Morphological characteristics of a unique intracytoplasmic neuronal inclusion body

Unique intracytoplasmic inclusion bodies unaccompanied by a clinically apparent neurologic disease were found in the neurons of the hippocampus, subiculum, and mammillary body of a man who died suddenly, presumably of cardiac disease. The eosinophilic inclusions were round and often targetoid, with a central core that had the staining characteristics of RNA. Ultrastructurally, the inclusions were mainly composed of osmiophilic granular material. Rabies viral antigen was not detected by immunofluorescence, and heavy metals were not detected by energy dispersive spectrometry. These neuronal inclusions should be distinguished from Negri bodies.