Presence of an osmiophilic feltwork distinct from the Golgi apparatus in spinal ganglion cells of the rat.

Rat dorsal root ganglia were osmicated for 48 h at 42 degrees C in a 2% unbuffered aqueous solution of osmium tetroxide. In addition to the osmiophilic cis-element of the Golgi apparatus, the osmium stained a cytoplasmic structure which, although present in the perikaryon of all ganglionic neurons, was well developed in type B1 cells. In photographic stereopairs of 1-2 microns thick sections examined with the electron microscope at 100 kV, these osmiophilic elements appeared as long, wavy thread-like elements with fusiform enlargements. Their average diameter was smaller than that of the thinner cisternae of the smooth endoplasmic reticulum. Occasionally branched, these osmiophilic structures were oriented in all directions of space. When examined in 1.5-7 microns thick sections with a high voltage electron microscope, they formed an osmiophilic feltwork which extended from the juxtanuclear to the subplasmalemmal regions of the perikaryon. It was not connected with the osmiophilic cis-element of the Golgi apparatus. In sections of glutaraldehyde-fixed tissues impregnated with the double impregnation technique or postfixed with reduced osmium, the osmiophilic tubules were clearly distinguished from microtubules, cisternae of endoplasmic reticulum or endocytic structures.