The distribution and function of DL-[3H]2-amino-4-phosphonobutyrate binding sites in the rat striatum

The binding of the glutamate-like radioligand, DL-[3H]2-amino-4-phosphonobutyrate (DL-[3H]APB), to L-glutamate-sensitive sites in the rat striatum was investigated. A single, saturable population of binding sites, indistinguishable from that characterized previously on rat whole brain synaptic membranes, was identified. The effects of specific lesions of the striatum: decortication; striatal injection of kainic acid; and 6-hydroxydopamine injections into the substantia nigra, were also examined. Specific DL-[3H]APB binding in the striatum was elevated significantly following decortication. An increase in the number of binding sites was found to be responsible for this enhancement in binding. Lesions of the postsynaptic targets of corticostriatal fibres reduced the number of DL-[3H]APB binding sites in the striatum without affecting binding site affinity. This finding suggests that L-APB sensitive excitatory amino acid receptors are located predominantly on membranes derived from structures postsynaptic with regard to the glutamatergic innervation. The possible physiological role of these receptors was examined using an in vitro release technique. Both L-glutamate and L-APB were found to facilitate potassium evoked [3H]dopamine release from striatal slices. This finding supports the proposed existence of functional acidic amino acid receptors on dopaminergic terminals in the striatum. These receptors may play an important role in the control of motor function.