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Neuronal mechanisms underlying recognition of odor information

Coordinated odor coding strategy in the brain

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University Hospital
2013/05/09

Understanding the functional significance of network units such as multineuronal “barrels” and “columns” in the mammalian brain is an ongoing topic of interest in neuroscience.

© Shu Kikuta.Cover headline; Heterogeneity within a single glomerulus module Cover legend; Neuronal networks that are directly associated with glomeruli in the olfactory bulb are thought to be homogeneous functional modules. Shu Kikuta et al demonstrated that the component neurons associated with a single glomerulus showed functionally distinct odorant selectivity depending on the location of the cell body. The image represents a putative vineyard. Each bunch of grapes represents a single glomerulus module, and each grape represents an individual component neuron. The center bunch of grapes struck by lightning (electroporation method in this study) is highlighted. Spotlights from different directions reveal the detailed color of the grapes, but show that heterogeneous colored grapes exist at each distinct location (heterogeneous odor representation of a subset of component neurons).

Olfactory sensory neurons expressing the same type of the odorant receptor converge onto one or a few specific glomeruli in the olfactory bulb (OB). Within each glomerulus, odor information is transferred to the principal neurons. These neurons typically have a primary dendrite that projects to a single glomerulus and form a translaminar glomerular module. This anatomical module is thought to be a functional module in the processing of odor information, in analogy with “barrels” and “columns” in the cerebral cortex.

As a first step toward developing a systematic understanding of the functional role of network modules, Research Associate Shu Kikuta and his colleagues at the University of Tokyo Hospital Department of Otolaryngology explored the anatomical and functional architecture of glomerular modules using in vivo two-photon calcium imaging. The anatomical distribution ranges of the neurons comprising the module were wider than the glomerulus, suggesting that distinct modules heavily overlap with each other. Response properties of individual component neurons varied depending on the location of the cell body along the longitudinal and horizontal axes. Although the glomerulus module was thought to be a homologous odor processing unit, neuronal circuits in the OB could produce heterogeneous responses to individual neurons originating from the same glomerulus. This implies that coordinated neuronal circuits in the glomerular module generate a large number of outputs to olfactory cortices. By having a large number of bulbar outputs to encode odor information, a subset of neurons could send their odor information to a specific olfactory cortex, thus enabling the olfactory cortex to extract a large amount of odor information from a limited number of odorant receptors.

Press release (Japanese)

Paper

Shu Kikuta, Max L. Fletcher, Ryota Homma, Tatsuya Yamasoba, Shin Nagayama,
“Odorant Response Properties of Individual Neurons in an Olfactory Glomerular Module”,
Neuron Vol. 77, Issue 6, 2013, March 20, 1122-1135, doi: 10.1016/j.neuron.2013.01.022.
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Links

The University of Tokyo Hospital

Department of Otolaryngology, The University of Tokyo Hospital (Japanese)

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