A single intraperitoneal injection of ketamine does not affect spatial working, reference memory or neurodegeneration in adult mice: An animal study

Remimazolam induced cognitive dysfunction in mice via glutamate excitotoxicity

Objective

Several lines of evidence demonstrated the role of anesthetic drugs in cognitive functions. Some anesthetic agents have been confirmed to be associated with long-term spatial memory and learning in aged animal models.

Methods

C57BL/6 mice were divided into four different groups based on different concentrations of remimazolam treatments. Behavioral phenotype was observed by open field, rota rod, Morris water maze, and elevated plus maze test. Western blot was performed to see the expression pattern of different proteins. Confocal microscopy images were taken for neuronal and glial cells to see the effect of remimazolam on CNS cells.

Results

We showed that remimazolam, a new anesthetic drug, impaired cognitive behavior. Repetitive doses of remimazolam have been found to induce neuronal loss with a significant change in morphology. Here, we showed that a higher concentration of remimazolam had a significant effect on CNS cell activation. We showed that remimazolam caused memory dysfunction by inducing neuronal apoptosis via glutamate excitotoxicity. It also exhibited amyloid β plaque in the brain via abnormal phosphorylation of tau protein. Remimazolam-mediated regulation of glial cells in mouse cortex was observed and robust activation of astrocytes and microglial cells was found. Finally, we assessed the behavioral phenotype of mice and found that treatment with remimazolam induced significant behavioral changes and memory dysfunction.

Conclusions

This study provides insight into the mechanism of anesthetic drug-induced memory deficits and may help improve the therapeutic effects of anesthesia agents in clinical applications.

Context-Specific Tolerance and Pharmacological Changes in the Infralimbic Cortex-Nucleus Accumbens Shell Pathway Evoked by Ketamine

Like other drugs, ketamine is abused due to its ability to act as a positive reinforcer in the control of behavior, just as natural reinforcers do. Besides, through Pavlovian conditioning, tolerance to drug effects can become conditioned to specific contextual cues showing that environmental stimuli can act as powerful mediators of craving and relapse. In the present study, we shall investigate the effects of long-term ketamine administration and withdrawal on behavioral measures and emotionality, the drug-context-specific influence on the tolerance to the sedative effects of an anesthetic dose of ketamine, and the neuropharmacological events underlying this phenomenon, in rats conditioned with 10 mg/kg of ketamine and later challenged with a dose of ketamine of 80 mg/kg in a familiar and non-familiar environment. Variations in dopamine and serotonin efflux in the infralimbic cortex-nucleus accumbens shell circuitry (IL-NAcSh) was further recorded in the same conditions. Our results highlight that besides its well-known reinforcing properties, ketamine also shares the ability to induce behavioral and pharmacological conditioned tolerance, associated with increases in cortical (IL), and decreases in striatal (NAcSh) dopamine release. To our knowledge, we are presenting the first set of behavioral and neurochemical data showing that, like other drugs of abuse, ketamine can induce learned context-specific tolerance.

Impact of ketamine on the behavior and immune system of adult medaka (Oryzias latipes) at environmentally relevant concentrations and eco-risk assessment in surface water

This work for the first time investigated the bioconcentration factor (BCF), toxicity, and eco-risk of KET using adult medaka fish (Oryzias latipes) as model organism after exposure at environmental concentrations (0.05-0.5 μg L^-1) and higher levels (5-100 μg L^-1) for 90 days. The BCF of KET was approximately 1.07- to 10.94- folds. The behavioral functions, including swimming properties, feeding rate, and food preference, were significantly impacted by KET (≥0.05 μg L^-1). After 90-days exposure, KET induced histological abnormalities in liver and kidney tissue at 0.1 and 0.2 μg L^-1, respectively. Additionally, the condition factor, hepatic-somatic index (HSI), and nephric-somatic index (NSI) of medaka were markedly impacted by KET treatment at 0.5, 0.5, and 0.1 μg L^-1, respectively. Morphological inflammation (i.e., haemorrhage and erosion) in the fish body was observed exposed to KET, and the EC₁₀ value was 0.407 μg L^-1. Alterations in the expressions of genes (i.e., cacna1c, oxtr, erk1, and c-fos) and proteins (i.e., OXT and PKA), involved in in calcium ion channels induced by KET, could partly elucidate the underlying mechanism of the toxicity. The inflammatory risk to fish posed by KET in some rivers in southern China was at high level, suggesting the long-term concentration monitoring was required.

