Proceedings of the International scientific and practical conference ―Science at the Frontier of Progress‖ (January 27-29, 2026) / Publisher website: www.naukainfo.com. – Paris, France, 2026. - 302 p.

114 formation of emotional and locomotor activity in rats under conditions of thyroid hypofunction during early ontogenesis. Materials and Methods. Experimental hypothyroidism was induced by oral administration of mercazolil with food for two weeks at a dose of 100 mg/kg body weight. The effectiveness of the model was confirmed by measuring plasma levels of thyroxine (T4) and thyroid-stimulating hormone (TSH). Behavioral activity was assessed using the elevated plus maze (EPM) and the open field test. Levels of neurotransmitters (norepinephrine, γ-aminobutyric acid, glycine, and serotonin) were determined by thin-layer chromatography followed by spectrophotometric analysis. The study was performed on 36 outbred white rats aged 30–40 days, weighing 40–60 g. Behavioral testing was conducted after induction of experimental hypothyroidism, as well as after exposure to chronic and acute emotional stress on the background of hypothyroidism. The experimental data were subjected to statistical analysis using the Spearman method. Results. Experimental hypothyroidism in juvenile rats was associated with a pronounced anxiogenic effect, manifested by a decrease in both the number (by 41%) and duration (by 77%) of entries into the open arms of the EPM, as well as an increase in the duration of non-comfort grooming behavior (by 39%) in the open field test. These behavioral changes correlated with increased levels of serotonin (r= – 0.30) and glutamate (r= –0.32) in the cerebral cortex and hippocampus, respectively. Emotional stress exposure under conditions of experimental hypothyroidism induced opposite behavioral changes, namely an anxiolytic effect. The number of entries into the open arms of the maze increased nearly twofold under chronic emotional stress and threefold under acute emotional stress. These effects coincided with alterations in serotonin and glutamate levels, while the direction of correlations changed to positive (r= 0.33 and r= 0.38, respectively). Discussion. According to literature data, the anxiogenic effect observed under hypothyroid dysfunction has been primarily associated with an imbalance of the noradrenergic system. Correction with 5-hydroxytryptophan and glutamate reduced anxiety levels in adult rats, indicating a key role of serotonergic and glutamatergic