Together, these data imply that mGluR-induced OPHN1 mediates LTD by promoting MAPK Inhibitor Library high throughput the internalization of AMPARs. Further support for these results, and mechanistic insight into how OPHN1 induction could regulate AMPAR endocytosis during mGluR-LTD, were provided by our finding that OPHN1 interacts with N-BAR domain-containing Endo2/3 core components of the postsynaptic clathrin-dependent endocytic machinery (Chowdhury et al., 2006). Interestingly, our data show that mGluR stimulation enhances OPHN1 association with Endo2/3 in a protein synthesis

dependent manner. And importantly, disruption of the OPHN1-Endo2/3 interaction impedes both mGluR-elicited persistent decreases in surface AMPARs and LTD. Notably, these effects are not attributable to some general disruption of AMPARs or the machinery that controls their trafficking, because disruption of the OPHN1-Endo2/3 interaction does not affect basal AMPAR levels or basal synaptic function. Thus, these data imply that the downregulation of surface AMPARs during mGluR-LTD requires OPHN1 induction and its ability to bind Endo2/3. Likely, OPHN1 induced upon mGluR activation, via the regulation of Endo2/3′s activities, increases the rate of AMPAR endocytosis. While our data demonstrate a requirement for

OPHN1 synthesis in mGluR-LTD, previous studies have shown that newly synthesized Obeticholic Acid cell line Arc protein is also required for this process (Waung et al., 2008), implying that both mGluR-induced OPHN1 and Arc, and perhaps other proteins, such as MAP1B and

STEP (Davidkova and Carroll, 2007 and Zhang et al., 2008), are likely to contribute jointly to LTD, and, moreover, that mGluR1/5 must coordinate the various translational control mechanisms involved. Of particular interest is that Arc also interacts with Endo2/3 and this interaction is important for the role of Arc in AMPAR trafficking (Chowdhury et al., 2006). Of note, OPHN1 and Arc interact with different regions of Endo2/3, with OPHN1 binding to the SH3 domain of Endo2/3, and Arc to the C terminus of the N-BAR domain of Endo2/3 (Chowdhury et al., 2006). Isotretinoin Therefore, it is possible that newly synthesized OPHN1 and Arc cooperate at the level of Endo2/3 to promote mGluR-driven AMPAR endocytosis, either by regulating distinct aspects of Endo2/3 function or by promoting/engaging a common mechanism, at least under wild-type conditions. Importantly, a different mode of mGluR-LTD regulation seems to occur upon loss of FMRP. Indeed, previous studies demonstrated that mGluR-LTD in Fmr1 KO mice is distinctly different from that in wild-type mice. For instance, whereas mGluR-LTD in wild-type mice is protein synthesis dependent, it persists in the absence of protein synthesis in Fmr1 KO mice ( Hou et al., 2006 and Nosyreva and Huber, 2006).