Sex Difference and Steroid Modulation of Pheromone-Induced Immediate Early Genes in the Two Zones of the Mouse Accessory Olfactory System

Abstract

Two anatomically and neurochemically distinct zones within the vomeronasal organ (VNO) and accessory olfactory bulb (AOB) have been identified that are responsible for the detection of pheromones. Using markers to distinguish between apical and basal neurons of the VNO neuroepithelium and rostral versus caudal AOB glomeruli, we examined immediate early gene immunoreactivity (IEG-IR) in gonadectomized, steroid-treated mice in response to pheromones of male and female conspecifics. After exposure of estradiol-treated females to soiled male bedding, more VNO neurons in the basal than the apical layer exhibited IEG-IR compared with VNO neurons of estradiol-treated males. Conversely, whereas soiled female bedding failed to induce IEG-IR in VNO neurons of estradioltreated males or females, both apical and basal neurons were activated in testosterone-treated males. Male and female pheromones also activated mitral and granule cells in the AOBs of all subjects, but responses to different pheromones were distributed across the boundary of the rostral and caudal regions. These data show that differences in the response of males and females to the same pheromonal stimulus are found in the sensory neurons of the VNO. We propose that centrifugal, noradrenergic inputs to VNO neurons, which may differ in the two sexes and respond differently to adult sex steroids, modulate sensitivity to pheromonal stimulation.

Roles of sex and gonadal steroids in mammalian pheromonal communication

“…There were no consistent effects of sex or estradiol treatment on the number of Fos-ir granule or mitral cells in the AOB following exposure to soiled male bedding. The former result was extended in a study (Halem et al, 2001a) in which the expression of another immediate early gene, Egr-1, in the VNO basal zone was found to be significantly greater in female than in male mice that were gonadectomized in adulthood and given estradiol prior to being exposed to male bedding. Again, the respective AOB responses to this stimulus did not differ between estradiol-treated females and males.…”

“…Sex differences in the detection and processing of reproductive pheromones by the main olfactory nervous system 4.1. Sex differences in the activation of the AOB by volatile pheromones acting via a centrifugal pathway As already stated, no systematic differences were found between male and female mice in the ability of soiled male (or female) bedding (which is supposed to consist primarily nonvolatile odors) to elicit Fos responses in either the granule or mitral cell layers of the AOB (Halem et al, 2001a(Halem et al, , 1999. More recently a small subset of MOB mitral cells was identified that extend axons directly to the medial amygdala (both the anterior and posteriordorsal subdivisions) (Kang et al, 2009).…”

Transgenerational epigenetic imprints on mate preference

“…Some of these chemical cues are hormonedependent, whereas others depend on the social status of the individual. These socially relevant odors are detected and processed in rodents primarily by the vomeronasal organ (VNO), and both sexes exhibit increased Fos activation in the VNO after exposure to the odor of breeding conspecifics (27)(28)(29)(30)(31)(32). It has recently been discovered that male rodents (both mouse and rat) secrete from the eyes a male-specific exocrine gland-secreting peptide (ESP1) contained in the extraorbital lachrymal gland, that is deposited on the facial hair, and that is critical to the female for assessing the stimulus qualities of males; a second peptide (ESP34) is similarly produced by females and serves a complementary function in males (30).…”

The main and the accessory olfactory systems interact in the control of mate recognition and sexual behavior

“…This regionalization is conserved at the level of the first olfactory relay, the AOB, where V1Rs neurons send projections exclusively to the rostral part of the AOB while the V2Rs neurons project to the caudal part of the AOB. It has been shown that these subdivisions of the VNO and AOB sustain functional differences as they respond differentially to pheromonal stimuli in mice [16,37]. After the first olfactory relay, mitral cells of the AOB project in turn to the medial nucleus of the amygdala, where information processed in the two parts (rostral vs caudal) of the vomeronasal pathway converge when their projections overlap in this structure [111].…”