Influence of gender on working and spatial memory in the novel object recognition task in the rat

Gender differences in many behavioural tasks have been observed in both humans and laboratory animals. The novel object recognition (NOR) task is increasingly used to investigate drug effects on working memory processes, although, the influence of sexually dimorphic behaviours have not yet been evaluated. In addition, the role of natural fluctuations in the sex steroids during the oestrous cycle has received little attention during object recognition tasks. Therefore, the aim of the current study was to investigate the influence of gender and oestrous cycle phase on working and spatial memory using the NOR task. Animals were tested in the NOR task and the spatial NOR task. Male and female rats completed an acquisition trial followed by an inter-trial interval of a specified length, then a final retention trial. Vaginal cytology enabled the influence of oestrous cycle phase to be determined in both the NOR and spatial NOR, each animal was tested during one phase of their regular oestrous cycle only. It was found that female rats performed significantly better than male rats in the standard NOR paradigm (p < 0.05 compared to no significance (NS) at 3 h, respectively), while male rats showed improved memory in the spatial NOR paradigm compared with female rats (p < 0.05 compared to NS at 3 h, respectively). There was no influence of phase of oestrous cycle on the NOR task, however, during the spatial NOR there was a significant improvement in ability when oestrogen and progesterone levels have been shown to be at their lowest (i.e. p < 0.05 during oestrous compared to NS at other stages). In conclusion, it is clear that gonadal hormones can influence components of memory and gender is an important consideration in experimental design.