Mammal-Like Striatal Functions in Anolis

We used in situ autoradiographic ligand binding methods to determine the occurrence and distribution of dopamine D1 and D2 receptor sub-types in the anole lizard, Anolis carolinensis. Both were present and exhibited pharmacological specificity characteristics similar to those described for mammals. However, unlike in mammals where in the neostriatum [outside the nucleus accumbens/olfactory tubercle complex (NA/OT)] these receptors exhibit only slight dorsolateral (D2 high, D1 low) to ventromedial (D1 high, D2 low) gradients that co mingle extensively, in the anole striatum outside the NA/OT there was a striking laminar pattern, with little if any overlap between D2 (high in a dorsal band) and D1 (high ventral to the D2 band) distributions. As D1 receptors are related to the direct and D2 to the indirect basal ganglia (BG) subsystems in mammals, we also determined anole striatal distributions of pre-proenkephalin mRNA, a marker for striatal efferents to the indirect BG subsystem in mammals. Here, too, there was a striking laminar pattern, with pre-proenkephalin mRNA in a band similar to that seen for D2 receptors. The crisp neuroanatomical separation between these classic BG subsystem markers in Anolis striatum make this species attractive for the study of such systems'' functions during behavior.