Modulation of claw-closing behavior in the crayfishProcambarus clarkiiby extrinsic factors and biogenic amines

Abstract

Claw closure in the crayfish can be elicited by tactile stimulation of the closer-field sensory hairs located along the biting surfaces of the apposed dactyl and propodite. The possibility that this simple behavior can be extrinsically modulated was examined by stimulating closer-field hairs in specimens of the crayfish Procambarus clarkii while the animals were either unrestrained, restrained, or bathed in chemical feeding stimulants. Restraint increases both the probability of closure and the average angular velocity of the dactyl during closure compared with responses in unrestrained specimens. Chemical feeding stimulants increase the probability, but not the average angular velocity, of closure compared with the unrestrained condition. Injection of octopamine into unrestrained animals produces effects on claw closure that resemble those accompanying restraint. Injection of serotonin, however, is followed by decreases in both the probability and the average angular velocity of closure. It is argued that extrinsic factors modulate claw-closure behavior in ways appropriate to current circumstances, and that biogenic amines are implicated as "gain-setters" in this process.