The brain as a source and a target of prolactin in mammals

Prolactin is a polypeptide hormone associated with an extensive variety of biological functions. Among the roles of prolactin in vertebrates, some were preserved throughout evolution. This is the case of its function in the brain, where prolactin receptors, are expressed in different structures of the central nervous system. In the brain, prolactin actions are principally associated with reproduction and parental behavior, and involves the modulation of adult neurogenesis, neuroprotection, and neuroplasticity, especially during pregnancy, thereby preparing the brain to parenthood. Prolactin is mainly produced by specialized cells in the anterior pituitary gland. However, during vertebrate evolution many other extrapituitary tissues do also produce prolactin, like the immune system, endothelial cells, reproductive structures and in several regions of the brain. This review summarizes the relevance of prolactin for brain function, the sources of prolactin in the central nervous system, as well as its local production and secretion. A highlight on the impact of prolactin in human neurological diseases is also provided.