Opposite behaviours in the forced swimming test are linked to differences in spatial working memory performances in the rat.

Despite consistent evidence of an association between depression and impaired memory performance, only a few studies have investigated memory processes in animal models of depression. The aim of the present study was to determine if rats selected for marked differences in their immobility response in the forced swimming test (FST, i.e. high-immobility, [HI] and low-immobility [LI] rats) exhibit differences in spatial and non-spatial memory performances. In a classic radial maze elimination task, we observed that HI rats made significantly more errors than LI rats, and their first error appeared significantly earlier. In a delayed spatial win-shift procedure where rats have to hold spatially relevant information in working memory across a 30 min delay, HI rats tended initially to perform more poorly than LI rats. HI rats made more across-phase errors, the occurrence of the first error was earlier and by the end of the experiment the differences between the two groups disappeared. Thus, HI rats present more difficulties to learn the rules in a spatial task and show weaker performances in spatial working memory in comparison to LI rats. On the other hand, performances in the two groups of animals were similar in a non-spatial task, the object recognition task. Complementary behavioral data indicate that the differences observed between the two groups are not attributable to opposite locomotor activities or to different levels of anxiety. Overall we can conclude that opposite swimming behavior in the FST could parallel some differences in cognitive performances, more specifically linked to spatial working memory.