The vasopressin V1a and V1b receptors in the medial preoptic area mediate maternal care in lactating rats
Final Report Abstract
According to the overall aim of the project, the results contributed to increase our understanding regarding the complex interactions of the arginine‐vasopressin (AVP) receptor subtypes V1a and V1b within the medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST) in mediating maternal care, maternal motivation (i.e. retrieval of the pups) and maternal aggression against a female virgin intruder (i.e. the maternal defense test) in lactating rats. In line with the effects of V1a receptor blockade, central V1b receptor antagonism decreased mother–pup interaction, only. The subsequent brain region‐specific study revealed that the expression of V1b receptors within the BNST or the MPOA was similar between virgin and lactating rats, whereas V1a receptor mRNA is upregulated in lactation. With respect to maternal behavior, in the BNST, V1a and V1b receptors complement each other as receptor blockade impairs maternal defense and protection of the offspring, respectively. Moreover, in the MPOA, maternal motivation is increased after V1b receptor antagonism both in the conventional as well as in the newly established modified pup retrieval test (lactating mothers are provided with a house made of red Perspex thereby increasing the speed of pup retrieval), which is in contrast to V1a receptor blockade causing decreased maternal motivation. Thus, it is feasible that the behavioral outcome of locally released AVP within the MPOA, and thereby parallel activation of V1aR and V1bR, reflects the integration of facilitating and impairing maternal motivation, respectively. These results demonstrate the brain region‐specific roles of V1a and V1b receptors, at least for maternal behavior. Studies characterizing the neuronal activation patterns in the MPOA and BNST based on the display of specific maternal behaviors as well as behavioral consequences after V1b receptor antagonism in other “maternal” brain regions are currently finalized. In a further project we could demonstrate that maternal care is displayed in a diurnal rhythm; 24‐hour observations revealed that the mothers spent most of the day‐time calm on the nest whereas they became mobile, i.e. leaving the nest frequently, as soon as the light went off. The diurnal rhythm is triggered by the supra-chiasmatic nucleus (SCN), which sends AVP projections to the MPOA, among others. In the SCN, AVP mRNA expression of lactating versus virgin rats was found to be similar, i.e. lack a peripartum adaptation. In order to identify further sources of AVP released in the MPOA, we extensively studied AVP eGFP rats as well as ovariectomized, primed rats. The data is not published, yet; therefore, a summary of the findings is not available at this point. Another important component of maternal behavior is maternal aggression towards a potentially dangerous intruder in order to defend the pups. We showed that the intensity of aggression dramatically changes over the peripartum period. It first appeared on the day before parturition, dropped immediately afterwards, peaked during early lactation, before it almost disappeared at weaning. These changes were accompanied by central changes in V1a and OXT receptor binding (immediately after the maternal defense test). Furthermore, we completed and proved the picture of how increased release of AVP and OXT in the BNST, lateral septum and PVN modulate maternal aggression. In summary, these data complement our knowledge on the role of the brain AVP and OXT systems in maternal aggression, which together with fluctuations in V1a and OXT receptor expression ensure the expression of maternal aggression at the correct time peripartum. In conclusion, the project was very successful with respect to scientific publications, the promotion of young scientists, and subsequent collaborations with distinguished international neuroscientists.
Publications
- (2011) Changes in the intensity of maternal aggression and central oxytocin and vasopressin V1a receptors across the peripartum period in the rat. J Neuroendocrinol 23: 1113‐1124
Caughey S, Klampfl SM, Bishop VR, Pförtsch J, Neumann ID, Bosch OJ, Meddle SL
(See online at https://doi.org/10.1111/j.1365-2826.2011.02224.x) - (2013) Maternal aggression in rodents: Brain oxytocin and vasopressin mediate pup defence. Phil Trans R Soc B: 368 20130085
Bosch OJ
(See online at https://doi.org/10.1098/rstb.2013.0085) - (2014) Central V1b receptor antagonism in lactating rats: Impairment of maternal care but not of maternal aggression. J Neuroendocrinol 26: 918‐926
Bayerl DS, Klampfl SM, Bosch OJ
(See online at https://doi.org/10.1111/jne.12226)
