We investigated the effect of adenosine on astrocyte morphology by using cell cultures prepared from the cerebral cortices of neonatal rats. Cultured rat cortical astrocytes exhibited flattened, polygonal morphology in the absence of stimulation, but differentiated into process-bearing stellate cells in response to adenosine (1-1000 microM). Adenosine-induced astrocyte stellation was abolished by treatment with microtubule inhibitors, colchicine and paclitaxel, indicating the involvement of cytoskeletal elements. The effect of adenosine was mimicked by other adenosine receptor agonists, and blocked by adenosine receptor antagonists and guanosine 5'-O-(2-thiodiphosphate), indicating that the effect of adenosine is mediated by G protein-coupled adenosine receptors. Although adenosine receptors are known to be linked to adenylate cyclase or phospholipase C, adenosine did not change intracellular cyclic AMP level nor intracellular Ca2+ concentration in astrocytes. Alternatively, adenosine-induced stellation was abolished by tyrosine phosphatase inhibitors, orthovanadate and phenylarsine oxide, suggesting that adenosine causes astrocyte stellation through tyrosine dephosphorylation. Adenosine may function as a factor regulating astrocyte differentiation.