Male chemosignals inhibit the neural responses of male mice to female chemosignals

Bmal1 Is Required for Normal Reproductive Behaviors in Male Mice

Circadian rhythms synchronize physiological processes with the light-dark cycle and are regulated by a hierarchical system initiated in the suprachiasmatic nucleus, a hypothalamic region that receives direct photic input. The suprachiasmatic nucleus then entrains additional oscillators in the periphery. Circadian rhythms are maintained by a molecular transcriptional feedback loop, of which brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein 1 (BMAL1) is a key member. Disruption of circadian rhythms by deletion of the BMAL1 gene (Bmal1 knockout [KO]) induces a variety of disease states, including infertility in males, due to unidentified mechanisms. We find that, despite normal sperm function, Bmal1 KO males fail to mate with receptive females, indicating a behavioral defect. Mating is dependent on pheromone detection, as are several other behaviors. We determined that Bmal1 KO males also fail to display aggression and avoidance of predator scent, despite intact main olfactory function. Moreover, the vomeronasal organ, a specialized pheromone-responsive organ, was also functionally intact, as determined by calcium imaging in response to urine pheromone stimulus. However, neural circuit tracing using c-FOS activation revealed that, although Bmal1 KO males displayed appropriate activation in the olfactory bulb and accessory olfactory bulb, the bed nucleus of the stria terminalis and the medial preoptic area (areas responsible for integration of copulatory behaviors) failed to activate highly in response to the female scent. This indicates that neural signaling in select behavioral centers is impaired in the absence of BMAL1, likely underlying Bmal1 KO male copulatory defects, demonstrating the importance of the BMAL1 protein in the maintenance of neural circuits that drive pheromone-mediated mating behaviors.

An anti-steroidogenic inhibitory primer pheromone in male sea lamprey (Petromyzon marinus)

Reproductive functions can be modulated by both stimulatory and inhibitory primer pheromones released by conspecifics. Many stimulatory primer pheromones have been documented, but relatively few inhibitory primer pheromones have been reported in vertebrates. The sea lamprey male sex pheromone system presents an advantageous model to explore the stimulatory and inhibitory primer pheromone functions in vertebrates since several pheromone components have been identified. We hypothesized that a candidate sex pheromone component, 7α, 12α-dihydroxy-5α-cholan-3-one-24-oic acid (3 keto-allocholic acid or 3kACA), exerts priming effects through the hypothalamic-pituitary-gonadal (HPG) axis. To test this hypothesis, we measured the peptide concentrations and gene expressions of lamprey gonadotropin releasing hormones (lGnRH) and the HPG output in immature male sea lamprey exposed to waterborne 3kACA. Exposure to waterborne 3kACA altered neuronal activation markers such as jun and jun N-terminal kinase (JNK), and lGnRH mRNA levels in the brain. Waterborne 3kACA also increased lGnRH-III, but not lGnRH-I or -II, in the forebrain. In the plasma, 3kACA exposure decreased all three lGnRH peptide concentrations after 1h exposure. After 2h exposure, 3kACA increased lGnRH-I and -III, but decreased lGnRH-II peptide concentrations in the plasma. Plasma lGnRH peptide concentrations showed differential phasic patterns. Group housing condition appeared to increase the averaged plasma lGnRH levels in male sea lamprey compared to isolated males. Interestingly, 15α-hydroxyprogesterone (15α-P) concentrations decreased after prolonged 3kACA exposure (at least 24h). To our knowledge, this is the only known synthetic vertebrate pheromone component that inhibits steroidogenesis in males.

Female mice deficient in alpha-fetoprotein show female-typical neural responses to conspecific-derived pheromones

The neural mechanisms controlling sexual behavior are sexually differentiated by the perinatal actions of sex steroid hormones. We recently observed using female mice deficient in alpha-fetoprotein (AFP-KO) and which lack the protective actions of AFP against maternal estradiol, that exposure to prenatal estradiol completely defeminized the potential to show lordosis behavior in adulthood. Furthermore, AFP-KO females failed to show any male-directed mate preferences following treatment with estradiol and progesterone, indicating a reduced sexual motivation to seek out the male. In the present study, we asked whether neural responses to male- and female-derived odors are also affected in AFP-KO female mice. Therefore, we compared patterns of Fos, the protein product of the immediate early gene, c-fos, commonly used as a marker of neuronal activation, between wild-type (WT) and AFP-KO female mice following exposure to male or estrous female urine. We also tested WT males to confirm the previously observed sex differences in neural responses to male urinary odors. Interestingly, AFP-KO females showed normal, female-like Fos responses, i.e. exposure to urinary odors from male but not estrous female mice induced equivalent levels of Fos protein in the accessory olfactory pathways (e.g. the medial part of the preoptic nucleus, the bed nucleus of the stria terminalis, the amygdala, and the lateral part of the ventromedial hypothalamic nucleus) as well as in the main olfactory pathways (e.g. the piriform cortex and the anterior cortical amygdaloid nucleus), as WT females. By contrast, WT males did not show any significant induction of Fos protein in these brain areas upon exposure to either male or estrous female urinary odors. These results thus suggest that prenatal estradiol is not involved in the sexual differentiation of neural Fos responses to male-derived odors.