Abstract
The fragile X mental retardation 1 mutant mouse (Fmr1 KO) recapitulates several of the neurologic deficits associated with Fragile X syndrome (FXS). As tactile hypersensitivity is a hallmark of FXS, we examined the sensory representation of individual whiskers in somatosensory barrel cortex of Fmr1 KO and wild-type (WT) mice and compared their performance in a whisker-dependent learning paradigm, the gap cross assay. Fmr1 KO mice exhibited elevated responses to stimulation of individual whiskers as measured by optical imaging of intrinsic signals. In the gap cross task, initial performance of Fmr1 KO mice was indistinguishable from WT controls. However, while WT mice improved significantly with experience at all gap distances, Fmr1 KO mice displayed significant and specific deficits in improvement at longer distances which rely solely on tactile information from whiskers. Thus, Fmr1 KO mice possess altered cortical responses to sensory input that correlates with a deficit in tactile learning.
Highlights
Fragile X Syndrome (FXS) is a leading inheritable cause of mental impairment, affecting approximately 1:4000 males and 1:8000 females in the United States [1]
We examined the cortical response to stimulation of the C2 whisker for both Fmr1 mutants and WT mice (Fig. 1C)
FXS is characterized by cognitive impairment, anxiety, developmental delay, increased seizure susceptibility, and behavioral hyper-excitability
Summary
Fragile X Syndrome (FXS) is a leading inheritable cause of mental impairment, affecting approximately 1:4000 males and 1:8000 females in the United States [1]. The symptoms of FXS patients vary in severity and expression, characteristic phenotypes include reduced intellectual abilities, hyperactivity, increased seizure susceptibility, and impaired visuo-spatial processing [4]. There is no known cure for FXS or treatment than reverses the collective pathology. This Fmr mutant mouse exhibits several phenotypes similar to Fragile X syndrome including increased seizure susceptibility and hyperactivity, as well as deficits in spatial and motor learning [7,8,9,10,11]. Whether Fmr KO mice exhibit differences in somatosensory responsiveness akin to the characteristic tactile hypersensitivity to sensory stimuli in FXS is unknown. Whether Fmr KO possess normal tactile-dependent learning is unclear
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