According so Snyder et al, caffeine differs from adenosine in that caffeine______
A.stimulates behavior. in the mouse and in humans, whereas adenosine stimulates behavior. in humans only
B.has mixed effects in the brain, whereas adenosine has only a stimulatory effect
C.increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrations
D.permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such release
E.inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing