Seventy-five nonkiller male rats were divided into two groups, 38 animals receiving 3 mg/kg reserpine and the other 37 receiving saline. Fifty percent of the reserpine-treated animals showed mouse killing, whereas none of the other animals did so. Mouse-kill responses were already exhibited within 32 h after treatment, while the animals were still heavily sedated.Much experimental work has been done on the pharmacological inhibition of aggressive behavior, e.g., the tranquilizing effects of reserpine upon various forms of aggressive behavior. Thus, Tedeschi, Mucha, Cook, Mattis, and Fellows (1959) found an inhibitory effect of reserpine upon footshock-induced aggressive behavior in male mice, and a similar effect was shown for isolation-induced fighting (Valzelli, Giacalone, & Garattini, 1967; Yen, Stanger, & Millman, 1959). The aggressiveness of rhesus monkeys toward humans was reported to be strongly reduced by reserpine administration (plummer, Earl, Schneider, Trapold, & Barrett, 1954). Finally, clinical studies indicate a diminished aggressive behavior of psychiatric patients toward the nursing staff (Kline & Stanley, 1955; Mielke, 1956).On the other hand, reserpine fails to inhibit the mouse-kill response in rats (Karli, 1959a, b). The present experiment will show that, in fact, reserpine induces mouse killing in a large proportion of non killer rats.
METHODOne-hundred and five male Wistar rats weighing about 350 g were individually caged, with constant access to food and water.reserpine-treated animals responded to mice introduced in the home cages at least once with a killing response, whereas none of the animals of the control group did (F = 22.15, p < .001). Figure 1 presents the cumulative data of the reserpineand saline-treated animals. Most animals continued to kill even after the sedating effect of reserpine had disappeared. This effect was seen up to 3 months following reserpine administration, at which time testing was discontinued.
DISCUSSIONThe results of this experiment show that a large percentage of a group of nonkiller rats can, within 32 h, be transformed into mouse killers by a single injection of reserpine. Because the subsequent incidence of mouse killing in many rats exceeds several weeks, it seems highly unlikely that the effect can be attributed to a correspondingly prolonged action of reserpine. Possibly, learning factors are involved in these behavioral changes.Several experiments suggest an inhibitory role of both noradrenalin and serotonin in the regulation of the mouse-kill response. Inhibition of mouse killing is seen following systemic a~ministration of amphetamine, MAO-inhibitors or tricyclic antiIn four preexperimental tests of 24 h, all animals were screened ... with respect to mouse-killing behavior. Thirty "killers" were excluded from further experimentation, and the remaining 75 subjects were divided into two groups: 38 animals received RESERPINE 3 mg/kg reserpine (Serpasil, CIBA) in saline subcutaneously, and the other 37 received .9% saline only.The mouse-kill test...