HISTOPATHOLOGY OF THE DEVELOPMENT OF THE AXIAL SKELETON AND SPINAL CORD IN THE IRRADIATED TAIL OF THE YOUNG AXOLOTL (SIREDON MEXICANUM)

¹ From the Radiobiology Laboratory, Roswell Park Memorial Institute (New York State Department of Health), Buffalo, New York

The tails of axolotls (Siredon mexicanum) were irradiated locally in five groups of 25 animals each, receiving 500, 1,000, 2,000, 3,000 and 6,000 r, respectively, 1 month after hatching, and in one group of 20 animals, receiving 3,000 r 38 days after hatching; 35 animals served as untreated controls.

1. In control animals, the development of the axial skeleton of the tail is completely different during the later stages than during the earlier stages. The first period of development lasts 2 or 3 months. During this period, development of the axial skeleton of the tail is limited to growth and differentiation of the notochord. The second period begins with the formation of the cartilaginous trunk from the end of the notochord or from the distal end of the last caudal vertebra. Further development is characterized by growth and differentiation of the cartilaginous trunk.

2. During the first 20 days after irradiation, the appearance of the axial skeleton usually is approximately normal. Around the 20th day, macrophages start accumulating near the end of the notochord. A few days later, they begin to penetrate into it, destroying the cells of the notochord itself and its sheaths. Destruction of the axial skeleton occurs proximad, usually almost to the proximal border of the irradiated region of the tail. In the more proximal portion of the tail, probably only partially irradiated, the cartilaginous trunk sometimes undergoes limited development.

3. Changes in development following irradiation are much rarer and are ordinarily observed much later in the spinal cord than in the axial skeleton. In a few cases, the spinal cord may bend on expand considerably, and the central canal may be transformed into a large cavity on may be duplicated. Irradiated nerve cells are generally normal in appearance, size, and distribution, but sometimes reach a giant size. Highly unusual development of neural outgrowths from the distal portion of the spinal cord was noted in one animal.

4. In the present study, no distinct"zone of stimulation" was observed. but irradition did occasionally stimulate the development of portions of the axial skeleton or spinal cord. An instance of unusual development of neural outgrowths from the distal portion of the spinal cord and another of unusually early development of the cartilaginous trunk can be considered examples or roentgen-ray stimulation.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?