These would not rely upon the global re-expression of intracellular molecules, such as BDNF signaling or Mecp2 itself (Chang et al., C646 2006; Guy et al., 2007; Kline et al., 2010). Importantly, NR2A transcription, translation and posttranslational modifications

are regulated by multiple factors, including but not limited to Mecp2 binding (Sanz-Clemente et al., 2010). For example, novel NR2A receptor antagonists (Liu et al., 2004; de Marchena et al., 2008), as well as the casein kinase pathway (Sanz-Clemente et al., 2010), can now be assayed. Ketamine—an NMDA receptor antagonist acting preferentially on PV cells (Behrens et al., 2007)—has recently been reported to reverse functional deficits in key forebrain nodes of the default mode network in Mecp2 KO mice (Kron et al., 2012). Other factors, such as the Otx2 homeoprotein, have been found to maintain PV-cells in a mature state (Beurdeley et al., 2012). Knockdown strategies regulating Otx2 content may also be fruitful in treating the Mecp2 KO mice. Maturation of visual cortical circuits is reportedly impaired in another autism model, the Angelman syndrome mouse deficient in Ube3a (Yashiro et al., 2009), which can also be reversed

by sensory deprivation. Our results indicate that ongoing endogenous neural activity may ensure the stability of cortical circuits. At a synaptic level, spontaneous transmitter release is required to maintain Selumetinib clinical trial postsynaptic receptors (McKinney et al., 1999; Saitoe et al., 2001), while spontaneous action potentials observe spike-timing-dependent plasticity rules for synapse strengthening and maintenance of connectivity (Gilson et al.,

2009; Kolodziejski et al., 2010). DR or NR2A disruption, while degrading orientation tuning even further (Figure 6), is sufficient to rescue both spontaneous neural activity and normal Tryptophan synthase visual acuity in Mecp2 KO mice. Retinogeniculate circuits are instead unaffected by late DR, responding as if deprived in the Mecp2 KO mouse (Noutel et al., 2011). Our findings ultimately reveal that vision in Rett syndrome patients may serve as a robust biomarker of both cortical status and its response to therapy. To date, visual processing and vision, in general, have never been analyzed in a systematic manner in RTT patients. Available data in the literature are limited and mixed ( Saunders et al., 1995; von Tetzchner et al., 1996) and a few studies have suggested some abnormal visual processing in RTT patients ( Bader et al., 1989, Stauder et al., 2006; von Tetzchner et al., 1996). This is a missed opportunity, given that eye gaze is one of the relatively well-preserved functions in non-verbal RTT girls, making vision testing feasible. Preliminary data indicate a clear correlation between visual processing and the clinical stage of RTT patients (G. DeGregorio, O. Khwaja, W. Kaufmann, M.F., and C.A. Nelson, unpublished data).