Ultrastructural and Circadian Morphometric Characteristics of Rat Pinealocytes Under Physiological and Toxic Conditions

Abstract

Carbon tetrachloride (CCl₄) exhibits pronounced neurotoxic effects following acute or chronic exposure. Recent studies indicate that the pineal gland responds to CCl₄ intoxication by altering its secretory function, although detailed ultrastructural changes in pinealocytes remain inadequately investigated. This research addresses the urgent need to elucidate the mechanisms of CCl₄ toxicity on the pineal gland, which could contribute to developing strategies for mitigating disorders induced by chlorinated hydrocarbons. The study aims to examine CCl₄-induced alterations in rat pinealocyte ultrastructure, melatonin secretion rhythms, and micromorphometric parameters of pineal organoids. Eighty male Wistar rats, allocated into two equal groups, were included in the study. Group I was under the fixed lighting regime (light: dark / 10:14). Group II was under the same conditions with additional injection of CCl₄ oil solution. All animals were kept in the experiment for 21 days, with removal on the 22nd day, and the pineal gland was taken, and blood collection was performed. Electron microscopic study of the pineal gland, micromorphometric analysis of some parameters of mitochondria, Golgi Complex (GC), and lipid droplets were performed. Quantitative determination of melatonin concentration was performed. Graphs of 24-hour dynamics of the analyzed parameters were plotted and statistically processed. Circadian rhythm amplitude and acrophase were calculated using cosinor analysis. The conducted study allowed for the revelation of significant changes in the morphology and function of the rat pineal gland under the influence of carbon tetrachloride, accompanied by impaired melatonin synthesis and ultrastructural restructuring of pinealocytes.