Ketamine affects memory consolidation: Differential effects in T-maze and passive avoidance paradigms in mice

The dynamic strategy shifting task: Optimisation of an operant task for assessing cognitive flexibility in rats

Introduction

Although schizophrenia is associated with a broad range of symptoms including hallucinations, delusions, and reduced motivation, measures of cognitive dysfunction, including cognitive flexibility and executive function, are the strongest predictors of functional outcomes. Antipsychotic medications are useful for reducing psychotic symptoms, but they are ineffective at improving cognitive deficits. Despite extensive investment by industry, the transition from preclinical to clinical trials has not been successful for developing precognitive medications for individuals with schizophrenia. Here, we describe the optimisation of a novel dynamic strategy shifting task (DSST) using standard operant chambers to investigate the optimal stimuli required to limit the extensive training times required in previous tasks.

Methods

We determined that optimal learning by male and female Sprague Dawley rats for the flexibility task incorporated dynamic strategy shifts between spatial rules, such as following a visual cue or responding at one location, and non-spatial rules, such as responding to a central visual or auditory cue. A minimum of 6 correct consecutive responses were required to make a within-session change in the behavioural strategies. As a proof of concept, we trained and tested 84 Sprague Dawley rats on the DSST, and then assessed their cognitive flexibility using a within-subject design after an acute dose of ketamine (0, 3, 10 mg/kg). Rats made fewer premature and more perseverant responses to initiate a trial following ketamine. The effects of ketamine on trials to criterion was dependent on the rule.

Results

Ketamine induced a significant improvement on the reversal of a non-spatial visual discrimination rule. There was no significant effect of ketamine on the spatial visual or response discrimination rules.

Discussion

The DSST is a novel assay for studying distinct forms of cognitive flexibility and offers a rapid and adaptable means of assessing the ability to shift between increasingly challenging rule conditions. The DSST has potential utility in advancing our understanding of cognitive processes and the underlying neurobiological mechanisms related to flexibility in neuropsychiatric and neurological conditions where executive dysfunctions occur.>.

Repeated dextromethorphan administration in adolescent rats produces long-lasting behavioral alterations

Initiation of non-medical dextromethorphan (DXM) use often occurs in adolescence, yet little is known about the consequences when use begins during this developmental period. The current experiments examined the acute response and the effects of repeated exposure to DXM in adolescence on behavior in adulthood. We examined locomotor activity, locomotor sensitization, and cognitive function, in rats that received repeated administration of DXM. Groups of adolescent (PND 30) and adult (PND 60) male rats were treated with DXM (60 mg/kg) once daily for 10 days. Locomotor activity in response to DXM was assessed following the first injection, on the 10th day of injection (adolescent - PND 39; adult - PND 69), and following 20 days of abstinence (adolescent - PND 60; adult - PND 90). Acute locomotor effects and locomotor sensitization were compared in adolescents and adults; cross-sensitization to ketamine, another dissociative with abuse potential, was also examined. In a separate group of rodents cognitive deficits were assessed following a 20 day abstinence period (adolescent - PND 60; adult - PND 90) in spatial learning and novel object recognition tasks. The locomotor stimulant effect of DXM was much greater in adolescents than adults. Also, only adolescent rats that were repeatedly administered DXM demonstrated locomotor sensitization at the end of 10 days of injection. However, sensitization occurred after the abstinence period in all rats regardless of age. Nonetheless, cross-sensitization to ketamine was only evident in adolescent-treated rats. DXM also led to an increase in perseverative errors in reversal learning only in the adolescent-treated group. We conclude that repeated use of DXM produces long-lasting neuroadaptations that may contribute to addiction. Deficits in cognitive flexibility occur in adolescents, although further work is necessary to confirm these findings. The results extend the understanding of potential long-term consequences of DXM use in adolescents and adults.

Effect of Letrozole on hippocampal Let-7 microRNAs and their correlation with working memory and phosphorylated Tau protein in an Alzheimer's disease-like rat model

Background

Let-7 microRNAs (miRNAs) may contribute to neurodegeneration, including Alzheimer's disease (AD), but, they were not investigated in Streptozotocin (STZ)-induced AD. Letrozole increases the expression of Let-7 in cell lines, with conflicting evidence regarding its effects on memory. This study examined Let-7 miRNAs in STZ-induced AD, their correlation with memory and hyperphosphorylated Tau (p-Tau) and the effects of Letrozole on them.

