GLIAL-LIKE CELLS OF THE RAT PITUITARY INTERMEDIATE LOPE CHANGE MORPHOLOGY AND SHIFT FROM VIMENTIN TO GFAP EXPRESSION DURING DEVELOPMENT

This study demonstrated morphological changes in glial-like cells of the rat pituitary intermediate lobe during early postnatal development, and a subsequent shift in protein expression from vimentin to GFAP, Vimentin immunoreactivity was detected in the lobe at embryo day 14 and was localized in radially-oriented, bipolar cells whose processes spanned the thickness of the intermediate lobe. At electron microscopical resolution, processes contained intermediate filaments, cell nuclei were indented while secretory vesicles characteristic of the endocrine cells were not found. Vimentin immunoreactive intensity began to decrease at postnatal day 5. By postnatal day 7, vimentin-positive, stellate cells were observed, with few radial processes found by day 10. The intensity of vimentin immunoreactivity decreased through day 25. Within the Lobe parenchyma, vimentin was localized in glial-like cells since double-label immunohistochemistry revealed no colocalization of P-endorphin and vimentin, or fibronectin and vimentin. Dopamine-containing axons were in close apposition to vimentin-positive processes. GFAP immunoreactivity first appeared on postnatal day 20 and, by day 25, stellate cell bodies with three to six extended processes were evident. Cells were primarily distributed in the caudal third of the lobe. The characteristic adult pattern of cell clusters in latero-dorsal and ventral portions of the lobe was fully established by postnatal day 55, The transition from vimentin to GFAP expression and concurrent morphological changes resemble those described for radial glia during cerebral cortical development.