Arginine vasopressin (AVP), released from the CNS, plays an important role in regulating several aspects of CNS functions including aggression, anxiety, and cognition. In this study, we report a novel finding that AVP induces glutamate release from astrocytes isolated from the cerebral cortex and hippocampus. We also investigated the types of AVP receptors involved in the AVP-induced increase in glutamate release from astrocytes isolated from the hippocampus and cortex of neonatal rats. We showed that the AVP (0.1-1000 nmol/L) induced increase in glutamate release and [Ca(2+)](i) is brought about by two distinct subtypes of V(1) receptors (V(1a) and V(1b)). Our results suggested that V(1b) receptors are predominantly expressed in astrocytes isolated from the hippocampus and V(1a) receptors are solely expressed in astrocytes isolated from the cerebral cortex of neonatal rats. The results of the western blot analyses confirmed these pharmacological data. In addition, the AVP-induced increase in glutamate did not contribute to an increase in [Ca(2+)](i), as blockade of metabotropic glutamate receptors did not alter the AVP-induced increase in [Ca(2+)](i). In addition, the administration of a phospholipase A(2) inhibitor failed to alter AVP-induced [Ca(2+)](i) increase suggesting the lack of involvement of this enzyme.