Prolactin is a hormone for which actions on the central nervous system such as neurogenesis and neuroprotection have been described by acting on specific receptors. The presence of prolactin receptors in the brain, including the hippocampus, is well documented; however, it is unknown whether these receptors change with age and whether they are related to sex. For this reason, a study of the expression of prolactin receptors, in the short and long isoforms, in the hippocampus of male and female rats has been carried out by qPCR and in situ hybridization, with a densitometric analysis in the following life stages: prepubertal, postpubertal, young adult, adult, and old. The results revealed the greater expression of the long isoform than of the short isoform in males, but not in females, with significant differences between males and females and in the different life stages studied. With significant differences, the highest expression of both isoforms appeared in male rats in the postpubertal stage, and the lowest expression was observed in adult and old animals. In situ hybridization showed differences in the localization of PRLR mRNA expression in CA1, CA3, and DG depending on the age and sex of the rats. The results obtained suggest that hippocampal aging is related to a decrease in prolactin receptors, which helps to better understand brain aging.

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 Prl 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.

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level and play important roles in the development and function of the nervous system. Through the coordinated regulation of multiple target genes and signalling pathways, miRNAs participate in key neurodevelopmental processes, including neural progenitor proliferation and differentiation, neuronal specification and migration, morphological maturation, synaptic development, and circuit formation. Their functions are strongly dependent on developmental stage, cell type, brain region, and expression level, and the extent of mechanistic characterization varies considerably among individual miRNAs. This review examines well-characterized and emerging neurodevelopment-related miRNAs, including members of the miR-9, miR-34, miR-107, miR-124, miR-132, miR-134, miR-137, miR-181, miR-185, miR-191, miR-200, miR-218, and miR-344 families, integrating evidence on their molecular mechanisms and functions during nervous system development. Their dysregulation is further considered in neurodevelopmental, neuropsychiatric, neurological, and neurodegenerative disorders, as well as in selected rare and metabolic or endocrine disorders with neurological involvement. We also examine the potential of circulating and tissue-associated miRNAs as diagnostic and prognostic biomarkers and the emerging therapeutic possibilities of miRNA modulation. Current evidence supports important roles for miRNAs in neurodevelopment and neurological disease but also highlights substantial differences between mechanistic and associative evidence. Methodological heterogeneity, differences between central and peripheral miRNA profiles, limited independent validation, and challenges associated with targeted delivery and off-target effects remain major barriers to their clinical translation.