FMR1 and fragile X syndrome: It has been shown that 5-HT7 receptor (agonist 8-OH-DPAT) activation could reverse mGluR-induced AMPA receptor internalization and correct excessive mGluR-LTD in hippocampal neurons of Fmr1 knockout mice, suggesting that 5-HT receptors may represent a novel therapeutic target for fragile X syndrome (Costa et al., 2012).