Hyperphosphorylated tau in the brains of mice and monkeys with long-term administration of ketamine

Esketamine induces tripartite motif-containing protein 24 to improve cognitive dysfunction in Alzheimer's disease

Esketamine has been revealed to improve cognitive impairments under different conditions, while its function in Alzheimer's disease (AD) has not been well characterized. We expounded the effects and detailed mechanism of esketamine in triple transgenic AD (3xTg-AD) mice in the present study. The impaired spatial learning and memory retention of 3xTg-AD mice were ameliorated by esketamine, whereas tripartite motif-containing protein 24 (TRIM24) depletion reversed the ameliorative effects of esketamine in 3xTg-AD mice. Esketamine elevated the extent of PI3K and AKT phosphorylation in the hippocampus by promoting TRIM24 expression, and knockdown of TRIM24 impaired the PI3K/AKT pathway. AD-like mice had increased expression of pro-inflammatory molecules and elevated expression of GFAP and p-Tau. Esketamine reduced inflammation, but its therapeutic effect was reversed by TRIM24 knockdown. The PI3K/AKT pathway blockage exacerbated cognitive deficits and neuroinflammatory responses in mice. Thus, esketamine has the potential to improve the cognitive and memory functions of 3xTg-AD mice by repressing neuroinflammation by activating TRIM24 and the downstream PI3K/AKT pathway.

Ketamine administration causes cognitive impairment by destroying the circulation function of the glymphatic system

BACKGROUND

Ketamine, as a non-competitive antagonist of N-methyl-D-aspartate (NMDA) receptors, was originally used in general anesthesia. Epidemiological data show that ketamine has become one of the most commonly abused drugs in China. Ketamine administration might cause cognitive impairment; however, its molecular mechanism remains unclear. The glymphatic system is a lymphoid system that plays a key role in metabolic waste removal and cognitive regulation in the central nervous system.

METHODS

Focusing on the glymphatic system, this study evaluated the behavioral performance and circulatory function of the glymphatic system by building a short-term ketamine administration model in mice, and detected the expression levels of the 5-HT2c receptor, ΔFosb, Pten, Akt, and Aqp4 in the hippocampus. Primary astrocytes were cultured to verify the regulatory relationships among related indexes using a 5-HT2c receptor antagonist, a 5-HT2c receptor short interfering RNA (siRNA), and a ΔFosb siRNA.

RESULTS

Ketamine administration induced ΔFosb accumulation by increasing 5-HT2c receptor expression in mouse hippocampal astrocytes and primary astrocytes. ΔFosb acted as a transcription factor to recognize the AATGATTAAT bases in the 5' regulatory region of the Aqp4 gene (-1096 bp to -1087 bp), which inhibited Aqp4 expression, thus causing the circulatory dysfunction of the glymphatic system, leading to cognitive impairment.

CONCLUSIONS

Although this regulatory mechanism does not involve the Pten/Akt pathway, this study revealed a new mechanism of ketamine-induced cognitive impairment in non-neuronal systems, and provided a theoretical basis for the safety of clinical treatment and the effectiveness of withdrawal.

Long-term quality of life after repeated ketamine infusions in anxious and nonanxious patients with depression

BACKGROUND

There have been many studies on the benefits of repeated ketamine infusions on patients' depression but few on the impact of ketamine on patients' long-term quality of life (QoL). This study investigated long-term QoL in individuals with depression, both anxious and nonanxious.

METHODS

A total of 107 individuals with a diagnosis of depression were included in the study. The patients were evaluated on Days 0, 13 and 26 and Months 6 and 9, and they received six ketamine infusions over the course of two weeks. The World Health Organization Quality of Life-BREF (WHOQOL-BREF) Scale and the Patient Health Questionnaire-9 (PHQ-9) Scale were used to measure depressive symptoms and QoL. Linear mixed models were used to evaluate depressive symptoms and QoL during ketamine treatment.

RESULTS

A total of 67.2 % of patients were diagnosed with anxious depression. In the long term, there were no significant differences in the time-by-group interactions for general QoL (F = 0.510; P = 0.676), physical QoL (F = 2.092; P = 0.102), psychological QoL (F = 0.102; P = 0.959), social QoL (F = 2.180; P = 0.091), or environmental QoL (F = 1.849; P = 0.139) between the two groups.

LIMITATIONS

The main limitation of this study is its open-label design.

CONCLUSION

The improvement in depression symptoms and QoL following ketamine treatment was not impacted by the presence or absence of anxiety in patients who were depressed prior to treatment. Only occasionally did depressed individuals with anxiety experience a worsening of their quality of life compared to those without anxiety.

Targeting Sigma Receptors for the Treatment of Neurodegenerative and Neurodevelopmental Disorders

The sigma-1 receptor is a 223 amino acid-long protein with a recently identified structure. The sigma-2 receptor is a genetically unrelated protein with a similarly shaped binding pocket and acts to influence cellular activities similar to the sigma-1 receptor. Both proteins are highly expressed in neuronal tissues. As such, they have become targets for treating neurological diseases, including Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), multiple sclerosis (MS), Rett syndrome (RS), developmental and epileptic encephalopathies (DEE), and motor neuron disease/amyotrophic lateral sclerosis (MND/ALS). In recent years, there have been many pre-clinical and clinical studies of sigma receptor (1 and 2) ligands for treating neurological disease. Drugs such as blarcamesine, dextromethorphan and pridopidine, which have sigma-1 receptor activity as part of their pharmacological profile, are effective in treating multiple aspects of several neurological diseases. Furthermore, several sigma-2 receptor ligands are under investigation, including CT1812, rivastigmine and SAS0132. This review aims to provide a current and up-to-date analysis of the current clinical and pre-clinical data of drugs with sigma receptor activities for treating neurological disease.

Tau protein plays a role in the mechanism of cognitive disorders induced by anesthetic drugs

Cognitive disorders are mental health disorders that can affect cognitive ability. Surgery and anesthesia have been proposed to increase the incidence of cognitive dysfunction, including declines in memory, learning, attention and executive function. Tau protein is a microtubule-associated protein located in the axons of neurons and is important for microtubule assembly and stability; its biological function is mainly regulated by phosphorylation. Phosphorylated tau protein has been associated with cognitive dysfunction mediated by disrupting the stability of the microtubule structure. There is an increasing consensus that anesthetic drugs can cause cognitive impairment. Herein, we reviewed the latest literature and compared the relationship between tau protein and cognitive impairment caused by different anesthetics. Our results substantiated that tau protein phosphorylation is essential in cognitive dysfunction caused by anesthetic drugs, and the possible mechanism can be summarized as "anesthetic drugs-kinase/phosphatase-p-Tau-cognitive impairment".

