Passive-avoidance behavior in Wistar-Kyoto (WKY), Wistar, and Fischer-344 rats.

In Experiment 1, Wistar-Kyoto (WKY), Wistar, and Fischer-344 (F-344) rats were tested on two passive-avoidance tasks: a platform step-down task and a one-way avoidance task. Wistars had shorter response latency scores in the step-down task, whereas F-344 rats had shorter scores in the one-way task. A subsequent ulcerogenic water-restraint stress produced significantly fewer ulcers in Wistar rats as compared to WKY and F-344 rats. In Experiment 2, rearings, grooming, ambulation, defecation, and response ambivalence behaviors were recorded in the one-way avoidance task in addition to response latency. WKY rats defecated more and produced lower scores on the three activity measures as compared to Wistar and F-344 rats. Response latency and ambivalence scores were higher for WKY rats. The subsequent ulcerogenic procedure also produced more ulcers in WKY rats. These data verify the ulcer susceptibility of WKY rats and underscore the assertion that their predominant stress coping behaviors are immobility and freezing. High ambivalence scores in WKY rats suggest behavioral inhibition, which is readily elicited by stressors. These behaviors resemble depressive behavior and suggest that WKY rat may be a useful animal model of depression.