Regeneration of Hemopoietic Organs in the Silkworm, Bombyx mori, After Locally Targeted Irradiation with Heavy Ion Beams

抄録

The purpose of this study was to determine whether the regeneration of hemopoietic organ occurs in the silkworm, Bombyx mori, after locally targeted irradiation with heavy ion beams. Hemopoietic organs of 4th and 5th instar larvae were selectively irradiated with carbon ions (¹²C⁵⁺, 220 MeV, 18.3 MeV/u, 100, 250, 500 Gy), and morphological changes of these organs in the 5th instar were studied using light and electron microscopy. Carbon ions were considered to pass through the entire hemopoietic organ because the beam depth (range in water = 1.2 mm) was more than enough to reach the organ. Light microscopic observations suggested a possibility that the irradiated hemopoietic organs regenerate at a high frequency. The organs seemed to be able to regenerate even after irradiated at 500 Gy when a JH analog, methoprene, was applied to prolong the larval life.
Electron microscopic observations showed that the irradiation of carbon ions (100 Gy) caused serious damage to the hemopoietic organs in the early 5th instar. They lost acellular sheaths surrounding the organs and islets, and characteristic features of cell disruption and melt necrosis were observed. However, the cells of the hemopoietic organs appeared to be proliferating again in the late 5th instar: the organs were again surrounded by acellular sheaths, and were composed of spherical islets packed with many cells (both immature and mature hemocytes). These results indicate that the hemopoietic organs regenerate after irradiation with heavy ions at a high dose of more than 100 Gy.