Safety and effectiveness of NMDA receptor antagonists for depression: A multidisciplinary review

Ketamine, an anesthetic available since 1970, and esketamine, its newer S-enantiomer, provide a novel approach for the treatment of depression and other psychiatric disorders. At subanesthetic doses, the two drugs, along with their older congener, phencyclidine (PCP), induce a transient, altered mental state by blocking the N-methyl-D-aspartate (NMDA) receptor for glutamate, the primary excitatory neurotransmitter in the mammalian central nervous system. This multidisciplinary review examines the pharmacology/direct effects on consciousness, effectiveness in depression and acute suicidality, and safety of these fast-acting NMDA antagonists. To capture the essence of 60 years of peer-reviewed literature, we used a semi-structured approach to the subtopics, each of which required a different search strategy. We review the evidence for the three primary reported benefits of the two clinical drugs when used for depression: success in difficult-to-treat patients, rapid onset of action within a day, and immediate effects on suicidality. Key safety issues include the evidence-and lack thereof-for the effects of repeatedly inducing this altered mental state, and whether an adequate safety margin exists to rule out the neurotoxic effects seen in animal studies. This review includes evidence from multiple sources that raise substantial questions about both safety and effectiveness of ketamine and esketamine for psychiatric disorders.

A review of potential neuropathological changes associated with ketamine

INTRODUCTION

: Ketamine is an established intervention for treatment resistant depression (TRD). However, long-term adverse effects with repeated doses remain insufficiently characterized. Although several animal models have shown N-methyl-D-aspartate glutamate receptor antagonists to produce various neuropathological reactions, attention surrounding the risk of brain lesions has been minimal.

AREAS COVERED

: The current review focuses on potential neuropathological changes associated with ketamine. Search terms included variations of ketamine, Olney lesions, tau hyperphosphorylation, and parvalbumin interneurons.

EXPERT OPINION

: Daily high-dose ketamine use in substance use disorder (SUD) populations was associated with clear neurotoxic effects, while no studies specifically evaluated effects of ketamine protocols used for TRD. It is difficult to discern effects directly attributable to ketamine due to methodological factors, such as comorbidities and dramatic differences in dose in SUD populations versus infrequent sub-anesthetic doses typically prescribed for TRD. Taken together, animal models and human ketamine SUD populations suggest potential neuropathology with chronic high-dose ketamine exposure exceeding those recommended for adults with TRD. It is unknown whether repeat sub-anesthetic dosing of ketamine in adults with TRD is associated with Olney lesions or other neuropathologies. In the interim, practitioners should be vigilant for this possibility recognizing that the condition itself is associated with neurodegenerative processes.

Ketamine use disorder: preclinical, clinical, and neuroimaging evidence to support proposed mechanisms of actions

Ketamine, a noncompetitive NMDA receptor antagonist, has been exclusively used as an anesthetic in medicine and has led to new insights into the pathophysiology of neuropsychiatric disorders. Clinical studies have shown that low subanesthetic doses of ketamine produce antidepressant effects for individuals with depression. However, its use as a treatment for psychiatric disorders has been limited due to its reinforcing effects and high potential for diversion and misuse. Preclinical studies have focused on understanding the molecular mechanisms underlying ketamine's antidepressant effects, but a precise mechanism had yet to be elucidated. Here we review different hypotheses for ketamine's mechanism of action including the direct inhibition and disinhibition of NMDA receptors, AMPAR activation, and heightened activation of monoaminergic systems. The proposed mechanisms are not mutually exclusive, and their combined influence may exert the observed structural and functional neural impairments. Long term use of ketamine induces brain structural, functional impairments, and neurodevelopmental effects in both rodents and humans. Its misuse has increased rapidly in the past 20 years and is one of the most common addictive drugs used in Asia. The proposed mechanisms of action and supporting neuroimaging data allow for the development of tools to identify 'biotypes' of ketamine use disorder (KUD) using machine learning approaches, which could inform intervention and treatment.

Ketamine promotes the amyloidogenic pathway by regulating endosomal pH

Ketamine is an anesthetic and addictive drug that can cause cognitive dysfunction and neuroinflammation. Studies have shown that carboxy-terminal fragment derived from β-secretase (CTF-β) and amyloid beta (Aβ), the amyloidogenic products of amyloid precursor protein (APP), can also induce neuroinflammation and impair cognitive function. However, it remains unclear whether ketamine regulates the amyloidogenic pathway. In the endosome, APP is cleaved by beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), whose activity is influenced by pH. Endosomal acidification is mainly regulated by sodium hydrogen exchanger 6 (NHE6), which leaks protons out of endosomes, and vacuolar proton translocating ATPases (V-ATPase), which pump protons into endosomes. Therefore, we hypothesized that ketamine lowers the endosomal pH by reducing the endosomal NHE6 protein level, and this hyperacidification promotes the amyloidogenic pathway. We set up C57BL/6 J mouse models using 10, 20, 40, 80, and 100 mg/kg ketamine administration and SH-SY5Y cell models using 1, 10, 100, and 1000 μM ketamine administration to investigate its effects on the amyloidogenic pathway at different doses. Western blotting results showed that 100 mg/kg ketamine treatment in vivo and 1000 μM ketamine treatment in vitro increased endosomal BACE1 and CTF-β protein levels and reduced endosomal NHE6 and APP protein levels. The endosomal accumulation of BACE1 caused by ketamine administration was also observed using confocal imaging. Moreover, flow cytometry indicated that ketamine treatment lowered the endosomal pH value of SH-SY5Y cells. Later, cells were pretreated with monensin to restore the endosomal pH. Monensin did not affect amyloidogenic-related proteins or NHE6 directly; therefore, ketamine-promoted endosomal amyloidogenic processing and BACE1 accumulation were depleted by restoring endosomal acidity through monensin pretreatment. Finally, knockdown of NHE6 promoted the amyloidogenic pathway similarly and prevented further enhancement by ketamine. These results indicated that the effects of ketamine on the amyloidogenic pathway were dependent on the reduction of NHE6 and endosomal pH.

Brain Changes Associated With Long-Term Ketamine Abuse, A Systematic Review

Recently, the abuse of ketamine has soared. Therefore, it is of great importance to study its potential risks. The effects of prolonged ketamine on the brain can be observationally studied in chronic recreational users. We performed a systematic review of studies reporting functional and structural brain changes after repeated ketamine abuse. We searched the following electronic databases: Medline, Embase and PsycINFO We screened 11,438 records and 16 met inclusion criteria, totaling 440 chronic recreational ketamine users (2–9.7 years; mean use 2.4 g/day), 259 drug-free controls and 44 poly-drug controls. Long-term recreational ketamine use was associated with lower gray matter volume and less white matter integrity, lower functional thalamocortical and corticocortical connectivity. The observed differences in both structural and functional neuroanatomy between ketamine users and controls may explain some of its long-term cognitive and psychiatric side effects, such as memory impairment and executive functioning. Given the effect that long-term ketamine exposure may yield, an effort should be made to curb its abuse.

Long-term outcomes of repeated ketamine infusions in patients with unipolar and bipolar depression: A naturalistic follow-up study

OBJECTIVE

Ketamine was proven to have short-term antidepressant effects. There is a paucity of studies focused on the long-term outcomes of repeated infusions of ketamine. This study aimed to examine the long-term outcomes of repeated ketamine infusions in patients with unipolar and bipolar depression METHODS: One hundred and eight patients with unipolar and bipolar depression completed the repeated treatment phase (administered ketamine three times weekly over a 12-day) and entered a 9-month naturalistic follow-up phase. Assessments were obtained at week 2, month 6, and month 9 after the repeated treatment phase. The Patient Health Questionnaire-9 (PHQ-9) Scale and the Global Assessment of Functioning (GAF) Scale were used to assess depressive symptoms and global functional status, respectively.

