SELECTIVE BREEDING OF RATS FOR HIGH AND LOW MOTOR-ACTIVITY IN A SWIM TEST - TOWARD A NEW ANIMAL-MODEL OF DEPRESSION

Because low motor activity in a swim test has been found to represent ''depression-like'' behavior in the rat, Sprague-Dawley (SD) albino ra ts were selectively bred for low motor activity (low struggling time/h igh floating time) in a swim test, while others were bred for high mot or activity (high struggling time/low floating time). Eighty-four male and 42 female SD rats were initially purchased from Charles-River Bre eding Laboratories in 1987, their behavior assessed in a 15-min swim t est, and selective breeding carried out by mating those male and femal e rats that showed either low or high levels of motor activity in the test; results from behavioral testing of the first 18 generations prod uced by this selective breeding process are reported here. Two rat lin es have been obtained, Swim Low-Active (SwLo) and Swim High-Active (Sw Hi) rats, which differ dramatically in swim-test behavior-SwLo rats sh ow little struggling and much floating, while SwHi rats show the rever se. Activity scores of individual SwLo and SwHi rats now show no overl ap. Selective breeding has produced bidirectional changes; that is, Sw Lo rats are considerably less active than randomly bred Sprague-Dawley albino rats, while SwHi rats are considerably more active than random ly bred rats. Measuring activity of SwLo and SwHi rats in other situat ions-ambulation in the home cage, open-field activity, exploratory act ivity in a novel, home cage-like situation, and immobility in the Pors olt swim test-revealed that differences are most pronounced when anima ls respond ro acute challenges; under these conditions, SwHi rats show active, assertive behavior, whereas SwLo rats show a distinct absence of this type of response. When SwLo rats from the 8th to the 11th gen erations were given antidepressant medication [desipramine, (DMI), a t ricyclic, or phenelzine, an MAO inhibitor], chronic but not acute admi nistration of both drugs increased swim-test activity of SwLo rats. Bu spirone, an anxiolytic, did not increase activity of SwLo rats. Use of animals selectively bred for high and low activity in the swim test m ay represent a new tool for studying physiological processes relevant to affective disorders and for testing antidepressant drugs/treatments . (C) 1998 Elsevier Science Inc.