Adenosine is an important neuromodulator. In the present study, we used mice with expression of human ENT1 (hENT1) and deficiency of CD73, respectively, to address the relative importance of intracellular and extracellular pathways in adenosine regulation. [3H]Nitrobenzylthioinosine binding assays were performed and found increased expression of hENT1 with increased gene dose. We performed a series of behavioural experiments with caffeine and ethanol and compared hENT1 heterozygous and homozygous transgenic mice to their wild type littermates. We found that the expression of hENT1 leads to a change in behavioural responses relative to wild type mice, but no sign of a gene dose dependent increase was observed. With CD73 knockout mice, we performed a series of behavioural experiments with caffeine and ethanol that showed a change in adenosine related behaviours. We also performed experiments that tested anxiety-like behaviours and found reduced anxiety-like behaviours with CD73 knockout mice relative to wild type mice. These studies show that mice with enhanced expression of ENT1 or knockout of CD73 have altered extracellular level of adenosine.