Ketamine alters the neurogenesis of rat cortical neural stem progenitor cells

Neuroplasticity and psychedelics: A comprehensive examination of classic and non-classic compounds in pre and clinical models

Neuroplasticity, the ability of the nervous system to adapt throughout an organism's lifespan, offers potential as both a biomarker and treatment target for neuropsychiatric conditions. Psychedelics, a burgeoning category of drugs, are increasingly prominent in psychiatric research, prompting inquiries into their mechanisms of action. Distinguishing themselves from traditional medications, psychedelics demonstrate rapid and enduring therapeutic effects after a single or few administrations, believed to stem from their neuroplasticity-enhancing properties. This review examines how classic psychedelics (e.g., LSD, psilocybin, N,N-DMT) and non-classic psychedelics (e.g., ketamine, MDMA) influence neuroplasticity. Drawing from preclinical and clinical studies, we explore the molecular, structural, and functional changes triggered by these agents. Animal studies suggest psychedelics induce heightened sensitivity of the nervous system to environmental stimuli (meta-plasticity), re-opening developmental windows for long-term structural changes (hyper-plasticity), with implications for mood and behavior. Translating these findings to humans faces challenges due to limitations in current imaging techniques. Nonetheless, promising new directions for human research are emerging, including the employment of novel positron-emission tomography (PET) radioligands, non-invasive brain stimulation methods, and multimodal approaches. By elucidating the interplay between psychedelics and neuroplasticity, this review informs the development of targeted interventions for neuropsychiatric disorders and advances understanding of psychedelics' therapeutic potential.

Ketamine Prevents Inflammation-Induced Reduction of Human Hippocampal Neurogenesis via Inhibiting the Production of Neurotoxic Metabolites of the Kynurenine Pathway

BACKGROUND

Understanding the precise mechanisms of ketamine is crucial for replicating its rapid antidepressant effects without inducing psychomimetic changes. Here, we explore whether the antidepressant-like effects of ketamine enantiomers are underscored by protection against cytokine-induced reductions in hippocampal neurogenesis and activation of the neurotoxic kynurenine pathway in our well-established in vitro model of depression in a dish.

METHODS

We used the fetal hippocampal progenitor cell line (HPC0A07/03C) to investigate ketamine's impact on cytokine-induced reductions in neurogenesis in vitro. Cells were treated with interleukin- 1beta (IL-1b) (10 ng/mL) or IL-6 (50 pg/mL), alone or in combination with ketamine enantiomers arketamine (R-ketamine, 400 nM) or esketamine (S-ketamine, 400 nM) or antidepressants sertraline (1 mM) or venlafaxine (1 mM).

RESULTS

Resembling the effect of antidepressants, both ketamine enantiomers prevented IL-1b- and IL-6-induced reduction in neurogenesis and increase in apoptosis. This was mediated by inhibition of IL-1b-induced production of IL-2 and IL-13 by R-ketamine and of IL-1b-induced tumor necrosis factor-alpha by S-ketamine. Likewise, R-ketamine inhibited IL-6-induced production of IL-13, whereas S-ketamine inhibited IL-6-induced IL-1b and IL-8. Moreover, both R- and S-ketamine prevented IL-1b-induced increases in indoleamine 2,3-dioxygenase expression as well as kynurenine production, which in turn was shown to mediate the detrimental effects of IL-1b on neurogenesis and apoptosis. In contrast, neither R- nor S-ketamine prevented IL-6-induced kynurenine pathway activation.

CONCLUSIONS

Results suggest that R- and S-ketamine have pro-neurogenic and anti-inflammatory properties; however, this is mediated by inhibition of the kynurenine pathway only in the context of IL-1b. Overall, this study enhances our understanding of the mechanisms underlying ketamine's antidepressant effects in the context of different inflammatory phenotypes, ultimately leading to the development of more effective, personalized therapeutic approaches for patients suffering from depression.

Very Low-Dose Sublingual Ketamine for Borderline Personality Disorder and Treatment-Resistant Depression

Borderline personality disorder (BPD) and treatment-resistant depression (TRD) are common mental disorders that are challenging to treat. Ketamine is an N-methyl-D-aspartate receptor antagonist that has shown promise as a rapid-acting antidepressant when administered intravenously. BPD symptoms have also been demonstrated to improve with repeated intravenous administration of ketamine, and a single case report described improvement in BPD following the intranasal administration of esketamine. We present a case report of a woman with BPD and TRD who responded to treatment with very low-dose sublingual ketamine. Very low-dose sublingual ketamine may be effective for the treatment of psychiatric disorders such as BPD and/or comorbid TRD.

Ketamine exerts dual effects on the apoptosis of primary cultured hippocampal neurons from fetal rats in vitro

Ketamine, a noncompetitive N-methyl D-aspartate (NMDA) receptor antagonist, is widely used in pediatric clinical practice. The neuroprotective and neurotoxic effects of ketamine on brain neurons during development remain controversial. The reason may be related to the different concentrations of ketamine used in practice and the small range of concentrations used in previous studies. In this study, cultured hippocampal neurons were treated with ketamine in a wide range of concentrations to comprehensively observe the effects of different concentrations of ketamine on neurons. We demonstrated that low concentrations of ketamine (10 μM, 100 μM and 1000 μM) promoted neuronal survival (p < 0.05) and reduced neuronal apoptosis (p < 0.05) compared with those of the control group. High concentrations of ketamine (2000 μM, 2500 μM and 3000 μM) reduced neuronal survival (p < 0.05) and promoted neuronal apoptosis (p < 0.05). The p38 MAPK inhibitor SB203580 reduced neuronal apoptosis induced by high concentrations of ketamine (2500 μM) (p < 0.05). Our findings indicate that ketamine exerts a dual effect on the apoptosis of primary cultured fetal rat hippocampal neurons in vitro and that the neurotoxic effects of ketamine are related to activation of the p38 MAPK signaling pathway.

Prenatal Exposure to General Anesthesia Drug Esketamine Impaired Neurobehavior in Offspring

Prenatal exposure to anesthetics has raised increasing attention about the neuronal development in offspring. Animal models are usually used for investigation. As a new drug, esketamine is the s-isoform of ketamine and is twice as potent as the racemic ketamine with less reported adverse effects. Esketamine is currently being used and become more favorable in clinical anesthesia work, including surgeries during pregnancy, yet the effect on the offspring is unknown. The present study aimed to elucidate the effects of gestational administration of esketamine on neuronal development in offspring, using a rat model. Gestational day 14.5 pregnant rats received intravenous injections of esketamine. The postnatal day 0 (P0) hippocampus was digested and cultured in vitro to display the neuronal growth morphology. On Day 4 the in vitro experiments revealed a shorter axon length and fewer dendrite branches in the esketamine group. The results from the EdU- imaging kit showed decreased proliferative capacity in the subventricular zone (SVZ) and dentate gyrus (DG) in both P0 and P30 offspring brains in the esketamine group. Moreover, neurogenesis, neuron maturity and spine density were impaired, resulting in attenuated long-term potentiation (LTP). Compromised hippocampal function accounted for the deficits in neuronal cognition, memory and emotion. The evidence obtained suggests that the neurobehavioral deficit due to prenatal exposure to esketamine may be related to the decrease phosphorylation of CREB and abnormalities in N-methyl-D-aspartic acid receptor subunits. Taken together, these results demonstrate the negative effect of prenatal esketamine exposure on neuronal development in offspring rats. G14.5 esketamine administration influenced the neurobehavior of the offspring in adolescence. Poorer neuronal growth and reduced brain proliferative capacity in late gestation and juvenile pups resulted in impaired P30 neuronal plasticity and synaptic spines as well as abnormalities in NMDAR subunits. Attenuated LTP reflected compromised hippocampal function, as confirmed by behavioral tests of cognition, memory and emotions. This figure was completed on the website of Figdraw.

