The pharmacology of a dopamine receptor in the locust nervous tissue

A dopamine receptor in the nervous tissue of the desert locust (Schistocerca gregaria Forskâl) was studied using ¿3Hlysergic acid diethylamide (LSD) as the radioligand. Its expression is almost entirely restricted to the mushroom bodies, centres for learning and memory in the insect brain. This G-protein coupled receptor is present in relatively low concentrations in the locust brain (35 fmol/mg protein). The pharmacological characterisation reveals high affinity for the putative natural agonist dopamine (K(i)=28 nM). Substances with high subtype specificity for vertebrate dopamine receptors such as SCH 23390 (K(i)=639 nM) and sulpiride (K(i)=21,200 nM) have low affinity for the locust neuronal dopamine receptor. In opposite, substances with a broad pharmacological profile such as LSD, spiperone (K(i)=7.26 nM), and chlorpromazine (K(i)=9.52 nM) have high affinity properties. Comparison of the pharmacological data reveals no significant homology to any vertebrate dopamine receptor class characterised so far. This uncertainty about the pharmacological relatedness of insect dopamine receptors mirrors the available molecular data. It is almost impossible to classify cloned insect dopamine receptors into vertebrate dopamine receptor schemes. This lack of pharmacological relatedness opens the opportunity to develop highly specific insecticides against insect dopamine receptors.