S-antigen and glial fibrillary acidic protein immunoreactivity in the in situ pineal gland of hamster and gerbil and in pineal grafts: developmental expression of pinealocyte and glial markers.

Postnatal development of S-Ag and GFAP immunoreactivity in the in situ pineal glands of golden hamsters and gerbils was examined using the avidin-biotin-peroxidase immunohistochemical technique. S-Ag was present in the gerbil pineal gland on the first postnatal day (P1), whereas it did not appear in the hamster pineal until P6. GFAP-immunoreactive astrocytes were first observed in the hamster pineal gland on P7 and in the gerbil pineal gland on P10. The number of S-Ag-immunoreactive pinealocytes and GFAP-immunoreactive astrocytes in the pineal glands of hamsters and gerbils increased with increasing age from P7 to 3 weeks. By 4 weeks, strong S-Ag and GFAP immunoreactivity was observed in both hamster and gerbil pineal glands. GFAP-immunoreactive stellate astrocytes were distributed evenly throughout the gerbil superficial pineal gland, but they were more often located in the peripheral region of the hamster superficial pineal. For the pineal grafts, pineal glands from neonatal (3-5 day old) hamsters were transplanted into the third cerebral ventricle (infundibular recess or posterior third ventricle) or beneath the renal capsule of adult male hamsters. S-Ag immunoreactivity appeared in the pineal grafts within 1 week following transplantation. By 4 weeks the pineal grafts showed strong S-Ag immunoreactivity which was maintained until at least 12 weeks after transplantation. The time course of glial cell maturation in the cerebroventricular pineal grafts is generally parallel to the hamster pineal gland in situ before 4 weeks. By 12 weeks, however, more astrocytes differentiated and developed GFAP-immunoreactivity in the pineal grafts than in the in situ pineals. These studies have described the postnatal development of S-Ag and GFAP immunoreactivity in in situ pineal glands and in neonatal pineal grafts.