Psychopharmacology 59, 179-182 (1978) Psycho pharmacology ~) by Springer-Verlag 1978 Instinctive Predatory Behavior of the Ferret ( Putorius putorius furo L.) Modified by Chlordiazepoxide Hydrochloride (Librium | R. Apfelbach Universitfit Ttibingen, Lehrstuhl ftir Zoophysiologie, Morgenstelle 28, D-7400 T/ibingen, Federal Republic of Germany Abstract. The predatory behavior of ferrets (Putorius putoriusfuro L.) consists mainly of instinctive behavior- al patterns that are elicited by simple external stimuli. For the ferret, the time needed to catch and kill rats depends on the size of the rats in relation to that of the ferret. Killing success decreases with a relative increase in prey size. Chlordiazepoxide hydrochloride injections (1 mg/kg, i. m.) modified this behavior. Drugged fer- rets needed less time and less bites to kill relatively large rats; killing success was also increased. Chlordiazepoxide seemed to disinhibit the ferrets when they were presented with large rats, which they normally attack more cautiously. Key words: Ferret - Predatory behavior - Chlordiazepoxide hydrochloride - Disinhibition Chlordiazepoxide hydrochloride (Librium| a benzo- diazepine derivative, reduces anxiety in human subjects (Harris, 1960; Tobin and Lewis, 1960) and diminishes aggressive behavior in several species (Heuschele, 1961 ; Heise and Boff, 1961 ; Randall, 1961 ; Gardner, 1971). In general, chlordiazepoxide is regarded as a drug that calms spontaneous and elicited vicious behavior in animals. Some literature indicates, however, that benzo- diazepines might also cause a paradoxic increase of aggressive behavior in psychotic patients (Hollister et al., 1961) and in normal individuals (Salzman et al., 1974). Because of their highly developed social behavior, which can be disturbed easily, and because of their great learning abilities, primates seem to be rather unsuitable animals for studying the behavioral effects of psychopharmaca. Changes in behavioral reactions might be due to drug administration, but also to other disturbances. But changes in behavioral reactions can be more reliably related to drug administration when the behavior in question occurs in a stereotyped manner that is not easily modified by, for example, learning processes. Such a stereotyped behavior was found in the predatory behavior of the ferret, a member of the carnivorous family Mustelidae. In this species, pre- datory reactions mainly consist of instinctive be- havioral patterns that are elicited only by specific external stimuli (Apfelbach, 1973; Eibl-Eibesfeldt, 1956; Goethe, 1940; Gossow, 1970; Wtistehube, 1960). When elicited, these reactions are performed in a predictable and quantifiable way. According to earlier studies (Apfelbach and Wester, 1977), an important external factor for eliciting hunting behavior in ferrets is the size of the prey; an increase in its size decreases the probability of a successful attack. Prey killing, in turn, does not depend on hunger alone, since hungry and satiated animals react equally potential prey (Apfelbach, 1978). In the present study we investigated the possibility that chlordiazepoxide hydrochloride 'tames' the prey- catching behavior of ferrets. Materials and Methods Subjects. The subject was the ferret (Putorius putoriusfuro L.), the domesticated form of the European polecat (Putorius putorius L.). Three females (450, 720, and 850 g) and five males (900-1.500 g) were used. Housing and feeding conditions as well as the general experimen- tal design were the same as those described in a previous paper (Schmidt and Apfelbach, 1977). Procedure. In all control experiments, male rats (Wistar, 80- 370 g) served as prey. In the experiment, a rat was placed onto a round observation table (2 m diameter, side wall 50 cm high), and allowed to acquainted itself with the environment for 10 min. Then a ferret was released onto the table, opposite the position of the rat. All ferrets were familiar with the experimental table before the prey-catching 0033-3158/78/0059/0179/$01.00