Purpose/Hypothesis: The purpose of this study was to investigate whether L-dopa or L-dopa combined with Ex can influence the frequency-dependent depression of the H-reflex over a period of 30 days. Number of Subjects: Fifty-six adult, female, Sprague-Dawley rats. Materials/Methods: These rats were divided into five experimental groups (G): G1: Tx only (15), G2: Tx+Ex (16), G3: Tx + L-dopa (7), G4: Tx+Ex+L-dopa (7), and G5: control (11). All rats in G1-G4 groups received complete spinal Tx at T8. G2-G4 received exercise (60 min/day, 5 days/week for 30 days). G3 and G4 also received Sinemet (L-dopa + decarboxylase inhibitor) treatment 5 days/week (1.4 mg/kg, p.o. gavage, 1 hr prior to Ex). G5 received no treatment. At the end of each treatment period, the H-reflex was averaged following stimulation at 0.2, 1, 5, and 10 Hz. The change in the response was calculated as the percent of the response at 0.2 Hz in order to determine depression of the H-reflex as a function of simulation frequency. A two-way ANOVA was conducted. Results: There were significant main effects on H-reflex habituation for both independent variables (treatment groups and stimulation frequency) (both p <; 0.01). The interaction effect between these two independent variables was significant as well (p <;0.01). Post hoc comparison revealed that there were no significant differences in frequency-dependent H-reflex between groups at 1 Hz (all p >; 0.05); but there were significant differences between G1 and G2, and G1 and G5 at 5 Hz (both p <; 0.01), and between G1 and all other groups (G2-G5) at 10 Hz (all p <; 0.01). It should be noted that G3 and G4 were not significantly different from G5 at any frequency (all p >;0.01). Conclusions: The treatments implemented in this study (L-dopa, Ex, and Ex + L-dopa) all proved to be efficacious in the restoration of H-reflex depression at high frequencies (5 and 10 Hz) to the level of controls. The absence of difference in H-reflex amplitude between the L-dopa and the L-dopa + Ex groups suggests that Ex did not have a summative effect with L-dopa on H-reflex habituation after SCI. Clinical Relevance: The results from this study suggest that a similar novel treatment regimen (L-dopa or L-dopa + EX) may be useful in treating spasticity resulting from SCI, stroke, and other movement disorders.
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