PUPS ON THE BRAIN: MEDIAL AMYGDALA PLASTICITY DURING PREGNANCY

During mouse pregnancy, performance of parental behaviours such as pup retrieval to the nest improves. This enhancement is driven by pregnancy-induced plasticity of medial preoptic area galanin (MPOA^Gal) neurons, mediated by estrogen and progesterone. Notably, progesterone increases recruitment of excitatory inputs to the MPOA^Gal neurons, but the source of these inputs and the information they convey to the MPOA remain unclear. Here, we aim to identify upstream excitatory circuits contributing to pregnancy-induced enhancements in parental behaviour. Given the role of the posterodorsal medial amygdala (MeApd) in processing hormonal and chemosensory cues and its involvement in maternal behaviour, we focus on glutamatergic neurons in this region (MeApd^VGlut2). We find that tetanus toxin light chain (TeLC)-mediated silencing of MeApd^VGlut2 neurons impairs the pregnancy-induced enhancement in pup retrieval normally seen in controls. Preliminary 1-photon calcium imaging results suggest that the representation of pup chemosensory cues in this population is altered during pregnancy, reflected in differences in activity during pup contact and parental interactions in late-pregnant compared to non-pregnant females. Furthermore, selective silencing of the MeApd^VGlut2→MPOA projection abolishes the pregnancy-induced increase in stable retrieval – retrieval events not followed by aggression. Based on these findings, we hypothesise that pregnancy reshapes pup chemosensory representation within MeApd^Vglut2 neurons, potentially through hormonal action. We propose that this change in representation, possibly accompanied by a shift in valence, provides instructive cues to the MPOA to promote caregiving over pup ignoring. Overall, this study highlights the medial amygdala as a key upstream regulator of MPOA-driven parental behaviour during pregnancy.