Combined neuroprotective action of adenosine A1 and cannabinoid CB1 receptors against NMDA-induced excitotoxicity in the hippocampus

Both adenosine A1 and cannabinoid CB1 receptors trigger similar transduction pathways and protect against neurotoxic insults at the hippocampus, but their combined neuroprotective potential has not been investigated. We set forth to assess the combined action of A1 and CB1 receptors against glutamate NMDA receptor-mediated excitotoxicity at the hippocampus. Cell damage was assessed by measuring propidium iodide (PI) uptake and lactate dehydrogenase (LDH) activity released from cultured hippocampal slices exposed to NMDA. Exposure to NMDA (50 µM) for 1 h increased LDH activity by 92% ± 16%. WIN55212-2 (30 µM), a cannabinoid CB1 receptor agonist, decreased NMDA-induced LDH activity by 53% ± 10% while N6-cyclopentyladenosine (CPA, 100 nM), an adenosine A1 receptor selective agonist, decreased it by 37% ± 11%. The combined inhibitory effect of WIN55212-2 and CPA (88% ± 12%) did not differ from the sum of the individual inhibitory effects of each agonist (90% ± 15%) but was different from the effects of CPA or WIN55212-2 alone. An additive inhibitory effect of co-application of WIN55212-2 (30 µM) and CPA (100 nM) on NMDA (50 µM)-induced PI uptake was also observed in CA3 but not in CA1 area of the hippocampal slice. The results suggest that both CB1 and A1 receptors produce additive cumulative neuroprotection against NMDA-induced excitotoxicity in the hippocampus.