Purpose: Adenosine is a neuromodulator that has been proposed to act as an anticonvulsant mainly via inhibitory A1 receptors, but recent data show that genetic deletion of facilitatory A 2A receptors might also attenuate convulsions. Since both A1 and A 2A receptors are prone to down- and upregulation in different stressful situations, we investigated if convulsive behavior leads to a long-term change in A1 and A 2A receptor density in the rat cerebral cortex.
Methods: Stage 4-5 convulsions (Racine's scale) were induced in adult Wistar rats either through amygdala stimulation (kindling) or by intraperitoneal injection of kainate (10 mg/ml). Rats were killed after 4 weeks to evaluate adenosine A1 and A 2A receptor density in the cerebral cortex using both Western blot and membrane binding assays.
Results: The binding density of the A1 antagonist, 3H-DPCPX, decreased by 40. +/- 4.4% and by 20.7 +/- 0.5% after kindling or kainate injection. Likewise, A1 receptor immunoreactivity in cortical membranes from kindled or kainate-injected rats decreased by 19.1 +/- 3.3% and 12.7 +/- 5.7%, respectively. In contrast, the binding density of the A 2A receptor antagonist 3H-SCH 58261 increased by 293 +/- 34% and by 159 +/- 32% in cortical membranes from kindled or kainate-injected rats, and A 2A receptor immunoreactivity also increased by 151 +/- 12% and 79.6 +/- 7.0%.
Conclusions: This indicates that after convulsive behavior there is a long-term decrease of A1 receptors accompanied by an increased density of A 2A receptors, suggesting that A 2A antagonists rather than A1 agonists may be more promising anticonvulsive drugs.