In vitro studies have shown that kainic acid (10(-6) M) but not N-methyl-D-aspartate (NMDA) in the same concentration reduces the number of striatal [3H]glutamate binding sites and increases their affinity in striatal membranes. In vitro studies also show that L-glutamate (10(-8) M) but not NMDA (10(-6) M) increases the number of [3H]kainic acid binding sites and reduces their affinity in striatal membranes. Ibotenic acid (10(-6) M) can also reduce the affinity of [3H]kainic acid binding sites in striatal membranes. These results give indications for the existence of bidirectional receptor-receptor interactions between two receptors for excitatory amino acids in local striatal circuits. These interactions could partly explain the involvement of glutamate in kainate neurotoxicity.