In the mammalian central nervous system (CNS) coupling of neurons by gap junctions (electrical synapses) increases during early postnatal development then decreases but increases in the mature CNS following neuronal injury such as ischemia traumatic brain injury and epilepsy. an ischemic model. In addition three other injury models in mouse mature cortical cultures were used: hyposmotic shock as a model of cytotoxic and osmotic edemas that occur during stroke and TBI (Unterberg et al. 2004); hydrostatic pressure injury that represents mechanical aspects of TBI (Morrison et al. 1998); and administration of 4-aminopyridine to cultures as a model of epileptic seizures (Wong and Yamada 2001). In these models neuronal gap junction coupling and/or Cx36 expression were studied and showed a significant increase 2 hours post-injury (schematically illustrated in Physique 1d) (Wang et al. 2012). As stated earlier activation of group II mGluRs leads to increased neuronal gap junction coupling during Bortezomib (Velcade) development (Park et al. 2011). Since neuronal injury results in extensive and rapid release of glutamate from cells (Lobner and Choi 1994; De Cristobal et al. 2001; Guyot et al. 2001) we tested whether an activation of group II mGluRs by glutamate also produces up-regulation of neuronal gap junction coupling following injury. Indeed blockade of group II mGluRs prevented any injury-mediated increases in neuronal gap junction coupling and expression of Cx36. Consistent with this activation of group II mGluRs rapidly (within 1-3 hrs) increased the coupling and Cx36 expression in mature neuronal cultures and in the mouse cortex model of TBI in mice utilizing controlled cortical impact (Belousov et al. 2012). We concluded that neuronal gap junction coupling plays critical role in the injury-mediated neuronal death. We also suggested that group II mGluRs not only control the injury-mediated increase in neuronal gap junction coupling (Physique 1d) but via this regulation they also control the death/survival mechanisms in injured neurons (Physique 1e) (Wang et al. 2012; Belousov et al. 2012). The central role of neuronal gap junctions in neuronal death extends to a model of NMDAR-mediated excitotoxicity in adult mice (Wang et al. 2010). A single intraperitoneal administration of NMDA to wild-type (WT) mice induced 24 hrs later a substantial neuronal death in three regions of the forebrain: hippocampus (particularly rostral dentate gyrus) hypothalamus and medial habenula (Physique 2a b). This neuronal death was dramatically reduced by co-administration of mefloquine a relatively selective blocker Bortezomib (Velcade) for Cx36-made up of gap junctions and was statistically insignificant in Cx36 knockout mice (Physique 2c d). The expression of NR1 subunit of the NMDAR and the amplitude of NMDAR-mediated neuronal Ca2+ responses were not lower MRPS31 (but even higher) in Cx36 knockout than in WT mice suggesting that the reduced level of NMDAR-mediated neuronal death in Cx36 knockout animals is not due to the reduced expression or activity of NMDARs. In addition NMDA permeability of the blood-brain barrier (BBB) in the whole brain was not different between WT and Cx36 knockout mice suggesting that the reduced neuronal death in Cx36 knockout mice is not due to the reduced permeability of the BBB to NMDA. Finally mefloquine did not have any additional neuroprotective effects in Cx36 knockout mice (Physique 2e) indicating that the neuroprotective mechanism of mefloquine likely is based upon blockade of Cx36-made up of neuronal gap junctions. Physique 2 Inactivation of neuronal gap junctions prevents NMDAR-mediated neuronal death An interesting aspect in that study (Wang et al. 2010) was as indicated Bortezomib (Velcade) above that this NMDAR-mediated neuronal death was found in the forebrain only in three regions (Wang et al. 2010). This was observed in both WT (substantial neuronal death) and Cx36 knockout mice (statistically non-significant but still detectable neuronal death). Although permeability of the BBB in the whole brain to NMDA was not different between WT and Cx36 knockout mice we believe that the only logical explanation for neuronal death only in three forebrain regions is that somehow permeability of the BBB to NMDA in those three regions is higher than in the rest of the forebrain. Together these data supported Bortezomib (Velcade) a critical role for neuronal gap junctions in neuronal death following injury. They also suggested that this coupling of neurons by gap junctions is required for NMDAR-mediated.