A. Franco et al., A COMBINED IMMUNOHISTOCHEMICAL AND ELECTRON-MICROSCOPIC STUDY OF THE 2ND CELL-TYPE IN THE DEVELOPING SHEEP PINEAL-GLAND, Journal of pineal research, 22(3), 1997, pp. 130-136
Ultrastructural and immunohistochemical techniques were used to study
the second cell type in sheep embryo pineal glands. Thirty-two embryos
were studied from day 54 of development through birth. Specimens were
arranged in four age groups, defined in terms of the most relevant hi
stological features: Group 1 (54-67 days of prenatal development), Gro
up 2 (71-92 days), Group 3 (98-113 days), and Group 3 (118-150 days).
At 98 days. a second cell type was observed which differed from pineal
oblasts and showed uniform ultrastructural characteristics similar to
those of astrocytes in the central nervous system. Ultrastructural hom
ogeneity was not matched by the results of histochemical and immunohis
tochemical analysis: while all Type II cells stained positive to phosp
hotungstic acid hematoxylin, only 50% expressed glial fibrillary acidi
c protein. In the course of ovine intrauterine development, the vascul
ar affinity of this second cell population, composed of glial-like or
astrocytic cells at varying stages of maturity, leads to the formation
of a limiting pineal barrier. This barrier may constitute the morphol
ogical expression of a hypothetical functional involvement in the exch
ange of substances between blood and pineal parenchyma.