A method to identify microinjected nephrons of rat

Visualization of three-dimensional nephron structure with microcomputed tomography

The three-dimensional architecture of nephrons in situ and their interrelationship with other nephrons are difficult to visualize by microscopic methods. The present study uses microcomputed X-ray tomography (micro-CT) to visualize intact nephrons in situ. Rat kidneys were perfusion-fixed with buffered formalin and their vasculature was subsequently perfused with radiopaque silicone. Cortical tissue was stained en bloc with osmium tetroxide, embedded in plastic, scanned, and reconstructed at voxel resolutions of 6, 2, and 1 microm. At 6 microm resolution, large blood vessels and glomeruli could be visualized but nephrons and their lumens were small and difficult to visualize. Optimal images were obtained using a synchrotron radiation source at 2 microm resolution where nephron components could be identified, correlated with histological sections, and traced. Proximal tubules had large diameters and opaque walls, whereas distal tubules, connecting tubules, and collecting ducts had smaller diameters and less opaque walls. Blood vessels could be distinguished from nephrons by the luminal presence of radiopaque silicone. Proximal tubules were three times longer than distal tubules. Proximal and distal tubules were tightly coiled in the outer cortex but were loosely coiled in the middle and inner cortex. The connecting tubules had the narrowest diameters of the tubules and converged to form arcades that paralleled the radial vessels as they extended to the outer cortex. These results illustrate a potential use of micro-CT to obtain three-dimensional information about nephron architecture and nephron interrelationships, which could be useful in evaluating experimental tubular hypertrophy, atrophy, and necrosis.

Proximal tubule morphology after single nephron obstruction in the rat kidney

This study examined the effects on proximal tubule morphology of blocking single nephrons with paraffin wax for one day, one week, or one month in the rat. Proximal tubule lumens were blocked with a short column of wax using micropuncture. Chronically blocked and control (normal) tubules were fixed by either intravascular or intraluminal perfusion of glutaraldehyde solution. Proximal tubule segments downstream to the wax block were examined by light and transmission electron microscopy. Intraluminal Alcian blue dye, serial sectioning, and nephron microdissection techniques were used to identify nephrons. One day after obstruction, all proximal tubule cells downstream to the block were injured. Some recovery was seen. S1 and S2 segments showed more severe damage than S3 segments. Alcian blue, which normally is excluded from cells, entered the cytoplasm of some damaged S1-S2 cells. After one week of obstruction, the tubule appeared to have reconstituted itself, but cells were less differentiated than normal. One month after obstruction, blocked tubules were atrophied. Tubule cells were simplified and were surrounded by a thickened basement membrane. The results suggest that prolonged proximal tubule blockade produces injury and atrophy of the proximal tubule probably due to ischemia and interruption of normal reabsorptive activity.