Lifetime Variations in Prolactin Expression in the Hippocampus and Dentate Gyrus of the Rat.

Prolactin is a hormone with demonstrated roles in the brain, including neurogenesis, neuroprotection, learning, stress response or memory consolidation. To determine the prolactin expression in the rat hippocampus during aging and to resolve some controversies related to the presence of prolactin in the hippocampus, the aim of this study was to analyze whether changes occur in the expression of prolactin during different stages of life. To determine this, we designed an experimental study in which we analyzed the expression and location of prolactin in the rat hippocampus, Ammon's horn and Dentate Gyrus, during different stages of life (prepubertal, postpubertal, young adult, adult and old) and checked if there are differences related to sex. Overall, the results obtained show that prolactin is present in the rat hippocampus and that prolactin is synthesized, as deduced from the findings obtained via ELISA, immunohistochemistry, qPCR and in situ hybridization. After analyzing the correlation between serum and hippocampal prolactin levels and comparing the amounts of mRNA and the hormone, the results obtained suggest that hippocampal prolactin has a dual origin: local synthesis of the hormone and its passage from the blood. On the other hand, the amounts of prolactin and its mRNA in the hippocampus vary with sex and age, suggesting the existence of age-related sexual dimorphism. The results obtained suggest that hippocampal aging is related to a decrease in the hippocampal prolactin system, which helps to better understand brain aging.