Olfactory Sensory Neuron: Immunohistochemical Markers, Technique of Flat-Mounted Mucosa and Cell Count

A classification of olfactory sensory neuron (OSN) markers, a simple and robust technique of immunostaining on flat-mounted olfactory epithelium (OE) and a reliable quantification of the density of mature and immature OSNs are three crucial tools to study the pathophysiology of olfactory dysfunction. Using the rat model, we first categorized the main OSN markers by immunohistochemistry (IHC) on cross sections of OE. The OSN markers were divided into 3 groups: mature OSNs (OMP), immature OSNs (Tuj-1, DCX, OLIG2) and both (N-cadherin, LHX2, PGP9.5). The subcellular localization of each marker was also described. Tuj-1, OMP, DCX, PGP9.5 and N-cadherin were selected for immunostaining on flat-mounted OE because of their staining of OSN dendrites. We were able to successfully label OE with all the 5 markers using a simple technique for flat-mounted OE. In addition, this technique allowed the first mapping of the OE directly on the ethmoid turbinates. Finally, we quantified the mature (OMP+, Tuj-1-), immature (OMP-, Tuj-1+), transitory (OMP+, Tuj-1+) and total OSN density which were respectively 42080 ± 11820, 49384 ± 7134, 14448 ± 5865 and 105912 ± 13899 per mm2 (mean ± SD). The transitory population was quantified for the first time.

Stress and odorant receptor feedback during a critical period after hatching regulates olfactory sensory neuron differentiation in Drosophila

Here, we reveal that the regulation of Drosophila odorant receptor (OR) expression during the pupal stage is permissive and imprecise. We found that directly after hatching an OR feedback mechanism both directs and refines OR expression. We demonstrate that, as in mice, dLsd1 and Su(var)3-9 balance heterochromatin formation to direct OR expression. We show that the expressed OR induces dLsd1 and Su(var)3-9 expression, linking OR level and possibly function to OR expression. OR expression refinement shows a restricted duration, suggesting that a gene regulatory critical period brings olfactory sensory neuron differentiation to an end. Consistent with a change in differentiation, stress during the critical period represses dLsd1 and Su(var)3-9 expression and makes the early permissive OR expression permanent. This induced permissive gene regulatory state makes OR expression resilient to stress later in life. Hence, during a critical period OR feedback, similar to in mouse OR selection, defines adult OR expression in Drosophila.

Activity and stress during a critical period regulate olfactory sensory neuron differentiation

Here, we reveal that the regulation of Drosophila odorant receptor (OR) expression during the pupal stage is permissive and imprecise. We found that olfactory sensory neuron activity directly after hatching both directs and refines OR expression. We demonstrate that, as in mice, dLsd1 and Su(var)3-9 balance heterochromatin formation to direct OR expression. Neuronal activity induces dLsd1 and Su(var)3-9 expression, linking neuronal activity to OR expression. OR expression refinement shows a restricted duration, suggesting a gene regulatory critical period brings olfactory sensory neuron differentiation to an end. Consistent with a change in differentiation, stress during the critical period represses dLsd1 and Su(var)3-9 expression and makes the early permissive OR expression permanent. This induced permissive gene regulatory state makes OR expression resilient to stress later in life. Hence, during a critical period, OR activity feedback similar to in mouse OR selection, defines adult OR expression in Drosophila.

Intranasal Administration of Functionalized Soot Particles Disrupts Olfactory Sensory Neuron Progenitor Cells in the Neuroepithelium

Exposure to air pollution has been linked to the development of neurodegenerative diseases and anosmia, but the underlying mechanism is not known. Additionally, the loss of olfactory function often precedes the onset of neurodegenerative diseases. Chemical ablation of olfactory sensory neurons blocks the drainage of cerebrospinal fluid (CSF) through the cribriform plate and alters normal CSF production and/or circulation. Damage to this drainage pathway could contribute to the development of neurodegenerative diseases and could link olfactory sensory neuron health and neurodegeneration. Here, we investigated the impact of intranasal treatment of combustion products (laboratory-generated soots) and their oxygen functionalized derivatives on mouse olfactory sensory neurons, olfactory nerve cell progenitors, and the behavior of the mouse. We found that after a month of every-other-day intranasal treatment of soots, there was minimal effect on olfactory sensory neuron anatomy or exploratory behavior in the mouse. However, oxygen-functionalized soot caused a large decrease in globose basal cells, which are olfactory progenitor cells. These results suggest that exposure to air pollution damages the olfactory neuron progenitor cells, and could lead to decreases in the number of olfactory neurons, potentially disrupting CSF drainage.