1Mice in small groups develop a despotic type of social hierarchy, a feature of which is to resist alteration through the medium of psychotropic drugs. This makes a rapid pharmacologically induced change in the social hierarchy impossible. 2 Patrolling the territory and a certain level of social interaction are both critical factors in maintaining the phenomenon of inertia in the social hierarchy. Psychotropic drugs (diazepam, droperidol and mescaline) altered both these factors to a varying degree and also displayed a differing ability to maintain the inertia of the social hierarchy. 3 A drug-induced alteration in the level of aggression in a subordinate mouse in a group of three does not cause an alteration in its social position. 4 Chronic administration of diazepam, droperidol or mescaline, all of which alter the level of aggression in different ways, can result in an inversion of the social hierarchy where a competitive rival is present in the group of mice. The rate of inversion of the social hierarachy depends on the type of pre-existing social hierarchy. 5 It is suggested that the ability of psychotropic drugs to maintain the inertia of the hierarchy be used as an index of their effect upon certain types of species-specific behaviour; in particular aggression.

Experiments on mice have demonstrated changes in the relationships, interdependence and sequence of behavioral items following prolonged isolation. It was found that aggression in isolates was stereotyped and hardly amenable to the control not only by intraspecific but also by interspecific factors. Isolated mice, in contrast to the group‐reared animals, spontaneously attacked adult rats. This finding was interpreted as being due to a disruption of behavioral plasticity under circumstances of prolonged isolation from conspecifics.

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612.821.i/.3.014.46:547.95:547.943 and M. I. Titov KEY WORDS: aggression; defense; intraspecific behavior; met-enkephalin; leu-enkephalin.The role of enkephalins and their analogs in the regulation of mechanisms of memory, analgesia, certain motor acts, and autonomic reactions has been demonstrated recently [4,[6][7][8]. However, the spectra of their action on intraspecific (zoosocial) behavior have not been analyzed.The aim of the present investigation was to analyze the spectrum of action of met-and leu-enkephalins and of the tetrapeptide Tyr-D-AIa-GIy-Phe-NH2 on various forms of intraspecific behavior of isolated aggressive mice and to compare it with the analgesic activity of these peptides.Identification and analysis of effects of this sort are important in order to understand the role of endogenous peptides and their synthetic analogs in the regulation of complex forms of behavior. EXPERIMENTAL METHODExperiments were carried out on 30 male CC57W mice kept in single cages for 12 weeks. Free interaction of an aggressive isolant with a standard partner from the group was recorded by means of a special combination of Ethograph and EC 1022 computer [3]. The frequency and order of appearance of 25 different behavioral acts and postures of the isolated animal were recorded.All acts and postures were classified in motivation categories and coded on a binary code for computer analysis.The behavioral acts were subdivided into categories characterizing zoosocial behavior (intraspecific sociality), aggression, ambivalent (double motivational) behavior, defense, and individual behavior ( Table I). The degree of analgesia was estimated in points on the basis of behavioral criteria [i, 2]. Met-and leu-enkephalins and the tetrapeptide were injected intraperitoneally in a volume of 0.i ml/10 g body weight.Metenkephalin also was injected into the lateral ventricle in doses of 50 ~g. The effects were assessed 5 and 30 min after injection of the preparations.The significance of the results was estimated by means of Wilcoxon's nonparametric criterion for conjugate sets. EXPERIMENTAL RESULTSMet-enkephalin in a dose of 50 mg/kg increased the likelihood of an aggressive attack on the partner 5 min after systemic injection (Table i), reduced intraspecific sociality, potentiated ambivalent forms of behavior, and reduced the likelihood of individual forms of behavioroIn the above-mentioned doses, met-enkephalin did not cause analgesia, as assessed by behavioral criteria (n = 6, T A = O; P <0~ ~fter 30 min the frequency of overt aggressive acts was close to the control values, but threatening manifestations were increased, as also was vertical motor activity (standing up on the hind limbs).Leu-enkephalin, in a dose of 50 mg/kg, reduced intraspecific sociality after 5 min (Table I) and potentiated aggressive behavior.Unlike met-enkephalin, leu-enkephalin induced defensive behavior in the mice, which was not observed in the control.Leu-enkephalin depressed dynamic and intensified static (sitting) forms of individual behavior.After 3...