Hyperreactivity, muricide, and intraspecific aggression in the rat produced by infusion of local anesthetic into the lateral septum or surrounding areas.

Intracranial infusions of a local anesthetic (lidocaine, 2%) were made bilaterally (4 microliter over 20 min) through permanently implanted cannulas ending in the lateral septum or adjacent areas. Increases in irritability and reactivity to the experimenter, muricide, and intermale aggression were produced by injections into the lateral septum and the region ventral to it. The increases in reactivity and interanimal aggresion occurred in varying degrees and were independent of one another, but intermale aggression occurred only in animals showing muricide. The most effective site for eliciting the entire spectrum of aggressive behaviors was the region ventral to the anterior septum. The region ventral to the posterior septum (medial preoptic area, anterior hypothalamic area, straia terminalis) was unique in that it tended to produce a high incidence of muricide, with only modest increases in reactivity. The lateral septum was moderately effective in producing the entire range of aggressive behaviors. No changes in behavior were noted with infusions into the medial septum or th medial forebrain bundle/lateral preoptic area ventrolateral to the septum. It is suggested that the hyperreactivity and irritability may be relat to hyperdefensiveness and that muricide and intermale aggression are points on a continuum of interanimal aggressiveness.