Crystalline ribosomes are present in brains from senile humans.

Paracrystalline inclusions known as Hirano bodies characteristically appear in the hippocampal region of the brains of humans exhibiting senile and presenile dementias as well as several other neurodegenerative diseases. We present evidence that the currently accepted model for those structures based on alternating filament sheets is not correct, but that Hirano bodies are stacked sheets of membrane-bound ribosomal particles derived from partially degraded rough endoplasmic reticulum or Nissl substance. Using fluorescence staining with acridine orange and ethidium bromide, were have shown that the bodies contain RNA. Spatial filtering of electron micrographs by Fourier techniques shows that the individual particles that make up the arrays have a characteristic shape previously reported for the large subunit of eukaryotic ribosomes. The storage of these ribosomal particles in inclusion bodies may indicate a quiescent state of protein synthesis in the cells. This withdrawal of synthetic mechanisms in the hippocampus may have significant consequences in the loss of ability to consolidate short-term to long-term memory.