OPEN-FIELD, LEARNED HELPLESSNESS, CONDITIONED DEFENSIVE BURYING, AND FORCED-SWIM TESTS IN WKY RATS

Wistar Kyoto (WKY) and Wistar rats were observed in four tests; the open field test (OFT), the conditioned defensive burying (DB) test, and two tests which are considered animal models of depressive behavior, namely the Porsolt forced-swim test (FST) and the shuttlebox escape responding following exposure to inescapable shock, that is, learned helplessness (LH). The four tests were administered according to a semirandomized schedule to control for sequence effects. All rats were later exposed to water-restraint stress and stomachs were subsequently inspected for ulcers. Stress ulcer severity was greater in WKY rats. WKY rats, as compared to Wistar rats, were hypoactive in the OFT, did not engage in DB, rapidly acquired the LH task, and were significantly more immobile in the FST. The FST was positively correlated with behaviors in the LH procedure and, to a lesser degree, with DB, but these relationships were observed only with WKY rats, not Wistar rats. The data suggested that the use of WKY rats represented a more sensitive procedure for detecting possible relationships between putative animal models of depressive behaviour.