The relationship between size and vascularity in the spinal cord of developing Xenopus laevis

Abstract

ABSTRACT The ability of the blood vessels of the spinal cord to increase in number during growth without differentiation of the nerve cells was tested on six sexually immature female Xenopus and eight thyroidectomized tadpoles with suitable control animals. The mean number of blood vessels in the region of spinal cord between the origins of the second and third spinal nerves is greater in metamorphosed Xenopus which are 50 mm. long than in those which are 25 mm. long, and greater in thyroidectomized tadpoles which are 100 mm. long than in normal tadpoles at the same stage of development which are 30 mm. long. The mean number of vessels, which enter the cord from the ventral spinal artery, per unit length of spinal cord between the second and third spinal nerves is inversely proportional to the length of the cord in the metamorphosed animals, but is constant in the two groups of tadpoles. It is concluded that the ability to form new branches of the ventral spinal artery is lost during metamorphosis; the development of blood vessels in the central nervous system is not associated solely with differentiation of the nerve cells; and the histogenetic cell deaths in the developing spinal cord are not precipitated by an inadequate vascular system. The hypothesis is proposed that the growth of new blood vessels is stimulated by a humoral agent produced by the nerve tissue.