This suggests that mechanisms other than Homer1a regulate surface mGluR expression during homeostatic scaling, and that changes in surface expression of mGluR5 are not critical for AMPAR trafficking. mGluR5 endocytosis has been reported to occur by both activity-dependent and activity-independent Gefitinib clinical trial pathways (Dhami and Ferguson, 2006). Mechanisms that

control mGluR trafficking in homeostatic scaling and the physiological significance remain to be determined. Group I mGluRs are implicated in several diseases of cognition. For example, mGluR5 signaling is increased in mouse models of fragile X mental retardation syndrome (Huber et al., 2002) and may be relevant in developing therapies (Bear, 2005). Group I mGluR are considered important targets for treatment Ku-0059436 purchase of depression, schizophrenia, and Alzheimer disease (Conn et al., 2009).

Drug addiction is also dependent on mGluR5 signaling as mGluR5 KO mice show a reduced behavioral response to cocaine (Chiamulera et al., 2001) and mGluR5 inverse agonists prevent self administration in monkeys (Lee et al., 2005). The present study focuses attention on the possible role of homeostatic scaling in the pathogenesis of these disorders, and identifies an important physiology to consider in the chronic use of mGluR pharmaceuticals. The following antibodies were previously described or obtained commercially: mGluR1 (mouse monoclonal) from BD Biosciences; mGluR5 from Upstate; N-GluA2 from Chemicon; horse radish peroxidase (HRP)

conjugated HA antibody, HRP-conjugated myc antibody, myc (mouse monoclonal) from Santa Cruz; actin (mouse monoclonal) from Sigma Aldrich. GluA2CPY was described previously (Hayashi and Huganir, 2004). Homer1, Homer2, and Homer3 were generated and described before. The following almost drugs and chemicals were purchased from Tocris Biosciences: tetrodotoxin, bicuculline, Bay 36-7620, MPEP, LY367385, and (S)-MCPG, CPCCOEt. The Homer1a targeting construct was generated by fusing 2.7 kb of genomic DNA, including intron 4 (part thereof) and exon 5 of the Homer1 gene, with part of the rat Homer1c cDNA (2 kb), containing exons 6–10, the hGH polyadenylation site and a “floxed” Pgk-neo cassette, followed by 7.2 kb of Homer1 gene sequence. The linearized (NotI, KpnI) targeting construct was electroporated into ES ([129X1/SvJ × 129S1] F1) cells. G418 resistant ES cell clones were screened by PCR and Southern blotting for homologous recombination. Correctly targeted ES cells were injected into blastocysts, and chimeras were mated with C57BL/6 mice to produce heterozygous Homer1a knockouts. Neuronal cortical cultures from embryonic day 18 (E18) pups were prepared as reported previously (Rumbaugh et al., 2003), with minor alterations. For biochemistry experiments, 1 × 106 neurons were added to each well of a 6-well plate (Corning) coated with poly-L-lysine.