The Role of Sex and Sex Steroids in the Novel Object Recognition Task

Abstract The novel object recognition task is a behavioural assay of memory that relies on rodents' inherent predilection for novelty. The one-trial task avoids the use of reinforcing or aversive stimuli typically used in other cognitive tests, resulting in a relatively low-stress task with reduced influence of motivational and affective effects. As such factors are influenced by sex and sex hormones; this experimental paradigm has a number of advantages specific to the challenges associated with behavioural neuroendocrine research. The present chapter reviews literature investigating the effects of sex and sex steroids, namely the ovarian hormones, on the novel object recognition task. While the data are slightly variable, some overall trends are apparent. Sex appears to differentially affect performance dependent on the use of a spatial or nonspatial variant of the task. Higher levels of endogenous ovarian hormones (throughout the oestrous cycle, pregnancy, ageing) in gonadally intact animals as well as high levels of exogenous administration (acute and chronic) to ovariectomized females generally enhance object recognition memory. Although many potential underlying mechanisms have been identified, the critical pathways remain unclear and are likely dependent on the endogenous cycle phase and the dose/timing of treatment being assessed. The discrepancy between results and a number of limitations of these investigations are apparent, and future avenues for research into the hormone regulation of memory are addressed. Additionally, as sex steroids have been implicated in many psychiatric and neurological disorders, such as schizophrenia, depression, and Alzheimer's disease, clinical implications of this research is considered.