Long-term experimental hypodynamy affects the structure of spongy bone and osteoclasts in Japanese quails

We studied the effect of experimental hypodynamy on the structure of the two long bones (femur and tibiotarsus) of adult Japanes quail with special regard to osteoclasts. The quails were 70-day-old at the beginning of teh experiment, they were euthanized after 28, 56,and 84 days of hypodynamy. Small pieces of bones were fixed, decalcified in EDTA, and routinely processed further for light and transmission electron microscopy. Structural changes in spongy bone and in the osteoclasts were found in all the experimental animals, compact bone was not affected. It seems that osteoclasts were found in all the experimental animals, compact bone was not affected. It seems that osteoclasts respond biphasically. First, after 28 days of hypodynamy, the number of osteoclasts diminishedthey became vacuolated and had ruffled borders poor in microvilli. after 56 days of hypodynamy the osteoclasts recovered and became more numerous than in control animalsthese osteoclasts possessed fully developed ruffled borders with many microvilli. After 84 days of hypodynamy the osteoclasts covered nearly the whole surface of the bone spicules and showed structural signs indicating their full activity.