RESULTS

Seventy-one (65.7%) of patients completed the 9-month follow-up. On month 9, the response and remission rate were 80.3% and 78.9%, respectively. Among 56 patients who achieved response after the repeated treatment phase, 26 (46.4%) of patients sustained response during 9-month follow-up and their GAF score remained over 70. Sixteen patients relapsed during the 9-month follow-up and 14 (85.7%) of the relapse occurred during the first 2-week follow-up.

LIMITATION

The major limitation of this study is the open-label design.

CONCLUSIONS

This small sample study suggested that patients with unipolar and bipolar depression who response to repeated treatment with continued oral antidepressant may be a viable treatment option, and their global functional status improved with a follow-up. Relapse of depression tended to occur during the 2 weeks follow-up.

Neurofilament light chain as novel blood biomarker of disturbed neuroaxonal integrity in patients with ketamine dependence

OBJECTIVES

Chronic and heavy ketamine use has been associated with persistent neurocognitive impairment and structural brain abnormalities. Blood levels of neurofilament light chain (NFL) was recently proposed as a measure of axonal integrity in several neuropsychiatric disorders. We aimed to characterise the axonal neurotoxicity of chronic ketamine use and its relationship to relevant clinical outcomes.

METHODS

We enrolled 65 treatment-seeking ketamine-dependent patients (55 males and 10 females) and 60 healthy controls (51 males and 9 females). Blood NFL levels measured by single molecule array (SiMoA) immunoassay. We compared NFL levels between groups and used regression analyses to identify clinical variables related to NFL levels.

RESULTS

Ketamine-dependent patients had significantly higher NFL levels compared to controls (p < 0.001). A multivariate regression showed that age (p < 0.05) and lifetime history of major depressive disorder (MDD) (p < 0.01) predicted high NFL blood levels in patients. Subsequent group comparisons showed that specifically ketamine-dependent patients with a lifetime history of MDD had significantly increased NFL levels than those without (p < 0.05).

CONCLUSIONS

These results suggest substantial neuroaxonal alterations following chronic and heavy ketamine use. The pronounced increase of NFL levels in the MDD subgroup warrants further investigation of a potential neuroaxonal vulnerability of depressed patients to ketamine.

Intranasal esketamine: From origins to future implications in treatment-resistant depression

The approval of intranasal esketamine for treatment-resistant depression marks the next step in our understanding of and ability to treat treatment-resistant depression. The origin of ketamine is rooted in the search for a phencyclidine analog that could be used as a pre-surgical anesthetic with less emergence delirium. Following its inception, ketamine has been used in a variety of contexts. However, it was the seminal Berman et al., 2000 study, which published positive findings from the first human trial using subanesthetic intravenous ketamine for depression. Since then, a large body of research has investigated ketamine's various proposed antidepressant mechanisms of action, and the role its pharmacokinetic properties and route of administration play in producing its antidepressant effects. The results of this research were the eventual approval of intranasal esketamine for treatment-resistant depression by the U.S. Food and Drug Administration (FDA) in March 2019. By identifying and utilizing predictors of response, we can continue to refine our approach to treating treatment-resistant depression and optimize patient response to intranasal esketamine. In this article, we look at the history, pharmacology, landmark studies, and future implications of intranasal esketamine for treatment-resistant depression.

Psychedelics in Psychiatry: Neuroplastic, Immunomodulatory, and Neurotransmitter Mechanisms

Mounting evidence suggests safety and efficacy of psychedelic compounds as potential novel therapeutics in psychiatry. Ketamine has been approved by the Food and Drug Administration in a new class of antidepressants, and 3,4-methylenedioxymethamphetamine (MDMA) is undergoing phase III clinical trials for post-traumatic stress disorder. Psilocybin and lysergic acid diethylamide (LSD) are being investigated in several phase II and phase I clinical trials. Hence, the concept of psychedelics as therapeutics may be incorporated into modern society. Here, we discuss the main known neurobiological therapeutic mechanisms of psychedelics, which are thought to be mediated by the effects of these compounds on the serotonergic (via 5-HT2A and 5-HT1A receptors) and glutamatergic [via N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors] systems. We focus on 1) neuroplasticity mediated by the modulation of mammalian target of rapamycin-, brain-derived neurotrophic factor-, and early growth response-related pathways; 2) immunomodulation via effects on the hypothalamic-pituitary-adrenal axis, nuclear factor ĸB, and cytokines such as tumor necrosis factor-α and interleukin 1, 6, and 10 production and release; and 3) modulation of serotonergic, dopaminergic, glutamatergic, GABAergic, and norepinephrinergic receptors, transporters, and turnover systems. We discuss arising concerns and ways to assess potential neurobiological changes, dependence, and immunosuppression. Although larger cohorts are required to corroborate preliminary findings, the results obtained so far are promising and represent a critical opportunity for improvement of pharmacotherapies in psychiatry, an area that has seen limited therapeutic advancement in the last 20 years. Studies are underway that are trying to decouple the psychedelic effects from the therapeutic effects of these compounds. SIGNIFICANCE STATEMENT: Psychedelic compounds are emerging as potential novel therapeutics in psychiatry. However, understanding of molecular mechanisms mediating improvement remains limited. This paper reviews the available evidence concerning the effects of psychedelic compounds on pathways that modulate neuroplasticity, immunity, and neurotransmitter systems. This work aims to be a reference for psychiatrists who may soon be faced with the possibility of prescribing psychedelic compounds as medications, helping them assess which compound(s) and regimen could be most useful for decreasing specific psychiatric symptoms.

Effects of Single-Dose and Long-Term Ketamine Administration on Tau Phosphorylation-Related Enzymes GSK-3β, CDK5, PP2A, and PP2B in the Mouse Hippocampus

Ketamine is a recreational drug that causes emotional and cognitive impairments, but its specific mechanisms of action are still unclear. Recent evidence suggests that Tau protein phosphorylation and targeted delivery to the postsynaptic area are closely related to its neurotoxicity, and our recent studies have shown that long-term ketamine administration causes excessive Tau protein phosphorylation. However, the regulatory mechanism of Tau protein phosphorylation induced by ketamine has not been clarified. In the present study, we administered a single ketamine injection and long-term (6 months) ketamine injections in C57BL/6 mice, to investigate the effects of different doses of ketamine on the expression levels of Tau protein and its phosphorylation, the expression levels and activities of the related protein phosphokinases GSK-3β and CDK5, and the expression levels and activities of the related protein phosphatases PP2A and PP2B in the mouse hippocampus. Our results showed that both single-dose and long-term ketamine administration induced excessive phosphorylation of the Tau protein at ser202/thr205 and ser396. A single ketamine administration caused an increase in the activity of GSK-3β (at high doses) and a decrease in the activity of PP2A. On the other hand, long-term ketamine administration resulted in an increase in the activities of GSK-3β (at high doses) and CDK5, and a decrease in the activity of PP2A. Our results indicate that GSK-3β, CDK5, and PP2A may be involved in ketamine-induced Tau protein phosphorylation.