Lipoxin A4 methyl ester attenuated ketamine-induced neurotoxicity in SH-SY5Y cells via regulating leptin pathway

Ketamine, the widely used intravenous anesthetic, has been reported to cause neurotoxicity and disturbs normal neurogenesis. However, the efficacy of current treatment strategies targeting ketamine's neurotoxicity remains limited. Lipoxin A4 methyl ester (LXA4 ME) is relatively stable lipoxin analog, which serves an important role in protecting against early brain injury. The purpose of this study was to investigate the protective effect of LXA4 ME on ketamine-caused cytotoxicity in SH-SY5Y cells, as well as the underlying mechanisms. Cell viability, apoptosis and endoplasmic reticulum stress (ER stress) were detected by adopting experimental techniques including CCK-8 assay, flow cytometry, western blotting and transmission electron microscope. Furthermore, examining the expression of leptin and its receptor (LepRb), we also measured the levels of activation of the leptin signaling pathway. Our results showed that LXA4 ME intervention promoted the cell viability, inhibited cell apoptosis, and reduced the expression of ER stress related protein and morphological changes induced by ketamine. In addition, inhibition of leptin signaling pathway caused by ketamine could be reversed by LXA4 ME. However, as the specific inhibitor of leptin pathway, leptin antagonist triple mutant human recombinant (leptin tA) attenuated the cytoprotective effect of LXA4 ME against ketamine-induced neurotoxicity. In conclusion, our findings demonstrated LXA4 ME could exert a neuroprotective effect on ketamine-induced neuronal injury via activation of the leptin signaling pathway.

Ketamine modulates neural stem cell differentiation by regulating TRPC3 expression through the GSK3β/β-catenin pathway

Ketamine, a popular anesthetic, is often abused by people for its hallucinogenic effect. Thus, the safety of ketamine in pediatric populations has been called into question for potential neurotoxic effects. However, ketamine also has neuroprotective effects in many brain injury models. The differentiation of neural stem cells (NSCs) was influenced significantly by ketamine, but the molecular mechanism is still unclear. NSCs were extracted from the hippocampi of postnatal day 1 rats and treated with ketamine to induce NSCs differentiation. Our results found that ketamine promoted neuronal differentiation of NSCs dose-dependently in a small dose range (P < 0.001). The main types of neurons from NSCs were cholinergic (51 ± 4 %; 95 % CI: 41-61 %) and glutamatergic neurons (34 ± 3 %; 95 % CI: 27-42 %). Furthermore, we performed RNA sequencing to promise a more comprehensive understanding of the molecules regulated by ketamine. Finally, we combined bioimaging and multiple molecular biology techniques to clarify that ketamine influences NSC differentiation by regulating transient receptor potential canonical 3 (TRPC3) expressions. Ketamine dramatically repressed TRPC3 expression (MD [95 % CI]=0.67 [0.40-0.95], P < 0.001) with a significant increase of phosphorylated glycogen synthase kinase 3β (p-GSK3β; MD [95 % CI]=1.00 [0.74-1.27], P < 0.001) and a decrease of β-catenin protein expression (MD [95 % CI]=0.60 [0.32-0.89], P = 0.001), thereby promoting the differentiation of NSCs into neurons and inhibiting their differentiation into astrocytes. These results suggest that TRPC3 is necessary for ketamine to modulate NSC differentiation, which occurs partly via regulation of the GSK3β/β-catenin pathway.

Nonapoptotic caspases in neural development and in anesthesia-induced neurotoxicity

Apoptosis, classically initiated by caspase pathway activation, plays a prominent role during normal brain development as well as in neurodegeneration. The noncanonical, nonlethal arm of the caspase pathway is evolutionarily conserved and has also been implicated in both processes, yet is relatively understudied. Dysregulated pathway activation during critical periods of neurodevelopment due to environmental neurotoxins or exposure to compounds such as anesthetics can have detrimental consequences for brain maturation and long-term effects on behavior. In this review, we discuss key molecular characteristics and roles of the noncanonical caspase pathway and how its dysregulation may adversely affect brain development. We highlight both genetic and environmental factors that regulate apoptotic and sublethal caspase responses and discuss potential interventions that target the noncanonical caspase pathway for developmental brain injuries.

Early Developmental PMCA2b Expression Protects From Ketamine-Induced Apoptosis and GABA Impairments in Differentiating Hippocampal Progenitor Cells

PMCA2 is not expressed until the late embryonic state when the control of subtle Ca²⁺ fluxes becomes important for neuronal specialization. During this period, immature neurons are especially vulnerable to degenerative insults induced by the N-methyl-D-aspartate (NMDA) receptor blocker, ketamine. As H19-7 hippocampal progenitor cells isolated from E17 do not express the PMCA2 isoform, they constitute a valuable model for studying its role in neuronal development. In this study, we demonstrated that heterologous expression of PMCA2b enhanced the differentiation of H19-7 cells and protected from ketamine-induced death. PMCA2b did not affect resting [Ca²⁺]_c in the presence or absence of ketamine and had no effect on the rate of Ca²⁺ clearance following membrane depolarization in the presence of the drug. The upregulation of endogenous PMCA1 demonstrated in response to PMCA2b expression as well as ketamine-induced PMCA4 depletion were indifferent to the rate of Ca²⁺ clearance in the presence of ketamine. Yet, co-expression of PMCA4b and PMCA2b was able to partially restore Ca²⁺ extrusion diminished by ketamine. The profiling of NMDA receptor expression showed upregulation of the NMDAR1 subunit in PMCA2b-expressing cells and increased co-immunoprecipitation of both proteins following ketamine treatment. Further microarray screening demonstrated a significant influence of PMCA2b on GABA signaling in differentiating progenitor cells, manifested by the unique regulation of several genes key to the GABAergic transmission. The overall activity of glutamate decarboxylase remained unchanged, but Ca²⁺-induced GABA release was inhibited in the presence of ketamine. Interestingly, PMCA2b expression was able to reverse this effect. The mechanism of GABA secretion normalization in the presence of ketamine may involve PMCA2b-mediated inhibition of GABA transaminase, thus shifting GABA utilization from energetic purposes to neurosecretion. In this study, we show for the first time that developmentally controlled PMCA expression may dictate the pattern of differentiation of hippocampal progenitor cells. Moreover, the appearance of PMCA2 early in development has long-standing consequences for GABA metabolism with yet an unpredictable influence on GABAergic neurotransmission during later stages of brain maturation. In contrast, the presence of PMCA2b seems to be protective for differentiating progenitor cells from ketamine-induced apoptotic death.

Rapid-acting antidepressants and the circadian clock

A growing number of epidemiological and experimental studies has established that circadian disruption is strongly associated with psychiatric disorders, including major depressive disorder (MDD). This association is becoming increasingly relevant considering that modern lifestyles, social zeitgebers (time cues) and genetic variants contribute to disrupting circadian rhythms that may lead to psychiatric disorders. Circadian abnormalities associated with MDD include dysregulated rhythms of sleep, temperature, hormonal secretions, and mood which are modulated by the molecular clock. Rapid-acting antidepressants such as subanesthetic ketamine and sleep deprivation therapy can improve symptoms within 24 h in a subset of depressed patients, in striking contrast to conventional treatments, which generally require weeks for a full clinical response. Importantly, animal data show that sleep deprivation and ketamine have overlapping effects on clock gene expression. Furthermore, emerging data implicate the circadian system as a critical component involved in rapid antidepressant responses via several intracellular signaling pathways such as GSK3β, mTOR, MAPK, and NOTCH to initiate synaptic plasticity. Future research on the relationship between depression and the circadian clock may contribute to the development of novel therapeutic strategies for depression-like symptoms. In this review we summarize recent evidence describing: (1) how the circadian clock is implicated in depression, (2) how clock genes may contribute to fast-acting antidepressants, and (3) the mechanistic links between the clock genes driving circadian rhythms and neuroplasticity.

Is (R)-ketamine a Potential Therapeutic Agent for Treatment-Resistant Depression with Less Detrimental Side Effects? A Review of Molecular Mechanisms Underlying Ketamine and its Enantiomers

Approximately one-third of individuals with major depressive disorder are resistant to conventional antidepressants (i.e., monoamine-based therapies), and, even among respondents, a proper therapeutic effect may require weeks of treatment. Ketamine, a racemic mixture of the two enantiomers, (R)-ketamine and (S)-ketamine, is an N-methyl-d-aspartate receptor (NMDAR) antagonist and has been shown to have rapid-acting antidepressant properties in patients with treatment-resistant depression (TRD). Although (R)-ketamine has a lower affinity for NMDAR, it presents greater potency and longer-lasting antidepressant properties, with no major side effects, than racemic ketamine or (S)-ketamine in preclinical findings. Thereby, ketamine and its enantiomers have not only an antagonistic effect on NMDAR but also a strong synaptogenic-modulatory effect, which is impaired in TRD pathophysiology. In this review, we summarize the current evidence regarding the modulation of neurotransmission, neuroplasticity, and neural network activity as putative mechanisms of these rapid-acting antidepressants, highlighting differences on intracellular signaling pathways of synaptic proteins such as mammalian target of rapamycin (mTOR), extracellular signal-regulated kinase (ERK) and brain-derived neurotrophic factor (BDNF). In addition, we discuss probable mechanisms involved in the side effects of ketamine and its enantiomers.

