Origin and termination of dorsal raphe-median eminence projection

The origin and termination of the dorsal raphe (DR)-median eminence (ME) projection were studied by combining well-limited small electrolytic lesions of different parts of the DR, the axonal degeneration and the serotonin content in the median eminence. Our results show that the rostral third of the DR is a source of serotonergic innervation to the ME and that the rest of the nucleus does not contribute to this projection. The light microscopy study revealed that degenerating fibers occupy the internal layer of the ME. These results were confirmed by electron microscopy which in addition showed degenerating terminals.