GABAergic circuits in the basal ganglia and movement disorders

The effect of exercise training in improving motor performance and corticomotor excitability in people with early Parkinson's disease

OBJECTIVES

To obtain preliminary data on the effects of high-intensity exercise on functional performance in people with Parkinson's disease (PD) relative to exercise at low and no intensity and to determine whether improved performance is accompanied by alterations in corticomotor excitability as measured through transcranial magnetic stimulation (TMS).

DESIGN

Cohort (prospective), randomized controlled trial.

SETTING

University-based clinical and research facilities.

PARTICIPANTS

Thirty people with PD, within 3 years of diagnosis with Hoehn and Yahr stage 1 or 2.

INTERVENTIONS

Subjects were randomized to high-intensity exercise using body weight-supported treadmill training, low-intensity exercise, or a zero-intensity education group. Subjects in the 2 exercise groups completed 24 exercise sessions over 8 weeks. Subjects in the zero-intensity group completed 6 education classes over 8 weeks.

MAIN OUTCOME MEASURES

Unified Parkinson's Disease Rating Scales (UPDRS), biomechanic analysis of self-selected and fast walking and sit-to-stand tasks; corticomotor excitability was assessed with cortical silent period (CSP) durations in response to single-pulse TMS.

RESULTS

A small improvement in total and motor UPDRS was observed in all groups. High-intensity group subjects showed postexercise increases in gait speed, step and stride length, and hip and ankle joint excursion during self-selected and fast gait and improved weight distribution during sit-to-stand tasks. Improvements in gait and sit-to-stand measures were not consistently observed in low- and zero-intensity groups. The high-intensity group showed lengthening in CSP.

CONCLUSIONS

The findings suggest the dose-dependent benefits of exercise and that high-intensity exercise can normalize corticomotor excitability in early PD.

Pre-synaptic dopaminergic compensation after moderate nigrostriatal damage in non-human primates

Despite a dramatic loss of nigrostriatal dopaminergic neurons in Parkinson's disease, clinical symptoms only arise with 70-80% reduction of striatal dopamine. The mechanisms responsible for this functional compensation are currently under debate. Although initial studies showed an enhanced pre-synaptic dopaminergic function with nigrostriatal degeneration, more recent work suggests that functional compensation is not dopamine-mediated. To address this issue, we used cyclic voltammetry to directly measure endogenous dopamine release from striatal slices of control monkeys and animals with a moderate or severe MPTP-induced dopaminergic lesion. The moderately lesioned monkeys were asymptomatic, while the severely lesioned animals were parkinsonian. In monkeys with a moderate lesion, a 300% increase was obtained in endogenous striatal dopamine release. In contrast, in striatal slices from severely lesioned animals, a small % of evoked dopamine signals were similar in amplitude to control while the greater majority were undetectable. These findings suggest that pre-synaptic dopaminergic compensation develops in residual dopaminergic terminals with moderate lesioning, but that this response is lost with severe nigrostriatal damage. Such an interpretation is supported by the results of dopamine turnover studies. This enhanced pre-synaptic dopaminergic activity may be important in maintaining normal motor function during the initial stages of Parkinson's disease.