Fetal surgery has no additional effect to general anesthesia on brain development in neonatal rabbits

BACKGROUND

Fetal surgery is part of modern fetal medicine, and some procedures, such as fetal spina bifida repair, are performed under general anesthesia. Fetuses are operated on in a time window when the developing brain is extremely vulnerable to external, potentially harmful factors. To date, little is known about the effect of fetal surgery on fetal brain development.

OBJECTIVE

This study aimed to assess the effect of fetal surgery on the developing fetal brain in the rabbit model.

STUDY DESIGN

This was a randomized, sham-controlled study in time-mated pregnant does at 28 days' gestation (term, 31 days), which corresponds to the start of the peak of brain development and end of the second trimester of pregnancy in humans. We included 4 different groups in this experiment: no-surgery, general anesthesia, general anesthesia+hysterotomy, and general anesthesia+fetal surgery. In 11 does, anesthesia was induced using propofol and maintained for 75 minutes with 3.6 vol% (4% is the equivalent of 1 minimum alveolar concentration) sevoflurane. Maternal blood pressure, heart rate, oxygen saturation, temperature, end-tidal CO2 were continuously monitored. For each operated doe, 6 fetuses were part of the experiment. Randomization determined which cornual sac and what opposing third sac were assigned to fetal surgery: hysterotomy, fetal injection (atropine, fentanyl, and cisatracurium), fetal skin incision, and suturing. Only hysterotomy was performed on the opposing cornual and third amniotic sacs of the does. The fetus in these experimental sacs was used as internal unmanipulated control (general anesthesia). All fetuses (n=38) from unmanipulated does (n=4) served as external controls (no-surgery). At term, the does were delivered by cesarean delivery under ketamine-medetomidine sedation and local anesthesia. The pups underwent standardized motoric and sensory neurologic testing on day 1 followed by euthanasia and brain harvesting for histologic assessment of neurons, synapses, proliferation, and glial cells.

RESULTS

Maternal vital signs were stable during surgery. Survival was similar in the 4 groups (75%-94%), and brain-to-body weight ratio was comparable; only the no-surgery pups had a higher brain weight. On postnatal day 1, the pups in the 4 groups had a comparable neurobehavioral outcome on both motoric and sensory testing. In the prefrontal cortex, no-surgery pups had significantly higher neuron density than pups who underwent maternal surgery, but there was no difference among pups that underwent general anesthesia, hysterotomy, or fetal surgery. The measurements of proliferation had a similar outcome: a higher proliferation rate in the prefrontal cortex of no-surgery pups. Moreover, synaptic density values were higher in the no-surgery pups, but there was no difference observed among pups who underwent general anesthesia, hysterotomy, and fetal surgery. Lastly, there was no difference in gliosis among the 4 groups.

CONCLUSION

In rabbits, fetal surgery through hysterotomy under maternal general anesthesia did not affect brain development, in addition to the effects of general anesthesia per se.

Mechanisms of the Rapid Effects of Ketamine on Depression and Sleep Disturbances: A Narrative Review

Recently, sleep has been recognized as a crucial factor for health and longevity. The daily sleep/wake cycle provides the basis of biorhythm, which controls whole-body homeostasis and homeodynamics. Sleep disturbances can contribute to several physical and psychological disorders, including cardiovascular disease, obesity, depression, and cognitive dysfunction. The clinical use of the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine began in the 1970s. Over the years, physicians have used it as a short-acting anesthetic, analgesic, and antidepressant; however, in-depth research has revealed new possible applications for ketamine, such as for treating sleep disturbances and circadian rhythm disorders. The aim of this narrative review is to examine the literature on the mechanistic role of the antidepressant ketamine in affecting sleep disturbance. Additionally, we discuss the pharmacologic and pharmacokinetic mechanisms of ketamine as an antidepressant and the predictive biomarkers for ketamine’s effect on sleep and cognitive function.

Implication of microglia in ketamine-induced long-term cognitive impairment in murine pups

BACKGROUND

Ketamine, a non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist, is widely applicable to anesthesia, analgesia, and sedation. However, the function and mechanisms of ketamine in the long-term learning and memory function of neonatal mice are unclear.

OBJECTIVE

The present study aims to investigate whether long-term learning and memory function will be affected by multiple ketamine exposures in the early development period.

METHODS

The mRNA and protein levels were measured by RT-qPCR and western blot, respectively. The Morris Water Maze test was performed to assess spatial learning and memory.

RESULTS

We identified that neonatal exposure to ketamine downsized the positive neurons for microtubule-associated protein doublecortin (DCX) and Ki67 in hippocampal dentate gyrus at the juvenile and late adolescence stages. Double-labeling tests demonstrated that the counts of Iba1⁺ cells and Ki67⁺ cells were pronouncedly diminished with exposure to ketamine. Further, qPCR assays to screen the key factors predisposing the populations and maturation of microglia exhibited remarkable decline of CX3CR1 mRNA levels in ketamine group versus the control group. The close relation of microglia to synaptic plasticity was depicted by the significantly downregulated synaptic plasticity-related proteins NR2B and PSD-95 subsequent to multiple exposures to ketamine. Finally, we found that both the protein and mRNA levels of BDNF were markedly decreased in ketamine group versus the control group.

CONCLUSION

We found that multiple exposures to ketamine in neonatal mice lead to spatial learning and memory dysfunction. The alterations of microglial development and function are the possible mechanisms of long-term learning and memory impairment.

Neonatal Anesthesia by Ketamine in Neonatal Rats Inhibits the Proliferation and Differentiation of Hippocampal Neural Stem Cells and Decreases Neurocognitive Function in Adulthood via Inhibition of the Notch1 Signaling Pathway

The Notch signaling pathway plays an important role in the regulation of neurogenesis. The objective of this study was to investigate whether the Notch signaling pathway was involved in the neurogenesis impairment and long-term neurocognitive dysfunction caused by neonatal exposure to ketamine. On postnatal day 7 (PND-7), male Sprague-Dawley (SD) rats were intraperitoneally injected with 40 mg/kg ketamine four consecutive times (40 mg/kg × 4) at 1-h intervals. Notch ligand Jagged1 (0.5 mg/kg) and lentivirus overexpressing the Notch1 intracellular domain (LV-NICD1) were microinjected into the hippocampal dentate gyrus (DG) 1 h or 4 days before ketamine administration, respectively. The expression of Notch1 signaling pathway-related proteins was detected by Western blotting 24 h after ketamine administration. The proliferation and differentiation of the neural stem cells (NSCs) in the hippocampal DG were evaluated by double immunofluorescence staining 24 h after treatment. Moreover, changes in hippocampus-dependent spatial memory of 2-month-old rats were investigated with the Morris water maze test. Ketamine anesthesia in neonatal rats decreased the expression levels of Jagged1, Notch1, NICD1, and hairy enhancer of split 1 (Hes1); inhibited the proliferation and astrocytic differentiation of NSCs; and promoted the differentiation of neurons. Neonatal exposure to ketamine caused deficits in hippocampus-dependent spatial reference memory tasks in 2-month-old rats. Microinjection of Jagged1 or LV-NICD1 reversed the inhibitory effect of ketamine on the expression of Notch1-related proteins in the hippocampal DG, attenuated the ketamine-mediated decrease in NSC proliferation and differentiation, and improved the cognitive function of 2-month-old rats after neonatal exposure to ketamine. These results suggest that neonatal exposure to ketamine in rats inhibits the proliferation and differentiation of hippocampal NSCs and impairs neurocognitive function in adulthood. The Notch1 signaling pathway may be involved in the impairment of hippocampus-dependent learning and memory during adulthood caused by neonatal exposure to ketamine. These findings contribute to further understanding the neurotoxicity induced by neonatal exposure to ketamine and the underlying mechanisms.

