The synaptic terminals of the ventral horn of rat spinal cords were demonstrated by electron microscopy using a modification of the zinc iodideosmium tetroxide staining technique in which zinc iodide was substituted for a mixture of zinc powder and iodine sublimate.
The best staining reaction consistent with tissue preservation was obtained by incubating specimens for 16 hours at 4°C in solutions containing 1% or 2% zinc iodide. Synaptic vesicles staining black were observed in both F and S types of synaptic terminals. With the exception of some parts of the myelin sheath no other neuronal or glial elements gave a positive reaction.
The modified technique was compared with that of other investigators and the possible nature of the reaction between the stain and the synaptic vesicles was briefly discussed.