A zonal pattern of neuroglial cells during the development of the intermediate lobe of the rat pituitary

In this paper the development of the intermediate lobe (IL) of the pituitary of the rat is described using alkaline phosphatase (AP) (EC 3.1.3.1.) enzyme histochemistry and stage-specific embryonic antigen 1 (SSEA-1) immunocytochemistry. SSEA-1 and AP are co-localized during late development and reveal the existence of two cytochemically different cell types within the IL, i.e. SSEA-1/AP-positive and SSEA-1/AP-negative cells. The SSEA-1/AP-positive cells are initially arranged along the hypophyseal lumen, in a number of longitudinally oriented zones. alpha-Melanocyte-stimulating hormone (alpha-MSH) immunoreactivity is expressed in the SSEA-1/AP-negative cells from E20 onwards. Eventually the SSEA-1/AP-positive cells develop into a layer of cells covering the luminal surface of the IL lobules. These cells represent the glio-epithelial or neuroglial cells of the IL.