Ultrastructure of the dynorphin-immunoreactivity in rat brain hippocampal mossy fiber system

In rat hippocampus, the opioid peptide dynorphin A (1-17) is present in a subpopulation of the mossy fiber terminals, as shown by ultrastructural immunocytochemistry. The immunoreactive boutons exhibit all features characteristic for giant mossy fiber boutons, as e.g. inclusions of neighboring giant boutons which may or may not be dynorphin A-positive. At early survival times after selective lesioning the mossy fiber system with colchicine, lysosomes indicative for the proceeding degeneration are present in boutons still immunoreactive for dynorphin A as well as in non-immunoreactive boutons. This observation provides evidence that the dynorphinergic terminals are in fact the endings of the granule cells.