Raising overlapping litters: differential activation of the rats' maternal neural circuitry after interacting with newborn or juvenile pups.

The maternal behavior of a rat dynamically changes during the postpartum period, adjusting to the characteristics and physiological needs of the pups. This adaptation has been attributed to functional modifications in the maternal circuitry. Maternal behavior can also flexibly adapt according to different litter compositions. Thus, mothers with two overlapping litters can concurrently take care of neonate and juvenile pups; mostly directing their attention to the newborns. We hypothesized that the maternal circuitry of these mothers would show a differential activation pattern after interacting with pups depending on their offspring's developmental stage. Thus, we evaluated the activation of several areas of the maternal circuitry in mothers of overlapping litters, by using c-Fos immunoreactivity as a marker of neuronal activation, after interacting with newborns or juveniles. Results showed that mothers with overlapping litters display different behavioral responses towards their newborn and their juvenile pups. Interestingly, these behavioral displays co-occurred with specific patterns of activation of the maternal neural circuitry. Thus, a similar expression of c-Fos was observed in some key brain areas of mothers that interacted with newborns or juveniles, such as the medial preoptic area and the nucleus accumbens, while a differential activation was quantified in the ventral region of the bed nucleus of the stria terminalis, the infralimbic and prelimbic subregions of the medial prefrontal cortex and the basolateral and medial nuclei of the amygdala. We posit that the specific profile of activation of the neural circuitry that controls maternal behavior in mothers with overlapping litters, allow dams to respond adequately to the newborn and the juvenile pups. This article is protected by copyright. All rights reserved.