Pheromone-induced stimulation of hypothalamic gonadotropin-releasing hormone pulse generator in ovariectomized, estrogen-primed goats.

As an example of pheromone-induced activation of reproductive function, the 'male effect' is well known in seasonally anestrous goats. The effect of this male pheromone on the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator activity was examined by monitoring the characteristic increases in the multiple-unit activity (MUA volleys) of the medial basal hypothalamus which had been associated with the pulsatile secretion of luteinizing hormone in ovariectomized goats carrying estradiol implants under 16L/8D condition. Male goat hair was used as the source of male pheromones, and the exposure to the hair was accurately timed to be midway between succeeding MUA volleys. The interval from the pheromone exposure to the subsequent volley was measured, so that the primer pheromone effect was assessed in terms of the stimulation of the GnRH pulse generator activity. Exposure to hair from an intact male goat resulted in occurrence of a MUA volley within a few minutes (1.7 +/- 0.2 min, n = 15) with the intervolley interval being apparently shortened as compared with the preexposure period. Hair from castrated male goats, on the other hand, had no such stimulatory effect at all on the hypothalamic GnRH pulse generator activity, but treatment of the castrated goats with testosterone for 2 months resumed the pheromone activity. The present results provide first direct evidence for the central action of the primer pheromone in a mammalian species, and pheromonal stimulation of the reproductive neuroendocrine system is shown to be exerted by instantaneously stimulating the hypothalamic GnRH pulse generator activity.