Ketamine treatment upon memory retrieval reduces fear memory in marmoset monkeys

Emotionally arousing experiences are retained very well as seen in posttraumatic stress disorder (PTSD). Various lines of evidence indicate that reactivation of these memories renders them labile which offers a potential time-window for intervention. We tested in non-human primates whether ketamine, administered during fear memory reactivation, affected passive (inhibitory) avoidance learning. For the consolidation of contextual emotional memory, the unescapable foot-shock paradigm in a passive avoidance task with two compartments (dark vs illuminated) was used. After entering the dark compartment, marmoset monkeys received four random foot-shocks (1 mA, 4 s) within 15-min. This stressful exposure increased the saliva cortisol and heart rate and impaired REM-sleep (p<0.05). One week later the monkeys were re-exposed to the stressful situation for the reconsolidation of the fearful experience. During the re-exposure the monkeys were treated with ketamine (0.5 mg/kg) or saline. In week 3, the monkeys were placed in the experimental setting to test their memory for the fearful experience. In contrast to the vehicle-treated monkeys, who avoided the dark compartment, the ketamine-treated monkeys entered the dark compartment that was previously associated with the fearful experience (p<0.05). Post-mortem analysis of the hippocampus showed that ketamine-treated animals exhibited less doublecortin positive neurons and BrdU-labeled cells in the dentate gyrus. This study reveals that a single low dose of ketamine, administered upon fear retrieval in monkeys, reduce contextual fear memory and attenuate neurogenesis in the hippocampus. These are important findings for considering ketamine as a potential candidate to target traumatic memories in PTSD.

Ketamine for Acute Pain Management and Sedation

TOPIC

Ketamine is beneficial in clinical settings ranging from procedural sedation to the treatment of chronic pain. This article describes the clinical benefits of ketamine for treatment of acute pain and for sedation of patients undergoing mechanical ventilation.

CLINICAL RELEVANCE

Ketamine causes analgesic and amnestic effects by noncompetitive inhibition of the N-methyl-D-aspartate receptor and activation of the opioid μ and κ receptors. Unlike other sedatives, ketamine provides analgesia and amnesia without causing hypotension or respiratory depression. Several studies have elucidated the clinical benefits of ketamine. The use of ketamine has extended beyond critical care areas such as the operating room and intensive care units. Nurses must be familiar with optimal clinical scenarios, monitoring parameters, and contraindications of ketamine.

PURPOSE

To highlight the clinical utility and pharmacological properties of ketamine through a literature review. Current studies of ketamine in acute pain and sedation management are summarized.

CONTENT COVERED

This narrative review describes pharmacological properties, dosing strategies, adminis-tration considerations, and adverse effects of ketamine.

Molecular pathways underlying tissue injuries in the bladder with ketamine cystitis

Ketamine cystitis (KC) is a chronic bladder inflammation leading to urinary urgency, frequency, and pain. The pathogenesis of KC is complicated and involves multiple tissue injuries in the bladder. Recent studies indicated that urothelium disruption, lamina propria fibrosis and inflammation, microvascular injury, neuropathological alterations, and bladder smooth muscle (BSM) abnormalities all contribute to the pathogenesis of KC. Ketamine has been shown to induce these tissue injuries by regulating different signaling pathways. Ketamine can stimulate antiproliferative factor, adenosine triphosphate, and oxidative stress to disrupt urothelium. Lamina propria fibrosis and inflammation are associated with the activation of cyclooxygenase-2, nitric oxide synthase, immunoglobulin E, and transforming growth factor β1. Ketamine contributes to microvascular injury via the N-methyl-D aspartic receptor (NMDAR), and multiple inflammatory and angiogenic factors such as tumor necrosis factor α and vascular endothelial growth factor. For BSM abnormalities, ketamine can depress the protein kinase B, extracellular signal-regulated kinase, Cav1.2, and muscarinic receptor signaling. Elevated purinergic signaling also plays a role in BSM abnormalities. In addition, ketamine affects neuropathological alterations in the bladder by regulating NMDAR- and brain-derived neurotrophic factor-dependent signaling. Inflammatory cells also contribute to neuropathological changes via the secretion of chemical mediators. Clarifying the role and function of these signaling underlying tissue injuries in the bladder with KC can contribute to a better understanding of the pathophysiology of this disease and to the design of effective treatments for KC.

Clozapine protects adult neural stem cells from ketamine-induced cell death in correlation with decreased apoptosis and autophagy

Adult neurogenesis, the production of newborn neurons from neural stem cells (NSCs) has been suggested to be decreased in patients with schizophrenia. A similar finding was observed in an animal model of schizophrenia, as indicated by decreased bromodeoxyuridine (BrdU) labelling cells in response to a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist. The antipsychotic drug clozapine was shown to counteract the observed decrease in BrdU-labelled cells in hippocampal dentate gyrus (DG). However, phenotypic determination by immunohistochemistry analysis could not reveal whether BrdU-positive cells were indeed NSCs. Using a previously established cell model for analysing NSC protection in vitro, we investigated a protective effect of clozapine on NSCs.

Primary NSCs were isolated from the mouse subventricular zone (SVZ), we show that clozapine had a NSC protective activity alone, as evident by employing an ATP cell viability assay. In contrast, haloperidol did not show any NSC protective properties. Subsequently, cells were exposed to the non-competitive NMDA-receptor antagonist ketamine. Clozapine, but not haloperidol, had a NSC protective/anti-apoptotic activity against ketamine-induced cytotoxicity. The observed NSC protective activity of clozapine was associated with increased expression of the anti-apoptotic marker Bcl-2, decreased expression of the pro-apoptotic cleaved form of caspase-3 and associated with decreased expression of the autophagosome marker 1A/1B-light chain 3 (LC3-II).

Collectively, our findings suggest that clozapine may have a protective/anti-apoptotic effect on NSCs, supporting previous in vivo observations, indicating a neurogenesis-promoting activity for clozapine. If the data are further confirmed in vivo, the results may encourage an expanded use of clozapine to restore impaired neurogenesis in schizophrenia.

Effects of Maternal Abdominal Surgery on Fetal Brain Development in the Rabbit Model

INTRODUCTION

Anesthesia during pregnancy can impair fetal neurodevelopment, but effects of surgery remain unknown. The aim is to investigate effects of abdominal surgery on fetal brain development. Hypothesis is that surgery impairs outcome.

METHODS

Pregnant rabbits were randomized at 28 days of gestation to 2 h of general anesthesia (sevoflurane group, n = 6) or to anesthesia plus laparoscopic appendectomy (surgery group, n = 13). On postnatal day 1, neurobehavior of pups was assessed and brains harvested. Primary outcome was neuron density in the frontal cortex, and secondary outcomes included neurobehavioral assessment and other histological parameters.

RESULTS

Fetal survival was lower in the surgery group: 54 versus 100% litters alive at birth (p = 0.0442). In alive litters, pup survival until harvesting was 50 versus 69% (p = 0.0352). No differences were observed for primary outcome (p = 0.5114) for surviving pups. Neuron densities were significantly lower in the surgery group in the caudate nucleus (p = 0.0180), but not different in other regions. No differences were observed for secondary outcomes. Conclusions did not change after adjustment for mortality.

CONCLUSION

Abdominal surgery in pregnant rabbits at a gestational age corresponding to the end of human second trimester results in limited neurohistological changes but not in neurobehavioral impairments. High intrauterine mortality limits translation to clinical scenario, where fetal mortality is close to zero.

Neuroprotective Effects of Dexmedetomidine on the Ketamine-Induced Disruption of the Proliferation and Differentiation of Developing Neural Stem Cells in the Subventricular Zone

Background: Ketamine disrupts the proliferation and differentiation of developing neural stem cells (NSCs). Therefore, the safe use of ketamine in pediatric anesthesia has been an issue of increasing concern among anesthesiologists and children's parents. Dexmedetomidine (DEX) is widely used in sedation as an antianxiety agent and for analgesia. DEX has recently been shown to provide neuroprotection against anesthetic-induced neurotoxicity in the developing brain. The aim of this in vivo study was to investigate whether DEX exerted neuroprotective effects on the proliferation and differentiation of NSCs in the subventricular zone (SVZ) following neonatal ketamine exposure. Methods: Postnatal day 7 (PND-7) male Sprague-Dawley rats were equally divided into the following five groups: control group (n = 8), ketamine group (n = 8), 1 μg/kg DEX+ketamine group (n = 8), 5 μg/kg DEX+ketamine group (n = 8) and 10 μg/kg DEX+ketamine group (n = 8). Immediately after treatment, rats received a single intraperitoneal injection of BrdU, and the proliferation and differentiation of NSCs in the SVZ were assessed using immunostaining at 24 h after the BrdU injection. In the olfactory behavioral tests, rats in each group were raised until 2 months old, and the buried food test and olfactory memory test were performed. Results: The proliferation of NSCs and astrocytic differentiation in the SVZ were significantly inhibited at 24 h after repeated ketamine exposure in the neonatal period, and neuronal differentiation was markedly increased. Furthermore, pretreatment with moderately high (5 μg/kg) or high doses (10 μg/kg) of DEX reversed ketamine-induced disturbances in the proliferation and differentiation of NSCs. In the behavior tests, repeated neonatal ketamine exposure induced olfactory cognitive dysfunction in the adult stage, and moderately high and high doses of DEX reversed the olfactory cognitive dysfunction induced by ketamine. Conclusions: Based on the present findings, pretreatment with a moderately high (5 μg/kg) or high dose (10 μg/kg) of DEX may alleviate the developmental neurogenesis disorder in the SVZ at 24 h after repeated ketamine exposure and improve olfactory cognitive dysfunction in adulthood.

