Ethological analyses of crayfish behavior: a new invertebrate system for measuring the rewarding properties of psychostimulants.

Recent investigations in invertebrate neurobiology have opened up a new line of research into the basic behavioral, neurochemical and genomic alterations that accompany psychostimulant drug exposure. However, the extent to which such findings relate to changes in motivational and learning processes, such as those that typify drug addictions, remains unclear. The present study addressed this issue in the crayfish, Orconectes rusticus. The first set of experiments demonstrated that intramuscular injections of cocaine and amphetamine have robust and distinguishable effects on crayfish behavior. In the second part of the study, the reinforcing properties of psychostimulants were tested in a series of conditioned place preference experiments. Amphetamine and, to a lesser extent, cocaine were both found to serve as rewards when their intra-circulatory infusion was coupled to a distinct visual environment. The monoaminergic regulation of behavior has been extensively studied in decapod crustaceans and the present experiments demonstrated that (mammalian) drugs of abuse, capable of interfering with monoamine chemistry, are similarly rewarding to crayfish. Behavioral studies in crayfish can provide a complementary approach to using other invertebrate species in addiction research.