Methods

Seven groups of adult Sprague Dawley rats were used: Negative control, Letrozole, Letrozole Vehicle, STZ (with AD induced by intracerebroventricular injection of STZ in artificial cerebrospinal fluid (aCSF)), CSF Control, STZ + Letrozole (STZ-L), and CSF + Letrozole Vehicle. Alternation percentage in T-maze was used as a measure of working memory. Let-7a, b and e and p-Tau levels in the hippocampus were estimated using quantitative real-time reverse transcription–polymerase chain reaction (qRT–PCR) and enzyme-linked immunosorbent assay (ELISA), respectively.

Results

Significant decreases in alternation percentage and increase in p-Tau concentration were found in the STZ, Letrozole and STZ-L groups. Expression levels of all studied microRNAs were significantly elevated in the Letrozole and the STZ-L groups, with no difference between the two, suggesting that this elevation might be linked to Letrozole administration. Negative correlations were found between alternation percentage and the levels of all studied microRNAs, while positive ones were found between p-Tau concentration and the levels of studied microRNAs.

Conclusions

This study shows changes in the expression of Let-7a, b and e miRNAs in association with Letrozole administration, and correlations between the expression of the studied Let-7 miRNAs and both the status of working memory and the hippocampal p-Tau levels. These findings might support the theory suggesting that Letrozole aggravates pre-existing lesions. They also add to the possibility of Let-7’s neurotoxicity.

(R,S)-ketamine and (2R,6R)-hydroxynorketamine differentially affect memory as a function of dosing frequency

A single subanesthetic infusion of ketamine can rapidly alleviate symptoms of treatment-resistant major depression. Since repeated administration is required to sustain symptom remission, it is important to characterize the potential untoward effects of prolonged ketamine exposure. While studies suggest that ketamine can alter cognitive function, it is unclear to what extent these effects are modulated by the frequency or chronicity of treatment. To test this, male and female adolescent (postnatal day [PD] 35) and adult (PD 60) BALB/c mice were treated for four consecutive weeks, either daily or thrice-weekly, with (R,S)-ketamine (30 mg/kg, intraperitoneal) or its biologically active metabolite, (2R,6R)-hydroxynorketamine (HNK; 30 mg/kg, intraperitoneal). Following drug cessation, memory performance was assessed in three operationally distinct tasks: (1) novel object recognition to assess explicit memory, (2) Y-maze to assess working memory, and (3) passive avoidance to assess implicit memory. While drug exposure did not influence working memory performance, thrice-weekly ketamine and daily (2R,6R)-HNK led to explicit memory impairment in novel object recognition independent of sex or age of exposure. Daily (2R,6R)-HNK impaired implicit memory in the passive-avoidance task whereas thrice-weekly (2R,6R)-HNK tended to improve it. These differential effects on explicit and implicit memory possibly reflect the unique mechanisms by which ketamine and (2R,6R)-HNK alter the functional integrity of neural circuits that subserve these distinct cognitive domains, a topic of clinical and mechanistic relevance to their antidepressant actions. Our findings also provide additional support for the importance of dosing frequency in establishing the cognitive effects of repeated ketamine exposure.

Crocins, the Bioactive Components of Crocus sativus L., Counteract the Disrupting Effects of Anesthetic Ketamine on Memory in Rats

Consistent experimental evidence suggests that anesthetic doses of the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist ketamine cause severe memory impairments in rodents. Crocins are among the various bioactive ingredients of the plant Crocus sativus L., and their implication in memory is well-documented. It has not yet been elucidated if crocins are able to attenuate the memory deficits produced by anesthetic ketamine. The present study was undertaken aiming to clarify this issue in the rat. For this aim, the object recognition, the object location and the habituation tests, reflecting non-spatial recognition memory, spatial recognition memory and associative memory, respectively, were utilized. A post-training challenge with crocins (15–30 mg/kg, intraperitoneally (i.p.), acutely) counteracted anesthetic ketamine (100 mg/kg, i.p.)-induced performance impairments in all the above-mentioned behavioral memory paradigms. The current findings suggest that crocins modulate anesthetic ketamine’s amnestic effects.

