The fight and flight responses of crickets depleted of biogenic amines

Aggressive and escape behaviors were analysed in crickets (Orthoptera) trea ted with either reserpine, a nonspecific depleter of biogenic amines, or th e synthesis inhibitors alpha-methyltryptophan (AR ITP) and alpha-methyl-p-t yrosine (AMT) to specifically deplete serotonin, respectively dopamine and octopamine, Standard immunocytochemical techniques were used to verify depl etion from central nervous tissue, and determine the effective dosages, Res erpinized crickets became exceedingly lethargic and had severely depressed escape responses. However, they were still able to express all the major el ements of the escalating sequences of stereotype motor performances that ty pifies normal aggressive behavior in the cricket. AMT and AMTP treatment ha d opposing influences on escape behavior, being enhanced by serotonin deple tion, but depressed by dopamine/octopamine depletion. AMTP-induced serotoni n depletion had no influence on aggressive or submissive behaviors. AMT-tre ated crickets could normally only be brought to fight by coaxing. Though ca pable of expressing aggressive behavior per se, agonistic encounters betwee n AMT-treated crickets were shorter, and rarely involved actual physical in teractions. Hence, although amines seem to have similar actions on escape b ehavior in insects and crustaceans, the aminergic control of aggression see ms to be fundamentally different in these arthropods groups. We conclude th at amines are not in principle required for the initiation and operation of the motor circuits underlying aggression in the cricket. However, octopami ne and/or dopamine seem necessary for establishing a level of excitability sufficient for aggressive behavior to become overt in response to appropria te natural releasing stimuli. (C) 2000 John Wiley & Sons, Inc. J neurobiol 43: 107-120, 2000.