonadal hormone-independent mechanisms restrain kisspeptin/NKB-dependent activation of the male reproductive axis before puberty. Notably, adult mice of both sexes showed comparable rapid increases in Kiss1/NKB expression and LH secretion following gonadectomy, signifying that sex differences in the regulation of ARC Kiss1/NKB neurons are manifest only during peripubertal development. Our findings demonstrate that the mechanisms controlling pubertal activation of reproduction in mice are different between the sexes and suggest that gonadal hormone-independent central restraint on pubertal timing involves Kiss1/NKB neurons in the ARC.

The influence of human menopausal gonadotropin, natrium fluoride and cyproterone acetate on the spermatogenesis in immature rats

Human menopausal gonadotropin (HMG), natrium fluoride (NaF) and cyproterone acetate (CYA) were applied to immature male rats between the 26th and 32nd day of life and histological examination was performed in testes of 33rd-day-old rats. HMG treatment alone slightly influenced the spermatid completion process, while NaF evidently increased frequency of occurrence of various seminiferous tubules containing spermatids. CYA alone damaged the spermatid completion process (especially the cap-phase of spermiogenesis), produced a degeneration of meiotic spermatocytes, and decreased the tubular diameter. Those changes were prevented by addition of HMG to the CYA treated animals. The results suggest a possible regulatory role of FSH at the end of the first meiosis, and, also, in the progression of spermiogenesis. The mechanism of action of NaF may be hypothetical, but it probably consists of direct action on the seminiferous epithelium level.