Mice heterozygous for both A1 and A2A adenosine receptor genes show similarities to mice given long-term caffeine

Caffeine is believed to exert its stimulant effects by blocking A2A and A1 adenosine receptors (A2AR and A1R). Although a genetic knockout of A2AR eliminates effects of caffeine, the phenotype of the knockout animal does not resemble that of caffeine treatment. In this study we explored the possibility that a mere reduction of the number of A1Rs and A2ARs, achieved by deleting one of the two copies of the A1R and A2AR genes, would mimic some aspects of long-term caffeine ingestion. The A1R and A2AR double heterozygous (A1R-A2AR dHz) mice indeed had approximately one-half the number of A1R and A2AR, and there were little compensatory changes in A2B or A3 adenosine receptor (A2BR or A3R) expression. The ability of a stable adenosine analog to activate receptors was shifted to the right by caffeine and in A1R-A2AR dHz tissue. Caffeine (0.3 g/l in drinking water for 7–10 days) and A1R-A2AR dHz genotype increased locomotor activity (LA) and decreased heart rate without significantly influencing body temperature. The acute stimulatory effect of a single injection of caffeine was reduced in A1R-A2AR dHz mice and in mice treated long term with oral caffeine. Thus at least some aspects of long-term caffeine use can be mimicked by genetic manipulation of the A1R and A2AR.