Figure 2.

Schematic representation of the metabotropic glutamate receptor (mGluR) theory. In normal dendrites FMRP inhibits translation of pre-existing mRNAs after mGluR stimulation, with normal ionotropic glutamatergic receptor (AMPAR) endocytosis. FXS dendrite appears thinner compared to normal, because mGluR stimulation by glutamate causes an excess of local protein synthesis with exaggerated long term depression (LTD) due to a higher AMPAR endocytosis activity. The use of a mGluR inhibitor leads to a normalization of LTD in absence of FMRP.