Prolactin Secretion During Postnatal Development in Artificial Rearing Rats (Rattus norvegicus)

During the lactation period, rat pups are fed by their mother and are with their siblings. In the pituitary, lactotrope and somatolactotrope cells increase in number during this period and are associated with milk-borne factors. In the artificial rearing (AR) paradigm, pups are deprived of mother- and sibling-pup interactions and are fed artificial milk. AR rats present more hypothalamic neurons associated with less apoptosis during postnatal development. Moreover, AR infantile rats show growth hormone (GH), insulin-like growth factor-1 (IGF-1), and ghrelin alterations resulting from suckling behavior and the absence of meal transition at the second week of life. In the present study, the variation in prolactin (PRL) throughout the lactation period was analyzed in AR pups and compared with that in mother-reared (MR) pups. At postnatal Day 7 (pnd7), AR pups have less serum PRL than MR pups do, and a further decrease was observed at pnd14. However, only at pnd14, AR pituitary cells secrete less PRL, which was correlated with a smaller number of somatolactotrope cells unlike lactotrope cells. Analysis of the hypothalamic dopamine and DOPAC concentrations in both groups revealed no differences at 7, 14, and 21pnd. Nevertheless, the pituitary showed higher concentrations in AR pups than in MR pups at pnd14. However, the number of dopaminergic neurons in the arcuate nucleus was similar in both groups, but they were less spread in the AR pup hypothalamus. Our results revealed the importance of mothers' and siblings' interactions and mothers' milk in the maturation of the PRL hypothalamic‒pituitary axis during the lactating period.