Sex differences and stress response of WKY rats

Wistar Kyoto (WKY), Fischer-344 (F-344), and Wistar male and female rats during either proestrus-estrus or diestrus phases of the estrus cycle were exposed to the ulcerogenic procedure of water restraint. Both male and female WKY rats revealed significantly more stomach ulcers as compared to Wistar and F-344 rats of the same sex. No persistent sex difference was observed, but ulcer severity was more pronounced during the proestrus-estrus phase as compared to the diestrus phase of the estrus cycle particularly in WKY female rats. In the second study, WKY females were observed as more active in the open-field test (OFT), but more immobile in the forced swim test (FST), as compared to WKY male rats. In addition, proestrus-estrus WKY females were less active in the OFT and significantly more immobile in the FST as compared to diestrus females. Thus, proestrus-estrus WKY females were judged as more emotional in the OFT and as exhibiting more signs of behavioral depression according to the FST. These studies suggest that the steroid hormone milieu in WKY rats may be responsible for these behavioral changes as well as the stress responsiveness in this stress-susceptible rat strain.