Localization of Leu-enkephalin in dense core vesicles of axon terminals

The localization of enkephalins by immunofluorescence has already shown that these pentapeptides are largely distributed in the central nervous system. In order to clearly identify the structures and organelles containing enkephalins, an immunohistochemical localization of Leu-enkephalin was performed at the ultrastructural level. Leu-enkephalin was detected in dense core vesicles (70--100 nm in diameter) of many nerve fibers in the substantia gelatinosa of the spinal cord, the globus pallidus and the nucleus papabrachialis. These findings support the hypothesis that Leu-enkephalin could act as a neuromodulator.