Loizeau, M. | bioRxiv Science

bioRxiv2023

Dynamic intraglomerular neuronal ensembles represent odor identity and concentration

The olfactory system has been extensively studied from an anatomical and functional point of view, yet how and where certain basic odor characteristics such as identity and concentration are represented in the brain remains poorly understood. The glomerular layer of the olfactory bulb is the first brain region that integrates olfactory signals and enables a topographic representation of odor identity. We investigated this odor encoding at the intraglomerular network level using genetic labeling, in vivo imaging, and computational methods. Our analyses demonstrated that glomerular glutamatergic neurons encode both odor identity and concentration. Furthermore, in vivo structural and functional imaging of sister neurons revealed the emergence of intraglomerular neuronal ensembles governed by odor identity and concentration. These findings revealed a novel network mechanism that enables the simultaneous coding of odor identity and concentration within glomerular modules, suggesting a potential mechanism for odor decorrelation and a new model for odor information processing in the olfactory bulb. One-sentence summaryUnraveling the scent puzzle: Discovery of intraglomerular neuronal ensembles sheds light on odor representation in the brain.

neuroscience↗

bioRxiv2022

Sensory deprivation triggers phenotypic adjustment of dopaminergic interneurons in the mouse olfactory bulb

Olfactory sensory activity is a main factor factor controlling intergration and survival of neurons in the olfactory bulb. However, its impact on specific neuronal subtypes is unclear. Using reversible unilateral naris closure in concert with longitudinal in vivo imaging we show here that newborn GABAergic interneurons undergo significant cell death under sensory deprivation. In contrast, dopaminergic OB neurons survive under deprivation, but react with a reversible downregulation of tyrosine hydroxylase expression. long abstractNeurogenesis persists in the mammalian subventricular zone after birth, producing various populations of olfactory bulb (OB) interneurons. These include GABAergic and mixed dopaminergic/GABAergic double neurotransmitter neurons for the glomerular layer. While olfactory sensory activity is one of the main factors controlling newborn neuron integration, its effect on specific neuronal subtypes is far less clear. Here we use a reversible unilateral deprivation paradigm in combination with longitudinal in vivo imaging to characterize the behavior of newborn glomerular neurons. We find that a substantial fraction of purely GABAergic neurons die after four weeks of sensory deprivation. Tyrosine Hydroxylase (TH) positive dopaminergic/ GABAergic neurons show no signifficant cell death under deprivation, but react with an important decrease in TH expression levels. Importantly, this effect reverses after naris reopening, pointing to a specific adaptation of this neuron population to the level of sensory activity. We conclude that sensory deprivation induces adjustments in the excitation/inhibition balance of the OB implicating cell death and adaptation of neurotransmitter use in specific neuron types.

neuroscience↗