Modulation of motor function by stress: a novel concept of the effects of stress and corticosterone on behavior.

Stress and stress hormones affect a variety of behaviors and cognitive abilities. The influences of stress and glucocorticoids on motor function, however, have not been characterized although the presence of glucocorticoid receptors in the motor system has been documented. Here we demonstrate that stress and the stress hormone corticosterone influence motor system function in rats. Groups of adult female Long-Evans rats underwent either a daily stress-inducing procedure (immobilization or swimming in cold water) or oral corticosterone treatment. While these treatments continued, animals were tested in skilled reaching and skilled walking tasks for a period of 2 weeks. Both acute (day 1) and chronic (day 14) stress and corticosterone treatment reduced skilled movement accuracy in reaching and walking and increased performance speed. Furthermore, both chronic stress and chronic corticosterone treatment altered skilled movement patterns in the reaching task. These findings indicate that stress modulates motor system function and that these effects are partially mediated by glucocorticoids. To examine whether stress-induced changes might also derive from enhanced emotionality, rats were treated with the benzodiazepine diazepam. Based on an inverted U-shaped dose-response relationship, a moderate dose of diazepam significantly improved reaching success while at the same time reducing corticosterone levels. Thus, stress-associated emotional responses such as anxiety might account for diminished movement accuracy. These results suggest that stress affects the motor system both directly via hormonal changes and indirectly via changes in emotionality. These findings are discussed with respect to the role of stress in motor system function and movement disorders.