Redistribution of Monocarboxylate 1 and 4 in Hippocampus and Spatial Memory Impairment Induced by Long-term Ketamine Administration

The monocarboxylate transporters (MCTs) MCT1, MCT2, and MCT4 are essential components of the astrocyte-neuron lactate shuttle (ANLS), which is a fundamental element of brain energetics. Decreased expression of MCTs can induce cognitive dysfunction of the brain. In the present study, we established a mouse model of long-term ketamine administration by subjecting mice to a 6-month course of a daily intraperitoneal injection of ketamine. These mice demonstrated learning and memory deficits and a significant decline in MCT1 and MCT4 proteins in the hippocampal membrane fraction, while cytoplasmic MCT1 and MCT4 protein levels were significantly increased. In contrast, the levels of global MCT2 protein were significantly increased. Analysis of mRNA levels found no changes in MCT1/4 transcripts, although the expression of MCT2 mRNA was significantly increased. We suggest that redistribution of hippocampal MCT1 and MCT4, but not MCT2 up-regulation, may be related to learning and memory deficits induced by long-term ketamine administration.

Chronic sub-anesthetic ketamine induces permanent hypolocomotion and impairment of hippocampus in adolescent cynomolgus monkeys

Ketamine has gained increasing popularity in adolescent drug abusers worldwide. However, relatively little is known about the long-term effects of recreational ketamine on adolescent hippocampus. The present study investigates the effects of different periods (1, 3 and 6 months) of recreational ketamine administration on locomotor activity and neuron damage in the hippocampus of adolescent cynomolgus monkeys. 32 4-year-old male cynomolgus monkeys were divided into control, 1-month, 3-month and 6-month groups. All animals in ketamine groups received daily intravenous injection with 1 mg/kg ketamine in saline for respective 1, 3 or 6 months while control group received normal saline. Automatic behaviors were recorded for 10 min before and after ketamine and saline administration. Meanwhile, the markers of apoptosis in the hippocampus were assessed using terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling (TUNEL), electron microscopy and western blotting. Results showed that ketamine significantly decreased locomotor activity, increased apoptotic neurons and pro-apoptotic proteins, cleaved Caspase-3 and Bax, while decreased the anti-apoptotic protein Bcl-2 in the hippocampus after 6-month ketamine administration. Our study suggested that chronically recreational ketamine might induce hypolocomotion and neurotoxic effect via apoptotic pathway in adolescent hippocampus of monkeys.

Tau hyperphosphorylation induced by the anesthetic agent ketamine/xylazine involved the calmodulin-dependent protein kinase II

Tau hyperphosphorylation is a major neuropathological hallmark of many neurodegenerative disorders such as Alzheimer's disease. Several anesthetics have been shown previously to induced marked tau hyperphosphorylation. Although the ketamine/xylazine mixture is one of the most commonly used anesthetic agents in animal research and veterinary practice, the effect of this anesthetic agent on tau phosphorylation still remains to be determined. Here, we found that ketamine-/xylazine-induced a rapid and robust hyperphosphorylation of tau in a dose-dependent manner under normothermic and hypothermic conditions in mice. When used together, ketamine and xylazine exerted a synergistic action on tau phosphorylation most strongly not only on epitopes S396 and S262, but also on other residues (T181, and S202/T205). We observed that activation of the calmodulin-dependent protein kinase II (CaMKII) is the major upstream molecular event leading to tau hyperphosphorylation following ketamine/xylazine anesthesia in mice. Moreover, we observed that intracerebroventricular injection of the selective CaMKII inhibitor KN93 attenuated tau hyperphosphorylation. Since ketamine/xylazine also had a marked impact on other key molecular signaling pathways involving the MAP/microtubule affinity-regulating kinase (MARK), extracellular signal-regulated kinase (ERK), and glycogen synthase kinase-3 (GSK3), our study calls for high caution and careful monitoring when using this anesthetic agent in laboratory animal settings across all fields of biological sciences in order to avoid artifactual results.

Behavioral Changes and Neuronal Damage in Rhesus Monkeys after 10 Weeks of Ketamine Administration Involve Prefrontal Cortex Dopamine D2 Receptor and Dopamine Transporter

The dopamine D2 receptor (DRD2) and dopamine transporter (DAT) play a regulatory role in dopaminergic neurotransmission and thus play an important role in drug addiction. The prefrontal cortex (PFC), a critical part of the mesencephalic dopaminergic system, is thought to be involved in the development and maintenance of drug addiction. The addiction to ketamine is thought to induce behavioral effects primarily through actions on the central nervous system. However, the neural mechanism underlying the effects of ketamine addiction remains unclear. In this study, we investigate the involvement of PFC DRD2 and DAT in ketamine addiction effects after ketamine administration for 10 weeks in nonhuman primates. To this end, after administering ketamine to rhesus monkeys for 10 weeks, we assessed changes in body weight and behavior. Additionally, neuronal changes in the PFC were examined by hematoxylin and eosin (HE) staining; the DRD2 and DAT mRNA and protein expression levels in the PFC were determined by real-time PCR and Western blot analysis, respectively. After 10-week ketamine administration, the assessment of the manifestations of toxicity in rhesus monkeys revealed significant changes in body weight and behavior, decreased DRD2 and DAT mRNA and protein expression in the PFC, and histological abnormalities including neuronal eosinophilia, pyknosis and disorderly arrangement of neurons in the PFC. These results suggest that the reduced expression of DRD2 and DAT in PFC could be involved in the behavioral and the neurological changes induced by ketamine administration, which may play an important role in the molecular mechanisms of ketamine addiction.

Ketamine and depression: a narrative review

Depression is the third leading cause of disability in the world. Depressive symptoms may be reduced within several weeks after the start of conventional antidepressants, but treatment resistance concerns one-third of patients who fail to achieve recovery. Over the last 20 years, ketamine, an antagonist of the N-methyl-D-aspartate receptor, has been described to have antidepressant properties. A literature review was conducted through an exhaustive electronic search. It was restricted to Cochrane reviews, meta-analyses, and randomized controlled trials (RCTs) of ketamine for major depressive disorder and/or bipolar disorder. This review included two Cochrane reviews, 14 meta-analyses and 15 trials. Ketamine was studied versus placebo, versus other comparators and as an anesthetic adjuvant before electroconvulsive therapy. In 14 publications, ketamine provided a rapid antidepressant effect with a maximum efficacy reached at 24 hrs. Its effect lasted for 1–2 weeks after infusion, but a longer-term effect is little reported. Ketamine does not seem to improve depressive symptoms at the end of electroconvulsive sessions. Safety and tolerability profiles with ketamine at low single dose are generally good in depressed patients. However, there is a lack of data concerning ketamine with repeated administration at higher doses. The clinical use of ketamine is increasing. Intranasal (S)-ketamine has recently been approved for depression by the Food and Drug Administration. It could be a promising treatment in depressed patients with suicidal ideation. Collectively, the level of proof of efficacy remains low and more RCTs are needed to explore efficacy and safety issues of ketamine in depression.

