PROJECTION SITES OF SUPERFICIAL OR DEEP DORSAL HORN IN THE DORSAL RETICULAR NUCLEUS

THE termination sites in the medullary dorsal reticular nucleus (DRt) of axons arising from superficial or deep dorsal horn cells were analy sed by anterograde tracing with biotinylated dextran (ED). Following E D injections in spinal laminae I-III or in these laminae plus the dors al funiculus, labelled fibres and boutons were located in the dorsalmo st ipsilateral portion of the DRt. Injections covering laminae III-V o r laminae I-V resulted in bilateral labelling of the ventral DRt and i psilateral labelling of the dorsal DRt. These findings, together with previous data concerning the origin of DRt projections to the superfic ial or deep dorsal horn, suggest the occurrence of reciprocal anatomic al loops connecting the dorsal or the ventral areas of both regions.