[Acridine orange: a fluorochrome of nucleic acids for the study of muscle and nerve cells].

Acridine orange renders nucleic acids fluorescent when forming complexes with them: D.N.A. is coloured luminous yellow while R.N.A. is a brilliant orange. Its application to sections of muscle biopsies permits the identification of certain muscle fibres, recognized by their bright orange fluorescence which contrasts with the pale green of mature, normal myofibrils in three specific situations: denervation, regeneration following injury, and the rapid growth and maturation of fetal muscle. Moreover, myopathic nonregenerative atrophy, as well as histochemical type-specific atrophies, do not exhibit this same orange fluorescence. Because neurons, particularly motor neurons, contain large amounts of R.N.A. (by contrast with glial cells which have very little) the application of acridine orange in the central nervous system might help in understanding the development of the fetal brain, the evolution of some neurologic diseases, and the maturation of brain tumors. Since the technique does not require the exclusive use of frozen tissues, but also may be applied to formalin-fixed tissue in paraffin sections, it is well adapted to the study of tissue obtained at autopsy.