Fragile X Syndrome (FXS) is a genetic disorder caused by transcriptional silencing of the FMR1 gene, leading to the loss of Fragile X Mental Retardation Protein (FMRP), a translational regulator. FXS, the most common cause of autism, is characterized by developmental delays, impaired cognition and sensory hyper-sensitivity, including in the olfactory system. Olfactory sensory neurons (OSNs) are located in the olfactory epithelium where they detect and respond to olfactory stimuli perceived through smell. Previous evidence from our lab has indicated that in a mouse model of FXS, OSNs exhibit an increased response to odors. Here, we set out to determine whether this increase reflected a larger number of cells responding. To test this hypothesis, we exposed wild type and Fmr1 null mice to odorants for one hour. We then measured the number of OSNs activated (as assessed by expression of the immediate-early gene c-Fos) as a percentage of the total number of OSNs (as assessed by expression of olfactory marker protein).
