Alteration of c-Fos mRNA in the accessory lobe of crayfish is associated with a conditioned-cocaine induced reward.

The major molecular and anatomical substrates of drug related reward in mammals have received considerable attention. In contrast, molecular mechanisms and specific neuroanatomical targets of drug associated reward in invertebrate models of drug addiction have gone largely unexplored. With a modular nervous system amenable to molecular techniques, crayfish offer a novel system for simultaneously exploring molecular mechanism and neuroanatomical targets of cocaine-induced reward in an invertebrate system. We aimed to determine whether novelty in a cocaine-paired stimulus is accompanied by changes in c-Fos mRNA in the accessory lobe of crayfish. The first set of experiments revealed that cocaine-conditioned animals demonstrated reward in a drug-paired compartment in contrast to saline-conditioned animals. Following the expression of reward, we designed a second set of experiments to determine context-specificity of the cocaine-conditioned novelty effect in altering c-Fos mRNA expression in the accessory lobe of cocaine treated crayfish. This is the first report that characterized context-specific alteration of c-Fos mRNA expression in the accessory lobe of crayfish during drug-induced reward.