TIERNEY, A.J.*; AIG, S.D.; PERNA, A.M.; Colgate University; Colgate University; Colgate University: Serotonin and behavior in two crayfish species, Procambarus clarkii and Orconectes rusticus: effects of 5-HT₁ and 5-HT₂ receptor agonists.

Exogenous 5-HT induces an elevated, flexed posture in decapod crustaceans and has also been shown to affect aggressive and motor behaviors. Previous research has produced conflicting results, with some experiments suggesting that 5-HT enhances aggression and others reporting that the amine inhibits motor behavior, possibly leading to reduced aggression. The diverse behavioral effects of 5-HT in crayfish may be mediated by different receptor subtypes, and our experiments addressed this possibility using 5-HT₁ and 5-HT₂ receptor agonists. We selected drugs that have previously been shown to be active at invertebrate receptors and to display relatively specific action at different vertebrate 5-HT receptor subtypes. Agonists tested included 5-carboxamidotryptamine (5-CT), 1-(3-chlorophenyl)piperazine (mCPP), (+)-8-hydroxy-2-(di-n-dipropylamino) tetralin (8-OH-DPAT), 2,5-dimethoxy-4-iodoamphetamine (DOI), oxymetazoline, and CGS-12066A maleate (CGS). Posture and motor behavior were assessed in isolated male P. clarkii and O. rusticus following injections of 5-HT or a receptor agonist (10^-4 M to10^-2 M; 90-100 �l). Aggression was measured in pairs of interacting animals by recording the number and duration of specific agonistic behaviors following drug injection. mCPP and 8-OH-DPAT most closely mimicked the effects of 5-HT observed in our laboratory, causing animals to spend more time in the characteristic flexed posture and less time walking. Pairs of animals receiving mCPP and 8-OH-DPAT injections also displayed reductions in several agonistic behaviors. In current experiments, we are using additional 5-HT analogs to better characterize the receptor subtype that may mediate these behavioral changes.