Raloxifene recovers effects of prenatal immune activation on cognitive task-induced gamma power

There is currently no treatment available for the cognitive symptoms of schizophrenia, but evidence suggests that selective estrogen receptor modulators (SERMs) may provide relief. Our recent animal model data showed that a lack of female sex hormones in mice impairs the ability of hippocampal neurons to synchronise and generate oscillations within the frequency range of 30-80 Hz (gamma power) leading to cognitive impairment, while both estradiol and the SERM, raloxifene, recovered this. Given that cognitive impairment is accompanied by abnormal gamma power in schizophrenia, this study aimed to determine the effects of raloxifene on gamma power during spatial memory tasks in the prenatal immune challenged (poly-I:C) mouse model with relevance to schizophrenia. Pregnant dams received the viral mimetic poly-I:C (20 mg/kg, i.p.) at gestational day 17. Male and female offspring were treated with placebo or raloxifene implants at adulthood. Local field potentials from the CA1 hippocampus were simultaneously recorded during the Y-maze test of short term spatial memory and the cheeseboard maze test of long-term spatial learning and memory and cognitive flexibility. In female but not male mice, poly I:C exposure reduced gamma power during decision making and prolonged the time spent in the centre (decision making phase) during the Y-maze task. Female poly-I:C exposed mice also showed increased gamma power during acquisition of the cheeseboard long term memory task and perseverative behaviour. Treatment with raloxifene recovered gamma power and decision making deficits in the Y-maze and restored gamma power changes during the cheeseboard maze task as well as perseverative behaviour. Male mice showed no electrophysiological or behavioural effects of poly-I:C or raloxifene treatment. In summary, poly-I:C exposure induced female specific cognitive impairments accompanied by altered neural oscillations in the gamma frequency and raloxifene recovered these abnormalities.