Ketamine anesthesia enhances fear memory consolidation via noradrenergic activation in the basolateral amygdala

Trauma patients treated with ketamine during emergency care present aggravated early post- traumatic stress reaction which is highly predictive of post-traumatic stress disorder (PTSD) development and severity. The use of ketamine in the acute trauma phase may directly or indirectly interfere with neural processes of memory consolidation of the traumatic event, thus leading to the formation of maladaptive memories, a hallmark symptom of PTSD. We have recently shown that ketamine anesthesia, immediately after a traumatic event, enhances memory consolidation and leads to long-lasting alterations of social behavior in rats. Based on the evidence that ketamine induces a robust central and peripheral adrenergic/noradrenergic potentiation and that activation of this system is essential for the formation of memory for stressful events, we explored the possibility that the strong sympathomimetic action of ketamine might underlie its memory enhancing effects. We found that rats given immediate, but not delayed, post-training ketamine anesthesia (125 mg/kg) presented enhanced 48-h memory retention in an inhibitory avoidance task and that these effects were blocked by adrenal medullectomy, lesions of the locus coeruleus, systemic or intra-basolateral amygdala ß-adrenergic receptor antagonism. Thus, the memory enhancing effects of ketamine anesthesia are time-dependent and mediated by a combined peripheral-central sympathomimetic action. We elucidated a mechanism by which ketamine exacerbates acute post-traumatic reaction, possibly leading to development of PTSD symptomatology later in life. These findings will help guide for a better management of sedation/anesthesia in emergency care to promote the prophylaxis and reduce the risk of developing trauma-related disorders in trauma victims.

Ketamine disrupted storage but not retrieval of information in male rats and apomorphine counteracted its impairing effect

Ketamine, a non-competitive NMDA receptor antagonist, has been reported to mimic the cognitive symptoms of schizophrenia in animals. It has been reported to produce learning and memory deficits in rodents. However, there have limited number of reports that investigated the specific components of memory process that are affected with ketamine. In the present study, we investigated the effects of ketamine [8 and 20 mg/kg, intraperitoneally, (i.p.)] on storage and retrieval of information in rats using an object recognition test. We examined also whether a low dose range of the D1/D2 dopamine receptor agonist apomorphine (0.05 and 0.1 mg/kg, i.p.) would counteract the effects of ketamine. The results show that ketamine dose-dependently impaired storage of information while it did not affect rats' retrieval abilities. Administration of apomorphine reversed the ketamine-induced performance deficits in the ORT. The current findings show a differential modulation of post-training memory components (storage and retrieval of information) by ketamine and suggest a functional interaction between dopamine and NMDA receptors in the control of memory storage which may be of relevance to cognitive deficits a core feature of schizophrenia.

Ketamine Administration Leads to Learning-Memory Dysfunction and Decreases Serum Brain-Derived Neurotrophic Factor in Rats

OBJECTIVE

This study investigated the effects of acute or chronic ketamine administration on learning and memory function as well as levels of brain-derived neurotrophic factor (BDNF) in the hippocampus and blood in order to explore the potential correlation between learning-memory dysfunction and ketamine.

METHODS

Rats were treated with 25 mg/kg ketamine for 3 d (n = 20) or 14 d (n = 20). Saline-treated rats were used as controls. The Morris water maze test was used to evaluate spatial learning and memory after 10 d of withdrawal. The level of BDNF in serum and the hippocampus were measured by ELISA.

RESULTS

The number of platform crossings and residence time in the target platform quadrant were significantly reduced in ketamine 3 d and 14 d groups than in the saline controls (both p < 0.05). In addition, the average escape latency of ketamine 3 d and 14 d groups were significantly longer than that of the saline 3 d and 14 d groups (p < 0.0001), respectively. Further examination found that only serum samples from ketamine 14 d group showed significantly decreased BDNF level compared to that from saline 14 d groups (p < 0.05). However, no differences were detected in hippocampus samples.

