Modulation of the balance between cannabinoid CB(1) and CB(2) receptor activation during cerebral ischemic/reperfusion injury

Cannabinoid receptor activation has been shown to modulate both neurotransmission (CB(1)) and neuroinflammatory (CB(2)) responses. There are conflicting reports in the literature describing the influence of cannabinoid receptor activation on ischemic/reperfusion injury. The goal of this study was to evaluate how changing the balance between CB(1) and CB(2) activation following cerebral ischemia influences outcome. CB(1) and CB(2) expression were tested at different times after transient middle cerebral artery occlusion (MCAO) in mice by real-time RT-PCR. Animals subjected to 1 h MCAO were randomly assigned to receive different treatments: a CB(1) antagonist, a CB(2) antagonist, a CB(2) agonist, a CB(1) antagonist plus CB(2) agonist, a CB(2) antagonist plus CB(2) agonist or an equal volume of vehicle as control. Cerebral blood flow was continuously monitored during ischemia; cerebral infarction and neurological deficit were tested 24 h after MCAO. Cerebral CB(1) and CB(2) mRNA expression undertook dynamic changes during cerebral ischemia. The selective CB(1) antagonist significantly decreased cerebral infarction by 47%; the selective CB(2) antagonist increased infarction by 26% after 1 h MCAO followed by 23 h reperfusion in mice. The most striking changes were obtained by combining a CB(1) antagonist with a CB(2) agonist. This combination elevated the cerebral blood flow during ischemia and reduced infarction by 75%. In conclusion, during cerebral ischemia/reperfusion injury, inhibition of CB(1) receptor activation is protective while inhibition of CB(2) receptor activation is detrimental. The greatest degree of neuroprotection was obtained by combining an inhibitor of CB(1) activation with an exogenous CB(2) agonist.