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

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Abstract
Intracranial infusions of a local anesthetic (lidocaine, 2%) were made bilaterally (4 .mu.l 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 aggression occurred in varying degrees and were independent of 1 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, stria 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 the medial forebrain bundle/lateral preoptic area ventrolateral to the septum. The hyperreactivity and irritability may be related to hyperdefensiveness and that muricide and intermale aggression are points on a continuum of interanimal aggressiveness.