A new mouse line with reduced GluA2 Q/R site RNA editing exhibits loss of dendritic spines, hippocampal CA1-neuron loss, learning and memory impairments and NMDA receptor-independent seizure vulnerability.

Calcium (Ca2+)-permeable AMPA receptors may, in certain circumstances, contribute to normal synaptic plasticity or to neurodegeneration. AMPA receptors are Ca2+-permeable if they lack the GluA2 subunit or if GluA2 is unedited at a single nucleic acid, known as the Q/R site. In this study, we examined mice engineered with a point mutation in the intronic editing complementary sequence (ECS) of the GluA2 gene, Gria2. Mice heterozygous for the ECS mutation (named GluA2+/ECS(G)) had a ~ 20% reduction in GluA2 RNA editing at the Q/R site. We conducted an initial phenotypic analysis of these mice, finding altered current-voltage relations (confirming expression of Ca2+-permeable AMPA receptors at the synapse). Anatomically, we observed a loss of hippocampal CA1 neurons, altered dendritic morphology and reductions in CA1 pyramidal cell spine density. Behaviourally, GluA2+/ECS(G) mice exhibited reduced motor coordination, and learning and memory impairments. Notably, the mice also exhibited both NMDA receptor-independent long-term potentiation (LTP) and vulnerability to NMDA receptor-independent seizures. These NMDA receptor-independent seizures were rescued by the Ca2+-permeable AMPA receptor antagonist IEM-1460. In summary, unedited GluA2(Q) may have the potential to drive NMDA receptor-independent processes in brain function and disease. Our study provides an initial characterisation of a new mouse model for studying the role of unedited GluA2(Q) in synaptic and dendritic spine plasticity in disorders where unedited GluA2(Q), synapse loss, neurodegeneration, behavioural impairments and/or seizures are observed, such as ischemia, seizures and epilepsy, Huntington's disease, amyotrophic lateral sclerosis, astrocytoma, cocaine seeking behaviour and Alzheimer's disease.

Opioid and cannabinoid synergy in a mouse neuropathic pain model.

BACKGROUND AND PURPOSE: Clinical studies have reported that pan-cannabinoid receptor agonists may have efficacy in neuropathic pain states and that this might be enhanced by co-administration with opioids. While cannabinoid-opioid analgesic synergy has been demonstrated in animal models of acute pain, it has not been examined in neuropathic pain models. We examined the effect of combination treatment with cannabinoid and opioid receptor agonists on allodynia and side effects in a nerve injury-induced neuropathic pain model. EXPERIMENTAL APPROACH: C57BL/6 mice were subjected to chronic constriction injury (CCI) of the sciatic nerve. The effects of systemic administration of morphine and the pan-cannabinoid receptor agonist, WIN55212, on allodynia and side effects were examined at 7-10 days post-CCI surgery. Isobolographic analysis was used to determine whether the effects of the combination were synergistic. KEY RESULTS: The opioid agonist morphine reduced CCI-induced mechanical and cold allodynia and produced motor incoordination, in a dose-dependent manner. WIN55212 reduced CCI-induced allodynia and produced motor incoordination, catalepsy and sedation, in a dose-dependent manner, as we have observed previously. When administered together, WIN55212 and morphine reduced allodynia in a synergistic manner but had only an additive effect on motor incoordination. CONCLUSIONS AND IMPLICATIONS: These findings indicate that administration of a combination of a non-selective opioid and cannabinoid receptor agonist synergistically reduces nerve injury-induced allodynia, while producing side effects in an additive manner. This suggests that this combination treatment has an improved anti-allodynic potency and therapeutic index in a neuropathic pain model.