Sensory stimulation increases cortical expression of the fragile X mental retardation protein in vivo

Fragile X syndrome is a common cause of mental retardation that results fro m the absence of the fragile X mental retardation protein (FMRP), an RNA bi nding protein whose function remains unclear. Recent in vitro work has demo nstrated that the protein is translated near the synapse in an activity dep endent manner [33]. We therefore asked whether expression of FMRP might be altered by neuronal activity in vivo. Using immunoblots of different sub-ce llular fractions of the rat somatosensory cortex, lye show that the levels of FMRP increase significantly following unilateral whisker stimulation, a model of experience dependent plasticity. This increase is greatest between 2 and 8 h after the stimulus and is seen in both a synaptosomal fraction a s well as a sub-cellular fraction enriched for polyribosomal complexes. In contrast, detectable levels of FMRP within the somatosensory cortex show ei ther a decrease or no change after a kainic acid induced seizure compared t o water treated controls. Our findings demonstrate that FMRP expression lev els are modulated in vivo in response to neuronal activity and suggest a ro le for FMRP in activity dependent plasticity. (C) 2000 Elsevier Science B.V . All rights reserved.