First single movement of turkey embryos.

UNLABELLED: The purpose of the study was to characterize the first contraction of an isolated muscle in turkey embryo. The space of time of the contraction since beginning of incubation, topography, morphogenesis and histology of the concerned muscle and its mechanical counterpart are described. MATERIAL AND METHODS: From the 3rd day of incubation on until the 6th day the embryos were continuously watched through a cellophane window in the eggshell. The installing of the window followed a certain time schedule to reveal the influence of the experimental conditions. For histology the embryos were fixed in Bouin's fluid, then completely cut in serial sections of 5 microm thickness and stained according to Masson-Goldner's trichrome procedure plus resorcin-fuchsin. Wire frame 3D reconstructions were performed to reveal the topography of the region. RESULTS: A paired muscle 1 mm long and 0.1 mm broad, derived by fusion of the four occipital myomeres, is responsible for the first individual contraction. The contraction produces a stretching in the neck region. The muscle named M. occipitalis primordialis consists of four end-to-end connected groups of mononucleated muscle cells; insofar it looks like early muscle in fishes and amphibians. The muscle contains two types of cells according to the cell nuclei. The elastic rod-shaped notochord represents an endoskeleton. Immediately after contraction it brings the body of the embryo back into its former shape. In the neck region the diameter of the notochord is less and, therefore, the elasticity of notochord is higher than further caudal. The floor plate may prevent damage of the neural tube during excursion of the notochord. The floor plate is flanked by two floor plate posts, which have a filamentous content like the floor plate. Their function may be fastening of floor plate and protection of nerve tissue. The passive pulse movements in the occipital region for 2 days before first contraction are considered to be of importance in orientation and extent of the consecutive active reactions. CONCLUSION: Vital observation accompanying serial section examination showed to be a suitable approach to biomechanical investigations in embryology. It allowed even after nearly 180 years of intensive morphological studies of avian embryos to find a new, up till now not described muscle.