Anatomical mapping of the neuroepithelial projection to the olfactory bulb in the rat.

The topographical organization of the epithelium-to-bulb projections was studied in 15-day-old rats by the retrograde tracing method using horseradish peroxidase (HRP). Injections of HRP were placed in the glomerular layer of the 4 bulbar surfaces; the location and the maximal extent of labeled epithelial areas were assessed. Results have shown an important but variable degree of overlapping of peripheral projections to the bulb. The dorsal aspect received inputs from only the anterior dorsal recess and endoturbinate II. Epithelial projections to the lateral side included the anterior dorsal recess and turbinates 1, 2-2' and II-II'. Peripheral projections converging to the medial surface were the most various; they comprised the septal wall, the posterior dorsal recess, ectoturbinate 3 and all endoturbinates. The ventral pole received afferents from the lateral recess, lower parts of the septal wall and turbinates 2-2', 3, III, IV and also recesses between these turbinates. Otherwise, three epithelial areas showed divergent projections to the bulb. Information processing via convergence and divergence of epithelium-to-bulb connections may represent differential functions in olfactory information coding.