Nerve connections between mouse and rat hippocampal brain tissue: ultrastructural observations after intracerebral xenografting.

Fascia dentata tissue from embryonic mice was grafted to the hippocampal region of newborn Kyoto rats. After 1-7 months the recipients received lesions of the entorhinal cortex on the side of transplantation. Three days later their brains were processed for electron microscopy. The xenografts were identified by their content of mouse dentate granule cells which have smaller cell nuclei with more nucleoli than the corresponding host rat granule cells. Electron dense, degenerating host rat entorhinal fibers terminated in the outer parts of the mouse dentate molecular layer corresponding to the normal perforant path zones. They formed the normal type of synaptic contacts with dendritic spines. The findings demonstrate that precise synaptic contacts can be made across a species barrier.