Is melanin-concentrating hormone in the medial preoptic area a signal for the decline of maternal care in late postpartum?

This manuscript proposes that melanin-concentrating hormone (MCH) in the medial preoptic area (MPOA) is an neurochemical signal evolved to trigger the declining process of maternal care. MCH in the MPOA appears only after parturition and is progressively increased with the progression of lactation, while maternal behavior declines progressively. Intra-MPOA injection of MCH decreases active maternal responses. MCH is also highly responsive to infant characteristics and maternal condition. Behavioral changes induced by MCH in late postpartum period are conducive to the decline of infant-directed maternal behavior. The MPOA MCH system may mediate the maternal behavior decline by suppressing the maternal approach motivation and/or increasing maternal withdrawal via its inhibitory action onto the mesolimbic dopamine D₁/D₂ receptors and its stimulating action on serotonin 5-HT_2C receptors in the ventral tegmental area. Research into the MCH maternal effects will enhance our understanding of the neurochemical mechanisms underlying the maternal behavior decline.