Long-term ketamine administration causes Tau protein phosphorylation and Tau protein-dependent AMPA receptor reduction in the hippocampus of mice

As a recreational drug of abuse and an injectable anesthetic, ketamine has been shown to cause cognitive dysfunction and induce psychotic states. Although the specific mechanism is still unclear, it may be linked to synaptic receptors, including the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor. Recent evidence suggests that Tau protein phosphorylation and targeted delivery to the postsynaptic area is involved in maintaining neuronal plasticity, indicating that the neurotoxicity induced by ketamine may be related to the transfer of Tau protein after phosphorylation. In this study, we established a model of long-term (6 months) ketamine administration in wild-type (C57BL/6) and Tau knockout mice to investigate the effects of different doses of ketamine administration on Tau protein expression and phosphorylation in the mouse hippocampus. We also investigated changes in AMPA receptor expression in the synaptic membrane of wild-type and Tau knockout mice. Our results showed that long-term ketamine administration led to excessive Tau protein phosphorylation at Ser202/Thr205 and Ser396, but not at Ser199, Ser262 and Ser404. Most importantly, long-term ketamine administration decreased AMPA receptor levels in the hippocampal cell membrane in a Tau protein-dependent manner. Our results reveal the role of Tau protein phosphorylation in the mechanism of ketamine neurotoxicity, suggesting that the changes of membrane AMPA receptor and synaptic function induced by ketamine are mediated by abnormal phosphorylation of Tau protein at specific sites.

The effects of sub-anesthetic ketamine plus ethanol on behaviors and apoptosis in the prefrontal cortex and hippocampus of adolescent rats

Ketamine has become increasingly popular in adolescent drug abusers worldwide. Meanwhile, alcohol is usually used by ketamine users. However, little work has been conducted to examine the chronic combined effects of ketamine and ethanol on adolescent brain. Here we probed into the effects of chronic administration of ketamine at recreational doses alone or combined with ethanol on behaviors and neuron damage in an adolescent rat model. 28-day old rats were treated with either 20 or 30 mg/kg ketamine plus or not plus 10% ethanol daily for 21 days. Depressive like behaviors, anxiety like behavior and memory impairment were tested using open field test, forced swimming test, elevated plus maze and Morris water maze. Apoptosis in prefrontal cortex (PFC) and hippocampus (HIP) were determined by the TdT-mediated dUTP Nick-End Labeling (TUNEL) and protein and mRNA levels of caspase-3, Bax and Bcl-2. Results show that co-application of ketamine and ethanol significantly increased immobility time in the forced swimming test, up-regulated TUNEL positive cells and both protein and mRNA expressions of caspase-3 and Bax, compared with the control group and ketamine and ethanol use alone groups in the PFC, but not in the HIP. Our study suggests that chronic co-administration of ketamine and ethanol results in depressive-like behavior and the caspase-dependent apoptosis in the PFC of adolescent rats' brains.

GSK3β: a plausible mechanism of cognitive and hippocampal changes induced by erythropoietin treatment in mood disorders?

Mood disorders are associated with significant psychosocial and occupational disability. It is estimated that major depressive disorder (MDD) will become the second leading cause of disability worldwide by 2020. Existing pharmacological and psychological treatments are limited for targeting cognitive dysfunctions in mood disorders. However, growing evidence from human and animal studies has shown that treatment with erythropoietin (EPO) can improve cognitive function. A recent study involving EPO-treated patients with mood disorders showed that the neural basis for their cognitive improvements appeared to involve an increase in hippocampal volume. Molecular mechanisms underlying hippocampal changes have been proposed, including the activation of anti-apoptotic, antioxidant, pro-survival and anti-inflammatory signalling pathways. The aim of this review is to describe the potential importance of glycogen synthase kinase 3-beta (GSK3β) as a multi-potent molecular mechanism of EPO-induced hippocampal volume change in mood disorder patients. We first examine published associations between EPO administration, mood disorders, cognition and hippocampal volume. We then highlight evidence suggesting that GSK3β influences hippocampal volume in MDD patients, and how this could assist with targeting more precise treatments particularly for cognitive deficits in patients with mood disorders. We conclude by suggesting how this developing area of research can be further advanced, such as using pharmacogenetic studies of EPO treatment in patients with mood disorders.

Ketamine and Ketamine Metabolite Pharmacology: Insights into Therapeutic Mechanisms

Ketamine, a racemic mixture consisting of (S)- and (R)-ketamine, has been in clinical use since 1970. Although best characterized for its dissociative anesthetic properties, ketamine also exerts analgesic, anti-inflammatory, and antidepressant actions. We provide a comprehensive review of these therapeutic uses, emphasizing drug dose, route of administration, and the time course of these effects. Dissociative, psychotomimetic, cognitive, and peripheral side effects associated with short-term or prolonged exposure, as well as recreational ketamine use, are also discussed. We further describe ketamine's pharmacokinetics, including its rapid and extensive metabolism to norketamine, dehydronorketamine, hydroxyketamine, and hydroxynorketamine (HNK) metabolites. Whereas the anesthetic and analgesic properties of ketamine are generally attributed to direct ketamine-induced inhibition of N-methyl-D-aspartate receptors, other putative lower-affinity pharmacological targets of ketamine include, but are not limited to, γ-amynobutyric acid (GABA), dopamine, serotonin, sigma, opioid, and cholinergic receptors, as well as voltage-gated sodium and hyperpolarization-activated cyclic nucleotide-gated channels. We examine the evidence supporting the relevance of these targets of ketamine and its metabolites to the clinical effects of the drug. Ketamine metabolites may have broader clinical relevance than was previously considered, given that HNK metabolites have antidepressant efficacy in preclinical studies. Overall, pharmacological target deconvolution of ketamine and its metabolites will provide insight critical to the development of new pharmacotherapies that possess the desirable clinical effects of ketamine, but limit undesirable side effects.

How Ketamine Affects Livers of Pregnant Mice and Developing Mice?

It is well known that ketamine abuse can induce liver damage in adult addicts, but the effects of ketamine abuse in pregnant mothers on their offspring have received less attention. In this study, we investigated the effects of 5-day ketamine injections (30 mg/kg) to pregnant Institute for Cancer Research (ICR) mice during early gestation or mid-gestation on the aspartate aminotransferase (AST) and alkaline phosphatase (ALP) activities of the mothers and the offspring. We also looked into whether administering ketamine treatment to the mothers had any effects on the extent of fibrosis, cell proliferation and cell death in the livers of the newborns. No significant biochemical differences were found between treatment and control groups in the mothers. In the offspring, ketamine treatment mildly suppressed the gradual increase of hepatic AST activity in neonates during liver maturation. Measurements of hepatic ALP activity and lactic acid dehydrogenase (LDH) immunoreactivity revealed that ketamine treatment may lead to increased cell death. Proliferation of liver cells of the newborns was also retarded as shown by reduced proliferative cell nuclear antigen (PCNA) immunoreactivity in the ketamine groups. No obvious fibrosis was evident. Thus, we demonstrated that ketamine administration to pregnant mice suppressed hepatic development and also induced liver cell death of the offspring.

