Adenosine A1 receptors are crucial in keeping an epileptic focus localized.
Adenosine is an endogenous neuromodulator with anticonvulsant and neuroprotective properties presumably mediated by activation of adenosine A1 receptors (A1Rs). To study the involvement of A1Rs in neuroprotection during epileptogenesis, we induced status epilepticus by a unilateral intrahippocampal kainic acid (KA) injection (1 nmol) in wild-type C57BL/6 and homozygous adenosine A1R knock out (A1R-KO) mice of the same genetic background. Whereas the KA injection caused non-convulsive status epilepticus in wild-type mice, in A1R-KO mice KA induced status epilepticus with severe convulsions and subsequent death of the animals within 5 days. 24 h after KA injection, brains from wild-type C57BL/6 mice were characterized by slight neuronal cell loss confined to the immediate location of the KA injection. In contrast, KA-injected A1R-KO mice displayed massive neuronal cell loss in the ipsilateral hippocampus, and, importantly, the contralateral hippocampus was also affected with significant cell loss in the hilus and in the CA1 region of the pyramidal cell layer. We conclude that activation of A1 receptors by ambient adenosine is crucial in keeping epileptic foci localized. These results open up a new dimension of the A1 receptor's role in controlling excitotoxic cell death and further demonstrate its importance in preventing the progression of status epilepticus to lethal consequences.