Ketamine is widely used as a pediatric anesthetic. Studies in developing rodents have indicated that ketamine-induced anesthesia results in brain cell death. Additional studies are needed to determine if ketamine anesthesia results in brain cell death in the nonhuman primate and if so, to begin to define the stage of development and the duration of ketamine anesthesia necessary to produce brain cell death. Rhesus monkeys (N = 3 for each treatment and control group) at three stages of development (122 days of gestation and 5 and 35 postnatal days [PNDs]) were administered ketamine intravenously for 24 h to maintain a surgical anesthetic plane, followed by a 6-h withdrawal period. Similar studies were performed in PND 5 animals with 3 h of ketamine anesthesia. Animals were subsequently perfused and brain tissue processed for analyses. Ketamine (24-h infusion) produced a significant increase in the number of caspase 3-, Fluoro-Jade C- and silver stain-positive cells in the cortex of gestational and PND 5 animals but not in PND 35 animals. Electron microscopy indicated typical nuclear condensation and fragmentation in some neuronal cells, and cell body swelling was observed in others indicating that ketamine-induced neuronal cell death is most likely both apoptotic and necrotic in nature. Ketamine increased N-methyl-D-aspartate (NMDA) receptor NR1 subunit messenger RNA in the frontal cortex where enhanced cell death was apparent. Earlier developmental stages (122 days of gestation and 5 PNDs) appear more sensitive to ketamine-induced neuronal cell death than later in development (35 PNDs). However, a shorter duration of ketamine anesthesia (3 h) did not result in neuronal cell death in the 5-day-old monkey.

Ketamine, an N-methyl-D-aspartate (NMDA) receptor ion channel blocker, is a widely used anesthetic recently reported to enhance neuronal death in developing rodents and nonhuman primates. This study evaluated dose-response and time-course effects of ketamine, levels of ketamine in plasma and brain, and the relationship between altered NMDA receptor expression and ketamine-induced neuronal cell death during development. Postnatal day 7 rats were administered 5, 10, or 20 mg/kg ketamine using single or multiple injections (subcutaneously) at 2-h intervals, and the potential neurotoxic effects were examined 6 h after the last injection. No significant neurotoxic effects were detected in layers II or III of the frontal cortex of rats administered one, three, or six injections of 5 or 10 mg/kg ketamine. However, in rats administered six injections of 20 mg/kg ketamine, a significant increase in the number of caspase-3- and Fluoro-Jade C-positive neuronal cells was observed in the frontal cortex. Electron microscopic observations showed typical nuclear condensation and fragmentation indicating enhanced apoptotic characteristics. Increased cell death was also apparent in other brain regions. In addition, apoptosis occurred after plasma and brain levels of ketamine had returned to baseline levels. In situ hybridization also showed a remarkable increase in mRNA signals for the NMDA NR1 subunit in the frontal cortex. These data demonstrate that ketamine administration results in a dose-related and exposure-time dependent increase in neuronal cell death during development. Ketamine-induced cell death appears to be apoptotic in nature and closely associated with enhanced NMDA receptor subunit mRNA expression.

Ketamine, a widely used pediatric anesthetic, has been associated with enhanced neuronal toxicity in the developing brain, but mechanisms and neuronal susceptibility to neurotoxic insult leading to neuronal cell death remain poorly defined. One of the main goals of this study was to determine whether there is a duration of ketamine-induced anesthesia below which no significant ketamine-induced neurodegeneration can be detected. Newborn rhesus monkeys (postnatal day 5 or 6) were administered ketamine intravenously for 3, 9 or 24h to maintain a steady anesthetic plane, followed by a 6-h withdrawal period. The 9- and 24-h durations were selected as relatively long and extremely long exposures, respectively, while the 3-h treatment more closely approximates a typical duration of pediatric general anesthesia. Animals were subsequently perfused under anesthesia and brain tissue was processed for analyses using silver and Fluoro-Jade C stains and caspase-3 immunostain. The results indicated that no significant neurotoxic effects occurred if the anesthesia duration was 3h. However, ketamine infusions for either 9 or 24h significantly increased neuronal cell death in layers II and III of the frontal cortex. Although a few caspase-3- and Fluoro-Jade C-positive neuronal profiles were observed in some additional brain areas including the hippocampus, thalamus, striatum and amygdala, no significant differences were detected between ketamine-treated and control monkeys in these areas after 3, 9 or 24h of exposure. These data show that treatment with ketamine up to 3h is without adverse effects as determined by nerve cell death. However, anesthetic durations of 9h or greater are associated with significant brain cell death in the frontal cortex. Thus, the threshold duration below which no neurotoxicity would be expected is somewhere between 3 and 9h.

Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, is used as a general pediatric anesthetic. Recent data suggest that anesthetic drugs may cause neurodegeneration during development. The purpose of this study was to determine the robustness of ketamine-induced developmental neurotoxicity using rhesus monkey frontal cortical cultures and also to determine if dysregulation of NMDA receptor subunits promotes ketamine-induced cell death. Frontal cortical cells collected from the neonatal monkey were incubated for 24 h with 1, 10, or 20 microM ketamine alone or with ketamine plus either NR1 antisense oligonucleotides or the nuclear factor kB translocation inhibitor, SN-50. Ketamine caused a marked reduction in the neuronal marker polysialic acid neural cell adhesion molecule and mitochondrial metabolism, as well as an increase in DNA fragmentation and release of lactate dehydrogenase. Ketamine-induced effects were blocked by NR1 antisenses and SN-50. These data suggest that NR1 antisenses and SN-50 offer neuroprotection from the enhanced degeneration induced by ketamine in vitro.

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