lntroduction：The purpose of this study was to discuss the relation between an expansion of a trinucleotide (CTG) repeat in myotonic dystrophy (DM) and their muscle strength. Subjects 4 families consisted of 8 patients (5 congenital DM and 3 adult onset / carrier DM) were studied. For the normal control, 2 advanced students groups (13 men and 14 women) were included. Method：To detect an expansion of CTG repeat, polymerase chain reaction (PCR) analysis and non-radioactive Southern blot analysis were performed. For evaluation of muscle strength, occluding strength, grip strength, back strength, isometric extension and flexion strength of the knee, isometric dorsi-and plantar-flexion strength were measured. Results and discussion：By the Southern blot analysis, fragment include CTG repeat were detected. ln normal control subjects, the number of CTG repeat were under 20 repeat in contrast, in the congenital DM, expanded over 2000 repeat, and in the adult onset / carrier DM, the number of CTG repeat were about 100 - 1500. Grip strength, back strength, plantar-flexion strength tended to decrease in inverse relation to the size of CTG repeat, though, others were not related. Further patients are necessary, successive study will be needed.

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ln this study, we electron-microscopically investigated the number of sympathetic axons in the arteriolar walls of the extensor digitorum longus muscles of the rat rear leg. Arterioles in the muscle were divided into two groups: one group consisted of arterioles with accompanying muscle spindles, and the other consisted of arterioles without accompanying muscle spindles. The number of sympathetic axons present in the arteriolar walls and the ratios to the total number of sympathetic and non-sympathetic axons were compared between the groups. For electron-microscopic identification of sympathetic axons, 5-hydroxydopamine, a pseudotransmitter agent, was used. The number and ratio of sympathetic axons were significantly higher in arterioles with aocompanying muscle spindles than arterioles possibly unrelated to muscle spindles. From these results, we would like to suggest that one of the actions of sympathetic nerve is strong inhibition of blood flow in muscle spindle by reduction the artetiolar diameter.

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