Sexually Dimorphic Behavioral Profile in a Transgenic Model Enabling Targeted Recombination in Active Neurons in Response to Ketamine and (2R,6R)-Hydroxynorketamine Administration

Background: Rapid-acting antidepressants ketamine and (2R,6R)-hydroxynorketamine ((2R,6R)-HNK) have overcome some of the major limitations of classical antidepressants. However, little is known about sex-specific differences in the behavioral and molecular effects of ketamine and (2R,6R)-HNK in rodents. Methods: We treated mice with an intraperitoneal injection of either saline, ketamine (30 mg kg⁻¹) or (2R,6R)-HNK (10 mg kg⁻¹). We performed a comprehensive behavioral test battery to characterize the Arc-CreERT2 × CAG-Sun1/sfGFP mouse line which enables targeted recombination in active populations. We performed a molecular study in Arc-CreERT2 × CAG-Sun1/sfGFP female mice using both immunohistochemistry and in situ hybridization. Results: Arc-CreERT2 × CAG-Sun1/sfGFP mice showed sex differences in sociability and anxiety tests. Moreover, ketamine and (2R,6R)-HNK had opposite effects in the forced swim test (FST) depending on gender. In addition, in male mice, ketamine-treated animals were less immobile compared to (2R,6R)-HNK, thus showing a different profile of the two drugs in the FST. At the molecular level we identified Bdnf mRNA level to be increased after ketamine treatment in female mice. Conclusion: Arc-CreERT2 × CAG-Sun1/sfGFP mice showed sex differences in social and anxiety behavior and a different pattern between ketamine and (2R,6R)-HNK in the FST in male and female mice. At the molecular level, female mice treated with ketamine showed an increase of Bdnf mRNA level, as previously observed in male mice.

Effects of Anesthetic Ketamine on Anxiety-Like Behaviour in Rats

There is scarce information regarding the effects of anesthetic doses of the non-competitive N-methyl-D-aspartate receptor antagonist ketamine on anxiety. The current study evaluated the acute effects of intraperitoneally (i.p.) administered anesthetic ketamine (100 mg/kg) i.p. on anxiety in rats. For this purpose, the light/dark and the open field tests were utilized. The effects of anesthetic ketamine on motility were also examined using a motility cage. In the light/dark test, anesthetic ketamine, administered 24 h before testing reduced the number of transitions between the light and dark compartments and the time spent in the light compartment in the rats compared with their control cohorts. In addition, ketamine was found to exert a depressive effect on rats' motility. In the open field test, animals treated with anesthetic ketamine 24 h before testing spent essentially no time in the central area of the apparatus, decreased horizontal ambulatory activity, and preserved to a certain extent their exploratory behaviour compared to their control counterparts. The results suggest that, in spite of its hypokinetic effect, a single anesthetic ketamine administration apparently induces an anxiety-like state, while largely preserving exploratory behaviour in the rat. These effects were time-dependent they since they were extinguished when testing was carried out 48 h after anesthetic ketamine administration.

A New Paradigm for Evaluating Avoidance/Escape Motivation

BACKGROUND

Organisms have evolved to approach pleasurable opportunities and to avoid or escape from aversive experiences. These 2 distinct motivations are referred to as approach and avoidance/escape motivations and are both considered vital for survival. Despite several recent advances in understanding the neurobiology of motivation, most studies addressed approach but not avoidance/escape motivation. Here we develop a new experimental paradigm to quantify avoidance/escape motivation and examine the pharmacological validity.

METHODS

We set up an avoidance variable ratio 5 task in which mice were required to press a lever for variable times to avoid an upcoming aversive stimulus (foot shock) or to escape the ongoing aversive event if they failed to avoid it. We i.p. injected ketamine (0, 1, or 5 mg/kg) or buspirone (0, 5, or 10 mg/kg) 20 or 30 minutes before the behavioral task to see if ketamine enhanced avoidance/escape behavior and buspirone diminished it as previously reported.

