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