Protective Function of Nicotinamide Against Ketamine-induced Apoptotic Neurodegeneration in the Infant Rat Brain

During development, anesthetics activate neuroapoptosis and produce damage in the central nervous system that leads to several types of neurological disorders. A single dose of ketamine (40 mg/kg) during synaptogenesis in a 7-day-old rat brain activated the apoptotic cascade and caused extensive neuronal cell death in the forebrain. In this study, we investigated the protective effect of nicotinamide against ketamine-induced apoptotic neurodegeneration. After 4 h, neuronal cell death induced by ketamine was associated with the induction of Bax, release of cytochrome c into the cytosol, and activation of caspase-3. One single dose of 1 mg/g nicotinamide was administered to a developing rat and was found to inhibit ketamine-induced neuroapoptosis by downregulating Bax, inhibiting cytochrome c release from mitochondria into cytosol, and inhibiting the expression of activated caspase-3. TUNEL and immunohistochemical analyses showed that ketamine-induced cell death occurred through apoptosis and that it was inhibited by nicotinamide. Fluoro-Jade-B staining demonstrated an increased number of dead cells in the cortex and thalamus after ketamine treatment; treatment with nicotinamide reduced the number of dead cells in these brain regions. Our findings suggest that nicotinamide attenuated ketamine-induced neuronal cell loss in the developing rat brain and is a promising therapeutic and neuroprotective agent for the treatment of neurodevelopmental disorders.