“…Previous work has shown that peripheral or intra-VTA administration of glutamate antagonists is rewarding (Steinpreis et al, 1995;David et al, 1998;Panos et al, 1999) and can increase the rewarding properties of established cocaine reinforcement (Ranaldi et al, 1996;Pierce et al, 1997). Similar treatments, however, have also been shown to block learning reinforced by psychostimulants (Schenk et al, 1993;Cervo and Samanin, 1996;Kim et al, 1996) and to attenuate locomotor sensitization to psychostimulants (Kalivas and Alesdatter, 1993;Wolf and Jeziorski, 1993;Karler et al, 1994;Kim et al, 1996;Cornish et al, 2001). These findings indicate that glutamate antagonists do not alter the learning of cocaine reward because they are aversive (in fact they are rewarding), or because they decrease cocaine reward (they actually increase it if it has already been established).…”