Evidence for altered Fragile-X mental retardation protein expression in response to behavioral stimulation

The Fragile-X mental retardation protein, the protein absent in Fragile-X s yndrome, is synthesized near synapses upon neurotransmitter activation. Hum ans and mice lacking this protein exhibit abnormal dendritic spine lengths and numbers. Here we investigated Fragile-X protein levels in animals expos ed to behavioral paradigms that induce neuronal morphological change. Fragi le-X protein immunoreactivity was examined in visual cortices of rats reare d in a complex environment for 10 or 20 days, motor cortices of rats traine d on motor-skill tasks for 3 or 7 days, and either visual or motor cortices of inactive controls. Rats exposed to a complex environment for 20 days or trained for 7 days on motor-skill tasks exhibited increased Fragile-X prot ein immunoreactivity in visual or motor cortices, respectively. These resul ts provide the first evidence for a behaviorally induced alteration of Frag ile-X protein expression and are compatible with previous findings suggesti ng synaptic regulation of its expression. These results also strengthen the association of Fragile-X mental retardation protein expression with the al teration of synaptic structure. (C) 2000 Academic Press.