A1 and A2A Receptors Modulate Spontaneous Adenosine but Not Mechanically Stimulated Adenosine in the Caudate.

Abstract

Adenosine is a neuromodulator, and rapid increases in adenosine in the brain occur spontaneously or after mechanical stimulation. However, the regulation of rapid adenosine by adenosine receptors is unclear, and understanding it would allow better manipulation of neuromodulation. The two main adenosine receptors in the brain are A1 receptors, which are inhibitory, and A2A receptors, which are excitatory. Here, we investigated the regulation of spontaneous adenosine and mechanically stimulated adenosine by adenosine receptors, using global A1 or A2A knockout mice. Results were compared in vivo and in brain slices' models. A1 KO mice have increased frequency of spontaneous adenosine events, but no change in the average concentration of an event, while A2A KO mice had no change in frequency but increased average event concentration. Thus, both A1 and A2A self-regulate spontaneous adenosine release; however, A1 acts on the frequency of events, while A2A receptors regulate concentration. The trends are similar both in vivo and slices, so brain slices are a good model system to study spontaneous adenosine release. For mechanically stimulated adenosine, there was no effect of A1 or A2A KO in vivo, but in brain slices, there was a significant increase in concentration evoked in A1KO mice. Mechanically stimulated release was largely unregulated by A1 and A2A receptors, likely because of a different release mechanism than spontaneous adenosine. Thus, A1 receptors affect the frequency of spontaneous adenosine transients, and A2A receptors affect the concentration. Therefore, future studies could probe drug treatments targeting A1 and A2A receptors to increase rapid adenosine neuromodulation.