REGIONAL DIFFERENCES IN THE PINEAL-GLAND OF THE COTTON RAT, SIGMODON HISPIDUS - LIGHT-MICROSCOPIC, ELECTRON-MICROSCOPIC, AND IMMUNOHISTOCHEMICAL OBSERVATIONS

Light microscopic, electron microscopic and immunohistochemical observ ations of the various portions of the pineal gland of the cotton rat ( Sigmodon hispidus) were made. The volume of the proximal half occupied about 30% of the whole organ, and pinealocytes were slightly smaller in size in the proximal portion than elsewhere, The distal and interme diate portions contained few interstitial cells and numerous astrocyte s, but the proximal portion lacked interstitial cells and had more abu ndant astrocytes than elsewhere. Astrocytes, which were immunoreactive for glial fibrillary acidic protein, mainly lined the pericapillary s paces in the distal and intermediate portions, but in the proximal por tion these cells often surrounded isolated or groups of pinealocytes. In the distal and intermediate portions, abundant sympathetic fibers a nd less numerous non-sympathetic, peptidergic fibers were mainly local ized in the pericapillary spaces; these fibers were sparsely distribut ed in the parenchyma close to interstitial cells or astrocytes. In the proximal portion, non-sympathetic fibers were scarce and sympathetic fibers were distributed abundantly and almost exclusively in the paren chyma. Most of the sympathetic fibers were adjacent to astrocytes and, occasionally, made specialized contact with them. Fenestrae in the ca pillary endothelium were numerous in the distal portion but absent in the proximal portion. Thus, marked differences in structure existed be tween the distal and proximal portions of the pineal gland of the cott on rat, suggesting that both portions are functionally dissimilar. In addition, the present study indicates that the proximal portion of the cotton rat was well developed and showed morphological features simil ar to the deeply situated pineal glands of other mammals.