SEROTONIN ALTERS DECISIONS TO WITHDRAW IN FIGHTING CRAYFISH, ASTACUS-ASTACUS - THE MOTIVATIONAL CONCEPT REVISITED

The biogenic amine serotonin is thought to play an important role in a ggression in many species, including man. This paper summarizes experi mental approaches which attempt to link this neuromodulator with fight ing in a crayfish model for which the complex agonistic behavior is we ll characterized. Based on a quantitative analysis of fighting we demo nstrate that the infusion of small amounts of serotonin into freely-mo ving crayfish alters fighting behavior by specifically interfering wit h the timing of a treated animal's decision to withdraw from an encoun ter. In the presence of added serotonin, fights last considerably long er compared to controls, but no changes were detected in the rules of escalation, the likelihood of initiating an interaction, or its eventu al outcome. Attempts to dissect the underlying neuronal mechanisms pha rmacologically hinged on fluoxetine as a potent inhibitor of serotonin re-uptake. Although no behavioral changes were associated with acute infusion of fluoxetine alone, in combination with serotonin it effecti vely prevented the previously observed fight-enhancing effects. Our da ta strongly support the significance of functional amine reuptake mech anisms for behavior and continued use of this invertebrate model shoul d prove a promising route to unravel further the complex bases of aggr ession.