A1 ADENOSINE RECEPTOR REGULATES ATP-MEDIATED MICROGLIAL ACTIVATION IN VIVO AND IN VITRO: ROLE IN THE SPINAL NEURONAL PLASTICITY IN NEUROPATHIC MICE

Microglia are central nervous system (CNS) resident cells that sense pathological tissue alterations. Several microglia functions are governed by the purinergic system due to the presence on these cells of P1 and P2 (P2X, P2Y) receptors for adenosine and ATP/ADP, respectively. The P2X4 and P2X7 receptors are involved in microglia chemotaxis and activation processes. Recently, it has been demonstrated that also adenosine A2A receptors (A2AARs) are over-expressed in LPS-activated microglia and mediate microglial process retraction. The expression and function of A1AR in microglia remains a sort of mystery. Indeed, while the role of A1AR on macrophages/microglia in several CNS diseases has been reported, recent important data suggested that neither resting nor LPS-activated microglia express this receptor. Because of this puzzling confusion, we believed it worthwhile to clarify the effective existence of microglial A1AR and give the basis to investigate a possible functional role in microglia. Thus, we isolated primary microglial cells from neonatal (P2) mice and checked for A1AR through several approaches. Once we ascertained its expression and regulation by different stimuli, we performed functional experiments by using immunocytochemistry, live microscopy and live calcium imaging in vitro. Finally, we attempted to assign a function to this receptor through an in vivo electrophysiological approach. The data showed that the A1AR receptor is expressed by microglial cells and is positively regulated by ATP. Moreover, the A1AR selective stimulation is able to reduce the calcium-dependent morphological changes in microglia. Therefore, our data demonstrate that A1AR is expressed by microglia. The possible role of this receptor could be related to the cytoskeletal rearrangement of microglia occurring in migration or activation processes, as it has been also suggested recently for A2AAR. This study paves the way for further studies finalized to understand the effective role of A1AR on microglia