Histology and cytology of the islets of Langerhans in the Mongolian gerbil (Meriones unguiculatus).

The histology and cell types of the islets of Langerhans were studies in the Mongolian gerbil during post-natal development using granule stains, fluorescence methods and electron microscopy. Relative islet volume, islet size distribution, islet-duct association, islet-fat association, alpha- and D cell populations and the size distribution of secretion granules in islet cells were quantified. In adult gerbils islets have an elliptical profile enclosed by a thin collagenous capsule, a central core of beta-cells, a peripheral shell of alpha-cells and an incomplete layer of D cells between. In animals of 1 week or less, islets lack a capsule, are poorly vascularized and not innervated, though alpha, beta- and D cells are present. alpha-Cells exhibit green fluorescence during these early stages that disappears when adrenergic nerve fibres grow into the islets. Electron microscopy shows a fourth (unidentified) granular islet cell type, and small granular cells, that probably correspond to intensely fluorescent cells, were found within islets and neuroinsular complexes.