Biochemistry of rat single muscle fibres in newly assembled motor units following nerve crush.

A partial crush was applied surgically to the common peroneal nerves of rats, producing motor deficits lasting 4 weeks; the tibialis anterior muscles supplied by the crushed nerves were removed 5 weeks after recovery along with the contralateral control muscles. Myosin ATPase staining following pre-incubation at pH 4.5 was used to determine fibre types and to demonstrate areas of fibre-type grouping in the reinnervated areas of the muscles. Enzyme activities of lactate dehydrogenase (LDH), adenylokinase (AK) and malate dehydrogenase (MDH) were measured using micro-analytical techniques on the individual fibres within the histochemically identical groups and on fibres of the same types selected from areas of the test muscle or the contralateral control which appeared normal. The results show that the degree of enzymatic variation among single fibres reinnervated by a common axon is very small when compared to the general fibre population and, moreover, to fibres of the same histochemical type. Enzyme variability within the newly formed motor units was only slightly greater than the variability reported for normal motor units (Nemeth, Pette & Vrbová, 1981). The results indicate that skeletal muscle fibres originally having great differences in levels of enzyme activity, as demonstrated in the general fibre population, acquire considerable enzymatic similarity following reinnervation by a common motor neurone.