Chemosensory cues (pheromones) derived from urine or from anal and genital sebaceous gland secretions contribute to heterosexual partner selection and subsequent reproductive success in many vertebrate species. In rodents, pheromones are often detected by sensory neurons located in the vomeronasal organ (VNO), which send their axons to the accessory olfactory bulb (AOB) (reviewed in ). buy birth control online
Pheromonal inputs are then conveyed to the hypothalamus via a pathway that includes subdivisions of the medial amygdaloid nucleus (MA) and the bed nucleus of the stria terminals (BNST), with further projections to the medial preoptic area (mPOA) and ventrolateral portion of the ventromedial hypothalamic nucleus (VLH). Studies using hamsters, rats, and mice have monitored increases in nuclear Fos protein immunoreactivity (Fos-IR) as a marker of pheromone-induced neuronal activation throughout the VNO-AOB olfactory pathway. Androgen and estrogen receptors are expressed in the MA, BNST, mPOA, and VLH of the rat and hamster, allowing sex steroids to facilitate neuronal responses to olfactory inputs in these regions. Castration of male rats, hamsters, or mice eliminates their preference for estrous female odors.