Spatial coding of odorant features in the glomerular layer of the rat olfactory bulb

Abstract

In order to determine whether molecular features of odorants are represented spatially in the glomerular layer of the olfactory bulb, we used metabolic mapping of [14C] 2-deoxyglucose uptake in rats exposed to equal vapor concentrations of odorants differing systematically in chemical structure. The odorants were ethyl acetate, ethyl butyrate, isoamyl acetate, and isoamyl butyrate. Statistical analysis of anatomically standardized arrays of uptake revealed that each ester produced a characteristic spatial pattern of activity in the glomerular layer. The patterns were similar in different rats exposed to the same odorant, and their complexity increased with increasing odorant carbon number. This finding suggests that the presence of more potentially recognized molecular features is associated with a greater number of activated receptors. Individual regions of the glomerular layer responded specifically to isoamyl esters, and other regions preferred ethyl esters. Regions of similar specificity occurred in lateral and medial aspects of the bulb, the medial representation being more caudal and ventral than the lateral one. This pattern correlates with projections of olfactory sensory neurons expressing the same putative olfactory receptor gene. The patterns overlapped greatly in the posterolateral and posteromedial glomerular layer, a finding one should predict, given the large overlap in chemical structure across the aliphatic esters. Thus, molecular features appear to be encoded spatially in the glomerular layer, and the identity of the odorant may be determined by a subsequent decoding of the combination of molecular features represented in the glomerular layer.

Two-photon imaging of capillary blood flow in olfactory bulb glomeruli

“…Because sensory axons converging on a single glomerulus outnumber principal cells by a factor of several hundred and because action potentials are predicted to consume a major part of the energy budget during signaling (48), our study raises the question of how energy is distributed to olfactory nerve axons, whatever the percentage of them is activated during odor stimulation. Studies based on 2-deoxyglucose consumption (32,33,49) clearly demonstrated that energy consumption is significant in the ONL. It is thus possible that the oxygen present in the immediate vicinity of arterioles (50) contributes to the oxygen supply of the ONL.…”

“…As a result, odor stimulation reproducibly activates small glomeruli ensembles. These patterns of glomerular activation have been revealed by several methods including (i) BOLD fMRI (18)(19)(20), (ii) optical imaging of calcium (21), voltage (22), and intrinsic signals (23)(24)(25)(26)(27)(28), (iii) electrophysiological recordings (29)(30)(31), and (iv) measurements of 2-deoxyglucose consumption (32,33). Here, we use two-photon imaging to determine with a high spatial resolution the relationship between RBC flow in individual capillaries and neuronal activation.…”

Chemosensory Selectivity of Output Neurons Innervating an Identified, Sexually Isomorphic Olfactory Glomerulus

“…Imaging studies using various activity markers have shown that odor compounds evoke spatially organized, combinatorial patterns of neural activity in OBs (Mombaerts et al, 1996;Friedrich and Korsching, 1998;Johnson et al, 1998;Rubin and Katz, 1999;Belluscio and Katz, 2001;Xu et al, 2003; and ALs (Joerges et al, 1997;Carlsson et al, 2002;Hansson et al, 2003). In most of these cases, however, the cell types imaged were unknown, although in others (Zhao et al, 1998;Araneda et al, 2000;Ma and Shepherd, 2000;Gaillard et al, 2002;Wachowiak and Cohen, 2003) primary-afferent input was imaged.…”

Olfactory Fingerprints for Major Histocompatibility Complex-Determined Body Odors II: Relationship among Odor Maps, Genetics, Odor Composition, and Behavior

“…Anatomical landmarks determine the origins for the radial measurements. The first section is defined by the point at which complete mitral cell and external plexiform layers can be identified (Johnson and Leon, 1996;Johnson et al, 1998Johnson et al, , 1999Schaefer et al, 2001a). The 0 -180 o axis was drawn parallel to the more ventral aspect of the subependymal layer.…”