Oxytocin Facilitates Allomaternal Behavior under Stress in Laboratory Mice

Abstract

AbstractOxytocin (Oxt) controls reproductive physiology and various kinds of social behaviors, but the exact contribution of Oxt to different components of parental care still needs to be determined. Here, we illustrate the neuroanatomical relations of the parental nurturing-induced neuronal activation with magnocellular Oxt neurons and fibers in the medial preoptic area (MPOA), the brain region critical for parental and alloparental behaviors. We used genetically-targeted mouse lines forOxt,Oxt receptor(Oxtr),vasopressin receptor 1a(Avpr1a),vasopressin receptor 1b(Avpr1b), andthyrotropin-releasing hormone(Trh) to systematically examine the role of Oxt-related signaling in pup-directed behaviors. TheOxtr-Avpr1a-Avpr1btriple knock-out (TKO), andOxt-Trh-Avpr1a-Avpr1bquadruple KO (QKO) mice were grossly healthy and fertile, except for their complete deficiency in milk ejection and modest deficiency in parturition secondary to maternal loss of theOxtorOxtrgene. In our minimal stress conditions, pup-directed behaviors in TKO and QKO mothers and fathers, virgin females and males were essentially indistinguishable from those of their littermates with other genotypes. However,OxtrKO virgin females did show decreased pup retrieval in the pup-exposure assay performed right after restraint stress. This stress vulnerability in theOxtrKO was abolished by the additionalAvpr1bKO. The general stress sensitivity, as measured by plasma cortisol elevation after restraint stress or by the behavioral performance in the open field (OF) and elevated plus maze (EPM), were not altered in theOxtrKO but were reduced in theAvpr1bKO females, indicating that the balance of neurohypophysial hormones affects the outcome of pup-directed behaviors.