There are at least four subtypes of the adenosine receptor ¾ A1, A2A, A2B and A3 receptors. Adenosine receptors are all coupled to G-proteins and the A1 and A3 subtypes are associated with inhibitory G-proteins. Activation of the A1 and A3 receptors causes inhibition of adenylate cyclase and phospholipase C, which inhibits neurotransmission. The A1 receptors are highly expressed in the brain, especially in the hippocampus, thalamus, cerebellum and cortex. The A3 receptors are moderately expressed in the brain
There are at least four subtypes of the adenosine receptor ¾ A1, A2A, A2B and A3 receptors. Adenosine receptors are all coupled to G-proteins and the A2A and A2B subtypes are associated with stimulatory G-proteins. Activation of the A2A and A2B receptors causes activation of adenylate cyclase and phospholipase C, resulting in the stimulation of neurotransmission. A2A receptors are co-expressed in the brain with dopamine D2 receptors, especially in the striatum, olfactory tubercle and nucleus accumbens. Low levels of A2 receptors have been reported in the brains of rats.