Maternal care during infancy regulates the development of neural systems mediating the expression of fearfulness in the rat

TLDR

Individual differences in maternal licking/grooming and arched‑back nursing of rat pups influence the development of stress‑responsive behavior, and fear and anxiety are regulated by a neural circuitry involving locus ceruleus projections to forebrain structures. Offspring of mothers with high LG‑ABN exhibit lower adult fearfulness to novelty, higher benzodiazepine and alpha2 adrenoreceptor densities, lower CRH receptor density in the locus ceruleus, and these changes suggest maternal care programs stress responses by shaping fear‑mediating neural systems.

Abstract

The mothers of infant rats show individual differences in the frequency of licking/grooming and arched-back nursing (LG-ABN) of pups that contribute to the development of individual differences in behavioral responses to stress. As adults, the offspring of mothers that exhibited high levels of LG-ABN showed substantially reduced behavioral fearfulness in response to novelty compared with the offspring of low LG-ABN mothers. In addition, the adult offspring of the high LG-ABN mothers showed significantly (i) increased central benzodiazepine receptor density in the central, lateral, and basolateral nuclei of the amygdala as well as in the locus ceruleus, (ii) increased alpha2 adrenoreceptor density in the locus ceruleus, and (iii) decreased corticotropin-releasing hormone (CRH) receptor density in the locus ceruleus. The expression of fear and anxiety is regulated by a neural circuitry that includes the activation of ascending noradrenergic projections from the locus ceruleus to the forebrain structures. Considering the importance of the amygdala, notably the anxiogenic influence of CRH projections from the amygdala to the locus ceruleus, as well as the anxiolytic actions of benzodiazepines, for the expression of behavioral responses to stress, these findings suggest that maternal care during infancy serves to "program" behavioral responses to stress in the offspring by altering the development of the neural systems that mediate fearfulness.