Superficial pineal grafts: Development, reinnervation, and biochemical considerations

The development, innervation and biochemical characteristics of the in situ pineal gland and pineal graft were investigated using immunohistochemical and HPLC techniques. Tyrosine hydroxylase (TH)- and neuropeptide Y (NPY)-innervation of the in situ pineal gland commenced on the second postnatal day (P2) in hamsters and gerbils and appeared fully developed by 4 weeks. Superficial pineal grafts from 4-week-old donors appeared to undergo severe degeneration and eventually disappeared. In contrast, the grafts from neonatal hamsters survived and maintained morphology characteristic of healthy pineal tissue. Abundant TH- and NPY-fibers in the host brain surrounded the pineal grafts placed in the third ventricle, but rarely entered the graft paranchyma. A few TH-fibers were demonstrated in some renal pineal grafts (5 out 12) 4 weeks after transplantation.; S-antigen was present in the gerbil pineal on P1, but not in the hamster pineal until P6. Glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were first observed in the hamster pineal on P7 and in the gerbil pineal on P10. The expression of S-antigen and GFAP immunoreactivity consistently developed from P7 to P21 and appeared fully developed by 4 weeks. S-antigen immunoreactivity was present in the neonatal pineal grafts within one week after transplantation and was well developed by 4 weeks. The time course of glial cell maturation in the ventricular grafts is generally parallel to the in situ pineal before 4 weeks. By 8 and 12 weeks, however, more astrocytes developed GFAP-immunoreactivity in the grafts than in the in situ pineals.; Neonatal hamster superficial pineal glands were grafted beneath the renal capsule of 8-week-old, superficial pinealectomized (SPx), male hamsters. Four weeks following transplantation, the hamsters were exposed to light 7.5 h after lights off. The animals were then injected with isoproterenol to stimulate graft melatonin production. Two hours after isoproterenol injection, the graft melatonin content was significantly increased. The {dollar}beta{dollar}-adrenoreceptor agonist-induced synthesis of melatonin by neonatal pineal grafts suggests that the development of the {dollar}beta{dollar}-adrenoreceptors and associated melatonin production occurs in pinealocytes independent of intact sympathetic innervation.