Repeated ketamine administration induces recognition memory impairment together with morphological changes in neurons from ventromedial prefrontal cortex, dorsal striatum, and hippocampus.

Ketamine is an anesthetic agent that antagonizes N-methyl-d-aspartate receptors, inducing psychotic-like symptoms in healthy humans and animals. This agent has been used as a pharmacological tool for studying biochemical and physiological mechanisms underlying the clinical manifestations of schizophrenia. The main goal of this study was to evaluate the effect of repeated injections of ketamine (5 and 10 mg/kg, i.p., daily for 5 days) on recognition memory and neuronal morphology in ICR-CD1 mice. This treatment induced recognition memory impairment in the novel object recognition test and a decrease in dendritic spines density in both dorsal striatum and CA1-hippocampus. Sholl analysis showed that both ketamine doses decrease the dendritic arborization in ventromedial prefrontal cortex, dorsal striatum, and CA1-hippocampus. Finally, dendritic spines morphology was modified by both doses; that is, an increase of the filipodia-type spines (10 mg/kg) and a reduction of the mushroom-type spines (5 and 10 mg/kg) was observed in the ventromedial prefrontal cortex. In the dorsal striatum, the low dose of ketamine induced an increase in long thin spines and a decrease of mushroom spines. Interestingly, in CA1-hippocampus, there was an increase in the mushrooms type spines (5 mg/kg). Current findings suggest that the subchronic blockade of N-methyl-d-aspartate receptor changes the neuronal plasticity of several brain regions putatively related to recognition memory impairment.