METHODS IN LABORATORY INVESTIGATION - NONINVASIVE MICROSCOPIC EVALUATION OF THE INTACT LIVING NEPHROTIC KIDNEY

BACKGROUND: Tandem Scanning Confocal Microscopy (TSCM) is a new form o f microscopy that allows one to noninvasively ''optically section'' in to intact structures and record microscopic images in real-time. In th is study, we have evaluated the ability of this new technology to dist inguish histopathologic changes in unstained living kidneys that occur coincident with the onset of puromycin aminonucleoside-induced nephro sis. EXPERIMENTAL DESIGN: The rats were anesthetized and a laparotomy was performed to expose the kidneys. Using a TSCM equipped with a 24X water-immersion objective, we viewed and recorded real-time images of subcapsular living uriniferous tubules and glomeruli of puromycin amin onucleoside-induced nephrosis rats exhibiting different levels of prot einuria. RESULTS: TSCM revealed a variety of histopathologic changes i n the puromycin aminonucleoside-induced nephrosis uriniferous tubules including dilation of proximal tubular lumens, loss of microvillous br ush border, cellular debris in the tubule lumens, and focal regions of extensive tubular necrosis. Using the fluorescent probe carboxyfluore scein, we were able to demonstrate significant heterogeneity in the mo vement of this fluorescent probe through the uriniferous tubules (e.g. , some tubules were completely blocked), and irregular patterns in flo w of carboxyfluorescein through nephrotic glomeruli. CONCLUSIONS: Thes e observations indicate that TSCM is capable of revealing a variety of histopathologic changes in unstained, intact, living kidneys. In addi tion, many of the histopathologic features of the uriniferous tubules revealed by TSCM are difficult or impossible to distinguish in biopsie d samples of renal tissue.