Behavioral study in rats of paired accumbens-lesioned residents and intact intruders.

Behavior in accumbens-lesioned male Wistar rats during paired encounters was assessed by several parameters, scores and cluster analysis based on similarity between patterns. Encounters were videotaped and analyzed by an ethogram and a software package previously elaborated. Residents were lesioned (n = 23) or sham operated (n = 10). A reactivity score was used to corroborate the effectiveness of the lesions. Although accumbens lesions produced the well-known increase in reactivity and enhancement of piloerection, only subtle changes were elucidated by the ethological analysis. Dendrograms revealed postoperative changes in the lesioned rats as well as in the intruders paired with them. Threat category in the lesion group dissociated in threat with arched-back attitude and threat with erect posture. In intruders paired with lesioned rats, compared with those paired with sham-operated animals, the patterns of freezing and on-back became mainly associated with immobile-crouch instead of upright defense posture, and the category of defense/submission was not observed in dendrograms.