The effect of a muscle relaxant on the growth and differentiation of skeletal muscles in the chick embryo.

Abstract

AbstractThe present work is concerned with the extreme controversy of views over the problem of the dependency of embryonic muscular development on neural factors.A chemopharmacological method was adopted to selectively block the motor nerve endings. One hundred and seventy‐seven chick embryos, 6–7 days old, were injected in ovo with marginal doses of oily tubocurarine. The control embryos were injected with arachis oil. Eleven days after injection, the majority of the embryos injected with curare were macroscopically stunted, especially the limbs. Specimens from experimental and control embryos were fixed simultaneously in isotonic 10% formalin made in Howard's solution. Sections were stained with hematoxylin and eosin, Mallory's phosphotungstic acid hematoxylin and Van Gieson. Dawson's technique was used to demonstrate the whole of the embryo skeletons. Microscopic examination of the limb musculature revealed inhibition of development and differentiation. The muscle fibers were reduced in size and number, poorly striated and contained many centrally situated nuclei.In the chick, it is suggested that at a critical time of development the final differentiation and maturation of skeletal muscles begin to become dependent on the anatomical and physiological intactness of the motor nerves. This time is found to be approximately between the sixth and seventh days of incubation. The significance of these observations is discussed.