Behavioural Processes, 10 (1985) 341-354 Elsevier ETHOLOGICAL ANALYSES OF THE EFFECTS ICI 154, 129 ON SOCIAL INTERACTIONS 341 OF NALOXONE AND THE OPIATE ANTAGONIST IN MALE HOUSE MICE. PAUL F. BRAIN1 , SONJA BRAIN1 and DAVID BENTON Departments of 1Zoology and 2 Psychology, University College of Swansea, Swansea, SA2 i3PP (Great Britain) (Accepted 9 March 1984) ABSTRACT Brain, P.F., Brain, S. and Benton, D., 1985. Ethological analyses of the effects of naloxone and the opiate antagonist ICI 154, 129 on social interactions- in male house mice. Benav. Processes zyxwvutsrqponmlkjihgfedcbaZYXW 10: 3&l-354. The influences of the mu blocker naloxone and the novel opioid delta receptor antagonist ICI, 154, 129 on videotaped encounters between individually- housed, male Swiss mice and anosmic male 'standard opponents' were assessed using a variety of ethological analyses. The effects of drugs were studied on individual elements and on the times allocated by subjects to broad categories of behaviour. Neither of the drugs significantly altered times allocated to broad categories of behaviour. Both doses of both compounds significantly increased the incidences of some 'fearful'/defensive postures. A more detailed analysis considered the effects of the drugs on the sequences of postures used in the resident's behaviour. This involved the generation of 'dendrograms' which provided support for the view that both naloxone and ICI 154, 129 altered the associations between behavioural elements seen in saline controls (especially at higher doses) and that the effects of these antagonists were qualitatively different. INTRODUCTION A number of groups (e.g. Benton et al, 1983; Dixon, 1982; Jones, 1983; Mackintosh et al, 1977; Miczek and Krsiak, 1981; Olivier, 1981; Olivier and van Dalen, 1982) have strongly advocated applying ethological methodologies to psychopharmacological research. Such tests generally provide a more complete behavioural description than procedures based on psychological traditions. They may also give "built-in" controls for non-specific drug actions (e.g. reduction of aggression mediated via simple sedation) and (in some cases) generate behavioural profiles providing one with maximal information about drug actions. Although such techniques are often difficult, their early application has generated promising results. The varied populations of neural opioid receptors (Rance, 1983) are likely to be strongly implicated in behaviour. The most commonly used antagonist is naloxone which blocks mu receptors at low doses but, at higher concentrations, influences kappa receptors, delta receptors and GABAergic activity also.