Antagonism of Adenosine A1 or A2A Receptors Amplifies the Effects of 3,4-Methylendioxymethamphetamine (MDMA) on Glial Activation in the Mouse Brain: Relevance to Caffeine-MDMA Interactions

Background: Previous studies by our group have demonstrated that caffeine, an antagonist of adenosine A1 and A2A receptors, amplifies the glial activation induced by 3,4-methylendioxymethamphetamine (MDMA, “ecstasy”) in mice. To elucidate the mechanisms underlying this effect, the present study evaluated whether selective antagonists for the A1 or the A2A adenosine receptor had any influence on MDMA-induced glial activation. Methods: MDMA (4 × 20 mg/kg) was administered to mice, alone or in combination with either the A1 antagonist DPCPX (0.5 mg/kg), or the A2A antagonist SCH 58261 (0.5 mg/kg). Immunoreactivity for complement type 3 receptor (CD11b) and glial fibrillary acidic protein (GFAP) was then studied in the striatum and substantia nigra pars compacta (SNc) to evaluate microglial and astroglial activation. Results: DPCPX amplified the elevation of both CD11b and GFAP immunoreactivity triggered by MDMA in the striatum, but did not affect MDMAinduced glial activation in the SNc. This effect was similar to that previously observed in mice treated with caffeine and MDMA in combination. Conversely, SCH 58261 potentiated MDMA-elicited elevation of CD11b immunoreactivity in both the striatum and SNc, but did not modify the effects of MDMA on GFAP in either region. Conclusions: These results demonstrate that both A1 and A2A receptors regulate MDMA-stimulated glial activation, and suggest that caffeine elicits the same effect chiefly by acting on A1 receptors