Activation of 5-HT receptor disrupts rat maternal behavior.

Serotonin 5-HT receptor is widely distributed in the central nervous system and plays an important role in sensorimotor function, emotion regulation, motivation, executive control, learning and memory. We investigated its role in rat maternal behavior, a naturalistic behavior encompassing many psychological functions that the 5-HT receptor is involved in. We first showed that activation of 5-HT receptor by TCB-2 (a highly selective 5-HT agonist, 1, 2.5 or 5.0 mg/kg) disrupted maternal behavior dose-dependently, and this effect was reduced by pretreatment with a 5-HT receptor antagonist MDL 100907, but exacerbated by pretreatment with a 5-HT receptor antagonist SB242084 and a 5-HT receptor agonist MK212, indicating that the maternal disruptive effect of 5-HT activation is receptor-specific and can be modulated by 5-HT receptor bidirectionally. We then microinjected TCB-2 into two brain regions important for the normal expression of maternal behavior: the medial prefrontal cortex (mPFC) and the medial preoptic area (mPOA) and found that only acute intra-mPFC infusion of TCB-2 suppressed pup retrieval, whereas intra-mPOA had no effect. Finally, using c-Fos immunohistochemistry, we identified that the ventral bed nucleus of stria terminalis (vBNST), the central amygdala (CeA), and the dorsal raphe (DR) were additionally involved in the maternal-disruptive effect of TCB-2. These findings suggest that the 5-HT receptor in the mPFC and other maternally related regions is required for the normal expression of maternal behavior through its intrinsic action or interactions with other receptors (e.g. 5-HT). Functional disruption of this neuroreceptor system might contribute to postpartum mental disorders (e.g. depression and psychosis) that impair the quality of maternal care.