CONCLUSION

Chronic ketamine exposure (25 mg/kg) causes spatial learning and memory deficits in SD rats, which may be associated with decreased serum BDNF levels.

Long-lasting effects of repeated ketamine administration in adult and adolescent rats

Initiation of ketamine use often occurs in adolescence, yet little is known about long-term consequences when use begins in this developmental period. The current experiments were designed to examine the effects of repeated exposure to ketamine in adolescence on behavior in adulthood. We examined locomotor activity, as well as cognitive function, in animals that received repeated administration of ketamine. Groups of adolescent and adult male rats were treated with ketamine (25 mg/kg) once daily for 10 days. Locomotor activity was assessed following the first injection, following 10 days of injection, and following 20 days of abstinence. Acute locomotor effects and locomotor sensitization were compared in adolescents and adults; cross-sensitization to dextromethorphan, another dissociative with abusive potential, was also examined. In a separate group of animals cognitive deficits were assessed following the 20 day abstinence period in spatial learning and novel object recognition tasks. The locomotor stimulant effect of ketamine was much greater in adolescents than adults. Animals that were repeatedly administered ketamine demonstrated locomotor sensitization immediately after the final injection. However, sensitization only persisted after the abstinence period in animals treated as adults. No cross-sensitization to dextromethorphan was evident. Ketamine failed to produce statistically significant cognitive deficits in either age group, although drug-treated adults showed a trend towards deficits in spatial learning. Repeated use of ketamine produces long-lasting neuroadaptations that may contribute to addiction. Mild lasting memory deficits may occur in adults, although further work is necessary to confirm these findings. The results extend the understanding of potential long-term consequences of ketamine use in adolescents and adults.

Flumazenil but not bicuculline counteract the impairing effects of anesthetic ketamine on recognition memory in rats. Evidence for a functional interaction between the GABAA-benzodiazepine receptor and ketamine?

Experimental evidence indicates that anesthetic doses of the non-competitive NMDA receptor antagonist ketamine impair memory abilities in rodents. The mechanism by which anesthetic ketamine produces its adverse behavioural effects is not yet clarified. In this context, it has been proposed that the effects of anesthetic ketamine on memory might be attributed to its agonistic properties on the GABA type A receptor. The present study was designed to address this issue. Thus, we investigated the ability of the benzodiazepine receptor antagonist flumazenil (1, 3, 6 mg/kg, i.p.) and the GABA_A receptor antagonist bicuculline (0.5, 1.5, 3 mg/kg, i.p.) to counteract recognition memory deficits produced by anesthetic ketamine (100 mg/kg, i.p.) in rats. For this purpose, the novel object recognition task, a behavioural paradigm assessing recognition memory abilities in rodents was used. Compounds were coadministered 24 h before testing or retention. Pre (24 h before testing) or post-training (24 h before retention) administration of flumazenil (6 mg/kg, i.p.) counteracted anesthetic ketamine-induced performance deficits in the novel object recognition memory task. Conversely, bicuculline failed to attenuate the recognition memory deficits caused by anesthetic ketamine. Our findings propose a functional interaction between anesthetic ketamine and the GABA_A receptor allosteric modulator flumazenil on recognition memory.

Ketamine for the treatment of addiction: Evidence and potential mechanisms

Ketamine is a dissociative anaesthetic drug which acts on the central nervous system chiefly through antagonism of the n-methyl-d-aspartate (NMDA) receptor. Recently, ketamine has attracted attention as a rapid-acting anti-depressant but other studies have also reported its efficacy in reducing problematic alcohol and drug use. This review explores the preclinical and clinical research into ketamine's ability to treat addiction. Despite methodological limitations and the relative infancy of the field, results thus far are promising. Ketamine has been shown to effectively prolong abstinence from alcohol and heroin in detoxified alcoholics and heroin dependent individuals, respectively. Moreover, ketamine reduced craving for and self-administration of cocaine in non-treatment seeking cocaine users. However, further randomised controlled trials are urgently needed to confirm ketamine's efficacy. Possible mechanisms by which ketamine may work within addiction include: enhancement of neuroplasticity and neurogenesis, disruption of relevant functional neural networks, treating depressive symptoms, blocking reconsolidation of drug-related memories, provoking mystical experiences and enhancing psychological therapy efficacy. Identifying the mechanisms by which ketamine exerts its therapeutic effects in addiction, from the many possible candidates, is crucial for advancing this treatment and may have broader implications understanding other psychedelic therapies. In conclusion, ketamine shows great promise as a treatment for various addictions, but well-controlled research is urgently needed. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.

