Exposure of females to a male
pheromone accelerates pulsatile
gonadotropin-releasing hormone (
GnRH) secretion in goats. Recent evidence has suggested that neurons in the arcuate nucleus (
ARC) containing
kisspeptin and
neurokinin B (NKB) play a pivotal role in the control of
GnRH secretion. Therefore, we hypothesized that these neurons may be the central target of the male
pheromone. To test this hypothesis, we examined whether NKB signaling is involved in the
pheromone action, and whether
ARC kisspeptin/NKB neurons receive input from the medial nucleus of the amygdala (MeA)--the nucleus suggested to relay
pheromone signals. Ovariectomized goats were implanted with a recording
electrode aimed at a population of
ARC kisspeptin/NKB neurons, and
GnRH pulse generator activity, represented by characteristic increases in multiple-unit activity (MUA) volleys, was measured.
Pheromone exposure induced an MUA volley and
luteinizing hormone (LH) pulse in control animals, whereas the MUA and LH responses to the
pheromone were completely suppressed by the treatment with an NKB receptor antagonist. These results indicate that NKB signaling is a prerequisite for
pheromone action. In ovariectomized goats, an anterograde tracer was injected into the MeA, and possible connections between the MeA and
ARC kisspeptin/NKB neurons were examined. Histochemical observations demonstrated that a subset of
ARC kisspeptin/NKB neurons receive efferent projections from the MeA. These results suggest that the male
pheromone signal is conveyed via the MeA to
ARC kisspeptin neurons, wherein the signal stimulates
GnRH pulse generator activity through an NKB signaling-mediated mechanism in goats.