Histology and ultrastructure of the pineal organ in the domestic goose.

The pineal organs of 14-week-old domestic geese were investigated with light and electron microscopy. The pineals consisted of a wide distal part and a narrow middle-proximal one. The glands were attached to the intercommissural region via the choroid plexus. The pineal parenchyma was formed by round or elongated follicles. The follicular wall was composed predominantly by cells immunoreactive with antibodies against hydroxyindolo-O-methyltransferase (HIOMT) or glial fibrillary acid protein (GFAP). They formed two or more layers. HIOMT-positive elements were represented by elongated cells bordering the follicular lumen and oval cells located in the external layer of the follicular wall. These cells were identified in ultrastructural studies as rudimentary-receptor pinealocytes and secretory pinealocytes, respectively. Among rudimentary-receptor pinealocytes two types of cells, designed as A and B, were distinguished due to structural differences. Type A cells extended through the whole follicular wall and showed regular stratified distribution of organelles in well-recognizable zones with rough endoplasmic reticulum, the Golgi apparatus and mitochondria. Type B cells, like type A pinealocytes, contacted the pineal lumen and showed polarity of their internal structure. However, they were markedly shorter than the cells of type A and lacked stratified distribution of organelles. Secretory pinealocytes contained irregularly dispersed organelles. A prominent feature of all types of goose pinealocytes was the presence of numerous dense core vesicles. The population of GFAP-positive cells consisted of ependymal-like supporting cells and astrocyte-like cells.