ADENOSINE A(1) RECEPTOR-DOPAMINE D-1 RECEPTOR INTERACTION IN THE RAT LIMBIC SYSTEM - MODULATION OF DOPAMINE D-1 RECEPTOR ANTAGONIST BINDING-SITES

Antagonistic interactions between adenosine A(2a) and dopamine D-2 rec eptors and between adenosine A(1) and dopamine D-1 receptors have been previously found in the basal ganglia. Those interactions have been p roposed to be key mechanisms of action responsible for the motor depre ssant effects of adenosine agonists and the motor activating effects o f adenosine antagonists, like caffeine. By using quantitative receptor autoradiography, the selective adenosine A(1) receptor agonist N-6-cy clopentyladenosine was found to decrease the affinity of dopamine D-1 receptors for the specific D-1 antagonist [I-125]SCH 23982 in both the nucleus accumbens and the medial prefrontal cortex of the rat brain. The present results suggest that dopamine neurotransmission, through a n A(1)-D-1 interaction, might also be involved in the behavioural effe cts of adenosine agonists and antagonists not related to motor activit y, like the sedative-hypnogenic properties of adenosine analogues and the psychostimulant effects of caffeine.