l-Glutamate reduces the affinity of [3H]N-propylnorapomorphine binding sites in striatal membranes

l-Glutamate but not methyl-D-aspartate (NMDA) or quisqualate ( Quis ) (10(-6 M) in vitro with or without preincubation increased significantly the KD value of the [3H]N-propylnorapomorphine ( [3H]NPA) binding sites by 21 and 36% respectively in striatal membranes of rat without influencing the striatal [3H]spiperone binding sites. The number of striatal [3H]NPA binding sites was not changed by l-glutamate (10(-6) and 10(-5) M) in vitro. There may thus exist interactions between striatal glutamate receptors -- not related to excitatory amino-acid receptors of the NMDA or the QUIS type -- and high affinity striatal DA receptors.