Role of the tail of the ventral tegmental area in the regulation of maternal behaviour: a pharmacological study in postpartum rats.

Maternal behaviour is characterized by increased motivation for pups, which facilitates the expression of behaviours promoting offspring survival and development. Motivated behaviours are critically dependent on brain dopamine systems, thus, understanding its functioning is necessary to elucidate maternal reward brain processing. The activity of dopamine systems is controlled by the inhibitory GABA cells of the tail of the ventral tegmental area or rostromedial tegmental nucleus (tVTA/RMTg). This brain region is involved in reward and avoidance behaviour, among other functions, however, its role in maternal behaviour remains poorly understood. In the present study, we assess the effect of pharmacological manipulation of the tVTA/RMTg on maternal behaviour in postpartum female rats. To this end, pregnant Sprague-Dawley female rats underwent stereotaxic implantation of a guide cannula in the tVTA/RMTg. During the first week after delivery, female rats received intra-tVTA/RMTg microinjections of vehicle and/or several pharmacological agents (glutamate, DAMGO, muscimol, oxytocin or atosiban) in a cross-design. Our results reveal that pharmacological activation and inhibition of the tVTA/RMTg can increase or decrease maternal behaviour, respectively, by altering some specific behaviours, such as pup retrieval, pup exploration or time spent in nest. Otherwise, modulation of the oxytocinergic transmission at the tVTA/RMTg reveals mild effects on maternal behaviour and the observed effect depend on the oxytocin dose. Overall, our results reveal an involvement of the tVTA/RMTg in maternal reward processing, since its activation or inhibition can critically modulate maternal behaviour.