[Catecholaminergic structures of the human pineal gland.]

The pineal gland produces the hormone melatonin, the rate of synthesis of which, as shown in animal studies, is regulated by afferent catecholaminergic fibers. This study, for the first time, examined the presence of catecholaminergic structures in the human pineal gland using tyrosine hydroxylase immunohistochemistry. Tyrosine hydroxylase-immunoreactive fibers were found in large numbers in the human pineal gland, primarily in the connective tissue trabeculae and pineal capsule. The fibers were distributed with uneven density across different sections of the pineal gland and lacked typical varicosities described in the animal pineal gland. In the lobules, the number of fibers among the pinealocytes was minimal; however, neuron-like uni- and bipolar immunoreactive cells were present. It is hypothesized that these form an autonomous system for the intrapineal regulation of melatonin production and/or secretion. Based on the obtained data, a hypothesis was proposed about the possibility of secretion of the hormone melatonin into the bloodstream through astroglial processes and regulation of this process by afferent catecholaminergic nerve fibers through neuron-glial interactions.