Maps of Odorant Molecular Features in the Mammalian Olfactory Bulb

Abstract

The olfactory bulb (OB) is the first relay station of the central olfactory system in the mammalian brain and contains a few thousand glomeruli on its surface. Because individual glomeruli represent a single odorant receptor, the glomerular sheet of the OB forms odorant receptor maps. This review summarizes the emerging view of the spatial organization of the odorant receptor maps. Recent studies suggest that individual odorant receptors are molecular-feature detecting units, and so are individual glomeruli in the OB. How are the molecular-feature detecting units spatially arranged in the glomerular sheet? To characterize the molecular-feature specificity of an individual glomerulus, it is necessary to determine the molecular receptive range (MRR) of the glomerulus and to compare the molecular structure of odorants within the MRR. Studies of the MRR mapping show that 1) individual glomeruli typically respond to a range of odorants that share a specific combination of molecular features, 2) each glomerulus appears to be unique in its MRR property, and 3) glomeruli with similar MRR properties gather together in proximity and form molecular-feature clusters. The molecular-feature clusters are located at stereotypical positions in the OB and might be part of the neural representation of basic odor quality. Detailed studies suggest that the glomerular sheet represents the characteristic molecular features in a systematic, gradual, and multidimensional fashion. The molecular-feature maps provide a basis for understanding how the olfactory cortex reads the odor maps of the OB.

Synaptic Integration of Olfactory Information in Mouse Anterior Olfactory Nucleus

“…Similarly, one AON neuron responded to methyl valerate, propyl acetate, and (Ϫ)-limonene, and another AON neuron responded to methyl valerate, propyl acetate, and menthone in mixture 7. These odors also activate different regions of the MOB (Uchida et al, 2000;Takahashi et al, 2004;Mori et al, 2006). Nevertheless, a minority of the mitral cells in our sample exhibited broad Figure 1.…”

Olfactory projectome in the zebrafish forebrain revealed by genetic single-neuron labelling

“…Zebrafish larvae possess 10 large, identifiable glomeruli that emerge during embryonic development and persist in stable configurations afterwards 23 ; these include six glomeruli in mdG (mdG [1][2][3][4][5][6] ), two in lG (lG 3,4 ) and two in vpG (vpG 1,2 ). Individual glomeruli other than the 10 identifiable ones cannot readily be discerned by SV2 staining at early larval stages 23 , but we noticed that dendritic tufts of some output neurons shared and occupied a restricted area within the glomerular clusters: lateroventral and lateral portions of maG (maG-lv and maG-l).…”

“…The odour information is initially represented as a discrete pattern of neural activities across a glomerular array on the olfactory bulb (OB), which results from axonal convergence of olfactory sensory neurons (OSNs) expressing the same olfactory receptors 1 . Glomeruli responsive to structurally related odorants are often clustered within defined regions of the OB [2][3][4][5] , establishing a chemotopic map of molecular features, so-called odour map. The odour map in the OB is transmitted by output neurons, mitral cells, to higher olfactory centres and eventually translated to elicit appropriate behavioural and physiological responses.…”

Behavioral State Regulation of Dendrodendritic Synaptic Inhibition in the Olfactory Bulb

“…The olfactory bulb (OB) is the first processing center of the olfactory system in the vertebrate brain and contains maps representing the molecular features of odorants (Mori et al, , 2006Takahashi et al, 2004). The OB has a cortical structure with well-ordered neuronal circuits and a characteristic synaptic organization (Shepherd et al, 2004).…”