Induced-ovulation in female dromedary camel involves kisspeptin neuron activation by β nerve growth factor†

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.