vendex and Substance-Withdrawal-Syndrome

This study explored whether patients with Parkinson's disease alter the regulation of upright standing according to constraints imposed by the environmental context. The provision of context-dependent adaptations was inferred from the presence of adjustments to standing postural control that would serve to reduce fall risk when balance was challenged by a threatening environmental context. Participants were asked to stand as still as possible in two environmental context conditions that differed in the level of imposed postural threat: LOW threat and HIGH threat. Eight levodopa dependent patients with Parkinson's disease (PD) and eight age-matched control subjects (CTRL) provided the subject sample. PD patients were tested following a 12-h withdrawal of anti-Parkinsonian medications and approximately 1h post-medication. The CTRL group showed altered postural control in the HIGH threat condition, in a manner that was indicative of appropriate context-dependent regulation of standing. PD patients, in the non-medicated or medicated states, did not modify stance regulation when the environmental context heightened postural threat. Our results extend the current understanding of Parkinsonian deficits in the context-dependent regulation of postural control to include upright standing.

Topics: Adaptation, Physiological; Aged; Aged, 80 and over; Case-Control Studies; Humans; Middle Aged; Multivariate Analysis; Parkinsonian Disorders; Postural Balance; Posture; Pressure; Substance Withdrawal Syndrome; Torque

This study evaluated reflex excitability and locomotor changes during chronic intrathecal infusion of the GABAb agonist baclofen (ITB) and its withdrawal, in the rat. We observed sustained velocity dependent decreases in ankle torque during four weeks of ITB treatment. These changes were correlated with a significant reduction of the EMG burst magnitude time locked to the dynamic phase of ankle dorsiflexion during the first ITB treatment week. However, a considerable recovery of EMG magnitude was observed during the third and fourth weeks of treatment. During baclofen withdrawal, significantly increased velocity dependent ankle torque was observed for 4 weeks. These increases in ankle torque were correlated with increased magnitudes of EMG time locked to the dynamic phase of ankle rotation. Measures of hind limb axis and base of support were obtained using analysis of footprints on a treadmill during ITB treatment and withdrawal periods. During ITB treatment and for up to 7 weeks of withdrawal, hindlimb axis and base of support were significantly altered compared with vehicle controls. These studies were performed to provide a foundation for evaluation of treatment and withdrawal in the setting of experimental chronic contusion spinal cord injury.

Topics: Animals; Baclofen; Electromyography; Female; GABA-B Receptor Agonists; Hindlimb; Injections, Spinal; Posture; Rats; Rats, Sprague-Dawley; Receptors, GABA-B; Substance Withdrawal Syndrome; Tarsus, Animal; Torque