minals. Our biochemical and immunohistological results show that AMPARs and their associated scaffold proteins present in the brain 5 February 2012 | Volume 7 | Issue 2 | e31451 Development of Glutamatergic Synapses postsynaptic densities were expressed by muscle cells and form complexes with rapsyn, a component of the scaffolding protein, that it is required to receptor clustering. These data are consistent with previously published work in which skeletal muscles are surgically innervated by spinal glutamatergic fibers. Analysis of GluR1 immunoprecipitates revealed the presence of rapsyn in membrane of myotube-neuron cocultures. In rapsyn-immunoprecipitates we detected GluR1 subunit together with stargazin, a scaffolding protein necessary for the AMPA receptor targeting to the synaptic membrane. Confocal analysis of immunofluorescence staining confirmed the co-localization of rapsyn with either GluR1 or stargazin. Differently from stargazin, SAP97, the key regulator of AMPA receptor trafficking, decreased in cocultured myotubes when compared to pure myotubes cultures, suggesting that in innervated muscle cells GluR1 subunits were stably inserted at the postsynaptic membrane. No change was present in the PSD95 content of the myotubes cultured with and without neurons, also confirming previous evidence. These data are further supported by electrophysiological analysis. In calcium imaging experiments, electrical stimulation of axons induced calcium increases in myotubes that were insensitive to the AChR blocker, curare, but totally prevented by GYKI 52466, the selective 19071018” blocker of glutamate AMPA receptors. Taken together, these findings expand on previous evidence showing that glutamatergic presynaptic terminals are able to induce a functional postsynaptic membrane structure in muscle cells. Synapse formation is the result of a complex and highly regulated process of membrane and molecular interactions between pre and postsynaptic components. Several works showed the fundamental role of electrical activity, genetic and transcription factors and signaling proteins in the synaptic assembling. However, one of the most intriguing question about buy 16037-91-5Sodium stibogluconate synaptogenesis is how the matching between neurotransmitter phenotype and the appropriate postsynaptic receptor is obtained. It has been hypothesized that this process could arise ” in a number of different ways: 1) the presynaptic terminal induces the expression of the appropriate receptors in postsynaptic membrane independently on the receptors already present on the membrane; 2) the postsynaptic structure activates the expression 
of a wide range of receptors and the presynaptic element chooses the appropriate receptor. In support of the former idea, Brunelli et al. have shown that in a particular reinnervation model, in which descending glutamatergic fibers of adult rat were diverted in the spinal cord to skeletal muscle by means of a peripheral nerve graft, the cholinergic synapses switch to the glutamatergic type. Additionally, February 2012 | Volume 7 | Issue 2 | e31451 Development of Glutamatergic Synapses Spitzer et al. have shown that embryonic muscle cells of Xenopus initially express several classes of transmitter receptors in addition to those for ACh. During normal differentiation and innervation of muscle, the other classes of receptors disappear. Changing the expression of transmitters by altering calcium spike activity leads to retention of the classes of cognate, non cholinergic receptor