Autoradiography of L-[3H]aspartate binding sites

The distribution, pharmacology and binding properties of L-[3H]aspartate were determined in sections from rat brain. No binding was detected in the absence of sodium ions. With the addition of sodium ions to the incubation medium, binding was found to be NMDA, AMPA and CNQX insensitive, but was potently inhibited by threo-beta-hydroxyaspartate, D-aspartate and L-2,4 trans-pyrrolidine dicarboxylate; compounds which have been shown to be specific inhibitors of the sodium-dependent EAA transporter. Autoradiography of L-[3H]aspartate closely resembled the pattern of sodium-dependent D-[3H]aspartate binding. Cerebellar binding showed higher affinity and maximal levels of binding than forebrain, consistent with reports of heterogeneous populations of sodium-dependent EAA binding sites. These results suggest that under these conditions, L-[3H]aspartate specifically labels the sodium-dependent EAA transporter.