Abstract
It is known that H-reflex is reduced in patients with Parkinson's disease. In the present study, we used a hemi-Parkinson's disease model to investigate the mechanism of the changes of H-reflex in Parkinson's disease in rats. In addition, the effect of L-dopa on the changes of H-reflex in the model was also observed. The hemi-Parkinson's disease model was achieved by administration of 6-OHDA into left medial forebrain bundle in male Wistar rat. The experiments were conducted two weeks after 6-OHDA administration. The H and M waves evoked by stimulation of sciatic nerve were recorded in both sides of the 5th digit of the hind limb. The threshold ratios of evoked H and M waves were compared before and after injection of L-dopa (100 mg/kg, ip). The results showed that the contralateral threshold ratio of H/M (1.782±0.361) was significantly higher (p<0.01) than that of ipsilateral one (1.346±0.265). After injection of L-dopa, the contralateral threshold ratios of H/M were gradually decreased and reached a significantly lower value (1.316±0.271; p<0.05) at 120 minutes after L-dopa injection. The higher values of contralateral threshold ratio of H/M in Parkinson's rats were supposed the result of depression of H-reflex excitability. The improvement of high threshold ratio of H/M by administration of L-dopa suggested that the absence of dopamine decreases the excitability of peripheral H-reflex. We concluded that the reduction of alpha motor neurons excitability by lacking of dopamine in Parkinson's disease may enhance the reciprocal or recurrent inhibition. [Jpn J Physiol 54 Suppl:S247 (2004)]
