State of the Hippocampus and Frontal Brain in Rats with Experimental Hypothyroidism

Abstract

Introduction. Despite the fact that today patients with hypothyroidism manage to correct their hormonal profile, perfect control is not always achieved during the course of the disease. This was noted in a study of 22 people with hypothyroidism according to medical records for 8.24±0.76 years: the average TSH level was 7.14±2.37 mIU∕l, T4 was 23.01±4.38 pmol/l, although at the start of the study TSH was 3.72±0.76 mIU∕l and T4 was 13.8±1.96 pmol/l. Ultimately, this affected cognitive functions, including attention, speech and memory, despite the fact that cognitive impairment with drug compensation of hypothyroidism is considered reversible.
 The results of a morphological study of the hippocampus and frontal lobe of the brain in rats with experimental hypothyroidism at an early stage can serve as a prototype for changes in the corresponding structures responsible for cognitive functions in individuals with hypothyroidism, even against the background of relative compensation with a long course of the disease.
 Objective. To study morphology of the brain areas responsible for cognitive functions, in particular the hippocampus and anterior-frontal cortex in rats in the early stages of experimental hypothyroidism.
 Materials and methods. The study included 12 white outbred sexually mature male rats. Hypothyroidism was modelled in 7 rats using the drug “Mercazolil” (“Zdorovye”, Ukraine). After 28 days, the animals underwent light-optical study of the histological structure of CA1, CA3 fields of the hippocampus, dentate gyrus and anterior-frontal cortex. Five animals were intact and, accordingly, served as controls.
 Results. The light-optical examination revealed the sequence and depth of the violations: the most pronounced dystrophic changes with vacuolation of structures occur in the dentate gyrus; in the hippocampus itself, the CA1 field is the most vulnerable; lateralisation of hippocampal morphological changes with left-sided dominance was detected; minor morphological changes were detected in the anterior-frontal cortex. It is important that neuro-glial changes occur in parallel with vascular disorders.
 Conclusions. Under the conditions of simulated hypothyroidism, changes occur in all studied brain components with their left-sided dominance, except for the anterior-frontal cortex.