A low concentration (10 nM) of adenosine potentiated hippocampal neuronal activity via A2a adenosine receptors without affecting presynaptic glutamate release or postsynaptic glutamatergic conductance. Adenosine inhibited glutamate uptake through the glial glutamate transporter, GLT-1, via A2a adenosine receptors. In addition, adenosine stimulated GLT-1-independent glutamate release from astrocytes, possibly in response to a rise in intracellular Ca2+, via A2a adenosine receptors involving PKA activation. Those adenosine actions could lead to an increase in synaptic glutamate concentrations responsible for the potentiation of hippocampal neuronal activity. The results of the present study thus represent a novel neuromodulatory pathway with a glial contribution, bearing both inhibition of GLT-1 function and stimulation of glial glutamate release, as mediated via A2a adenosine receptors. GLIA 39:133–147, 2002. © 2002 Wiley-Liss, Inc.