Distinct retrosplenial cortex cell populations and their spike dynamics during ketamine-induced unconscious state

Ketamine is known to induce psychotic-like symptoms, including delirium and visual hallucinations. It also causes neuronal damage and cell death in the retrosplenial cortex (RSC), an area that is thought to be a part of high visual cortical pathways and at least partially responsible for ketamine's psychotomimetic activities. However, the basic physiological properties of RSC cells as well as their response to ketamine in vivo remained largely unexplored. Here, we combine a computational method, the Inter-Spike Interval Classification Analysis (ISICA), and in vivo recordings to uncover and profile excitatory cell subtypes within layers 2&3 and 5&6 of the RSC in mice within both conscious, sleep, and ketamine-induced unconscious states. We demonstrate two distinct excitatory principal cell sub-populations, namely, high-bursting excitatory principal cells and low-bursting excitatory principal cells, within layers 2&3, and show that this classification is robust over the conscious states, namely quiet awake, and natural unconscious sleep periods. Similarly, we provide evidence of high-bursting and low-bursting excitatory principal cell sub-populations within layers 5&6 that remained distinct during quiet awake and sleep states. We further examined how these subtypes are dynamically altered by ketamine. During ketamine-induced unconscious state, these distinct excitatory principal cell subtypes in both layer 2&3 and layer 5&6 exhibited distinct dynamics. We also uncovered different dynamics of local field potential under various brain states in layer 2&3 and layer 5&6. Interestingly, ketamine administration induced high gamma oscillations in layer 2&3 of the RSC, but not layer 5&6. Our results show that excitatory principal cells within RSC layers 2&3 and 5&6 contain multiple physiologically distinct sub-populations, and they are differentially affected by ketamine.

Is Forced Swimming Immobility a Good Endpoint for Modeling Negative Symptoms of Schizophrenia? - Study of Sub-Anesthetic Ketamine Repeated Administration Effects

Immobility time in the forced swimming has been described as analogous to emotional blunting or apathy and has been used for characterizing schizophrenia animal models. Several clinical studies support the use of NMDA receptor antagonists to model schizophrenia in rodents. Some works describe the effects of ketamine on immobility behavior but there is variability in the experimental design used leading to controversial results. In this study, we evaluated the effects of repeated administration of ketamine sub-anesthetic doses in forced swimming, locomotion in response to novelty and novel object recognition, aiming a broader evaluation of the usefulness of this experimental approach for modeling schizophrenia in mice. Ketamine (30 mg/kg/day i.p. for 14 days) induced a not persistent decrease in immobility time, detected 24h but not 72h after treatment. This same administration protocol induced a deficit in novel object recognition. No change was observed in mice locomotion. Our results confirm that repeated administration of sub-anesthetic doses of ketamine is useful in modeling schizophrenia-related behavioral changes in mice. However, the immobility time during forced swimming does not seem to be a good endpoint to evaluate the modeling of negative symptoms in NMDAR antagonist animal models of schizophrenia.

Short- and long-term antidepressant effects of ketamine in a rat chronic unpredictable stress model

OBJECTIVE

This research was aimed to evaluate the behaviors of short- or long-term antidepressant effects of ketamine in rats exposed to chronic unpredictable stress (CUS).

BACKGROUND

Ketamine, a glutamate noncompetitive NMDA receptor antagonist, regulates excitatory amino acid functions, such as anxiety disorders and major depression, and plays an important role in synaptic plasticity and learning and memory.

