Cytological Changes in the Fat Body of the American Cockroach, Periplaneta aniericana,1 in Relation to Dietary Nitrogen Levels

Abstract

Light and transmission electron microscopic studies confirmed 3 cell types in fat body. Attention was focused on the urate cells in relation to dietary nitrogen. These cells are usually associated with mycetocytes, are essentially devoid of urate spherules (concretions) when dietary nitrogen is low, and have darkly-staining inclusions when attenuated. As dietary nitrogen increases the urate cells become progressively more loaded with urate spherules. At very high levels of dietary nitrogen or on a diet consisting of cellulose, the fat body may become overloaded by urate stores which tend to obscure cellular structure. Detailed examination of the urate spherules revealed that they have darkly-staining centers and are consistently associated with a discrete cytoplasmic entity which, in turn, is surrounded by a membrane-limited vacuole. This entire structure, including the urate spherule, is termed the “urate structural unit.” Its existence suggests a series of complex events associated with urate deposition and/or mobilization.