STEREO-ULTRASTRUCTURAL AND HISTOLOGICAL CHARACTERISTICS OF CANINE GASTROCNEMIUS MUSCLE IN THE PERIOD OF EARLY POSTNATAL ONTOGENESIS
A morphological study of puppy gastrocnemius muscle in the early postnatal period was performed: newborn puppies, 7-, 14-, 21-, 28-day old, (n=2) for each period. Methods of histology, stereometry, scanning electron microscopy, statistical analysis were used. Half-thin sections were stained according to M. Ontell, studied using AxioScope.A1 stereomicroscope and AxioCam built-in camera (Carl Zeiss MicroImaging GmbH, Germany). Cytoarchitectonics was investigated with «JSM-840» scanning electron microscope (JEOL, Japan). Cryostat sections with the revealed activity of myosin ATP-ase served for stereological analysis. The following was calculated: bulk density of muscular fibers, microvessels, endomysium; number density of myocytes and microvessels, vascularization index (species constant). The particular features of the muscle cytoarchitectonics were revealed, as well as those of the muscle stromal-parenchymal relationships, the wavelike character of the dynamics of microcirculatory bed values was noted. Parallels were determined for the main stereometric parameters for the anterior tibial and gastrocnemius muscles. Newborn puppies had narrow muscle fibers without cross striation, networks of thin elastic fibrils, the highest content of the connective-tissue component. The cross striation was identified in myocytes on day 7-14, and by 21-28 day the muscle fibers were criss-crossed with microvessels, including in the direction perpendicular to the myocyte course, the connective-tissue interlayers were minimal. Paired myoblasts, groups of nuclei (myotubes), contractually changed myocytes were characteristic of the growing muscle, there were elastic and collagen fibers, fibroblasts, fibrocytes, macrophages in the connective-tissue component. The results may be of interest for comparative morphological analysis in various experimental models.