Effects of gonadal hormones and persistent pain on non-spatial working memory in male and female rats

There are indications of a modulatory role carried out by gonadal hormones and pain in cognitive functions. We have examined this issue in male and fe male rats by assessing the impact of gonadectomy and persistent pain on the object recognition test. Intact and gonadectomized male and female rats we re exposed to an open field (15 min) in which three objects were placed (Tr ial 1); the same test was repeated 2 h later (Trial 2), after the replaceme nt of a "familiar" object with a novel one. Three days later (Day 2), the s ame procedure was repeated (Trial 3 and 4 with 2 h in between) but half of the animals were exposed to formalin-injection immediately before Trial 3. The latency, frequency and duration of approaching the three objects: were recorded in each trial and compared by sex, gonadectomy and formalin treatm ent. The results showed that gonadectomized males and females had lower lev els of approach to all objects and less locomotor/exploratory activity than intact animals in all experimental trials; their behaviour was not affecte d by repetition of the test or by pain. On Day 1, intact males showed a hig her level of approach to the novel object than females. In intact males, th e 2 h delay between the first and second trial failed to induce any signifi cant modification of exploration of the novel object with respect to the fa miliar one, while in intact females the novel object was approached much le ss than the familiar one. Similarly on Day 2, the novel object was: approac hed for a longer time by intact males than by all the other groups. In conc lusion, our data show that physiological levels of circulating gonadal horm ones significantly affected the performance of male but not female rats whe n exposed to the object recognition test. (C) 2001 Elsevier Science B.V. Al l rights reserved.