Linear correlation between the number of olfactory sensory neurons expressing a given mouse odorant receptor gene and the total volume of the corresponding glomeruli in the olfactory bulb

• Published in: Journal of comparative neurology (1911) 2016-01, Vol.524 (1), p.199-209
• Main Authors: Bressel, Olaf Christian, Khan, Mona, Mombaerts, Peter
• Format: Article
• Language: English
• Subjects: Animals; Cell Count; Cytoplasm - metabolism; Female; Image Processing, Computer-Assisted - methods; Linear Models; Luminescent Proteins - genetics; Luminescent Proteins - metabolism; main olfactory epithelium; Male; Mice, 129 Strain; Mice, Transgenic; Microscopy, Fluorescence; odorant receptor; Olfactory Bulb - anatomy & histology; Olfactory Bulb - metabolism; Olfactory Receptor Neurons - cytology; Olfactory Receptor Neurons - metabolism; olfactory sensory neuron; Organ Size; Receptors, Odorant - genetics; Receptors, Odorant - metabolism
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23835

ABSTRACT Chemosensory specificity in the main olfactory system of the mouse relies on the expression of ∼1,100 odorant receptor (OR) genes across millions of olfactory sensory neurons (OSNs) in the main olfactory epithelium (MOE), and on the coalescence of OSN axons into ∼3,600 glomeruli in the olfactory bulb. A traditional approach for visualizing OSNs and their axons consists of tagging an OR gene genetically with an axonal marker that is cotranslated with the OR by virtue of an internal ribosome entry site (IRES). Here we report full cell counts for 15 gene‐targeted strains of the OR‐IRES‐marker design coexpressing a fluorescent protein. These strains represent 11 targeted OR genes, a 1% sample of the OR gene repertoire. We took an empirical, “count every cell” strategy: we counted all fluorescent cell profiles with a nuclear profile within the cytoplasm, on all serial coronal sections under a confocal microscope, a total of 685,673 cells in 56 mice at postnatal day 21. We then applied a strain‐specific Abercrombie correction to these OSN counts in order to obtain a closer approximation of the true OSN numbers. We found a 17‐fold range in the average (corrected) OSN number across these 11 OR genes. In the same series of coronal sections, we then determined the total volume of the glomeruli (TGV) formed by coalescence of the fluorescent axons. We found a strong linear correlation between OSN number and TGV, suggesting that TGV can be used as a surrogate measurement for estimating OSN numbers in these gene‐targeted strains. J. Comp. Neurol. 524:199–209, 2016. © 2015 Wiley Periodicals, Inc. Using an empirical, “count every cell strategy” for mouse olfactory sensory neurons, the authors show a strong linear correlation between cell numbers and total glomerular volume in gene‐targeted strains in which an odorant receptor gene is coexpressed with a fluorescent protein. They also use this approach to improve systematic sampling in the olfactory system.