The Cannabinoid WIN 55,212-2-Mediated Protection of Dentate Gyrus Granule Cells is Driven by CB1 Receptors and Modulated by TRPA1 and Cav2.2 Channels

Cannabinoids regulate numerous physiological and pathological events like inflammation or neurodegeneration via CB1 and CB2 receptors. The mechanisms behind cannabinoid effects show a high variability and may also involve transient receptor potential channels (TRP) and N-type voltage-gated Ca2+ channels (Ca(v)2.2). In the present study we investigated the neuroprotective effects of the synthetic cannabinoid WIN 55,212-2 (WIN) on dentate gyrus (DG) granule cells and elucidated the involvement of TRP and Ca(v)2.2 that are shown to participate in inflammatory processes. Organotypic hippocampal slice cultures were excitotoxically lesioned using NMDA and subsequently incubated with different WIN concentrations (0.001-10 mu M). WIN showed neuroprotective properties in an inverse concentration-dependent manner, most effectively at 0.01 mu M. The CB1 receptor antagonist AM251 blocked neuroprotection mediated by WIN whereas the CB2 receptor antagonist AM630 showed no effects. Application of the TRPA1 blocker HC-030031 enhanced the neuroprotective efficacy of high (10 mu M) WIN concentrations and the number of degenerating neurons became equal to that seen after application of the most effective WIN dose (0.01 mu M). In contrast, the application of TRPA1 agonist icilin or allyl isothiocyanate (AITC) led to a stronger neurodegeneration. The use of TRPA1 blocker 6-iodo-nordihydrocapsaicin did not affect WIN-mediated neuroprotection. The selective Ca(v)2.2 blocker omega-conotoxin (GVIA) completely blocked neuroprotection shown by 10 mu M WIN. GVIA and HC-030031 exerted no effects at WIN concentrations lower than 10 mu M. Our data show that WIN protects dentate gyrus granule cells in a concentration dependent manner by acting upon CB1 receptors. At high (10 mu M) concentrations WIN additionally activates TRPA1 and Ca(v)2.2 within the hippocampal formation that both interfere with CB1 receptor-mediated neuroprotection. This leads to the conclusion that physiological and pharmacological effects of cannabinoids strongly depend on their concentration and the neuroprotective efficacy of cannabinoids may be determined by interaction of activated CB1 receptor, TRPA1, and Ca(v)2.2. (C) 2010 Wiley-Liss, Inc.