A review of the clinical applications of ketamine in pediatric oncology

Ketamine is a dissociative anesthetic agent with excellent analgesic properties and a favorable safety profile. The feasibility and efficacy of various routes of administration have been established, including intravenous (IV), intramuscular (IM), oral, intranasal, rectal, and transdermal routes. The advent of newer anesthetic agents has led to a decline in the use of ketamine as an anesthetic, but its utility in short-term sedation and analgesia has expanded. Its value for chronic pain management in children with cancer is being increasingly recognized but requires more evidence. The use of topical ketamine is largely in investigational stages. Medical use of ketamine is, to a great extent, free from significant long-term neurological side effects. The objective of this review is to provide a brief account of the pharmacology of ketamine and primarily focus on the clinical applications of ketamine in pediatric oncology.

L-Theanine Attenuates Isoflurane-Induced Injury in Neural Stem Cells and Cognitive Impairment in Neonatal Mice

The neurodevelopmental toxicity of isoflurane has been proved by many studies, which makes it essential to explore the underline mechanisms and search for protective agents to attenuate its neurotoxcity. Accumulating evidence showed that L-theanine had neuroprotective effects on injured neurons and the developing brain. The present study was designed to investigate whether L-theanine could attenuate isoflurane-induced damage in neural stem cells and cognitive impairment in young mice, and to discuss the role of protein kinase B (Akt)-glycogen synthase kinase 3β (GSK-3β) signaling pathway in this process. Multipotential neural stem cells (NSCs) and C57BL/6J mice were treated with either gas mixture, isoflurane, or L-theanine 30 min prior to isoflurane exposure, respectively. NSC viability was detected by CCK-8 assay. NSC proliferation and apoptosis were assessed by immunofluorescence and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay, respectively. The levels of cleaved caspase-3 and phosphorylated (p)-Akt and p-GSK-3β in NSCs were tested by Western blotting. Cognitive function of mice was tested by Morris Water Maze at postnatal day (P) 30-35. The results indicated that isoflurane exposure inhibited NSC viability and proliferation, promoted NSC apoptosis as well as increased caspase-3 activation and down-regulated the expressions of p-Akt and p-GSK-3β in NSCs, and that isoflurane exposure on neonatal mice would induce late cognitive impairment. Pretreatment with L-theanine could attenuate isoflurane-caused damage in NSCs and cognitive deficits in young mice. Addinonally, the protective effects of L-theanine on isoflurane-injured NSCs could be reversed by Akt inhibitor Triciribine. Our data showed that pretreatment with L-theanine eliminated the NSC damage and cognitive impairment induced by isoflurane exposure, and that the neuroprotective effect of L-theanine was associated with the Akt-GSK-3β signaling pathway.

Ketamine promotes the neural differentiation of mouse embryonic stem cells by activating mTOR

Ketamine is a widely used general anesthetic and has been reported to demonstrate neurotoxicity and neuroprotection. Investigation into the regulatory mechanism of ketamine on influencing neural development is of importance for a better and safer way of relieving pain. Reverse transcription‑quantitative polymerase chain reaction and western blotting were used to detect the critical neural associated gene expression, and flow cytometry to detect the neural differentiation effect. Hence, in the present study the underlying mechanism of ketamine (50 nM) on neural differentiation of the mouse embryonic stem cell (mESC) line 46C was investigated. The results demonstrated that a low dose of ketamine (50 nM) promoted the differentiation of mESCs to neural stem cells (NSCs) and activated mammalian target of rapamycin (mTOR) by upregulating the expression levels of phosphorylated (p)‑mTOR. Furthermore, inhibition of the mTOR signaling pathway by rapamycin or knockdown of mTOR suppressed neural differentiation. A rescue experiment further confirmed that downregulation of mTOR inhibited the promotion of neural differentiation induced by ketamine. Taken together, the present study indicated that a low level of ketamine upregulated p‑mTOR expression levels, promoting neural differentiation.

General Anesthetic-Induced Neurotoxicity in the Immature Brain: Reevaluating the Confounding Factors in the Preclinical Studies

General anesthetic (GA) is used clinically to millions of young children each year to facilitate surgical procedures, relieve perioperative stress, and provide analgesia and amnesia. During recent years, there is a growing concern regarding a causal association between early life GA exposure and subsequently long-term neurocognitive abnormalities. To address the increasing concern, mounting preclinical studies and clinical trials have been undergoing. Until now, nearly all of the preclinical findings show that neonatal exposure to GA causally leads to acute neural cell injury and delayed cognitive impairment. Unexpectedly, several influential clinical findings suggest that early life GA exposure, especially brief and single exposure, does not cause adverse neurodevelopmental outcome, which is not fully in line with the experimental findings and data from several previous cohort trials. As the clinical data have been critically discussed in previous reviews, in the present review, we try to analyze the potential factors of the experimental studies that may overestimate the adverse effect of GA on the developing brain. Meanwhile, we briefly summarized the advance in experimental research. Generally, our purpose is to provide some useful suggestions for forthcoming preclinical studies and strengthen the powerfulness of preclinical data.

Ca2+-PKCα-ERK1/2 signaling pathway is involved in the suppressive effect of propofol on proliferation of neural stem cells from the neonatal rat hippocampus

Neonatal exposure to propofol induces persistent behavioral abnormalities in adulthood. In addition to triggering the apoptosis of neurons in the developing brain, anesthetics may contribute to the development of cognitive deficits by interfering neurogenesis. Given the importance of neural stem cell (NSC) proliferation in neurogenesis, the effect of propofol on NSC proliferation and the mechanisms underlying this effect were investigated. Hippocampal NSC proliferation from neonatal rats was examined using 5-bromo-2'-deoxyuridine incorporation assays in vitro. The [Ca²⁺]i was analyzed using flow cytometry. The activations of protein kinase C (PKC)-α and extracellular signal-regulated kinases 1/2 (ERK1/2) were measured by western blot. Our results showed that propofol significantly inhibited NSC proliferation in vitro. [Ca²⁺]i and activations of PKCα and ERK1/2 in NSCs were markedly suppressed by propofol (5, 10, 20, 40 and 80 μM). Ca²⁺ channel blocker verapamil, PKCα inhibitor chelerythrine and ERK1/2 kinase inhibitor PD98059 exerted their maximal effects on NSC function at concentrations of 20, 10 and 20 μM, respectively. Propofol (20 μM) could not produce further additional suppression effects when used in combination with verapamil (20 μM), chelerythrine (10 μM) or PD98059 (20 μM). In addition, phorbol-12-myristate-13-acetate (PMA, a activator of PKC) markedly attenuated the suppressive effects of propofol on ERK1/2 phosphorylation and NSC proliferation. The inhibition effects on PKCα activation, ERK1/2 phosphorylation and NSC proliferation induced by propofol were significantly improved by BayK8644 (a calcium channel agonist). These results indicate that propofol can inhibits hippocampal NSC proliferation by suppressing the Ca²⁺-PKCα-ERK1/2 signaling pathway.

Effects of Perinatal Exposure to Ketamine on the Developing Brain

Initially used as an analgesic and anesthetic, ketamine has unfortunately been abused as a popular recreational party drug due to its psychotropic effects. Over the last decade, ketamine has also emerged as an effective rapid-onset anti-depressant. The increasingly widespread use and misuse of the drug in infants and pregnant women has posed a concern about the neurotoxicity of ketamine to the immature brains of developing fetuses and children. In this review, we summarize recent research findings on major possible mechanisms of perinatal ketamine-induced neurotoxicity. We also briefly summarize the neuroprotective effects of ketamine in the presence of noxious stimuli. Future actions include implementation of more drug abuse education and prevention campaigns to raise the public’s awareness of the harmful effects of ketamine abuse; further investigations to justify the clinical use of ketamine as analgesic, anesthetic and anti-depressant; and further studies to develop alternatives to ketamine or treatments that can alleviate the detrimental effects of ketamine use, especially in infants and pregnant women.

