Localizing the effect of serotonin in mPOA and BNST on pup-directed behavior in female mice

In many species, females show little to no interaction with pups as virgins but display an array of care behaviors towards pups when they become moms. Recent work from my mentor in the Luo lab, Alina Xiao, shows that serotonin (5-HT) is an important neuromodulator mediating such behavioral transition. While conditionally knocking out Tph2—a gene encoding for an enzyme required for 5-HT synthesis—in serotonin neurons that project to the medial preoptic area (mPOA) significantly suppresses pup interaction in moms, the same manipulation in serotonin neurons that project to the bed nucleus of the stria terminalis significantly increases pup interaction in virgins. However, because mPOA- and BNST-projecting serotonin neurons collateralize to other brain regions, it is unknown whether 5-HT activity is required at all axon collaterals or locally in mPOA or BNST to modulate pup interaction across reproductive stages. This current study thus investigates the local, short-term effects of disrupting 5-HT activity in mPOA or posterior BNST (BNSTpr) on pup interaction via serotonin receptor 2C antagonist (2C–) infusion. Consistent with the previous loss-of-function experiment, 2C– infusion in mPOA suppressed pup-interaction in moms but promoted pup-interaction in BNSTpr in virgins. However, unlike in the conditional knockout of Tph2, 2C– infusion in mPOA also significantly decreased pup interaction in virgins and disrupted pup retrieval in moms, demonstrating that an acute, local disruption of 5HT activity in mPOA disrupts pup interaction more severely than long-term, whole-cell deletion of serotonin synthesis. Together, findings from this current study support that 5HT activity in mPOA and BNSTpr is functionally heterogeneous and further highlight that 5HT is required locally in mPOA and BNSTpr to promote and suppress pup care behavior, respectively.