Levels of Neuroactive Steroids in the Brain and Gender-Related Characteristics of the Formation and Extinction of a Conditioned Reflex in Rats

Abstract

Model experiments were performed to study the gender-related characteristics of the dynamics of sex steroids in the brain during the acquisition and extinction of a conditioned reflex. Before acquisition of conditioned reflexes, females had greater anxiety and fear than males. On formation of the conditioned reflex, there were no significant gender-related differences between males and females, while extinction of the conditioned passive avoidance reaction in male rats occurred 2–3 days more quickly than in females. On acquisition of the conditioned passive avoidance reflex, adult rats showed increases in testosterone content in several brain structures, especially in the hippocampus and frontal cortex, without any change in the plasma level. There was also an increase in the amygdalar estradiol concentration in females, while extinction of the conditioned passive avoidance reaction was associated with increases in estradiol in the hippocampus and cingulate gyrus. There was no change in plasma testosterone, while the estradiol concentration decreased significantly after extinction of the conditioned reflex. The different dynamics of changes in sex steroid levels in the brain and plasma may point to the possibility that they are synthesized in nervous tissue. Correlation analysis supported the suggestion of the selective involvement of testosterone and estradiol from particular brain structures in mediating learning and memory processes in adult male and female rats.