Abstract
Motherhood entails changes in behavior with increased motivation for pups, induced in part by pregnancy hormones acting upon the brain. This work explores whether this alters sensory processing of pup-derived chemosignals. To do so, we analyse the expression of immediate early genes (IEGs) in the vomeronasal organ (VNO; Egr1) and centers of the olfactory and vomeronasal brain pathways (cFos) in virgin and late-pregnant females exposed to pups, as compared to buttons (socially neutral control). In pup-exposed females, we quantified diverse behaviors including pup retrieval, sniffing, pup-directed attack, nest building and time in nest or on nest, as well as time off nest. Pups induce Egr1 expression in the VNO of females, irrespective of their physiological condition, thus suggesting the existence of VNO-detected pup chemosignals. A similar situation is found in the accessory olfactory bulb (AOB) and posteromedial part of the medial bed nucleus of the stria terminalis (BSTMPM). By contrast, in the medial amygdala and posteromedial cortical amygdala (PMCo), responses to pups-vs-buttons are different in virgin and late-pregnant females, thus suggesting altered sensory processing during late pregnancy. The olfactory system also shows changes in sensory processing with pregnancy. In the main olfactory bulbs, as well as the anterior and posterior piriform cortex, buttons activate cFos expression in virgins more than in pregnant females. By contrast, in the anterior and especially posterior piriform cortex, pregnant females show more activation by pups than buttons. Correlation between IEGs expression and behavior suggests the existence of two vomeronasal subsystems: one associated to pup care (with PMCo as its main center) and another related to pup-directed aggression observed in some pregnant females (with the BSTMPM as the main nucleus). Our data also suggest a coactivation of the olfactory and vomeronasal systems during interaction with pups in pregnant females.
Highlights
Maternal behavior can be defined as any interaction of an adult female with infant conspecifics that helps the latter to survive until their maturity (Numan and Insel, 2003)
One of the aims of this work is to explore the response of the vomeronasal system to possible pup-derived chemosignals detected by the vomeronasal organ (VNO), and the possibility that adult females change their sensitivity to these stimuli and/or their sensory processing mechanisms during late pregnancy
Our results indicate that pups induced an increase in cFos expression in the accessory olfactory bulb (AOB) of females, this response was indistinguishable between virgin and LP females exposed to pups and a similar situation is found in the bed nucleus of the stria terminalis (BSTMPM)
Summary
Maternal behavior can be defined as any interaction of an adult female with infant conspecifics that helps the latter to survive until their maturity (Numan and Insel, 2003). Dams show an intense activity not directed to pups, such as building and maintaining the nest already before parturition and defending it against adult conspecific intruders that might constitute a threat for their pups (maternal aggression) (Numan and Insel, 2003). Maternal behaviors are normally expressed after delivery, when pups are present, they are already facilitated during pregnancy. It was shown that primigravid female rats that were hysterectomized before parturition, displayed facilitated pup-directed behaviors (Rosenblatt and Siegel, 1975; Bridges et al, 1978).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
