THE ROLE OF NEUROTRANSMITTERS IN THE FORMATION OF COGNITIVE FUNCTION IN EXPERIMENTAL HYPERTHYROIDISM IN EARLY ONTOGENY

Abstract

Background. One of the leading indicators of the stressors on the body effect is the level of thyroid hormones. The known role of thyroid hormones in the formation of a higher adaptive response of the central nervous system makes studies of the mechanism of cognitive function formation in hyperthyroidism under conditions of emotional stress essential, in particular in early ontogeny, when the need for these hormones increases. The aim of the work is to reveal the neurotransmitter mechanism of cognitive function formation in hyperthyroidism and emotional stress in early ontogeny in rats for further search for correction of disorders of the psychosymptom complex of young patients.

Materials and methods. The experiments were carried out on 32 white outbred rats aged 30-40 days and weighing 40-60 g, which were divided into two groups: "experimental hyperthyroidism" and "control". Hyperthyroidism was induced by administering L-thyroxine with food. Subsequently, the animals of each of the two groups were subjected to chronic emotional stress - staying in an open water space for 3 minutes at a temperature of 21°C (5 sessions, 1 per day). The behavior of rats was studied in the Morris water maze and elevated plus maze. The content of neurotransmitter compounds (glycine, GABA, glutamate) and serotonin in the cerebral cortex and hippocampus was determined chromatographically. Mathematical processing included the calculation of arithmetic means, standard deviations, Student’s t-test and Pearson's correlation analysis.

Results. Under the conditions of experimental hyperthyroidism in juvenile rats, a behavioral disorder was observed, which was accompanied by a decrease in the content of serotonin in the hippocampus by 32% and an increase in the level of GABA in the cortex of the large hemispheres by 39%. Chronic emotional stress against the background of experimental hyperthyroidism caused juvenile rats to develop a depressive-like state and impaired spatial learning, which was accompanied by an increase in the GABA content in the cortex by 40% and a decrease in the level of glycine in the cortex by 23% and in the hippocampus by 40% relative to animals without model thyroid pathology.

Conclusions. Under the conditions of experimental hyperthyroidism in juvenile rats, a behavioral disorder was observed, which was accompanied by a decrease in the content of serotonin in the hippocampus and an increase in the level of GABA in the cortex of the large hemispheres. A study of the spontaneous behavior of juvenile rats with experimental hyperthyroidism and chronic emotional stress revealed a significant increase in orientation-research activity, anxiety and emotionality, which indicates the development of a depressive-like state and, as a result, the deterioration of spatial memory. These behavioral disorders and cognitive deficits were accompanied by an imbalance of neurotransmitters, namely, an increase in GABA content in the cortex and a decrease in glycine in the cortex and hippocampus of experimental animals.