Repeated high-dose esketamine in early postnatal rats leads to behavioural deficits with long-term modifications in...

Esketamine is commonly used for sedation or general anaesthesia in infants and young children. However, repeated esketamine administration during periods of rapid brain growth and development may result in various pathophysiological and cognitive changes. Therefore, this study aimed to investigate the influence of recurrent esketamine exposure on long-term behavioural and white matter consequences. Seven-day-old (P7) male rats were allocated to control, high-, and low-dose groups. Behavioural paradigm assessment was conducted at P25-29. Diffusion tensor imaging revealed long-term effects on water diffusivity in the splenium and cingulum white matter of the corpus callosum at P30. Subsequent two-dimensional structure-tensor analysis of brain tissue sections stained with Luxol fast blue (LFB) showed marked changes in the white matter microstructure in rats after multiple exposures to varying esketamine doses. High-dose esketamine significantly reduced activity time and total distance in the open-field experiment. High-dose esketamine exposure might lead to impaired short-term memory in rats. Additionally, the high-dose group showed prolonged immobility time during the forced swimming test. On the balance beam, the high-dose group displayed more right turns and right-foot slips and lower time spent on the rotating bar, indicating motor defects, than did the other groups. Diffusion tensor imaging demonstrated a decreased water molecule diffusion ability in the corpus callosum in the high-dose group. LFB staining indicated microstructural differences in the white matter of animals in the high-dose group. These findings suggest that behavioural deficits in high-dose esketamine-treated rats are at least partially attributed to changes in the white matter microstructure.