Serotonin and aggression: insights gained from a lobster model system and speculations on the role of amine neurons in a complex behavior

The amine serotonin has been suggested to play a key role in aggression in many species of animals, including man. Precisely how the amine functions, however, has remained a mystery. As with other important physiological ques tions, with their large uniquely identifiable neurons, invertebrate systems offer special advantages for the study of behavior. In this article we ill ustrate that principal with a description of our studies of the role of ser otonin in aggression in a lobster model system. Aggression is a quantifiabl e behavior in crustaceans, the amine neuron systems believed to be importan t in that behavior have been completely mapped, and key physiological prope rties of an important subset of these neurons have been defined. These resu lts are summarized here, including descriptions of the "gain-setter" role a nd "autoinhibition" shown by these neurons. Results of other investigations showing socially modulated changes in amine responsiveness at particular s ynaptic sites also are described. In addition, speculations are offered abo ut how important developmental roles served by amines like serotonin, which have been well described by other investigators, may be related to the beh aviors we are examining. These speculations draw heavily from the organizat ional/activational roles proposed for steroid hormones by Phoenix et al. (1 959).