Catecholaminergic Innervation of Vessels of the Rat Pineal Gland

Introduction. The pineal gland has an extensive network of blood vessels through which the hormone melatonin, synthesized in pinealocytes, is secreted. The intensity of melatonin synthesis is regulated by afferent nerve fibers, primarily catecholaminergic ones. However, the morphological features of the relationship between catecholaminergic nerve fibers and blood vessels have not been elucidated.

The objective of this study was to establish the structural basis of the interaction between catecholaminergic fibers and blood vessels of the rat pineal gland.

Materials and Methods. The study was conducted on mature male Wistar rats (n=10) . Immunohistochemical reaction for tyrosine hydroxylase was carried out on histological preparations of the pineal gland. The preparations were counterstained with hematoxylin, alcian blue, or aniline blue.

Results. A large number of tyrosine hydroxylase-immunoreactive fibers with varicosities were detected in the rat pineal gland. These fibers were located primarily in the connective tissue capsule and subcapsular areas, and, to a lesser extent, in the inner part of the pineal gland, where they were predominantly localized in the interlobular connective tissue and often located close to blood vessels. Some tyrosine hydroxylaseimmunoreactive fibers penetrated deep into the blood vessel wall, lying adjacent to the endothelial basement membrane. The histological dyes, alcian blue and aniline blue, stained connective tissue well, allowing visualization of the connective tissue interstitium and capsule of the pineal gland, as well as the connective tissue components of blood vessel walls. The vascular wall was optimally stained with aniline blue.

Conclusion. The established pattern of catecholaminergic nerve fiber distribution in the vascular wall indicates a high probability of their regulatory effect on the functional activity of smooth muscle cells and endothelial cells and, consequently, on the hemodynamics in the pineal blood vessels and, likely, on melatonin secretion. 

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