Chronic Ketamine Exposure Causes White Matter Microstructural Abnormalities in Adolescent Cynomolgus Monkeys

Acute and repeated exposures to ketamine mimic aspects of positive, negative, and cognitive symptoms of schizophrenia in humans. Recent studies by our group and others have shown that chronicity of ketamine use may be a key element for establishing a more valid model of cognitive symptoms of schizophrenia. However, current understanding on the long-term consequences of ketamine exposure on brain circuits has remained incomplete, particularly with regard to microstructural changes of white matter tracts that underpin the neuropathology of schizophrenia. Thus, the present study aimed to expand on previous investigations by examining causal effects of repeated ketamine exposure on white matter integrity in a non-human primate model. Ketamine or saline (control) was administered intravenously for 3 months to male adolescent cynomolgus monkeys (n = 5/group). Diffusion tensor imaging (DTI) experiments were performed and tract-based spatial statistics (TBSS) was used for data analysis. Fractional anisotropy (FA) was quantified across the whole brain. Profoundly reduced FA on the right side of sagittal striatum, posterior thalamic radiation (PTR), retrolenticular limb of the internal capsule (RLIC) and superior longitudinal fasciculus (SLF), and on the left side of PTR, middle temporal gyrus and inferior frontal gyrus were observed in the ketamine group compared to controls. Diminished white matter integrity found in either fronto-thalamo-temporal or striato-thalamic connections with tracts including the SLF, PTR, and RLIC lends support to similar findings from DTI studies on schizophrenia in humans. This study suggests that chronic ketamine exposure is a useful pharmacological paradigm that might provide translational insights into the pathophysiology and treatment of schizophrenia.

Effects of Ketamine on Levels of Inflammatory Cytokines IL-6, IL-1β, and TNF-α in the Hippocampus of Mice Following Acute or Chronic Administration

Ketamine is an injectable anesthetic and recreational drug of abuse commonly used worldwide. Many experimental studies have shown that ketamine can impair cognitive function and induce psychotic states. Neuroinflammation has been suggested to play an important role in neurodegeneration. Meanwhile, ketamine has been shown to modulate the levels of inflammatory cytokines. We hypothesized that the effects of ketamine on the central nervous system are associated with inflammatory cytokines. Therefore, we set out to establish acute and chronic ketamine administration models in C57BL/6 mice, to evaluate spatial recognition memory and emotional response, to analyze the changes in the levels of the inflammatory cytokines interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) in the mouse hippocampus, employing behavioral tests, Western blot, quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and immunohistochemistry. Our results showed that ketamine at the dose of 60 mg/kg induced spatial recognition memory deficit and reduced anxiety-like behaviors in mice after chronic administration. Moreover, we found that ketamine increased the hippocampal levels of IL-6 and IL-1β after single, multiple and long-term administration in a dose-dependent manner. However, the expression level of TNF-α differed in the mouse hippocampus under different conditions. Single administration of ketamine increased the level of TNF-α, whereas multiple and long-term administration decreased it significantly. We considered that TNF-α expression could be controlled by a bi-directional regulatory pathway, which was associated with the dose and duration of ketamine administration. Our results suggest that the alterations in the levels of inflammatory cytokines IL-6, IL-1β, and TNF-α may be involved in the neurotoxicity of ketamine.

Changes in hippocampal AMPA receptors and cognitive impairments in chronic ketamine addiction models: another understanding of ketamine CNS toxicity

Ketamine has been reported to impair human cognitive function as a recreational drug of abuse. However, chronic effects of ketamine on central nervous system need to be further explored. We set out to establish chronic ketamine addiction models by giving mice a three or six month course of daily intraperitoneal injections of ketamine, then examined whether long-term ketamine administration induced cognition deficits and changed hippocampal post-synaptic protein expression in adult mice. Behavior tests results showed that mice exhibited dose- and time-dependent learning and memory deficits after long-term ketamine administration. Western blot results showed levels of GluA1, p-S845 and p-S831 proteins demonstrated significant decline with ketamine 60 mg/kg until six months administration paradigm. But levels of p-S845 and p-S831 proteins exhibited obvious increase with ketamine 60 mg/kg three months administration paradigm. NR1 protein levels significantly decrease with ketamine 60 mg/kg three and six months administration paradigm. Our results indicate that reduced expression levels and decreased phosphorylation levels of hippocampal post-synaptic membrane GluA1- containing AMPA receptors maybe involved in cognition impairment after long-term ketamine administration. These findings provide further evidence for the cognitive damage of chronic ketamine addiction as a recreational drug.

Ketamine induces tau hyperphosphorylation at serine 404 in the hippocampus of neonatal rats

Male Wistar 7-day-old rats were injected with 40 mg/kg ketamine intraperitoneally, followed by three additional injections of 20 mg/kg ketamine each upon restoration of the righting reflex. Neonatal rats injected with equivalent volumes of saline served as controls. Hippocampal samples were collected at 1, 7 or 14 days following administration. Electron microscopy showed that neuronal structure changed noticeably following ketamine treatment. Specifically, microtubular structure became irregular and disorganized. Quantitative real time-PCR revealed that phosphorylated tau mRNA was upregulated after ketamine. Western blot analysis demonstrated that phosphorylated tau levels at serine 396 initially decreased at 1 day after ketamine injection, and then gradually returned to control values. At 14 days after injection, levels of phosphorylated tau were higher in the ketamine group than in the control group. Tau protein phosphorylated at serine 404 significantly increased after ketamine injection, and then gradually decreased with time. However, the levels of tau protein at serine 404 were significantly greater in the ketamine group than in the control group until 14 days. The present results indicate that ketamine induces an increase of phosphorylated tau mRNA and excessive phosphorylation of tau protein at serine 404, causing disruption of microtubules in the neonatal rat hippocampus and potentially resulting in damage to hippocampal neurons.

Patterns of cortical activation following motor tasks and psychological-inducing movie cues in heroin users: an fMRI study

OBJECTIVE

Drug abuse and addiction are worldwide health problems. However, few studies have used fMRI to investigate the effect of chronic heroin use on brain activation. This is a study along this line.

METHOD

fMRI positive sites in the brain were recorded during different motor and sensory activities.

RESULTS

Following motor activities, heroin users had more sites globally activated in the brain than in normal volunteers, with ex-heroin users being least reactive. Conversely, a "heroin puffing" movie produced more activation in ongoing-heroin and ex-heroin users than in the normal individuals, whereas a movie with explicit sexual content was less stimulatory in both groups of heroin users compared to normal individuals.

CONCLUSIONS

These significant findings relative to the function of specific brain nuclei are discussed.

