Pineal gliosis and gland ageing. The possible role of the glia in the transfer of melatonin from pinealocytes to the blood and cerebrospinal fluid

ABSTRACT

Using immunohistochemical approaches appliedto 6 ìm-thick sections from the pineal glands ofcows with ages between 1 and 7 years, we studiedthe expression of GFAP, vimentin and S-100and of â-tubulin. The latter compound appearedin both pinealocytes and in some nerve fibres. Inboth younger and older cows, vimentin wasexpressed in the somata of cells localised inperipheral zones of the glands and in fibres witha bead-like aspect that coursed deep into the centresof the glands, as well as in pericapillary cells,apparently in the endothelia of vessels and, likeGFAP and S-100, in a thick network of prolongationslocated between the basal side of theepithelial cells of the pineal recess and pinealocytes,sometimes reaching the ependymal lumen.The network of glial prolongations formed aspace with a reticulated aspect interposedbetween the pinealocytes and the ependymalepithelium. The thickness of this network wasespecially striking in the older cows. The expressionof GFAP and S-100 was also observed in thesomata and the cytoplasmic prolongations of cellsdistributed throughout the gland that surroundedthe pinealocytes. In cows with ages of 4 and 7years the pineal gland showed a pronounceddegree of gliosis that isolated the pinealocytesfrom one another and from the vascular bed.Additionally, all three glial markers wereexpressed in cells whose somata and cytoplasmicprolongations configured spaces with a trabecularaspect, very poor in connective tissue, whichcoursed throughout the glands to reach the reticulatedspace, in especially thin neighbouringzones of the epithelium of the pineal recess. Theresults suggest a decisive role of the pineal glia ingland ageing, in the secretion of melatonin, andin the configuration of the vascular and ependymalpathways that the hormone must follow frompinealocytes to its target organs (AU)

RESUMEN

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