The pineal gland: thinking outside the box

MARÍA PAULA IBAÑEZ RODRIGUEZ; STEPHEN NOCTOR; ESTELA MARIS MUÑOZ

Huerta Grande, Cordoba

Congreso; SAN 2014; 2014

The pineal gland (PG) has been considered a homogeneous organ composed mainly of melatonin-synthesizing pinealocytes. We studied the PG beyond pinealocytes via a detailed characterization of the different cell lineages from E15 to adulthood. We analyzed markers for immature and mature pinealocytes, astrocytes, microglia, nerve fibers, blood vessels, and mitosis. Also, we challenged the local microglia by superior sympathetic ganglionectomy (SCGx) and decentralization (SCGd). Pax6 and vimentin were expressed in the entire PG ontogeny with the highest levels at earlier stages; their radial, rosette-like and randomly distributed arrangements correlated well with PG organogenesis. Serotonin, a marker for more mature Pax6-negative pinealocytes, was evident after birth. Mitotic pH3-positive cells were seen in the embryonic and neonatal PG, and their distribution was consistent with each stage. A heterogeneous astrocytic population was regionally dispersed in the adult PG. Surprisingly, microglia invaded the PG from E15 onward and showed an active morphology and proliferative potential in all the stages analyzed, being in close contact with and, in some cases, engulfing Pax6-positive precursors and nerve fibers. SCGx activated the local microglia with consequent enhancement of precursor and nerve fiber engulfment. In brief, the PG is not a homogenous organ. Microglia present in an organ without BBB within the CNS support immunological functions recently attributed to the PG.