Neuroprotective effects of extract of Acanthopanax senticosus harms on SH-SY5Y cells overexpressing wild-type or A53T mutant α-synuclein

Extract of Acanthopanax senticosus harms (EAS) has been shown to have neuroprotective effects on dopaminergic neurons in Parkinson's disease (PD) mice model. α-Synuclein is a key player in the pathogenesis of PD, the elevated level of which is deleterious to dopaminergic neurons, and enhancing its clearance might be a promising strategy for treating PD. To assess the potential of EAS in this regard, we investigated its effect on the SH-SY5Y cells overexpressing wild-type α-synuclein (WT-α-Syn) or A53T mutant α-synuclein (A53T-α-Syn), and the implicated pathway it might mediate. After treatment with EAS, the changes of α-synuclein, caspase-3, parkin, phospho-protein kinase B (Akt), phospho-glycogen synthase kinase 3 beta (GSK3β), and phospho-microtubule-associated protein tau (Tau) in WT-α-Syn or A53T-α-Syn transgenic cells were reverted back to near normal levels, demonstrated by the western blotting and quantitative real-time PCR outcomes. The neuroprotective effects of EAS may be able to protect WT-α-Syn or A53T-α-Syn transgenic SH-SY5Y cells from α-synuclein overexpression and toxicity. Therefore, we speculate that EAS might be a promising candidate for prevention or treatment of α-synuclein-related neurodegenerative disorders such as PD.

Chronic ketamine exposure induces permanent impairment of brain functions in adolescent cynomolgus monkeys

Ketamine, a non-competitive N-methyl-D-aspartic acid receptor antagonist, has emerged as an increasingly popular drug among young drug abusers worldwide. Available evidence suggests that ketamine produces acute impairments of working, episodic and semantic memory along with psychotogenic and dissociative effects when a single dose is given to healthy volunteers. However, understanding of the possible chronic effects of ketamine on behavior, cognitive anomalies and neurochemical homeostasis is still incomplete. Although previous human studies demonstrate that ketamine could impair a range of cognitive skills, investigation using non-human models would permit more precise exploration of the neurochemical mechanisms which may underlie the detrimental effects. The current study examined the abnormalities in behavior (move, walk, jump and climb) and apoptosis of the prefrontal cortex using terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling (TUNEL) and apoptotic markers, including Bax, Bcl-2 and caspase-3 in adolescent male cynomolgus monkeys (Macaca fascicularis) after 1 or 6 months of sub-anesthetic ketamine administration (1 mg/kg, i.v.). Results showed that ketamine decreased locomotor activity and increased cell death in the prefrontal cortex of monkeys with 6 months of ketamine treatment when compared with the control monkeys. Such decreases were not found in the 1-month ketamine-treated group. Our study suggested that ketamine administration of recreational dose in monkeys might produce permanent and irreversible deficits in brain functions due to neurotoxic effects, involving the activation of apoptotic pathways in the prefrontal cortex.

Ketamine as antidepressant? Current state and future perspectives

Major depressive disorder (MDD) is a serious mental disorder that ranks among the major causes of disease burden. Standard medical treatment targeting cerebral monoamines often provides only insufficient symptom relief and fails in approximately every fifth patient. The complexity of MDD therefore, reflects more than monoaminergic dysregulation. Initial research argues the case for excessive glutamate levels, suggesting that antiglutamatergic drugs might be useful in treating MDD. Ketamine is a non-selective, high-affinity N-methyl-D-aspartate receptor (NMDAR) antagonist most commonly used in pediatric and animal surgery. In the past, ketamine has gained popularity because of its ability to rapidly elevate mood, even in treatment-resistant and bipolar depression. However, there are still many obstacles before widespread clinical approval of ketamine treatment could become reality. In this review, ketamine's powerful antidepressant effects are discussed and further research necessary for therapeutic application is outlined. NMDAR antagonists provide an entirely new way of treating the manifold appearances of depression that should not be left unused.

Brain damages in ketamine addicts as revealed by magnetic resonance imaging

Ketamine, a known antagonist of N-methyl-D-aspartic (NMDA) glutamate receptors, had been used as an anesthetic particularly for pediatric or for cardiac patients. Unfortunately, ketamine has become an abusive drug in many parts of the world while chronic and prolonged usage led to damages of many organs including the brain. However, no studies on possible damages in the brains induced by chronic ketamine abuse have been documented in the human via neuroimaging. This paper described for the first time via employing magnetic resonance imaging (MRI) the changes in ketamine addicts of 0.5–12 years and illustrated the possible brain regions susceptible to ketamine abuse. Twenty-one ketamine addicts were recruited and the results showed that the lesions in the brains of ketamine addicts were located in many regions which appeared 2–4 years after ketamine addiction. Cortical atrophy was usually evident in the frontal, parietal or occipital cortices of addicts. Such study confirmed that many brain regions in the human were susceptible to chronic ketamine injury and presented a diffuse effect of ketamine on the brain which might differ from other central nervous system (CNS) drugs, such as cocaine, heroin, and methamphetamine.

Effects of chronic ketamine use on frontal and medial temporal cognition

BACKGROUND

Recreational ketamine use has been on the rise worldwide. Previous studies have demonstrated that it disrupts various memory systems, but few studies have examined how it affects learning and frontal functioning. The present study investigates the effects of repeated ketamine self-administration on frontal fluency, attention, learning, and memory along the verbal/nonverbal axis.

METHODS

Twenty-five ketamine users and 30 healthy controls took a battery of neuropsychological tests. Frontal fluency was measured by the Verbal Fluency Test for semantic organization ability and the Figural Fluency Test for nonverbal executive functioning. Learning and memory were measured with the Chinese Auditory-Verbal Learning Test for acquisition and retention abilities of verbal information, as well as with the Continuous Visual Memory Test for nonverbal information. Participants also took several tests tapping subdomains of attention. To test for the potential effects of other drug use, 10 polydrug controls were included for comparison with the ketamine users and healthy controls.

RESULTS

Ketamine users had impaired verbal fluency, cognitive processing speed, and verbal learning. Verbal learning impairment was strongly correlated with estimated lifetime ketamine use. Ketamine users showed no impairments in figural fluency, sustained attention, selective attention, visual learning, or verbal/nonverbal memory. However, heavier lifetime ketamine use was significantly correlated with deficits in verbal memory (both immediate recall and delayed recall) and visual recognition memory. Deficits in cognitive processing speed and verbal learning persisted even after polydrug controls were included in the control group, but their inclusion did make the impairment in verbal fluency barely reach statistical significance.

CONCLUSIONS

This study suggests that repeated ketamine use causes differential impairment to multiple domains of frontal and medial temporal functioning, possibly specific to verbal information processing.

Aging of the NMDA receptor: from a mouse's point of view

Our elderly population is growing and declines in cognitive abilities, such as memory, can be costly, because it can interfere with a person's ability to live independently. The NMDA receptor is very important for many different forms of memory and this receptor is negatively affected by aging. This review examines the progress that has been made recently in characterizing selective vulnerabilities of different subunits and splice variants of the NMDA receptor to normal aging in C57BL/6 mice. Evidence is also presented for changes in the relationships of NMDA receptors to plasticity across aging. Recent interventions show that enhancing NMDA receptors in aged individuals is associated with improvements in memory, but mouse models of neurodegenerative diseases suggest that finding the right balance between too little and too much NMDA receptor activity will be the key to enhancing memory without inducing pathology.