METHODS

After 42 days of CUS model, male rats received either a single injection of ketamine (10 mg/kg; day 43) or 15 daily injections (days 43-75). The influence of ketamine on behavioral reactivity was assessed 24 hr (short-term) or 7 weeks after ketamine treatment (long-term). Behavioral tests used to assess the effects of these treatments included the sucrose preference (SP), open field (OF), elevated plus maze (EPM), forced swimming (FS), and water maze (WM) to detect anxiety-like behavior (OF and EPM), forced swimming (FS), and water maze (WM). Results: Short-term ketamine administration resulted in increases of body weight gain, higher sensitivity to sucrose, augmented locomotor activity in the OF, more entries into the open arms of the EPM, along increased activity in the FS test; all responses indicative of reductions in depression/despair in anxiety-eliciting situations. No significant differences in these behaviors were obtained under conditions of long-term ketamine administration (p > .05). The CUS + Ketamine group showed significantly increased activity as compared with the CUS + Vehicle group for analysis of the long-term effects of ketamine (*p < .05). Nor were significant differences obtained in learning and memory performance in rats receiving ketamine (p > .05).

CONCLUSION

Taken together these findings demonstrate that a short-term administration of ketamine induced rapid antidepressant-like effects in adult male rats exposed to CUS conditions, effects that were not observed in response to the long-term treatment regime.

Acetyl L-carnitine targets adenosine triphosphate synthase in protecting zebrafish embryos from toxicities induced by verapamil and ketamine: An in vivo assessment

Verapamil is a Ca²⁺ channel blocker and is highly prescribed as an anti-anginal, antiarrhythmic and antihypertensive drug. Ketamine, an antagonist of the Ca²⁺ -permeable N-methyl-d-aspartate-type glutamate receptors, is a pediatric anesthetic. Previously we have shown that acetyl l-carnitine (ALCAR) reverses ketamine-induced attenuation of heart rate and neurotoxicity in zebrafish embryos. Here, we used 48 h post-fertilization zebrafish embryos that were exposed to relevant drugs for 2 or 4 h. Heart beat and overall development were monitored in vivo. In 48 h post-fertilization embryos, 2 mm ketamine reduced heart rate in a 2 or 4 h exposure and 0.5 mm ALCAR neutralized this effect. ALCAR could reverse ketamine's effect, possibly through a compensatory mechanism involving extracellular Ca²⁺ entry through L-type Ca²⁺ channels that ALCAR is known to activate. Hence, we used verapamil to block the L-type Ca²⁺ channels. Verapamil was more potent in attenuating heart rate and inducing morphological defects in the embryos compared to ketamine at specific times of exposure. ALCAR reversed cardiotoxicity and developmental toxicity in the embryos exposed to verapamil or verapamil plus ketamine, even in the presence of 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester, an inhibitor of intracellular Ca²⁺ release suggesting that ALCAR acts via effectors downstream of Ca²⁺ . In fact, ALCAR's protective effect was blunted by oligomycin A, an inhibitor of adenosine triphosphate synthase that acts downstream of Ca²⁺ during adenosine triphosphate generation. We have identified, for the first time, using in vivo studies, a downstream effector of ALCAR that is critical in abrogating ketamine- and verapamil-induced developmental toxicities. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

The effects of tamoxifen on spatial and nonspatial learning and memory impairments induced by scopolamine and the brain tissues oxidative damage in ovariectomized rats

Background:

Modulatory effects of tamoxifen (TAM) on the central nervous system have been reported. The effects of TAM on spatial and nonspatial learning and memory impairments induced by scopolamine and the brain tissues oxidative damage was investigated.

Materials and Methods:

The ovariectomized (OVX) rats were divided and treated: (1) Control (saline), (2) scopolamine (Sco; 2 mg/kg, 30 min before behavioral tests), (3–5) Sco-TAM 1, Sco-TAM 3 and Sco-TAM 10. TAM (1, 3 or 10 mg/kg; i.p.) was daily administered for 6 weeks.