Streptozotocin Impairs Proliferation and Differentiation of Adult Hippocampal Neural Stem Cells in Vitro-Correlation With Alterations in the Expression of Proteins Associated With the Insulin System

Rats intracerebroventricularily (icv) treated with streptozotocin (STZ), shown to generate an insulin resistant brain state, were used as an animal model for the sporadic form of Alzheimer’s disease (sAD). Previously, we showed in an in vivo study that 3 months after STZ icv treatment hippocampal adult neurogenesis (AN) is impaired. In the present study, we examined the effects of STZ on isolated adult hippocampal neural stem cells (NSCs) using an in vitro approach. We revealed that 2.5 mM STZ inhibits the proliferation of NSCs as indicated by reduced number and size of neurospheres as well as by less BrdU-immunoreactive NSCs. Double immunofluorescence stainings of NSCs already being triggered to start with their differentiation showed that STZ primarily impairs the generation of new neurons, but not of astrocytes. For revealing mechanisms possibly involved in mediating STZ effects we analyzed expression levels of insulin/glucose system-related molecules such as the glucose transporter (GLUT) 1 and 3, the insulin receptor (IR) and the insulin-like growth factor (IGF) 1 receptor. Applying quantitative Real time-PCR (qRT-PCR) and immunofluorescence stainings we showed that STZ exerts its strongest effects on GLUT3 expression, as GLUT3 mRNA levels were found to be reduced in NSCs, and less GLUT3-immunoreactive NSCs as well as differentiating cells were detected after STZ treatment. These findings suggest that cultured NSCs are a good model for developing new strategies to treat nerve cell loss in AD and other degenerative disorders.

Prospective follow-up of a cohort of preterm infants<33 WG receiving ketamine for tracheal intubation in the delivery room: Neurological outcome at 1 and 2 years

OBJECTIVE

Although ketamine analgesia is effective in reducing pain and facilitating the tracheal intubation of newborns in the delivery room, no data on the neurological effects of this treatment are available. This study compared the neurodevelopmental outcomes at 2 years of age in a cohort of preterm newborns having received ketamine prior to tracheal intubation at birth (the ketamine group) and in a control group.

METHODS

We included newborns delivered at less than 33 weeks gestational age (WGA) having undergone tracheal intubation at birth. The Ages and Stages Questionnaire (ASQ) was completed at 1 and 2 years of age. The development quotient (DQ) was calculated from the revised Brunet-Lezine score assessed at a corrected age of 2 years.

RESULTS

There were no statistically significant differences between the ketamine group (n=54 at 1 year and n=51 at 2 years) and the control group (n=16 at 1 and 2 years) in terms of the mean±standard deviation DQ at the age of 2 (98±12 vs. 103±9, respectively; P=0.17) and the ASQ score at the age of 2 (221±44 vs. 230±39, respectively; P=0.55).

DISCUSSION

This prospective cohort of 51 preterm newborns having received ketamine at birth did not reveal any differences in terms of neurological development at the age of 2 (relative to a control group and the literature data). These preliminary results must be confirmed in a randomized trial with longer follow-up.

KIF17 mediates the learning and memory impairment in offspring induced by maternal exposure to propofol during middle pregnancy

Preclinical studies suggest that propofol may cause neuronal injury to the developing brain. A previous study demonstrated that, in a rat model, maternal exposure to propofol during early or late pregnancy caused learning and memory impairment in the offspring. However, whether propofol exposure during middle pregnancy can cause long‑term behavioral deficits in the offspring remains to be elucidated. N‑methyl‑D‑aspartate receptor 2B subunit (NR2B) serves a critical role in memory modulation. To exert its function, NR2B must be transported to the neuronal membrane by kinesin family member 17 (KIF17). The aim of the present study was to investigate the role of KIF17 in learning and memory impairment in rat offspring caused by propofol exposure during middle pregnancy. Pregnant rats were exposed to propofol on gestational day 14 (G14) for 4 and 8 h, with control pregnant rats receiving an equal volume of normal saline. The learning and memory of the offspring was assessed using Morris water maze tests from postnatal day 30 (P30) to P36. The levels of KIF17 protein, total NR2B (T‑NR2B) and membrane NR2B (M‑NR2B) in the hippocampus were detected using western blotting. The results demonstrated that propofol exposure caused learning and memory deficits and decreased KIF17 and M‑NR2B protein levels in the hippocampus; however, no but changes in the expression of T‑NR2B were observed. These results indicate that maternal propofol exposure during middle pregnancy impairs learning and memory in offspring rats by suppressing the expression of KIF17 and inhibiting the translocation of NR2B to the neuronal membrane.

The Effects of Different Factors on the Behavior of Neural Stem Cells

The repair of central nervous system (CNS) injury has been a worldwide problem in the biomedical field. How to reduce the damage to the CNS and promote the reconstruction of the damaged nervous system structure and function recovery has always been the concern of nerve tissue engineering. Multiple differentiation potentials of neural stem cell (NSC) determine the application value for the repair of the CNS injury. Thus, how to regulate the behavior of NSCs becomes the key to treating the CNS injury. So far, a large number of researchers have devoted themselves to searching for a better way to regulate the behavior of NSCs. This paper summarizes the effects of different factors on the behavior of NSCs in the past 10 years, especially on the proliferation and differentiation of NSCs. The final purpose of this review is to provide a more detailed theoretical basis for the clinical repair of the CNS injury by nerve tissue engineering.

The neuroprotective effects of remifentanil on isoflurane-induced apoptosis in the neonatal rat brain

Remifentanil is one of the most frequently prescribed opioids used in combination with inhalation anesthetics in clinical practice, but the effects of such combinations on the developing rat brain are unknown. In our study, we investigated first the potential neurotoxic effects of remifentanil on the developing brain and then the effects of remifentanil on isoflurane-induced apoptosis in the neonatal rat brain following exposure to a nociceptive stimulus. In the first experiment, postnatal day (P) 7 rats were randomly exposed to 30% oxygen, 1.5% isoflurane alone, 1.5% isoflurane and a plantar incision, normal saline, or remifentanil at a low (5 µg·kg^-1·h^-1), moderate (20 µg·kg^-1·h^-1) or high (80 µg·kg^-1·h^-1) dose for 4 h. In the second 4-h experiment, P7 rats were randomly exposed to 1.5% isoflurane, infused with different doses of remifentanil (5, 10, and 20 µg·kg^-1·h^-1), and subjected to a plantar incision. In both experiments, the number of apoptotic neurons in the cortex, hippocampus, and thalamus was assessed after two hours by cleaved caspase-3 or TUNEL staining. Our data showed that unlike 1.5% isoflurane, remifentanil at any dose did not cause significant neuronal apoptosis in any brain section. In addition, in response to a nociceptive stimulus, the infusion of 10 µg·kg^-1·h^-1 remifentanil reduced isoflurane-induced apoptosis in the hippocampus (P = 0.003 in CA1, P = 0.002 in CA3) but not in the cortex or thalamus. Our findings suggest that remifentanil does not induce apoptosis and reduces isoflurane-induced apoptosis in the developing brain.

PACAP Protects Adult Neural Stem Cells from the Neurotoxic Effect of Ketamine Associated with Decreased Apoptosis, ER Stress and mTOR Pathway Activation

Ketamine administration is a well-established approach to mimic experimentally some aspects of schizophrenia. Adult neurogenesis dysregulation is associated with psychiatric disorders, including schizophrenia. The potential role of neurogenesis in the ketamine-induced phenotype is largely unknown. Recent results from human genetic studies have shown the pituitary adenylate cyclase-activating polypeptide (PACAP) gene is a risk factor for schizophrenia. Its potential role on the regulation of neurogenesis in experimental model of schizophrenia remains to be investigated. We aimed to determine whether ketamine affects the viability of adult neural stem cells (NSC). We also investigated whether the detrimental effect mediated by ketamine could be counteracted by PACAP. NSCs were isolated from the subventricular zone of the mouse and exposed to ketamine with/without PACAP. After 24 hours, cell viability, potential involvement of apoptosis, endoplasmic reticulum (ER) stress, mTOR and AMPA pathway activation were assessed by quantitative RT-PCR and Western blot analysis. We show that ketamine impairs NSC viability in correlation with increased apoptosis, ER stress and mTOR activation. The results also suggest that the effect of ketamine occurs via AMPA receptor activation. Finally, we show that PACAP counteracted the decreased NSC viability induced by ketamine via the specific activation of the PAC-1 receptor subtype. Our study shows that the NSC viability may be negatively affected by ketamine with putative importance for the development of a schizophrenia phenotype in the ketamine induced animal model of schizophrenia. The neuroprotective effect via PAC-1 activation suggests a potentially novel pharmacological target for the treatment of schizophrenia, via neurogenesis normalization.

