Serotonergic-linked alterations of aggression of the crayfish

Current theory suggests that aggressive behavior in the crayfish is largely modulated and regulated by the neurotransmitter serotonin (5-HT). To test this theory that links serotonin to aggression, we performed a series of drug treatments using various serotonin-related chemicals to measure their effects on subsequent aggressive behavior. Treatments included serotonin, the serotonin precursor tryptophan, agonists: 1-(3-chlorophenyl) piperazine (m-CPP) and 5-Carboxy, an antagonist: cinanserin, and a serotonin receptor specific neurotoxin: 5,7-dihydroxytryptamine creatinine sulfate (5,7-DHT). Significant increases in aggression of Faxonius rusticus crayfish were observed when injected with serotonin and both agonists, however no decrease in aggression occurred with the antagonist. Crayfish injected with the agonist m-CPP increased aggression but did not directly confer success in fights. Our data support the current literature that the internal aggressive state of crayfish is altered by serotonin and its agonist/antagonists, however it does not on its own improve the aggressive fighting response and/or dominance status.