Final answer:
Testosterone, produced by Leydig cells in the testes, affects the brain's processing of pheromonal signals related to reproductive behavior. These signals are routed to the amygdala and then to the hypothalamus. The role of testosterone in olfactory signaling is mainly connected to its influence on the pheromone detection and reproductive physiology.
Step-by-step explanation:
Testosterone contributes to olfactory signalling primarily in the context of reproductive physiology and behavior. In males, testosterone is produced by Leydig cells in the testes upon stimulation by luteinizing hormone (LH) from the pituitary gland. This process is regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. Testosterone can affect the brain's processing of pheromonal signals, which are chemical cues that impact social and reproductive behavior. These signals do not go to the main olfactory bulb but rather to a secondary neural structure that projects to the amygdala, further impacting the hypothalamus which is critical for reproductive physiology.
Although there is debate about the functionality of the vomeronasal organ (VNO) in humans, pheromones are detected by receptors in this organ, which then send signals to the brain, affecting behavior. In context with olfactory signaling, testosterone and its related hormones can modulate the sensitivity and response to these odorant cues, influencing reproductive behavior and possibly playing a role in phenomena like the synchronization of menstrual cycles among women living in close proximity.