Interactions of Stress and Motor System Function

Chronic stress has been shown to alter behaviour in both humans and rodents. For example, previous studies have shown that chronic stress can impair skilled motor function in animals. The stress response is defined by an increase in stress hormones, cortisol in humans and corticosterone (CORT) in rodents, both secreted by adrenal glands. CORT can cross the blood brain barrier easily to regulate homeostasis. The purpose of this study was to quantitatively investigate the relationship between circulating CORT and performance of skilled motor function in animals exposed to three different stress manipulations. Male and female rats were trained in skilled reaching and ladder rung tasks. Once baseline measurements were completed, rats underwent daily sessions of either swimming in 5 ̊C cold water, restraint stress, or oral CORT treatment. Manipulations lasted for 15 days and animals were tested in the skilled reaching task daily and twice in the ladder rung walking task. Blood samples were collected during baseline and on day 15 of manipulations. The results showed that successful reaching decreases in animals exposed to swim and restraint. Animals administered oral CORT showed a significant increase in circulating plasma CORT concentration but no decrease in skilled reaching success. Correlation analysis revealed a negative relationship between plasma CORT concentration and ladder rung walking score in swim stress animals, as well as reaching success in restrained animals. The results from this study suggest that