We first determined whether there was a disruption in the developmental switch from NR2B to NR2A in layer 2/3. We made whole-cell patch-clamp

recordings from layer 2/3 pyramidal neurons in slices of primary visual cortex and found that NMDA EPSCs elicited by layer 4 stimulation exhibited longer decay times and greater ifenprodil sensitivity in mGluR5 knockouts compared to wild-type (Figures 6E–6H). This indicates a deficiency in the development switch from NR2B to NR2A-containing receptors. Visual experience in dark-reared rodents causes a rapid switch from NR2B- to NR2A-containing NMDARs at layer 4 inputs onto layer 2/3 pyramidal neurons in primary visual cortex that depends upon NMDAR activation (Philpot Selleckchem Hydroxychloroquine et al., 2001 and Quinlan et al., 1999). Therefore, we next tested whether this experience-dependent plasticity is disrupted in mGluR5 knockout mice. We dark reared wild-type mice and mGluR5 knockout littermates from P6 until P17–P19, exposed some of these animals to 2.5 hr of light, and then investigated

the effects on NMDA EPSCs at layer 4 inputs onto layer 2/3 pyramidal cells. In wild-type mice NMDA EPSCs in animals exposed to light (+LE) exhibited faster kinetics and reduced ifenprodil sensitivity compared to mice that did not receive light exposure (Figures 7A–7E). The degree GSK1349572 research buy of change in these parameters was very similar to that previously reported (Philpot et al., 2001 and Quinlan et al., 1999) and confirms that 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase even brief exposure to light can drive the switch from NR2B to NR2A in visual cortex. In mGluR5 knockout

mice light exposure failed to produce any significant change in NMDA EPSC kinetics or ifenprodil sensitivity (Figures 7A–7E). It was also noticeable that the dark-reared wild-type and knockout mice (that were not exposed to light) exhibited very similar NMDA EPSC kinetics and ifenprodil sensitivity, indicating that visual experience and mGluR5 are necessary for the developmental change from NR2B to NR2A-containing NMDARs in visual cortex during the first few postnatal weeks. During the first postnatal week, most cortical synapses express NR2B-containing receptors, whereas later in development (>P14), many of these receptors are replaced with NR2A-containing NMDARs. Synaptic activity is involved in regulating this switch, and a role for sensory experience in primary sensory cortex has also been demonstrated; however, the molecular mechanisms driving this ubiquitous NMDAR subtype switch have hitherto been largely unexplored. Here, we find that activation of both mGluR5 and NMDARs is required for this switch to occur at synapses on hippocampal CA1 pyramidal neurons. Furthermore, we define a downstream signaling pathway involving PLC activation, release of Ca2+ from IP3R-dependent stores, and activation of PKC (see Figure 8 for model).