Morphological features of the innervation of the rat adrenal gland adipose tissue

BACKGROUND: The relevance of studying adipose tissue is due to a lack of understanding of the etiology and pathogenesis of obesity and a lack of research into the endocrine function of adipose tissue. The structure, functions, and innervation characteristics of white and brown adipose tissues of the adrenal gland have received the least attention. AIM: To determine the structure and innervation of rat adrenal adipose tissue using neuroimmunohistochemical markers. MATERIALS AND METHODS: The innervation of the rat adrenal gland’s adipose tissue was examined using immunohistochemical reactions for PGP 9.5 protein, tyrosine hydroxylase, and synaptophysin conducted on paraffin sections (n=10). RESULTS: Unmyelinated nerve fibers and catecholaminergic and cholinergic nerve terminal apparatuses were found in the white and brown adipose tissues of the rat adrenal gland. Parasympathetic and sympathetic postganglionic nerve fibers enter adipose tissue through arterial vessels. Remakov’s varicose axons intensely branch and form passant terminal synaptic networks, which are essential in the innervation of adipocytes in white and brown adipose tissues. Brown and mixed adipose tissues contain the most sympathetic and parasympathetic synaptic structures. Sympathetic fibers are closely connected to the arterial wall and contact brown adipocytes. Varicose axons are found in white adipose tissue, primarily surrounding arterial vessels and rarely between differentiated ring-shaped adipocytes. CONCLUSIONS: The observed differences in sympathetic innervation of white and brown adipose tissues are because brown adipose tissue cells, unlike white adipocytes, perform a secretory function. They impact corticosteroid synthesis by the adrenal gland by producing adipokines. The findings suggest that the sympathetic nervous system controls this process.