Date of Award

Fall 1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Program/Concentration

Biomedical Sciences

Committee Director

David E. Scott

Committee Member

George E. Goode

Committee Member

Francis J. Liuzzi

Committee Member

Keith A. Carson

Abstract

The survival, revascularization, reinnervation, and recovery of function of transplanted newborn rat pineal glands were studied following grafting into four different locations in pinealectomized rats. These locations were the third cerebral ventricle, in situ (where the pineal gland is normally located), the renal capsule, and the anterior chamber of the eye.

Pinealocytes in the grafts maintained high metabolic activity as evidenced by the presence of euchromatic nuclei, prominent nucleoli, infolded nuclear envelopes, numerous mitochondria and Golgi apparati, and relatively abundant endoplasmic reticulum and ribosomes. In addition, morphological correlates of two putative secretory processes were observed in the grafts. The first type was neurosecretory-like (Golgi apparatus--dense-core vesicles) and the second was ependymal-like (rough endoplasmic reticulum--vacuoles containing flocculent material).

Pineal grafts were well vascularized by fenestrated capillaries surrounded by consistently wide perivascular spaces. Moreover, nerve fibers and terminals were seen in the grafts within the anterior chamber of the eye, the third cerebral ventricle, and the pineal region (in situ transplantation). By contrast, no fibers or terminals were found in grafts placed beneath the renal capsule. Reinnervating neurites in the grafts within the anterior eye chamber were found throughout the graft while those in the ventricular grafts and the in situ grafts were more abundant in some regions than in others.

Nighttime serum melatonin levels increased significantly in pinealectomized rats with transplants into either the third cerebral ventricle or the anterior eye chamber. This increase might reflect graft reinnervation. Yet day-night differences in serum melatonin were observed only in host rats receiving transplants to the anterior eye chamber. These differences were eliminated by bilateral removal of the superior cervical ganglion.

In conclusion, pinealocytes survived transplantation and exhibited ultrastructural features indicative of active secretory processes. Moreover, pineal grafts were well vascularized by fenestrated capillaries. Synthesis and release of melatonin is restored following transplantation into the third cerebral ventricle or the anterior chamber of the eye. However, day-night differences in serum melatonin is only restored following transplants into the anterior eye chamber. Finally, reinnervation of the grafts by the host superior cervical ganglion is necessary for this restoration.

Comments

A Dissertation Submitted to the Faculties of Eastern Virginia Medical School and Old Dominion University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Biomedical Sciences.

DOI

10.25777/99qp-sf73

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