Results:

In Morris water maze (MWM), both the latency and traveled distance in the Sco-group were higher than control (P < 0.001) while, in the Sco-TAM 10 group it was lower than Sco-group (P < 0.05). In passive avoidance test, the latency to enter the dark compartment was higher than control (P < 0.05 – P < 0.01). Pretreatment by all three doses of TAM prolonged the latency to enter the dark compartment compared to Sco-group (P < 0.05 – P < 0.001). The brain tissues malondialdehyde (MDA) concentration was increased while, superoxide dismutase activity (SOD) decreased in the Sco-group compared to control (P < 0.05 – P < 0.01). Pretreatment by TAM lowered the concentration of MDA while, increased SOD compared to Sco-group (P < 0.05 – P < 0.001).

Conclusions:

It is suggested that TAM prevents spatial and nonspatial learning and memory impairments induced by scopolamine in OVX rats. The possible mechanism(s) might at least in part be due to protection against the brain tissues oxidative damage.

Effects of striatal ΔFosB overexpression and ketamine on social defeat stress-induced anhedonia in mice

BACKGROUND

Chronic social defeat stress (CSDS) produces persistent behavioral adaptations in mice. In many behavioral assays, it can be difficult to determine if these adaptations reflect core signs of depression. We designed studies to characterize the effects of CSDS on sensitivity to reward because anhedonia (reduced sensitivity to reward) is a defining characteristic of depressive disorders in humans. We also examined the effects of striatal ΔFosB overexpression and the N-methyl-D-aspartate receptor antagonist ketamine, both of which promote resilience, on CSDS-induced alterations in reward function and social interaction.

METHODS

Intracranial self-stimulation (ICSS) was used to quantify CSDS-induced changes in reward function. Mice were implanted with lateral hypothalamic electrodes, and ICSS thresholds were measured after each of 10 daily CSDS sessions and during a 5-day recovery period. We also examined if acute intraperitoneal administration of ketamine (2.5-20 mg/kg) reverses CSDS-induced effects on reward or, in separate mice, social interaction.

RESULTS

ICSS thresholds were increased by CSDS, indicating decreases in the rewarding impact of lateral hypothalamic stimulation (anhedonia). This effect was attenuated in mice overexpressing ∆FosB in striatum, consistent with pro-resilient actions of this transcription factor. High, but not low, doses of ketamine administered after completion of the CSDS regimen attenuated social avoidance in defeated mice, although this effect was transient. Ketamine did not block CSDS-induced anhedonia in the ICSS test.

CONCLUSIONS

This study found that CSDS triggers persistent anhedonia and confirms that ΔFosB overexpression produces stress resilience. The findings of this study also indicate that acute administration of ketamine fails to attenuate CSDS-induced anhedonia despite reducing other depression-related behavioral abnormalities.

Human reconsolidation: a reactivation and update

The reconsolidation hypothesis states that memories, when reactivated, enter a transient, labile state followed by a re-stabilization termed reconsolidation. By affecting the reconsolidation process, memory persistence can be influenced, leading to memory enhancement or decrement. This is a time-dependent process and the result of modulating reconsolidation is present only after the reconsolidation process is completed. Historically, reconsolidation research has been performed on non-human animals, since the methods originally used for reconsolidation disruption are not safe. However, there now exist several techniques safe for humans, and consequently, in recent years, papers on human reconsolidation have emerged. Here, the existing literature on human reconsolidation is reviewed and discussed, including studies on fear memories, appetitive memories, procedural memories, and declarative memories. Methods of memory reactivation are compared between studies, and the consistency and lack of consistency in results over reactivation methods and memory types are discussed. These results provide future challenges, both experimental and clinical, in defining the boundary conditions and mechanisms governing the reconsolidation phenomenon. This article is part of a Special Issue entitled 'Memory Enhancement'.

The memory stages of a spatial Y-maze task are not affected by a low dose of ketamine/midazolam

