Opposite effects of the A2A receptor agonist CGS21680 in the striatum of Huntington's disease versus wild-type mice

Huntington's disease (HD) is an inherited neurodegenerative disorder. Adenosine A2A receptors (A2ARs) are involved in excitotoxic/neurodegenerative processes, and A2AR ligands may be neuroprotective in models of HD. However, changes in the transcription, expression and function of A2ARs have been reported to occur in HD models. The aim of the present work was to verify whether A2AR-mediated effects are altered in the striatum of transgenic HD (R6/2) versus wild-type (WT) mice. Extracellular field potentials (FPs) were recorded in corticostriatal slices from R6/2 mice in early (7-8 weeks) or frankly (12-13 weeks) symptomatic phases, and age-matched WT. In 12-13 weeks aged WT animals, the application of 75 μM NMDA induced a transient disappearance of the FP followed by an almost complete recovery at washout. In slices from HD mice, the mean FP recovery was significantly reduced (P < 0.01 versus WT). A2AR activation oppositely modulated NMDA-induced toxicity in the striatum of HD versus WT mice. Indeed, the A2AR agonist CGS21680 reduced the FP recovery in slices from WT mice, while it significantly increased it in slices from R6/2 mice. In early symptomatic (7-8 weeks) mice, no differences were observed between WT and HD animals in terms of basal synaptic transmission and response to NMDA. At the same age, the behavioural effects elicited by CGS21680 were qualitatively identical in WT and HD mice. These findings may have very important implications for the neuroprotective potential of A2AR ligands in HD.