The dromedary camel (Camelus dromedarius) is a short-day desert breeder in which female ovulation is induced by mating. Current data indicate that male-induced ovulation is triggered by its seminal plasma nerve growth factor beta (β-NGF), but the exact mechanisms involved in the induction of ovulation are still unknown. In this study, we report that an intramuscular injection of β-NGF in sexually active short-day-adapted female camels induces an ovulation attested by a surge of circulating LH (2–6 h after treatment) followed by an oocyte release with its cumulus oophorus (confirmed by ultrasonography 72 h after treatment) and a large and progressive increase in circulating progesterone (significant from the 2nd to the 10th days after β-NGF injection). In addition, this β-NGF treatment induces a broad nuclear c-FOS activation in cells located in various hypothalamic areas, notably the preoptic area, the arcuate nucleus, the dorso- and ventromedial hypothalamus, the paraventricular nucleus, and the supraoptic nucleus. A double immunostaining with neuropeptides known to be involved in the central control of reproduction indicates that ∼28% kisspeptin neurons and 43% GnRH neurons in the proptic area, and ∼10% RFRP-3 neurons in the dorso- and ventromedial hypothalamus are activated following β-NGF injection. In conclusion, our study demonstrates that systemic β-NGF induces ovulation in the female dromedary camel and indicates that this effect involves the central activation of hypothalamic neurons, notably the kisspeptin neurons.

Summary Sentence

In conclusion, our study demonstrates that systemic β-NGF induces ovulation in the female dromedary camel and indicates that this effect involves the central activation of hypothalamic neurons, notably the kisspeptin neurons.

Graphical Abstract