Abstract
Although the avian brain dopamine system and its functions have been studied much less than the mammalian one, there is an increasing interest in the role of dopamine and its receptors in a wide variety of motor, cognitive and emotional functions in birds with implications for basic research, medicine or agriculture. Pharmacological characterisation of the avian dopamine receptors has had little attention. In this paper we characterise the two classes of dopamine receptors in Japanese quail brain by radioligand binding techniques using [(3)H]SCH 23390 (D(1)) and [(3)H]spiperone (D(2)). Association, dissociation and saturation analyses showed that the binding of both radioligands is time- and concentration-dependent, saturable and reversible. Apparent dissociation constants determined for [(3)H]SCH 23390 and [(3)H]spiperone from concentration isotherms were 1.07 and 0.302 nM and the maximum binding capacities were 89.3 and 389.3 fmol per mg of protein, respectively. Using competitive binding studies with a spectrum of dopamine and other neurotransmitter receptor agonists/antagonists, the [(3)H]SCH 23390 and [(3)H]spiperone binding sites were characterised pharmacologically. Pharmacological profiles of quail dopamine receptors showed a high degree of pharmacological homology with other vertebrate dopamine receptors. The data presented extend the knowledge of kinetics and pharmacology of D(1)- and D(2)-like dopamine receptors in birds, provide data for avian psychopharmacological and comparative studies and represent an important complement to studies using cell expression systems.