Substance P immunoreactivity in the superficial laminae of the hamster olfactory bulb.

The direct application of colchicine to the hamster olfactory bulb has engendered the appearance of a broader distribution of substance P-like immunoreactivity (SP-LI) than has been previously reported. In the glomerular layer, both external tufted and periglomerular cells were strongly immunopositive. These two classes could be identified by somal size and the presence and branching pattern of intraglomerular dendrites. SP-LI neurons were also identified in the external plexiform layer and many were similar to middle tufted cells. These findings demonstrate that substance P expression is not uniquely associated with classes of projection neurons, but is also found in periglomerular cells, a class of inhibitory local circuit neurons.