Keywords
Abstract
Thyroid hormones have a key effect on the central nervous system. Dysfunction of the thyroid gland is one of the main causes of cognitive impairment, especially in old age, but the specifics of these changes remain unclear.
The purpose of the study – to reveal the peculiarities in the formation of spatial memory in old rats with hyper- and hypothyroidism.
Behavioral activity was studied in an elevated plus maze; the formation of spatial memory – in the Morris water maze and by positive reinforcement test in the 8-rays maze. The validity of both models was confirmed by determining the content of thyroxine and thyrotropin in the blood plasma of experimental rats by enzyme-linked immunoenzyme assay.
The study of the innate spontaneous behavior of old rats in models of thyroid dysfunction revealed the formation of an anxiogenic effect and a depression-like state. In the elevated plus maze, a decrease in motor activity was observed in the illuminated parts with a simultaneous increase in the number of hangings from open areas of the maze, which indicated an anxiogenic effect formation under hypothyroidism. The state of experimental hyperthyroidism was also characterized by a decrease in motor activity in the maze light part with prolonged grooming time, an increase in the number of hang-ups, which indicates a violation of emotionality, the presence of fear, increased anxiety and the formation of a depression-like state. In the Morris water maze, the formation of spatial memory engrams was impaired in both hyper- and hypothyroid conditions. A study of the old rats' spatial memory in a positive reinforcement test confirmed a greater amnestic effect in rats with experimental hypothyroidism, as they made more errors.
Thus, the analysis of motor activity in an elevated plus maze indicates the development of anxiety and depression in hypothyroidism. When developing protective acquired behavior in the Morris water maze, the formation of spatial memory engrams was impaired in conditions of both types of thyroid dysfunction. The study of spatial memory by a positive reinforcement test revealed an amnestic effect in rats with hypothyroidism.