Although parenting behavior is necessary for development of infants, underlying neural mechanisms remain unclear. The amygdalohippocampal area (AHi) neurons projecting to the medial preoptic area (MPOA), a key region for parenting, were shown to be activated by both parenting and aggression toward pups using retrograde tracer and c-Fos immunostaining. We labeled MPOA-projecting AHi neurons in a projection-specific and activity-dependent manner using a retrograde adeno-associated virus vector expressing Cre recombinase activity-dependently and mice expressing tdTomato Cre-dependently. As a result, we observed the presence of two functionally distinct subpopulations of parenting and aggressive response neurons.
We next performed scRNA-seq to determine whether the two populations were molecularly distinct and found 395 genes exhibiting higher expression levels in the parenting subpopulation than in the aggression subpopulation, and 755 genes showing the opposite pattern. Among them, we focused on 5-HT7 receptor because of high expression of Htr7 in the parenting subpopulation. Intraperitoneal administration of LP44, 5-HT7 receptor agonist, resulted in activation of parenting-labeled, but not aggression-labeled, neurons. Finally, microinjection of LP44 into the AHi 15 min before behavioral test promoted parenting behavior.
In conclusion, we identified distinct subpopulations of MPOA-projecting AHi neurons encoding parenting and aggressive behaviors toward pups. The results demonstrated that parenting AHi neurons expressed 5-HT7 receptors and were activated by administration of 5-HT7 receptor agonist, which suppressed aggressive behavior toward pups.