Meeting Abstract

P2.120  Wednesday, Jan. 5  Olfactory hemi-bulb organization in the elasmobranch brain MEREDITH, Tricia*; HANSEN, Anne; Florida Atlantic University; University of Colorado, Denver, Anschutz Medical Campus tmeredi1@fau.edu

Olfactory cues are detected by olfactory receptor neurons (ORNs). The information is conveyed via the olfactory nerve to the olfactory bulb (OB), the first relay station in the brain. The axons of the ORNs make contact with mitral cells in glomeruli. In teleost fishes, both tracing and electro-physiological studies showed that the teleost OB is divided into separate functional zones that process different types of odorants with no suggestion of somatotopy. While the OB in teleosts has a round shape, the OB of elasmobranchs is a long structure that lies parallel to the olfactory lamellae. In some elasmobranchs, the OB is physically partitioned into “hemi-bulbs”, either as two distinct hemi-bulbs or as a succession of connected swellings along the OB. The functional significance of these hemi-bulbs is not fully understood. The present study examined the organization of the OBs in two elasmobranch species, the Atlantic stingray (Dasyatis sabina) and the bluntnose stingray (D. say) to test the hypothesis that axons projecting from the olfactory epithleium to the OB in elasmobranchs exhibit a somatotopic arrangement. We injected various fluorescent tracers into the OBs to retrogradely label ORNs in the epithelium; and into the olfactory epithelium to anterogradely label the OBs. Our results suggest that the distribution of glomeruli in the OB is different from that in teleosts and that glomeruli receive projections from three to four olfactory lamellae situated immediately adjacent to these glomeruli. This suggests a somatotopic arrangement of the elasmobranch OB, which may be unique among vertebrates.