Adenosine mechanisms and hypersensitive corticostriatal terminals in restless legs syndrome. Rationale for the use of inhibitors of adenosine transport.

Our working hypothesis is that a hypoadenosinergic state is a main pathogenetic factor that determines the sensory-motor symptoms and hyperarousal of restless legs syndrome (RLS). We have recently demonstrated that brain iron deficiency (BID) in rodents, a well-accepted animal model of RLS, is associated with a generalized downregulation of adenosine A receptors (A1R) in the brain and with hypersensitivity of corticostriatal glutamatergic terminals. Here, we first review the experimental evidence for a pivotal role of adenosine and A1R in the control of striatal glutamatergic transmission and the rationale for targeting putative downregulated striatal A1R in RLS patients, which is supported by recent clinical results obtained with dipyridamole, an inhibitor of the nucleoside transporters ENT1 and ENT2. Second, we perform optogenetic-microdialysis experiments in rats to demonstrate that A1R determine the sensitivity of corticostriatal glutamatergic terminals and the ability of dipyridamole to counteract optogenetically-induced corticostriatal glutamate release in both animals with BID and controls. Thus, a frequency of optogenetic stimulation that was ineffective at inducing cortico-striatal glutamate release in control rats became effective with the local perfusion of a selective A1R antagonist. Furthermore, in animals with and without BID, the striatal application of dipyridamole blocked the optogenetic-induced glutamate release and decreased basal levels of glutamate, which was counteracted by the A1R antagonist. The results support the clinical application of ENT1 inhibitors in RLS.