Morphogenesis of the Hirano body in neurons of the squirrel monkey dorsal horn.

Electron microscopic investigation of laminae I-III in the lumbosacral region of the squirrel monkey spinal cord has disclosed possible stages in the morphogenesis of the Hirano body. These bodies occur occasionally in nerve cell bodies and dendrites. They are round to oval in shape, measure up to 2.2 micrometer in diameter and are composed of circular layers of 10 nm filaments. In several instances in the present study, Hirano bodies were observed in close association with the Golgi apparatus. Here Golgi-related vesicles were attached to the external surface of the Hirano bodies. In one instance a cluster of developing Hirano bodies of various sizes was observed. The smaller bodies were located nearest the Golgi apparatus while the larger were further away. In this case several short filaments, which may be precursors of the longer filaments which make up the layers of the inclusion, were observed in the cytoplasm between the Golgi cisternae and the smaller Hirano bodies. These observations suggest that the Golgi apparatus plays a major role in the production of the Hirano body. The significance of the occurrence of these inclusions is discussed.