Meeting Abstract
All life on earth exhibits some degree of chemical sensitivity. Within the vertebrate clade, the organization of the olfactory system is largely conserved, despite their morphological diversity. Histological evidence suggests that the elasmobranch fishes demonstrate a remarkably different olfactory bulb organization than other vertebrates, including the teleost fishes. However, conventional histology is laborious, destroys intact structure, results in disjointed samples which must be reconstituted to elucidate three dimensional organization, and thus is inherently prone to tissue damage and registration errors. Here we show that Diffusion Tensor Microscopy (DTM) can be applied to facilitate Fiber Tract Mapping (FTM) of complex peripheral and central neural pathways. Using this non-invasive 3D digital imaging methodology, we imaged the olfactory organ and olfactory bulb of a basal vertebrate, the Atlantic stingray, Dasyatis sabina. We found that Olfactory Receptor Neurons (ORNs) project from the olfactory epithelium through the secondary and primary olfactory lamellae to the olfactory bulb. Within the bulb, the ORNs maintain their spatial integrity by projecting to glomeruli situated within one to two lamella widths of their point of origin producing a somatotopic bulbar organization. This contrasts with teleost fishes which possess a chemotopic organization whereby olfactory receptor neurons that share similar chemical sensitivity converge in glomeruli regardless of their point of origin within the olfactory epithelium. Our results illustrate the utility of DTM and FTM to efficiently inform us about intact neuronal structure by revealing a three dimensional bulbar organization that we believe may be fundamentally different from all other vertebrates.
