[Regional differences in the pineal gland of the cotton rat, Sigmodon hispidus. Light and electron microscopic...

The determination of volumes of the distal and proximal halves of the pineal glands of cotton rats (Sigmodon hispidus) and Sprague-Dawley rats revealed that the volume of the proximal half was far larger in cotton rats than in Sprague-Dawley rats. Light and electron microscopic examination of the distal, middle and proximal pineal regions in the cotton rat revealed the presence of regional differences in parenchymal cells, capillary endothelial cells and pericapillary spaces. Nuclear sizes of pinealocytes were larger in the distal region than in the middle and proximal regions. The diameter of granulated vesicles and the contents in lysosome-like bodies in pinealocytes in the distal and middle regions were different from those in the proximal region. Interstitial cells and astrocytes surrounded pericapillary spaces; the former was localized in the peripheral area of the distal and middle regions, whereas the latter was found throughout the organ. Astrocytes were more abundant towards the proximal region. The capillary endothelium was often fenestrated in the distal region, whereas the fenestrae were few in the middle region and absent in the proximal region. Pericapillary spaces were large in the distal and middle regions, but narrow in the proximal region. Postganglionic sympathetic nerve fibers were distributed throughout the organ, whereas myelinated and unmyelinated nerve fibers, survived after superior cervical ganglionectomy, were found in the distal and middle regions, but not in the proximal region. Sympathetic and non-sympathetic nerve fibers lay adjacent to interstitial cells and astrocytes. These regional differences may reflect functional differences in various pineal regions of the cotton rat.