IHC confirmed that Homer1a or Arc expression reduces surface GluA1 and GluA2 expression. Bay and MPEP blocked the action of Homer1a, but not the action of Arc (Figures 2C–2F), suggesting that Homer1a acts upstream of group I mGluR while Arc acts downstream. We generated gene-targeted mice carrying a modified Homer1 allele that selectively prevents the expression of immediate-early gene forms of Homer1 including Homer1a and Ania3 (termed Homer1a KO; Figures S2A–S2D and Experimental Procedures).

Homer1b/c, 2, and 3 protein expression is not changed in Homer1a KOs when compared with wild-type (WT) (Figure S2E). Similarly, expression of glutamate receptors mGluR1, mGluR5, GluA1, GluA2/3, and NR1 is not altered in Homer1a KO brains (Figure S2E). Homer1a KO mice are fertile, born at Mendelian frequency, and http://www.selleckchem.com/products/PD-0332991.html do not display obvious anatomical abnormalities. Maximal electroconvulsive seizure (MECS) induced Homer1a protein in WT mice, but not in Homer1a KO mice, and MECS did not alter Homer1b/c expression in either WT or Homer1a KO mice (Figure S2F). IHC and surface biotinylation assays revealed

GluA1 and GluA2 are elevated on the surface of Homer1a BI 6727 solubility dmso KO neurons prepared from E18 cortex and cultured 14 DIV (Figures 3A–3D), whereas total levels of GluA1 and GluA2/3 were not different from WT neurons (Figures 3C and 3D). Surface mGluR5 is also significantly increased on Homer 1a KO neurons (Figures 3C and 3D). Whole cell recordings of pyramidal neurons confirm an increase in the average amplitude of mEPSCs in Homer1a KO neurons (28.9 ± 1.3 pA; n = 33 cells; Figure 3E) compared to WT neurons (20.9 ± 1.1 pA; n = 24 cells; ∗∗∗p < 0.001), and indicate the increase is distributed over the entire range of recorded events consistent with scaling (Figure 3E). There was no difference in the frequency between WT (23.4 ± 2.6 Hz; n = 24 cells) and Homer1a KO neurons (25.3 ± 2.9 Hz; n = 33 cells; Figure 3E). We asked whether Homer1a expression would rescue the phenotype

of Homer1a KO neurons of increased synaptic AMPAR. To mimic the dynamic increase of most Homer1a that occurs with IEG expression, we used Sindbis virus infection for 14–18 hr. We noted that mEPSCs recorded from Sindbis virus-expressing neurons were generally less than noninfected neurons of the same DIV, perhaps due to effect of Sindbis to usurp host cell protein translation (Xiong et al., 1989). Accordingly, we compared Sindbis virus infected neurons expressing Homer1a versus GFP. mEPSC amplitudes recorded from Homer1a KO neurons expressing Homer1a transgene (13.7 ± 0.5 pA; n = 10 cells; ∗p < 0.05; Figures 4A and 4B) were significantly smaller than those recorded from neurons expressing only GFP (18.4 ± 1.6 pA; n = 13 cells). The shift to lower mEPSC amplitudes due to Homer1a expression was multiplicative. There was no difference in the frequency of mEPSCs between Homer1a (13.8 ± 1.7 Hz; n = 10 cells) and GFP expression (18.6 ± 3.0 Hz; n = 13 cells; Figure 4C).