RESULTS

We found that the performance on the avoidance variable ratio 5 task was sensitive to the intensity of the aversive stimulus. Treatment with ketamine increased while that with buspirone decreased the probability of avoidance from an aversive stimulus in the variable ratio 5 task, being consistent with previous reports.

CONCLUSION

Our new paradigm will prove useful for quantifying avoidance/escape motivation and will contribute to a more comprehensive understanding of motivation.

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 alone or combined with midazolam or dexmedetomidine does not affect anxiety-like behaviours and memory in adult Wistar rats

Ketamine administration has been associated with controversial behavioural impairments and psychotic episodes. Even though ketamine alone and in combination with midazolam or dexmedetomidine are frequently used in laboratory animals, the side-effects of such protocols are not well known. Therefore, our aim was to evaluate the effects of ketamine alone and in combination with midazolam or dexmedetomidine on emotional reactivity, as well as the effects on learning and memory in adult rats at least 48 h after anaesthesia. The evaluation of the potential influence of 100 mg/kg ketamine administered alone and in combination with midazolam (5 mg/kg), or dexmedetomidine (0.25 mg/kg) on spatial learning and recognition memory was studied in adult Wistar rats using the radial maze as well as object recognition and location tests. The influence of these combinations on emotional reactivity was investigated using the new exploration test and the elevated plus maze. Results showed that ketamine alone or in combination with midazolam or dexmedetomidine affected neither spatial and recognition memory, nor emotional reactivity. These results reinforce the safe clinical use of ketamine and its combinations in rats in a research context since the administration of these anaesthetic combinations did not produce significant changes with regard to spatial and recognition memory or emotional reactivity. Furthermore, these results indicate that the quality of scientific data produced in adult rat neurobehavioural research is not jeopardized by the use of these anaesthetic protocols.

Distinct Neuropsychological Mechanisms May Explain Delayed- Versus Rapid-Onset Antidepressant Efficacy

The biochemical targets for antidepressants are relatively well established, but we lack a clear understanding of how actions at these proteins translate to clinical benefits. This study used a novel rodent assay to investigate how different antidepressant drugs act to modify affective biases that have been implicated in depression. In this bowl-digging task, rats encounter two equal value learning experiences on separate days (one during an affective manipulation and the other during control conditions). This induces an affective bias that is quantified using a preference test in which both digging substrates are presented together and the individual rats' choices recorded. The assay can be used to measure affective biases associated with learning (when the treatment is given at the time of the experience) or examine the modification of previously acquired biases (when the treatment is administered before the preference test). The rapid-onset antidepressant ketamine, but not the delayed-onset antidepressant, venlafaxine, attenuated the previously acquired FG7142-induced negative bias following systemic administration. Venlafaxine but not ketamine induced a positive bias when administered before learning. We then used local drug infusions and excitotoxic lesions to localize the effects of ketamine to the medial prefrontal cortex and venlafaxine to the amygdala. Using a modified protocol we also showed that positive and negative biases amplified further when the numbers of substrate-reinforcer associations are increased. We propose that this pattern of results could explain the delayed onset of action of venlafaxine and the rapid onset of action but lack of long-term efficacy seen with ketamine.

Hippocampal long-term potentiation in adult mice after recovery from ketamine anesthesia

Ketamine is frequently used to induce analgesia or anesthesia in laboratory animals, but its effects on learning and memory are poorly characterized. Long-term potentiation (LTP) is considered a cellular mechanism for learning and memory. Ketamine administration immediately abolishes hippocampal LTP in vivo, but whether this effect persists is not known. The authors administered one of two doses of ketamine to adult male C57BL/6 mice and measured LTP in hippocampal slices from the mice 24 h later. Neither LTP induction nor LTP maintenance differed significantly in mice that were administered ketamine compared with mice that were administered saline. The findings suggest that a single intraperitoneal dose of ketamine does not persistently alter LTP in adult male mice.