Transcriptional plasticity of melanin-concentrating hormone neurons in the medial preoptic area of lactating mouse dams

The medial preoptic area (MPOA) is a central hub for maternal behavior, integrating hormonal and sensory signals to coordinate adaptive postpartum responses. Although melanin-concentrating hormone (MCH) neurons are well characterized in the lateral hypothalamus, their identity and functional engagement within MPOA circuits remain poorly defined. Here, through integrative reanalysis of a publicly available single-cell RNA sequencing dataset of the mouse MPOA (GSE295610), we identify two transcriptionally distinct Pmch-expressing neuronal populations. Both populations are GABAergic and emerge prominently during mid to late lactation. Lactation is characterized by significant upregulation of Pmch and coordinated enrichment of neuropeptidergic and hormone-responsive genes, including islet amyloid polypeptide (Iapp), prodynorphin (Pdyn), and prolactin receptor (Prlr). Independent single-cell gene expression profiling of FACS-isolated GAD67-GFP neurons from the MPOA further corroborated these findings, confirming the selective emergence of Pmch expression during lactation and its co-expression with neuropeptidergic and hormone-responsive genes. NeuroEstimator-based activity inference demonstrates increased predicted neuronal activity in lactating females, while pseudotime reconstruction reveals a lactation-associated transcriptional shift toward later trajectory states. hdWGCNA analysis identified gene co-expression modules significantly enriched during lactation. Regulatory network inference using SCENIC further revealed activation of activity-dependent transcriptional regulons, including cyclic AMP-responsive element-binding protein 3-like 1 (Creb3l1), early growth response 1 (Egr1), and FBJ osteosarcoma oncogene (Fos). These transcriptional programs converge on gene networks associated with synaptic plasticity, regulation of neurogenesis, and broader mechanisms of neuronal plasticity. Notably, these Pmch populations were not annotated in the original study, underscoring the power of systems-level reanalysis to uncover previously unrecognized components of maternal circuitry. Together, our findings provide single-cell evidence that MCH-expressing neurons in the MPOA undergo state-dependent transcriptional reorganization during lactation, suggesting a dynamic role for MCH signaling in postpartum neuroendocrine plasticity.