Ultrastructural and immunocytochemical characterization of interstitial cells in pre- and postnatal developing sheep pineal gland

Pineal gland interstitial cells from 32 sheep embryos (from day 54 of gesta tion until birth) and 18 sheep (from 1 month to >2 years) were analysed usi ng ultrastructural and immunohistochemical techniques. From day 98 of gesta tion and throughout postnatal development, a second cell type was observed in addition to pinealocytes; these cells displayed uniform ultrastructural features similar to those of CNS astrocytes. Ultrastructural homogeneity wa s not matched by the results of histochemical and immunohistochemical analy sis. Expression of phosphotungstic acid hematoxylin, glial fibrillary acidi c protein and vimentin indicates that the second cell population in the dev eloping ovine pineal gland is, in fact, a combination of glial-astrocyte ce lls at varying stages of maturity. Pineal interstitial cells started to sho w signs of functional activity evident in vascular tropism; such activity, evident from around day 98 of gestation, appeared to relate to the exchange of substances between the pineal parenchyma and blood vessels and, though it continued throughout postnatal development, was most evident in animals slaughtered between 9 months and 2 years of age (group II). Morphologically , functional activity in interstitial cells in this age-group was apparent in: 1, formation of specific contact sites between interstitial cells and n erve fibres in the perivascular space; and 2, the presence of numerous gap junctions between the bulbous endings of cytoplasmic processes.