[Differentiation of muscle fibers of various types during postnatal development of the ventral serrate muscle in a rat].

In the denticulate ventral muscle of Wistar rats at the age of 1 day--2 months activity of NAD-N-dehydrogenase, succynic dehydrogenase and cytochrome oxidase has been determined in transversal cryostat sections. Quantitative estimation of the enzymes activity has been carried on by the plag-method. With age, general tendency to increasing activity of the enzymes mentioned is noted, but the dynamics of the increase is peculiar for every enzyme. Analysing the histograms on muscular fibre distribution according to their optical density, it is possible to estimate the dynamics. Simultaneously, the width of variational series, central statistical moments, indices of asymmetry and excess are also estimated. The whole course of the muscular fibre development, in accordance to the range and moments of distribution, can be devided into four main stages: stable, initial stage, slow increase of events, rapid increase of events and stabilization of the process. The stages mentioned pass gradually one into another making it possible to mark transitional stages (5--11, 15--19, 34--60 days). Using standard indices, it is possible to characterize more strictly the processes occurring in the course of muscular fibre differentiation. Lack of parallelism in the dynamics of asimilarity and excess can be treated as variety in differentiation of muscular fibres with middle and large optic density, and parallelism in dynamics--as their simultaneous differentiation. By comparing the curves it can be concluded that up to the 12--14th days, variety in differentiation of muscular fibres occurs, while after the 14th day their differentiation is more regular and simultaneous. The method of cytophotometry with subsequent mathematical processing of the results helps to determine the stages of muscular fibres differentiation.