Anesthetics, such as the ketamine/midazolam combination, are used in research with animals and in human clinical practice; thus, it is essential to clarify the potential effects of these anesthetics on memory. This study aimed to evaluate how a low dose of the ketamine/midazolam combination affects the acquisition, consolidation, or recall of a spatial memory task. Thirty-three adult male C57BL/6 mice were divided into four treatment groups: unanesthetized control animals and three groups of animals treated with 40 mg/kg of ketamine and 10mg/kg of midazolam administered in a single intraperitoneal injection. The different treatment groups received the same anesthetic dose at different time points, to study the acquisition, consolidation, and recall of spatial memory in the Y-maze task. The percentage of correct choices was measured. Six mice were killed 4 days and 12 days after anesthesia for histopathological analyses. There were no differences between treatment and control groups regarding the acquisition of spatial memory, measured as the slope of the learning curve, or in the percentage of correct choices in the consolidation or recall periods of the task. Similarly, no differences were detected between groups regarding the number of cells per square millimeter in the visual and retrosplenial cortex, in the dentate gyrus, and in the CA1 and CA3 regions of the hippocampus. Hence, a low dose of the ketamine/midazolam combination did not impair memory processes or brain integrity in adult mice, suggesting that this combination is unlikely to cause cognitive complications.

The effect of sub-anesthetic and anesthetic ketamine on water maze memory acquisition, consolidation and retrieval

Ketamine, a non-selective inhibitor of NMDA (N-methyl-D-aspartate) channels is used in anesthetic or sub-anesthetic doses to induce analgesia, amnesia, to suppress fear, anxiety and depression. Although the ketamine's effect on memory acquisition is known, its effects on other aspects of memory are controversial. Morris water maze is a task which assesses spatial learning and memory. This study was aimed to assess the ketamine's differential effect on water maze memory acquisition, consolidation and retrieval. Male Sprague-Dawley rats (250-350 g) were trained in water maze single training session. 24h later a probe trial which was consisted of a single trial without platform was done. To assess the effect of ketamine on water maze memory acquisition it was administered before training; to assess its effect on memory consolidation it was administered immediately after training and to assess its effect on memory retrieval it was injected before probe trial. Ketamine both in sub-anesthetic and anesthetic doses impaired water maze memory acquisition, its anesthetic dose but not sub-anesthetic dose impaired memory consolidation and on retrieval stage, both doses deteriorated memory retrieval. It seems that NMDA receptor activity is not just necessary during water maze memory acquisition but also their post-learning reactivation is required to maintain memory consolidation and retrieval.

Learning large-scale spatial relationships in a maze and effects of MK-801 on retrieval in the rhesus monkey

Monkeys have strong abilities to remember the visual properties of potential food sources for survival in the nature. The present study demonstrated the first observations of rhesus monkeys learning to solve complex spatial mazes in which routes were guided by visual cues. Three monkeys were trained in a maze (6 m x 6 m) included of four different mazes. We recorded the cue and cup errors, latencies, and pathway for each trial. The data showed that monkeys learned the target place after three days in the first maze and spent a shorter time in learning the following mazes. The maze was an efficient method to measure the ability and proceeding of spatial memory in monkeys. Moreover, working memory can also be tested by using the maze. MK-801 at 0.02 mg/kg but not at 0.005 mg/kg impaired monkeys' retrieval of spatial memory after they learned all four mazes. The present maze may provide an efficient method to help bridging the gap in cognition between nonhuman primates and humans, and in particular to gain insight into human cognitive function and dysfunction.

Subsequent exposure to the choline uptake enhancer MKC-231 antagonizes phencyclidine-induced behavioral deficits and reduction in septal cholinergic neurons in rats

This study examined the effects of subsequent, subchronic, treatment with choline uptake enhancer MKC-231 on the behavioral and cellular deficits induced by repeated PCP exposure in rats. Prior subchronic PCP exposure resulted in increased locomotion following an acute PCP or cocaine challenge, but resulted in decreased locomotor activity in response to a carbachol-challenge. MKC-231 significantly antagonized the alterations in the locomotor responses to cocaine and carbachol, but not to PCP. In the novel object recognition test, repeated PCP exposure caused cognitive deficits in rats, and the PCP-induced cognitive deficits were antagonized by MKC-231. In contrast, no effects of PCP exposure were shown in the repeated passive avoidance test. Furthermore, repeated PCP exposure decreased a number of choline acetyltransferase (ChAT)-positive cells in the medial septum and increased dynorphin A expression in the ventral striatum. Moreover, MKC-231 significantly antagonized the changes in septal ChAT-positive cells, but not the changes in ventrostriatal dynorphin A expression. These results suggest that MKC-231 could be a therapeutic drug for the treatment of schizophrenia.