HISTOLOGICAL AND HISTOCHEMICAL OBSERVATIONS ON THE DEVELOPMENT AND DIFFERENTIATION OF MOUSE CARDIAC MUSCLE / 解剖学报

ABSTRACT

Cardiac muscles of mouse embryos, newborn and suckling mice were used for histological and histochemical studies. This paper presents the observations on the morphogenesis and ultrastructure of cardiac myocytes under electron microscope and on their reactions of nucleic acids (DNA and RNA), glycogen, lipids, succinodehydrogenase (SDH), alkaline and acid phosphatases (AKP and AcP), glucose-6-phosphatase (G-6-Pase) and adenosine triphosphatase (ATPase) under light microscope.The heart of mouse embryo before 12-day, contained numerous polygonal or star-shaped myoblasts which had not yet acquired myofibrils but a few myofilaments. As the myoblast developed, the number of myofilaments increased in number and formed myofibrils, then the cells became myocytes. By the end of embryonic period, all the special elements of myocyte were basically constituted. The myocytes of embryos were rich in RNA granules, and their DNA was deeply stained. Flourishing mitosis appeared only in the early embryonic phase. RNA of adult myocytes was much less than that of embryos. From the early phase of embryos myocytes were full of glycogen but short of lipid droplets. From the day it was born, glycogen decreased apparently but lipid droplets increased rapidly.The reaction of SDH steadily increased in intensity from its early phase to late one. After birth it became more intensive. G-6-pase first appeared in the myocytes of 14 day's embryos. In the fetal period it showed moderate positive reaction, but in the myocytes of suckling muose it appeared negative. The enzyme showed positive reaction again at the age of 2 weeks. The ATPase reaction was found to be weak in the fetal specimens, only appeared in the endothelium of the capillaries. After birth it gradually became intensive and from the 2nd week positive reaction was obvious in adult, it was very vigorous.The above observations showed that the embryonic development and differentiation were gradually completed. Histological and histochemical features of each developmental period showed their individualities, which confirmed the evidence that the cardiac muscle developed not only successively but also by stages, and approached adult's level at 2nd week end after birth.