Adaptation of skeletal muscle to immobilization in a shortened position

Association of iron-containing astrocytes with dopaminergic neurons of the arcuate nucleus

Specialized astrocytes, identified by cytoplasmic granules that are electron-dense and vividly stained by toluidine blue due to the presence in the granules of SH molecules and molecules of iron, have long been known to be present within the arcuate nucleus of the hypothalamus. Their function, however, is obscure. To determine whether or not these specialized astrocytes are in contact with dopaminergic neurons, rat brain sections were stained to detect tyrosine hydroxylase (TH) immunoreactive neurons by immunocytochemistry and were examined by both light and electron microscopy. Iron-rich astrocytes were located in the same general portion of the arcuate nucleus as were TH+ neurons, and most appeared closely associated with TH+ structures (somas, dendrites, and fibers) at the light-microscopic level. At the ultrastructural level, close contact between TH + neurons and processes of iron-rich glia was confirmed. This unique anatomical association suggests a functional relationship between the two cell types that may be related to unusual histochemical features of both cell types and/or to the location of these cells in an area with a highly permeable blood-brain barrier.

Bone formation in experimental myositis ossificans. Light and electron microscopy study

The development of ectopic ossification in experimental myositis ossificans of the rabbit thigh was studied. The right hind limb of 25 rabbits was immobilized with the knee in extension. Once a day the limb was passively mobilized for 2-3 minutes. The animals were killed 3, 5, 7, 14, 21, 28 and 35 days after the beginning of the experiment. Specimens for light and electron microscopy were obtained from both hind limbs. Extensive necrosis and fibrosis were observed in the right vastus intermedius muscle during the first week. Proliferation of chondrocytes and osteoblasts with newly formed woven bone and cartilage formation were found in the periosteum within 7 and 14 days after the beginning of the experiment. Intensive enchondral ossification and hard calcified tissue were observed later. It was evident that bone formation in this experimental model started in the periosteum after necrosis of the adjacent skeletal muscle. Therefore the temporal and spatial relationship of traumatic changes in the periosteum and muscle seems important for the development of myositis ossificans.