Pineal Gland Transplants into the Cerebral Hemisphere of Newborn Rats: A Study of the Blood Brain Barrier and Innervation

Pineal glands from neonatal (0-1 day) Long-Evans black-hooded rats were transplanted into the cerebral hemispheres of litter mates for periods of 1 to 5.5 months. Grafts exhibited differentiated pinealocytes that were intensely immunoreactive for serotonin. Transplant vasculature was permeable to endogenous IgG, comprised fenestrated endothelia with wide pericapillary spaces typical of in situ glands, and had a volume density intermediate to that of surrounding cortex and in situ pineals. Along the periphery, transplant capillaries tended to have continuous endothelia similar to those of host cortex. This peripheral zone was impermeable to endogenous IgG and appeared to increase in size in older grafts. The presence of noradrenergic-like fibers within the periváscular compartment suggested that transplants were innervated by peripheral sympathetic neurons from the superior cervical ganglia. In animals which had been superior cervical ganglionectomized, noradrenergic-like fibers were absent or degenerating. Neural regulation of transplant metabolic activity was suggested by the increased frequency of pinealocyte synaptic ribbons in denervated grafts. These findings are consistent with the hypothesis that factors from both graft and host influence vasculature physiology and differentiation in neural transplants. Furthermore, grafts appeared to receive appropriate neural input from the peripheral sympathetic system.