The behavioral responses of rats toward mice were studied. A portion of the rats killed the mice, as found in previous studies. Another group of rats exhibited a different, previously unstudied response of mouse carrying (without the kill). A behavioral study of the stability of mouse killing or carrying was carried out. The behaviors were found to be stable over two trials in 1 day and over 5 consecutive days of testing. The possible behavioral significance of the carrying response was also discussed.Predatory behavior can be elicited in laboratory rats by several species of test animals.

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Some rats will con,istently kill a mouse placed in their cage. other> will simply carry the mouse around th : cage (without killing). while about 50S-; of the rats show neither behavior. This experiment investigated the effect of chemical brain stimulation with a cholinergic or anticholinergic drug on mouse killing and mouse carrying by rats. Carbachol significantly inhibited both killing and carrying. while atropine had no effect on the behaviors. These data arc incomistent \\ith previous studics implicating chOlinergic mechanisms in the facilitation of mouse killing. The implicatiom of this >tudy are discussed.Acts of aggression among mammalian organisms are highly complex and diwrse phenomena. Indeed, the stimulus conditions that will elicit aggressive behavior and the exact forms the response will assume are quite varied . Mouse killing in rats is a type of predatory aggression which is both stereotyped and stimulus specific. The behavior is typified by vigorous and repea ted bites directed at the cervical spine of a mouse tKarli, 1956). Mouse killing is a stable behavior, and may be observed over several months (Karli. Vergnes, & Didiergeorges . 1969). Furthermore. mouse killers will not kill rat pups matched for size and shape to resemble adult mice (Myer & White. 1965).Some rats, however, do not engage in mouse killing .killing behavior comparable to irritable aggression (Moyer , 1968). Chemical stimulation of the rat brain provided further clues as to the neurobiochemical basis of predatory aggression. Smith, King, and Hoebel (I970) reported that central injections of carbachol (a cholinergic drug) into the LH elicited mouse killing in nonkilling rats. Furthermore, atropine in these sites inhibited mouse killing by killer rats. Bandler (1969Bandler ( , 1970Bandler ( , 1971a , however , using lower drug doses, reported a facilitation of killing with carbachol in the LH of killer rats but failed to replicate the conversion of nonkiller rats to killers. Carbachol injections were also found effective in facilitation of killing when placed in the medial thalamus and midbrain regions. Atropine in the LH did not inhibit mouse killing, but did so when placed in the thalamus or Cpon close observation. many of these rats may be observed to pick up a mouse by the skin of the back and carry it around the cage (Lonowski , Levitt, & Larson, 1973). This behavior. mouse carrying . appears to be as consistent and dynamic in its own right as mouse killing. Topographically, the behavior is similar to an attack directed at a mouse , but lacks the bite which chara.:terizes mouse killers.. midbrain .In re.:ent years . the neurological parameters of mouse killing haw been investigated. Electrical stimulation of the lateral hypothalamus (LH) in rats can both elicit (King & Hoebel. 1968) and facilitate mouse killing (Karli. Vergnes , & Didiergeorges. 1969).However. two forms of aggression may be elicited by electrical stimulation to the LH, affective attack and quiet biting attack (panksepp. 1971). In affective attack, rats wi...

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