Chronic ketamine administration modulates midbrain dopamine system in mice

Ketamine is an anesthetic and a popular abusive drug. As an anesthetic, effects of ketamine on glutamate and GABA transmission have been well documented but little is known about its long-term effects on the dopamine system. In the present study, the effects of ketamine on dopamine were studied in vitro and in vivo. In pheochromocytoma (PC 12) cells and NGF differentiated-PC 12 cells, ketamine decreased the cell viability while increasing dopamine (DA) concentrations in a dose-related manner. However, ketamine did not affect the expression of genes involved in DA synthesis. In the long-term (3 months) ketamine treated mice, significant increases of DA contents were found in the midbrain. Increased DA concentrations were further supported by up-regulation of tyrosine hydroxylase (TH), the rate limiting enzyme in catecholamine synthesis. Activation of midbrain dopaminergic neurons could be related to ketamine modulated cortical-subcortical glutamate connections. Using western blotting, significant increases in BDNF protein levels were found in the midbrain, suggesting that perhaps BDNF pathways in the cortical-subcortical connections might contribute to the long-term ketamine induced TH upregulation. These data suggest that long-term ketamine abuse caused a delayed and persistent upregulation of subcortical DA systems, which may contribute to the altered mental status in ketamine abusers.

Long-term ketamine and ketamine plus alcohol treatments produced damages in liver and kidney

Ketamine is one of the common recreational drugs used in rave parties and it is frequently taken with alcohol. In spite of this, the potential toxicity of ketamine in liver and kidney has not been fully documented. In this study, ICR mice were treated for periods of 6, 16 and 28 weeks with 30 mg/kg ketamine injected daily intraperitoneally, and together with alcohol (0.5 ml of 10% alcohol for each mouse) during the last 4 weeks of the treatment periods. Our experimental results showed significant damage in liver, including fatty degeneration of liver cells, fibrosis and increase in liver glutamic oxaloacetic transaminase, proliferative cell nuclear antigen and lactate dehydrogenase after 16 weeks of treatment with ketamine. Hydropic degenerations of the kidney tubules were observed as early as 6 weeks of treatment. Long-term ketamine administration (28 weeks) led to atresia of glomeruli in the kidney. Proteinuria was confirmed in the 67% of the ketamine-treated animals after 28 weeks of treatment. It was apparent that ketamine when taken chronically (16 weeks of treatment and thereafter) affected both liver and kidney definitively. The damages in both liver and kidney of these mice were more severe when the animals were treated with both ketamine and alcohol.

Cardiotoxicity induced in mice by long term ketamine and ketamine plus alcohol treatment

Increased use of ketamine as a recreational drug in rave party has raised lots of social concerns. Although its toxicity on the central nervous system (CNS) and urinary system had been reported, its potential adverse effects on the heart is still not addressed. Using our long term ketamine addiction model in which, 1-month-old ICR mice were given ketamine intraperitoneally (i.p. 30 mg/kg) for different study periods (6 weeks, 16 weeks and 28 weeks). The electrocardiogram (ECG) and the level of troponin as well as the presence of lactate dehydrogenase were used together to determine the cardiac function of mice. ST elevations were observed in 30% of mice from 6 weeks onwards. Concomitant increase in troponin in serum and presence of lactate dehydrogenase positive cardiac cells were taken together to indicate cardiac damages. The potential interactive effects of alcohol (ethanol) and ketamine were also addressed and 0.5 ml of 10% ethanol was administrated additionally to the mice daily and orally for the last 4 weeks in the 28-week long-term ketamine treated animals. The cardiac functions of these mice deteriorated more severely as indicated by further rise in troponin levels. In addition, high number of lactate dehydrogenase positive cardiac cells and abnormal ECGs in both ketamine and ketamine plus alcohol treated models also gave coherent conclusions.

Downregulation in the human and mice cerebella after ketamine versus ketamine plus ethanol treatment

To study the deleterious effects of ketamine and the potential interaction effects between ethanol and ketamine on the cerebellum, functional magnetic resonance imaging (fMRI) tests were performed on the habitual ketamine users (n = 3) when they flexed and extended their upper limbs. Another fMRI test was performed on the same participants in which they consumed alcohol (12%, 200 mL) 1 h before the test. Downregulation on the activity of cerebellum was observed and the level of activation in the cerebellum decreased dramatically in habitual ketamine users with alcohol consumption before the test. Further studies were performed by using male ICR mice receiving treatment of ketamine only [30 mg kg(-1) intraperitoneally (i.p.)] or ethanol only everyday (0.5 mL 12% orally) and those with coadministration of the above dosages of ketamine and ethanol for 3 months. Fewer Purkinje cells were observed in the cerebellar sections of ketamine treated mice under silver staining. For TUNEL test, a significant increase in the apoptotic cells were observed in the cerebella of the ketamine treated mice (P = 0.016) and of those with co-administration of ketamine and ethanol (P < 0.001), when compared with the control. A statistical significance (P < 0.001) in two-way ANOVA test indicated that there might be an interactive mechanism between ethanol and ketamine acting on the cerebellum.

Gene expression changes in GABA(A) receptors and cognition following chronic ketamine administration in mice

Ketamine is a well-known anesthetic agent and a drug of abuse. Despite its widespread use and abuse, little is known about its long-term effects on the central nervous system. The present study was designed to evaluate the effect of long-term (1- and 3-month) ketamine administration on learning and memory and associated gene expression levels in the brain. The Morris water maze was used to assess spatial memory and gene expression changes were assayed using Affymetrix Genechips; a focus on the expression of GABA(A) receptors that mediate a tonic inhibition in the brain, was confirmed by quantitative real-time PCR and western blot. Compared with saline controls, there was a decline in learning and memory performance in the ketamine-treated mice. Genechip results showed that 110 genes were up-regulated and 136 genes were down-regulated. An ontology analysis revealed the most significant effects of ketamine were on GABA(A) receptors. In particular, there was a significant up-regulation of both mRNA and protein levels of the alpha 5 subunit (Gabra5) of the GABA(A) receptors in the prefrontal cortex. In conclusion, chronic exposure to ketamine impairs working memory in mice, which may be explained at least partly by up-regulation of Gabra5 subunits in the prefrontal cortex.

Permanent deficits in brain functions caused by long-term ketamine treatment in mice

Ketamine, an injectable anesthetic, is also a popular recreational drug used by young adults worldwide. Ketamine is a non-competitive antagonist of N-methyl-d-aspartate receptor, which plays important roles in synaptic plasticity and neuronal learning. Most previous studies have examined the immediate and short-term effects of ketamine, which include learning and cognitive deficits plus impairment of working memory, whereas little is known about the long-term effects of repeated ketamine injections of common or usual recreational doses. Therefore, we aimed to evaluate the deficits in brain functions with behavioral tests, including wire hang, hot plate and water maze tests, plus examine prefrontal cortex apoptotic markers, including Bax, Bcl-2 and caspase-3, in mice treated with 6 months of daily ketamine administration. In our study, following 6 months of ketamine injection, mice showed significant deterioration in neuromuscular strength and nociception 4 hours post-dose, but learning and working memory were not affected nor was there significant apoptosis in the prefrontal cortex. Our research revealed the important clinical finding that long-term ketamine abuse with usual recreational doses can detrimentally affect neuromuscular strength and nociception as part of measurable, stable and persistent deficits in brain function.