Mammal-Like Striatal Functions in <i>Anolis</i>

Abstract

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 (D₁high, 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.