Protective Effect of Minocycline Against Ketamine-Induced Injury in Neural Stem Cell: Involvement of PI3K/Akt and Gsk-3 Beta Pathway

It has been suggested that ketamine cause injury during developing brain. Minocycline (MC) could prevent neuronal cell death through the activation of cell survival signals and the inhibition of apoptotic signals in models of neurodegenerative diseases. Here we investigated the protective effect of MC against ketamine-induced injury in neural stem cells (NSCs) from neonatal rat. Ketamine (100 μM/L) significantly inhibited NSC proliferation, promoted their differentiation into astrocytes and suppressed neuronal differentiation of NSCs. Moreover, the apoptotic level was increased following ketamine exposure. MC pretreatment greatly enhanced cell viability, decreased caspase-3-like activity, even reversed the differentiation changes caused by ketamine. To elucidate a possible mechanism of MC' neuroprotective effect, we investigated the phosphatidylinositol 3-kinase (PI3K) pathway using LY294002, a specific PI3K inhibitor. Immunoblotting revealed that MC enhanced the phosphorylation/activation of Akt and phosphorylation/inactivation of glycogen synthase kinase-3beta (Gsk-3β). Our results suggest that PI3K/Akt and Gsk-3β pathway are involved in the neuroprotective effect of MC.

Neurogenesis and developmental anesthetic neurotoxicity

The mechanism by which anesthetics might act on the developing brain in order to cause long term deficits remains incompletely understood. The hippocampus has been identified as a structure that is likely to be involved, as rodent models show numerous deficits in behavioral tasks of learning that are hippocampal-dependent. The hippocampus is an unusual structure in that it is the site of large amounts of neurogenesis postnatally, particularly in the first year of life in humans, and these newly generated neurons are critical to the function of this structure. Intriguingly, neurogenesis is a major developmental event that occurs during postulated windows of vulnerability to developmental anesthetic neurotoxicity across the different species in which it has been studied. In this review, we examine the evidence for anesthetic effects on neurogenesis in the early postnatal period and ask whether neurogenesis should be studied further as a putative mechanism of injury. Multiple anesthetics are considered, and both in vivo and in vitro work is presented. While there is abundant evidence that anesthetics act to suppress neurogenesis at several different phases, evidence of a causal link between these effects and any change in learning behavior remains elusive.

Differential Effects of Olanzapine and Haloperidol on MK-801-induced Memory Impairment in Mice

OBJECTIVE

We investigated the differential effects of the antipsychotic drugs olanzapine and haloperidol on MK-801-induced memory impairment and neurogenesis in mice.

METHODS

MK-801 (0.1 mg/kg) was administered 20 minutes prior to behavioral testing over 9 days. Beginning on the sixth day of MK-801 treatment, either olanzapine (0.05 mg/kg) or haloperidol (0.05 mg/kg) was administered 40 minutes prior to MK-801 for the final 4 days. Spatial memory performance was measured using a Morris water maze (MWM) test for 9 days (four trials/day). Immunohistochemistry with bromodeoxyuridine (BrdU) was used to identify newborn cells labeled in tissue sections from the dentate gyrus of the hippocampus.

RESULTS

MK-801 administration over 9 days significantly impaired memory performance in the MWM test compared to untreated controls (p＜0.05) and these deficits were blocked by treatment with olanzapine (p＜0.05) but not haloperidol. The administration of MK-801 also resulted in a decrease in the number of BrdU-labeled cells in the dentate gyrus (28.6%; p＜0.01), which was prevented by treatment with olanzapine (p＜0.05) but not haloperidol.

CONCLUSION

These results suggest that olanzapine has a protective effect against cognitive impairments induced by MK-801 in mice via the stimulating effects of neurogenesis.

Prolonged Treatment with Propofol Transiently Impairs Proliferation but Not Survival of Rat Neural Progenitor Cells In Vitro

Neurocognitive dysfunction is common in survivors of intensive care. Prolonged sedation has been implicated but the mechanisms are unclear. Neurogenesis continues into adulthood and is implicated in learning. The neural progenitor cells (NPC) that drive neurogenesis have receptors for the major classes of sedatives used clinically, suggesting that interruption of neurogenesis may partly contribute to cognitive decline in ICU survivors. Using an in vitro system, we tested the hypothesis that prolonged exposure to propofol concentration- and duration-dependently kills or markedly decreases the proliferation of NPCs. NPCs isolated from embryonic day 14 Sprague-Dawley rat pups were exposed to 0, 2.5, or 5.0 μg/mL of propofol, concentrations consistent with deep clinical anesthesia, for either 4 or 24 hours. Cells were assayed for cell death and proliferation either immediately following propofol exposure or 24 hours later. NPC death and apoptosis were measured by propidium iodine staining and cleaved caspase-3 immunocytochemistry, respectively, while proliferation was measured by EdU incorporation. Staurosporine (1μM for 6h) was used as a positive control for cell death. Cells were analyzed with unbiased high-throughput immunocytochemistry. There was no cell death at either concentration of propofol or duration of exposure. Neither concentration of propofol impaired NPC proliferation when exposure lasted 4 h, but when exposure lasted 24 h, propofol had an anti-proliferative effect at both concentrations (P < 0.0001, propofol vs. control). However, this effect was transient; proliferation returned to baseline 24 h after discontinuation of propofol (P = 0.37, propofol vs. control). The transient but reversible suppression of NPC proliferation, absence of cytotoxicity, and negligible effect on the neural stem cell pool pool suggest that propofol, even in concentrations used for clinical anesthesia, has limited impact on neural progenitor cell biology.

Ketamine exposure during embryogenesis inhibits cellular proliferation in rat fetal cortical neurogenic regions

BACKGROUND

Developmental neurotoxicity of ketamine, an N-methyl-D-aspartate receptor antagonist, must be considered due to its widespread uses for sedation/analgesia/anesthesia in pediatric and obstetric settings. Dose-dependent effects of ketamine on cellular proliferation in the neurogenic regions of rat fetal cortex [ventricular zone (VZ) and subventricular zone (SVZ)] were investigated in this in vivo study.

METHODS

Timed-pregnant Sprague-Dawley rats at embryonic day 17 (E17) were given with different doses of ketamine intraperitoneally (0, 1, 2, 10, 20, 40, and 100 mg/kg). Proliferating cells in the rat fetal brains were labeled by injecting 100 mg/kg of 5-bromo-2'-deoxyuridine (BrdU) intraperitoneally. BrdU-labeled cells were detected by immunostaining methods. The numbers of BrdU-positive cells in VZ and SVZ of rat fetal cortex were employed to quantify proliferation in the developing rat cortex.

RESULTS

Ketamine dose-dependently reduced the number of BrdU-positive cells in VZ (P < 0.001) and SVZ (P < 0.001) of the rat fetal cortex. SVZ showed greater susceptibility to ketamine-induced reduction of proliferation in rat fetal cortex, occurring even at clinically relevant doses (2 mg/kg).

CONCLUSION

These data suggest that exposure to ketamine during embryogenesis can dose-dependently inhibit the cellular proliferation in neurogenic regions of the rat fetal cortex.

Ketamine Affects the Neurogenesis of the Hippocampal Dentate Gyrus in 7-Day-Old Rats

Ketamine has been reported to cause neonatal neurotoxicity via a neuronal apoptosis mechanism; however, no in vivo research has reported whether ketamine could affect postnatal neurogenesis in the hippocampal dentate gyrus (DG). A growing number of experiments suggest that postnatal hippocampal neurogenesis is the foundation of maintaining normal hippocampus function into adulthood. Therefore, this study investigated the effect of ketamine on hippocampal neurogenesis. Male Sprague-Dawley rats were divided into two groups: the control group (equal volume of normal saline), and the ketamine-anesthesia group (40 mg/kg ketamine in four injections at 1 h intervals). The S-phase marker 5-bromodeoxyuridine (BrdU) was administered after ketamine exposure to postnatal day 7 (PND-7) rats, and the neurogenesis in the hippocampal DG was assessed using single- or double-immunofluorescence staining. The expression of GFAP in the hippocampal DG was measured by western blot analysis. Spatial reference memory was tested by Morris water maze at 2 months after PND-7 rats exposed to ketamine treatment. The present results showed that neonatal ketamine exposure significantly inhibited neural stem cell (NSC) proliferation, decreased astrocytic differentiation, and markedly enhanced neuronal differentiation. The disruptive effect of ketamine on the proliferation and differentiation of NSCs lasted at least 1 week and disappeared by 2 weeks after ketamine exposure. Moreover, the migration of newborn neurons in the granule cell layer and the growth of astrocytes in the hippocampal DG were inhibited by ketamine on PND-37 and PND-44. Finally, ketamine caused a deficit in hippocampal-dependent spatial reference memory tasks at 2 months old. Our results suggested that ketamine may interfere with hippocampal neurogenesis and long-term neurocognitive function in PND-7 rats. These findings may provide a new perspective to explain the adult neurocognitive dysfunction induced by neonatal ketamine exposure.

