The different effects of lithium and tamoxifen on memory formation and the levels of neurotrophic factors in the brain of male and female rats

Lithium (Li) is a mood-stabilizing drug used in the treatment of bipolar disorder (BD). Recently, preclinical studies have demonstrated the potential of tamoxifen (TMX) in the treatment of acute episodes of BD. However, the prolonged use of TMX for mood disorders treatment is controversial. In this study, we evaluated the effects of TMX or Li on cognitive behavior, as well as the levels of neurotrophic factors in the brain of male and female rats. Male and female Wistar rats received administrations of water (control group), TMX or Li via gavage for a period of 28 days; the rats were then subjected to the open-field test (to evaluate spontaneous locomotion), and the novel object recognition and step-down inhibitory avoidance tests (to evaluate cognition). The levels of NGF, BDNF and GDNF were evaluated in the hippocampus and frontal cortex of the subject rats. No significant differences were observed in the open-field and inhibitory avoidance tests after drug administration in either the male or female rats. The administration of TMX, but not Li, decreased the recognition index of both the male and female rats in the object recognition test. The chronic administration of TMX decreased, whereas Li increased the levels of BDNF in the hippocampus of both the male and female rats. Tamoxifen decreased the levels of NGF in the hippocampus of female rats. In conclusion, it can be suggested that long-term treatments with TMX can lead to significant cognitive impairments by reducing the levels of neurotrophic factors in the brain of rats.