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

Abstract

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.

Sex differences in skilled movement in response to restraint stress and recovery from stress

“…The behavioural impairments associated with stress, however, were not necessarily accompanied by corticosterone elevation. The presence of movement impairments in the absence of elevated corticosterone levels is in line with previous work [16] suggesting that stress-induced motor impairments might be independent of corticosterone. This is further supported by absent effects of the interval between stress and behavioural test session (i.e., 10 min versus 60 min) and by the finding of faster recovery of post-stress reaching success in females despite higher corticosterone levels.…”

“…The present data show that sex did not affect recovery from acute stress, however, an interesting finding is the observation that restraint stress exerts its effects slowly i.e., 60 min after the stress session, at a time when the peak of corticosterone elevation has passed [16,38]. Again, this observation supports the notion that stress might affect motor system function independently of elevated corticosterone levels.…”

“…The present stress-induced alterations in skilled limb use resemble those described earlier [16,17,69]. Acute and chronic restraint stress led to reduction in reaching success along with an increase in number of attempts needed to grasp a pellet.…”

“…In addition, locomotor effects of stress depend on rat strain with Long-Evans rats being less sensitive than other strains [13]. Recent studies have also shown that stress is a potent influence on both skilled and nonskilled movement performance [15][16][17]. With regard to sex differences in both motor performance and the stress response, it is reasonable to expect that gender and stress represent interacting factors to affect motor system function.…”

“…The rats' performance was tested in skilled reaching and skilled walking tasks, which represent highly sensitive tests to display slight aberrations in limb use and bodily adjustments [2,3,16]. Recovery from daily stress was assessed by comparing reaching performance at 10 min versus 60 min after restraint stress, and recovery from chronic stress was tested after cessation of the chronic stress period.…”