Caffeine, Adenosine Receptors, and Synaptic Plasticity

Few studies to date have looked at the effects of caffeine on synaptic plasticity, and those that did used very high concentrations of caffeine, whereas the brain concentrations attained by regular coffee consumption in humans should be in the low micromolar range, where caffeine exerts pharmacological actions mainly by antagonizing adenosine receptors. Accordingly, rats drinking caffeine (1 g/L) for 3 weeks, displayed a concentration of caffeine of circa 22 mu M in the hippocampus. It is known that selective adenosine A(1) receptor antagonists facilitate, whereas selective adenosine A(2A) receptor antagonists attenuate, long term potentiation (LTP) in the hippocampus. Although caffeine is a non-selective antagonist of adenosine receptors, it attenuates frequency-induced LTP in hippocampal slices in a manner similar to selective adenosine A(2A) receptor antagonists. These effects of low micromolar concentration of caffeine (30 mu M) are maintained in aged animals, which is important when a possible beneficial effect for caffeine in age-related cognitive decline is proposed. Future studies will still be required to confirm and detail the involvement of A(1) and A(2A) receptors in the effects of caffeine on hippocampal synaptic plasticity, using both pharmacological and genetic approaches.