Abstract
Llamas are induced non-reflex ovulators, which ovulate in response to the hormonal stimulus of the male protein beta-nerve growth factor (β-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.
Highlights
In female mammals, ovulation relies on the integration of different central and peripheral components that establish reciprocal interactions
We investigated the presence and distribution of kisspeptin and gonadotrophin-releasing hormone (GnRH) cells in the adult female llama hypothalamus; two crucial neuroendocrine systems involved in the luteinizing hormone (LH) surge and ovulation in mammals
We found that kisspeptin is abundantly expressed in the llama mediobasal hypothalamus (MBH), where kisspeptin cells were detected in the arcuate nucleus (ARC) to that reported in other spontaneous and induced ovulators
Summary
Ovulation relies on the integration of different central and peripheral components that establish reciprocal interactions. GnRH cells are distributed in a bilateral long scattered continuum [2, 3] that exhibit distinct species-related number and distribution. 50% of the GnRH cells send their fibres to the median eminence (ME) where nerve endings release their products into the hypophyseal portal system that transport GnRH molecules to the pituitary [6, 7]. The activity of these hypophysiotropic GnRH cells is regulated by several inputs and factors (such as environmental cues) that vary in different species [8]
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