RESUMO

Llamas are induced non-reflex ovulators, which ovulate in response to the hormonal stimulus of the male protein beta-nerve growth factor (ß-NGF) that is present in the seminal plasma; this response is dependent on the preovulatory gonadotrophin-releasing hormone (GnRH) release from the hypothalamus. GnRH neurones are vital for reproduction, as these provide the input that controls the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. However, in spontaneous ovulators, the activity of GnRH cells is regulated by kisspeptin neurones that relay the oestrogen signal arising from the periphery. Here, we investigated the organisation of GnRH and kisspeptin systems in the hypothalamus of receptive adult female llamas. We found that GnRH cells exhibiting different shapes were distributed throughout the ventral forebrain and some of these were located in proximity to blood vessels; sections of the mediobasal hypothalamus (MBH) displayed the highest number of cells. GnRH fibres were observed in both the organum vasculosum laminae terminalis (OVLT) and median eminence (ME). We also detected abundant kisspeptin fibres in the MBH and ME; kisspeptin cells were found in the arcuate nucleus (ARC), but not in rostral areas of the hypothalamus. Quantitative analysis of GnRH and kisspeptin fibres in the ME revealed a higher innervation density of kisspeptin than of GnRH fibres. The physiological significance of the anatomical findings reported here for the ovulatory mechanism in llamas is still to be determined.

RESUMO

The type of stimuli triggering GnRH secretion has been used to classify mammalian species into two categories: spontaneous or induced ovulators. In the former, ovarian steroids produced by a mature follicle elicit the release of GnRH from the hypothalamus, but in the latter, GnRH secretion requires coital stimulation. However, the mechanism responsible for eliciting the preovulatory LH surge in induced ovulators is still not well understood and seems to vary among species. The main goal of this review is to offer new information regarding the mechanism that regulates coitus-induced ovulation. Analysis of several studies documenting the discovery of ß-NGF in seminal plasma and its role in the control of ovulation in the llama and rabbit will be described. We also propose a working hypothesis regarding the sites of action of ß-NGF in the llama hypothalamus. Finally, we described the presence of ß-NGF in the semen of species categorized as spontaneous ovulators, mainly cattle, and its potential role in ovarian function. The discovery of this seminal molecule and its ovulatory effect in induced ovulators challenges previous concepts about the neuroendocrinology of reflex ovulation and has provided a new opportunity to examine the mechanism(s) involved in the cascade of events leading to ovulation. The presence of the factor in the semen of induced as well as spontaneous ovulators highlights the importance of understanding its signaling pathways and mechanism of action and may have broad implications in mammalian fertility.

Assuntos

Coito/fisiologia , Fator de Crescimento Neural/fisiologia , Indução da Ovulação/veterinária , Animais , Camelídeos Americanos , Bovinos , Feminino , Humanos , Mamíferos , Fator de Crescimento Neural/farmacologia , Ovulação/efeitos dos fármacos , Ovulação/fisiologia , Coelhos

RESUMO

The objective of the study was to determine the effect of different bovine gamete coincubation times on fertilization and embryo development performance. In vitro matured COCs were co-incubated with sperm at a concentration of 1.5 × 10(6) spermatozoa/ml in TALP medium for 3 hours (T 3, n = 362), 6 hours (T 6, n = 358), or 18 hours (T 18, n = 350). At the end of the coincubation period COCs from times 3 and 6 groups were post-incubated in a new well of fertilization medium without sperm for additional 15 and 12 h, respectively. Cumulus Oocyte Complexes from the T 18 were co-incubated with the sperm suspension for 18 hours. Presumptive zygotes were cultured for 9 days and embryo development was evaluated on days 2, 8, and 9. Thirty blastocysts from each group were stained and total number of nuclei was recorded. The mean (± SEM) percentages of zygotes to develop into ≥2 cell stage were 71.9 ± 5.0; 72.5 ± 5.3 and 81.2 ± 6.1 % for T 3, 6, and 18, respectively, on day 2 and they did not differ (P = .3) among groups. The mean percentage of blastocysts developed on day 8 (25.6 ± 2.8; 24.2 ± 3.3; 28.4 ± 4.2 % for T 3, 6, and 18, resp.) did not differ (P = .4) among groups. The total number of embryonic nuclei was greater (P < .05) for the blastocysts produced from the shortest co-incubation time (T 3).