Nerve fibers originating from the brain in the rat pineal complex

The distribution of central nerve fibers in the rat pineal complex was studied by means of fluorescence- and immunohistochemistry and electron microscopy. At 7 days after bilateral superior cervical ganglionectomy (SCG-X), blue-green fluorescent (catecholaminergic) fibers and tyrosine hydroxylase- and serotonin-immunoreactive fibers originating from the brainstem were detected in the deep pineal and the pineal stalk. These fibers were not observed in the superficial pineal. In some animals, a few oxytocin-immunopositive fibers were found in the proximal portion of the superficial pineal. The nerve fibers were submicroscopically counted in transverse sections at 6 levels with an interval of about 200 microns each in the pineal stalk. The number of nerve fibers showed 3 peaks, at the proximal-most, the intermediate and the distal-most levels. On the other hand, various types of synapses, axo-dendritic, axo-axonic and axo-pinealocytic, and many free terminals, were observed in the stalk. In these synapses, the majority of presynaptic swellings contained only clear vesicles, but some of them possessed aminergic (5-hydroxydopamine- or 5,6-dihidroxytriptamine-positive) vesicles or elementary granules. The reduction in the number of nerve fibers was most conspicuous in the distal-most level after the SCG-X. Based on these results, it is supposed that the proximal peak is formed by the central fibers going further to the stalk and turning back to the brain, the intermediate peak is formed by the terminal arborizations of the central fibers, and the distal peak shows penetration of the sympathetic fibers.(ABSTRACT TRUNCATED AT 250 WORDS)