Abstract
Regulation of maternal behavior in the immediate postpartum period involves neural circuits in reward and homeostasis systems responding to cues from the newborn. Our aim was to assess one specific regulatory mechanism: the role that olfaction plays in the onset and modulation of parenting behavior. We focused on changes in gene expression in olfactory brain regions, examining nine genes found in previous knockout studies to be necessary for maternal behavior. Using a quantitative PCR (qPCR)-based approach, we assessed changes in gene expression in response to exposure to pups in 11 microdissected olfactory brain regions. Over the first postpartum days, all nine genes were detected in all 11 regions (at differing levels) and their expression changed in response to pup exposure. As a general trend, five genes (Dbh, Esr1, FosB, Foxb1, and Oxtr) were found to decrease their expression in most of the olfactory regions examined, while two genes (Mest and Prlr) were found to increase expression. Nos1 and Peg3 levels remained relatively stable except in the accessory olfactory bulb (AOB), where greater than fourfold increases in expression were observed. The largest magnitude expression changes in this study were found in the AOB, which mediates a variety of olfactory cues that elicit stereotypic behaviors such as mating and aggression as well as some non-pheromone odors. Previous analyses of null mice for the nine genes assessed here have rarely examined olfactory function. Our data suggest that there may be olfactory effects in these null mice which contribute to the observed maternal behavioral phenotypes. Collectively, these data support the hypothesis that olfactory processing is an important sensory regulator of maternal behavior.
Highlights
Regulation of maternal behavior in the immediate postpartum period involves neural circuits in reward and homeostasis systems responding to newborn sensory cues from the somatosensory, visual, auditory, and olfactory systems
As a general trend, dopamine beta-hydroxylase (Dbh), estrogen receptor 1 (Esr1), forkhead box B1 (Foxb1), FBJ osteosarcoma oncogene B (FosB), and oxytocin receptor (Oxtr) decreased in expression in most regions after exposure to pups, while nitric oxide synthase 1 (Nos1), mesoderm-specific transcript (Mest), paternally expressed 3 (Peg3), and prolactin receptor 9 (Prlr) increased in most regions during the postpartum period
To examine changes in gene expression in the postpartum period we elected to look at postpartum day 0 (PPD0) to see if exposure to pups elicited changes in gene expression in olfactory regions, as well as at postpartum day 1 (PPD1) to see if expression remained stable or showed further changes after continued exposure to pups
Summary
Regulation of maternal behavior in the immediate postpartum period involves neural circuits in reward and homeostasis systems responding to newborn sensory cues from the somatosensory, visual, auditory, and olfactory systems. Olfactory regulation of maternal behavior is less well understood than other sensory modalities, especially visual and auditory. First-time mothers, with higher levels of circulating cortisol, are better able to identify their own infant’s odor (Fleming et al, 1997). Consistent with this small literature are studies in animal models where many aspects of social behavior, such as gender identification, control of mating and aggression responses, and pup recognition are mediated by olfaction. We have elected to perform our study in mice as rodents have been the mainstay of biomedical research and the insights provided into the workings of mammalian systems have proved to be applicable to human biological systems (Shively and Clarkson, 2009)
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