Comparison of active zones in spinal cord of anesthetized and unanesthetized rats: a high voltage electron microscope study.

High voltage electronmicroscopy was applied to the study of presynaptic nerve terminals and specifically the arrangement and staining properties of synaptic vesicles in and around the active zone. The zinc iodideosmium tetroxide technique was used for the impregnation of neuropil derived from the spinal cord of anesthetized (40 mg/kg pentobarbital sodium) and unanesthetized rats. Under optimal conditions of section thickness and tilt angles stereoscopic views of a paracrystalline lattice arrangement of synaptic vesicles could be ascertained. The ZIO affinity was significantly higher in synaptic vesicles of the anesthetized as compared with the unanesthetized preparations.