Modulation of Gonadotrophin‐Releasing Hormone Pulse Generator Activity by the Pheromone in Small Ruminants

Abstract

In small ruminants, such as goats and sheep, a primer pheromone produced by males induces an out‐of‐seasonal ovulation in anoestrous females, a phenomenon known as the male effect. The male effect is unique in that an external chemical stimulus can immediately modulate the activity of the hypothalamic gonadotrophin‐releasing hormone (GnRH) pulse generator. We have established a monitoring method of the GnRH pulse generator activity in Shiba goat. Using this method as a sensitive bioassay to assess the male effect pheromone activity, we have shown that the male effect pheromone is synthesised in an androgen‐dependent manner in the sebaceous glands or their vicinity in specific body regions in goats. Although chemical identity of the pheromone is yet to be determined, analyses of male goat hair extracts by gas chromatography fractionation suggest that the male effect pheromone is a volatile substance with relatively small molecular weight. From morphological and molecular biological studies in goats, it is suggested that the pheromone molecule is detected by a member of the V1R family located on both the olfactory neurones and the vomeronasal sensory neurones, and the pheromone signal is conveyed to the medial nucleus of amygdala via the main olfactory and vomeronasal pathways and, subsequently, to the hypothalamic GnRH pulse generator to enhance its activity.

Effects of Brief Exposure of Male Pheromone on Multiple-Unit Activity at Close Proximity to Kisspeptin Neurons in the Goat Arcuate Nucleus

“…57 : 197-202, 2011) n goats and sheep, exposure of seasonally anestrous females to the primer pheromone secreted by sexually mature males results in an out-of-seasonal ovulation [1][2][3][4]. Since the initial endocrine event following reception of the pheromone is the stimulation of pulsatile luteinizing hormone (LH) secretion, it has been thought that the central target of the pheromone signal is the GnRH pulse generator [1,[3][4][5], i.e., the neural substrate that generates intermittent GnRH discharges into the portal vessels, thereby regulating pulsatile LH secretion into the peripheral circulation [6,7].Although the neural identity of the GnRH pulse generator per se was unclear, it was possible to measure its activity by recording multiple-unit activity (MUA) at the mediobasal hypothalamus. It has been demonstrated that electrophysiological manifestations of the GnRH pulse generator are represented as characteristic increases in MUA (MUA volleys) that are exclusively associated with LH pulses in the monkey [8], rat [9] and goat [10,11].…”

“…57: [197][198][199][200][201][202]2011) n goats and sheep, exposure of seasonally anestrous females to the primer pheromone secreted by sexually mature males results in an out-of-seasonal ovulation [1][2][3][4]. Since the initial endocrine event following reception of the pheromone is the stimulation of pulsatile luteinizing hormone (LH) secretion, it has been thought that the central target of the pheromone signal is the GnRH pulse generator [1,[3][4][5], i.e., the neural substrate that generates intermittent GnRH discharges into the portal vessels, thereby regulating pulsatile LH secretion into the peripheral circulation [6,7].…”

Environmental and social cues can be used in combination to develop sustainable breeding techniques for goat reproduction in the subtropics

“…The indirect use of a photoperiod to control the sexual activity of females by means of sexually active males is a sustainable breeding technique for goat reproduction in the subtropics. The high response induced by the light-treated males could be due to the fact that photoperiodic treatment stimulates testosterone secretion, the odor of males and their sexual behavior, improving the quality of signals provided by the males to does during the 'male effect' (Delgadillo et al, 2006;Murata Months Figure 6 Changes (mean 6 s.e.m.) in plasma testosterone concentrations in local male goats from subtropical Mexico subjected to natural photoperiodic variations (J, or to 2.5 months of artificial long days (16 h of light/day) from November 1, and then treated with two s.c. melatonin implants (n) or exposed to natural short days (') (adapted from Delgadillo et al (2002)).…”

Identification of an Olfactory Signal Molecule that Activates the Central Regulator of Reproduction in Goats

“…In sheep and goats, the seasonally anestrous endocrine state of females is changed to the estrous state upon exposure to male scents [7,8]. This so-called ''male effect'' is one of the most conspicuous primer pheromone effects in mammals [9,10]. In this study, we have identified an olfactory signal molecule that activates the central regulator of reproduction, the gonadotropinreleasing hormone (GnRH) pulse generator, in goats.…”