Repeated, high-dose dextromethorphan treatment decreases neurogenesis and results in depression-like behavior in rats

Abuse of cough mixture is increasingly prevalent worldwide. Clinical studies showed that chronic consumption of cough mixture at high dosages may lead to psychiatric symptoms, especially affective disturbances, with the underlying mechanisms remain elusive. The present study aims at exploring the effect of repeated, high-dose dextromethorphan (DXM, a common active component of cough mixture) treatment on adult hippocampal neurogenesis, which is associated with pathophysiology of mood disturbances. After treatment with a high-dose of DXM (40 mg/kg/day) for 2 weeks, Sprague-Dawley rats showed increased depression-like behavior when compared to the control animals. Neurogenesis in the hippocampus was suppressed by DXM treatment, which was indicated by decreases in number of proliferative cells and doublecortin (an immature neuron marker)-positive new neurons. Furthermore, the dendritic complexity of the immature neurons was suppressed by DXM treatment. These findings suggest that DXM induces depression- and anxiety-like behavior and suppresses neurogenesis in rats. The current experimental paradigm may serve as an animal model for study on affective effect of cough mixture abuse, rehabilitation treatment options for abusers and the related neurological mechanisms.

Positron Emission Tomography with [(18)F]FLT Revealed Sevoflurane-Induced Inhibition of Neural Progenitor Cell Expansion in vivo

Neural progenitor cell expansion is critical for normal brain development and an appropriate response to injury. During the brain growth spurt, exposures to general anesthetics, which either block the N-methyl-d-aspartate receptor or enhance the γ-aminobutyric acid receptor type A can disturb neuronal transduction. This effect can be detrimental to brain development. Until now, the effects of anesthetic exposure on neural progenitor cell expansion in vivo had seldom been reported. Here, minimally invasive micro positron emission tomography (microPET) coupled with 3'-deoxy-3' [(18)F] fluoro-l-thymidine ([(18)F]FLT) was utilized to assess the effects of sevoflurane exposure on neural progenitor cell proliferation. FLT, a thymidine analog, is taken up by proliferating cells and phosphorylated in the cytoplasm, leading to its intracellular trapping. Intracellular retention of [(18)F]FLT, thus, represents an observable in vivo marker of cell proliferation. Here, postnatal day 7 rats (n = 11/group) were exposed to 2.5% sevoflurane or room air for 9 h. For up to 2 weeks following the exposure, standard uptake values (SUVs) for [(18)F]-FLT in the hippocampal formation were significantly attenuated in the sevoflurane-exposed rats (p < 0.0001), suggesting decreased uptake and retention of [(18)F]FLT (decreased proliferation) in these regions. Four weeks following exposure, SUVs for [(18)F]FLT were comparable in the sevoflurane-exposed rats and in controls. Co-administration of 7-nitroindazole (30 mg/kg, n = 5), a selective inhibitor of neuronal nitric oxide synthase, significantly attenuated the SUVs for [(18)F]FLT in both the air-exposed (p = 0.00006) and sevoflurane-exposed rats (p = 0.0427) in the first week following the exposure. These findings suggested that microPET in couple with [(18)F]FLT as cell proliferation marker could be used as a non-invasive modality to monitor the sevoflurane-induced inhibition of neural progenitor cell proliferation in vivo.

Ketamine affects the neurogenesis of rat fetal neural stem progenitor cells via the PI3K/Akt-p27 signaling pathway

Ketamine is widely used as an anesthetic, analgesic, or sedative in pediatric patients. We reported that ketamine alters the normal neurogenesis of rat fetal neural stem progenitor cells (NSPCs) in the developing brain, but the underlying mechanisms remain unknown. The PI3K-PKB/Akt (phosphatidylinositide 3-kinase/protein kinase B) signaling pathway plays many important roles in cell survival, apoptosis, and proliferation. We hypothesized that PI3K-PKB/Akt signaling may be involved in ketamine-altered neurogenesis of cultured NSPCs in vitro. NSPCs were isolated from Sprague-Dawley rat fetuses on gestational day 17. 5-bromo-2'-deoxyuridine (BrdU) incorporation, Ki67 staining, and differentiation tests were utilized to identify primary cultured NSPCs. Immunofluorescent staining was used to detect Akt expression, whereas Western blots measured phosphorylated Akt and p27 expression in NSPCs exposed to different treatments. We report that cultured NSPCs had properties of neurogenesis: proliferation and neural differentiation. PKB/Akt was expressed in cultured rat fetal cortical NSPCs. Ketamine inhibited the phosphorylation of Akt and further enhanced p27 expression in cultured NSPCs. All ketamine-induced PI3K/Akt signaling changes could be recovered by N-methyl-d-aspartate (NMDA) receptor agonist, NMDA. These data suggest that the inhibition of PI3K/Akt-p27 signaling may be involved in ketamine-induced neurotoxicity in the developing brain, whereas excitatory NMDA receptor activation may reverse these effects.

Neonatal ketamine exposure causes impairment of long-term synaptic plasticity in the anterior cingulate cortex of rats

Ketamine, a dissociative anesthetic most commonly used in many pediatric procedures, has been reported in many animal studies to cause widespread neuroapoptosis in the neonatal brain after exposure in high doses and/or for a prolonged period. This neurodegenerative change occurs most severely in the forebrain including the anterior cingulate cortex (ACC) that is an important brain structure for mediating a variety of cognitive functions. However, it is still unknown whether such apoptotic neurodegeneration early in life would subsequently impair the synaptic plasticity of the ACC later in life. In this study, we performed whole-cell patch-clamp recordings from the ACC brain slices of young adult rats to examine any alterations in long-term synaptic plasticity caused by neonatal ketamine exposure. Ketamine was administered at postnatal day 4-7 (subcutaneous injections, 20mg/kg given six times, once every 2h). At 3-4weeks of age, long-term potentiation (LTP) was induced and recorded by monitoring excitatory postsynaptic currents from ACC slices. We found that the induction of LTP in the ACC was significantly reduced when compared to the control group. The LTP impairment was accompanied by an increase in the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated excitatory synaptic transmission and a decrease in GABA inhibitory synaptic transmission in neurons of the ACC. Thus, our present findings show that neonatal ketamine exposure causes a significant LTP impairment in the ACC. We suggest that the imbalanced synaptic transmission is likely to contribute to ketamine-induced LTP impairment in the ACC.

Ketamine and atropine decrease pain for preterm newborn tracheal intubation in the delivery room: an observational pilot study

AIM

Various analgesic strategies are used before tracheal intubation of preterm newborns in the delivery room, due to the lack of a standard protocol and difficult venous access. This study evaluated the feasibility and efficacy of short venous catheter insertion and immediate ketamine analgesia for tracheal intubation of preterm newborns at birth in the delivery room.

METHODS

Prospective observational pilot study, with ketamine and atropine used at the paediatrician's discretion. Pain score, heart rate, SpO2 nadirs, procedure duration and neonatal intensive care unit morbidity were recorded.

RESULTS

Fifty-seven consecutive preterm newborns were included between January I and June 30, 2012: 15 in the no analgesia group and 39 in the intravenous ketamine group. Short catheter insertion failed in three newborns. The pain score was lower during laryngoscopy in the ketamine group (4 ± 0.7 vs. 2.9 ± 3.2 in the no analgesia group, p < 0.001). The heart rate nadir during tracheal intubation was 150.7 ± 29.6 bpm (vs. 112.6 ± 35.5 bpm in the no analgesia group, p < 0.01). Surfactant therapy was administered to 79.5% of newborns in the ketamine group (vs. 92.3%, p = 0.29) in the first 30 min of life.

CONCLUSION

Short venous catheter insertion with immediate ketamine analgesia plus atropine for tracheal intubation of preterm newborns in the delivery room was effective in decreasing pain and preventing vagal bradycardia.