Lectin identification of olfactory receptor neuron subclasses with segregated central projections.

Our previous studies have demonstrated that the primary olfactory projection in rainbow trout is organized nontopographically; the pattern of termination of olfactory axons in the olfactory bulb is unrelated to the distribution of their cell bodies in the olfactory mucosa. In the present research we have further characterized the organization of this projection by examining the lectin-binding properties of olfactory receptor neurons. The results indicate that in trout, as in mammals, populations of olfactory receptor neurons differ significantly from one another in their carbohydrate "signatures." We have identified subsets of olfactory receptor neurons, specified by unique lectin-binding properties, that are widely distributed and intermingled with the other receptor neurons in the olfactory mucosa and nerve, but that segregate as they enter the olfactory bulb and project to restricted regions of the glomerular layer. This pattern of terminations is bilaterally symmetrical, is remarkably consistent across individuals, and reappears when the primary olfactory projection is reconstituted following transection of the olfactory nerve. As revealed by the carbohydrates on subpopulations of receptor neurons, there is substantial order in the nontopographic projection of olfactory receptor neurons to the olfactory bulb. The functional significance of this organization and the means by which it develops and is maintained remain under investigation.