Morphological changes of capillaries in the rat soleus muscle following experimental tenotomy

Electron microscopic study of capillary network remodeling in the extensor digitorum longus muscle of normal adult rat

Capillary networks demonstrate structural changes during maturation, aging, vascular disease, and cancer. Their morphological structure and function have an important influence on each other. Understanding the process of morphological vascular changes in the capillary network with advancing age may help overcome fatal vascular diseases. Aging-related structural changes of the capillary segments may accompany degeneration and regeneration of muscle fibers and serve to remodel the capillary network as a means of adapting to the changing environment. However, difficulty in obtaining human samples has hampered clarification of these microstructural changes. Herein, we examined serial ultrathin sections of capillary segments in the extensor digitorum longus muscle of normal mature (12 months old) rats in an attempt to analyze their structural changes. After bifurcation, a minimum of one capillary segment was filled with erythrocytes and was found to have fenestrations and plural endothelial disruptions, or pores, at the fenestrated portions. Some of the stagnated erythrocytes demonstrated extended protrusions, and their processes appeared to penetrate the basal lamina through the pores. These findings can also show that capillary segments are involved in partial remodeling of the capillary network. A better understanding of age-related structural changes of the capillary networks will help in fine-tuning novel vascular therapy for not only several fatal vascular diseases but also malignant tumors.

Fine structural study of the regeneration of muscle fibers in the rat soleus muscle during aging

We examined the regeneration of muscle fibers in the soleus muscle of mature (12 months) and aged (24 and 27 months) rats by using electron microscopy. In both mature and aged muscles, regenerating muscle fibers were mainly formed within the scaffolds of basal laminae after necrosis. In the aged muscle, however, satellite cells within the scaffolds were occasionally destroyed, and immature muscle cells occurred in and around muscle bundles. These findings suggest that new muscle fibers formed in the interstitial spaces may contribute to the total number of regenerated muscle fibers. The origin of the immature muscle cells is briefly discussed.

Endothelial stomatal and fenestral diaphragms in normal vessels and angiogenesis

Vascular endothelium lines the entire cardiovascular system where performs a series of vital functions including the control of microvascular permeability, coagulation inflammation, vascular tone as well as the formation of new vessels via vasculogenesis and angiogenesis in normal and disease states. Normal endothelium consists of heterogeneous populations of cells differentiated according to the vascular bed and segment of the vascular tree where they occur. One of the cardinal features is the expression of specific subcellular structures such as plas-malemmal vesicles or caveolae, transendothelial channels, vesiculo-vacuolar organelles, endothelial pockets and fenestrae, whose presence define several endothelial morphological types. A less explored observation is the differential expression of such structures in diverse settings of angiogenesis. This review will focus on the latest developments on the components, structure and function of these specific endothelial structures in normal endothelium as well as in diverse settings of angiogenesis.

Nerve injury affects the capillary supply in rat slow and fast muscles differently

The goal of this study was to determine the acute effects of permanent denervation on the length density of the capillary network in rat slow soleus (SOL) and fast extensor digitorum longus (EDL) muscles and the effect of short-lasting reinnervation in slow muscle only. Denervation was performed by cutting the sciatic nerve. Both muscles were excised 2 weeks later. Reinnervation was studied 4 weeks after nerve crush in SOL muscle only. Capillaries and muscle fibres were visualised by triple immunofluorescent staining with antibodies against CD31 and laminin and with fluorescein-labelled Griffonia (Bandeira) simplicifolia lectin. A recently developed stereological approach allowing the estimation of the length of capillaries adjacent to each individual fibre (Lcap/Lfib) was employed. Three-dimensional virtual test grids were applied to stacks of optical images captured with a confocal microscope and their intersections with capillaries and muscle fibres were counted. Interrelationships among capillaries and muscle fibres were demonstrated with maximum intensity projection of the acquired stacks of optical images. The course of capillaries in EDL seemed to be parallel to the fibre axes, whereas in SOL, their preferential direction deviated from the fibre axes and formed more cross-connections among neighbouring capillaries. Lcap/Lfib was clearly reduced in denervated SOL but remained unchanged in EDL, although the muscle fibres significantly atrophied in both muscle types. When soleus muscle was reinnervated, capillary length per unit fibre length was completely restored. The physiological background for the different responses of the capillary network in slow and fast muscle is discussed.

Morphological changes and recovery process in the tenotomized soleus muscles of the rat

Tenotomized soleus muscles of adult rats were analyzed morphologically and biochemically with special reference to the recovery process. Light microscopic observations of semi-thin sections showed that the characteristic central core lesion was most extensive at 1 week after tenotomy and began to diminish in extent at 2 weeks until no trace of lesion could be seen by 6th week, as confirmed by thin-section electron microscopy. Three phases of changes in the cross-sectional area of muscle fibers after tenotomy were demonstrated by morphometry: phase I designated as the initial increase up to the 3rd day, phase II as the progressive decrease until the 4th week, and phase III as the recovery to normal or even hypertrophy. In electron microscopy, the earliest alteration of myofibrils was recognized at 3 days after tenotomy. The Z discs showed a wavy or zigzag profile with frequent longitudinal splitting of myofibrils. From the 2nd week on, muscle fibers underwent a process of recovery, replacing the central core lesion with new myofibrils in which a reassembly of thick filaments into bundles of thin filaments took place, with Z discs being aligned adjacent to the peripheral complete myofibrils. In SDS-polyacrylamide gel electrophoresis, the molar ratio of myosin to actin diminished markedly as the central core lesion developed and gradually returned to normal with time, correlating well with the loss and subsequent reassembly of thick filaments.