Proceedings of the International scientific and practical conference ―Synergy of Modern Science and Education‖ (February 2-4, 2026) / Publisher website: www.naukainfo.com. – New York, USA, 2026. - 324 p.

105 childhood and juvenile age may lead to changes in behavioral responses, anxiety levels, and stress reactivity. Particular attention is drawn to the interaction between thyroid hormones and the mechanisms of emotional stress, since the combination of hormonal imbalance and psychoemotional load can significantly modify the adaptive capacities of the organism. In this regard, the study of the role of thyroid hormones in the formation of behavioral responses under acute emotional load in early ontogenesis is relevant. Materials and methods. The study was conducted on 30 juvenile outbred rats aged 30–40 days with a body weight of 40–60 g. The animals were divided into two groups: the first — control (―acute emotional load‖, AEL); the second — ―acute emotional load under experimental hyperthyroidism‖ (AEL + EH). The model of acute emotional load consisted of daily single placement of animals in a closed water space (1 × 1 m) at a temperature of 21 °C for 5 minutes per day over 5 days. Spontaneous behavioral activity was assessed by determining individual parameters in the elevated plus maze (EPM). Behavioral testing was performed twice: after induction of experimental hyperthyroidism (first session) and after induction of acute emotional load in both experimental groups (second session). The content of neurotransmitter compounds in homogenates of the cerebral cortex and hippocampus (GABA, glycine, glutamate, serotonin) was determined using an amino acid analyzer followed by spectrophotometric analysis. Results. Experimental hyperthyroidism in early ontogenesis was accompanied by an anxiolytic effect. In particular, the number of entries into the open arms increased by 104% (p < 0.05), and the duration of stay in them increased 2.5-fold. This effect was associated with a decrease in serotonin levels in the hippocampus, as a negative correlation was established between the number of entries into the open arms and serotonin content in this brain structure of juvenile rats with experimental hyperthyroidism (r = –0.36, Pearson correlation). Acute emotional stress under conditions of experimental hyperthyroidism was accompanied by an anxiogenic effect and a depression-like state. The number of head dips and rearings increased relative to the ―AEL‖ condition by 44% (p < 0.05) and