A morphological and histochemical study of the scalded hairy mouse ear

The right ear of mice was scalded at 51 degrees C and 53 degrees C for 20 s, using the recently developed dip burn model, and examined morphologically and histochemically at intervals for 2 h postburn. The left, unburned ear served as control. Burned ears intended for light and electron microscopy were fixed in situ by means of vascular perfusion. Ears for histochemical studies were cut off and immediately frozen at -140 degrees C. The enzyme histochemical analyses comprised a variety of oxido-reductases and hydrolases. After a 51 degrees C scald, scattered epidermal cell damage was observed with intracellular edema and mitochondrial destruction. Most microvessels were patent. Scalding with 53 degrees C water produced extensive cellular changes in the epidermis from 5 min including mitochondrial alterations, tonofilament aggregation and intercellular separations, progressing into complete epidermal destruction and lysis at 2 h postburn. Morphologically, many microvessels were occluded by cellular aggregates or debris after endothelial cell destruction. Of the histochemical assays the test for succinic dehydrogenase gave conclusive results that correlated well with the morphological findings, indicating partial dysfunction of epidermal cells 2 h postburn after a 51 degrees C scald and early, almost total absence of activity from 5 min postburn after a 53 degrees C scald injury. Scalding at 53 degrees C invariably leads to ear necrosis. This might be explained by the epidermal destruction, which in turn seems related to mitochondrial viability, and microcirculatory blood flow. The sensitivity of this experimental model precludes direct comparisons with studies of scalds to skin covering large tissue volumes.