Sub-anesthetic and anesthetic ketamine produce different long-lasting behavioral phenotypes (24 h post-treatment) via inducing different brain-derived neurotrophic factor (BDNF) expression level in the hippocampus

Partial mGlu5 receptor NAM, M-5MPEP, induces rapid and sustained antidepressant-like effects in the BDNF-dependent mechanism and enhances (R)-ketamine action in mice

BACKGROUND

Partial negative allosteric modulators (NAM) of the metabotropic glutamate 5 (mGlu5) receptor are an excellent alternative to full antagonists and NAMs because they retain therapeutic effects and have a much broader therapeutic window. Here, we investigated whether partial mGlu5 NAM, 2-(2-(3-methoxyphenyl)ethynyl)-5-methylpyridine (M-5MPEP), induced a fast and sustained antidepressant-like effect, characteristic of rapid-acting antidepressant drugs (RAADs) like ketamine, in mice.

METHODS

A tail suspension test (TST) was used to investigate acute antidepressant-like effects. Sustained effects were studied 24 h after the four intraperitoneal (ip) administrations using the splash test, designed to measure apathy-like state, the sucrose preference test (SPT), reflecting anhedonia, and the TST. Western blot and ELISA techniques were used to measure brain-derived neurotrophic factor (BDNF) and selected protein levels.

METHODS

A tail suspension test (TST) was used to investigate acute antidepressant-like effects. Sustained effects were studied 24 h after the four intraperitoneal (ip) administrations using the splash test, designed to measure apathy-like state, the sucrose preference test (SPT), reflecting anhedonia, and the TST. Western blot and ELISA techniques were used to measure brain-derived neurotrophic factor (BDNF) and selected protein levels.

CONCLUSION

Partial mGlu5 receptor NAM, M-5MPEP, induced rapid and sustained antidepressant-like effects in the BDNF-dependent mechanism and enhanced (R)-ketamine action in mice, indicating both substances' convergent mechanisms of action and the possibility of their practical use in treating depression as RAAD.

Ketamine alleviates fear memory and spatial cognition deficits in a PTSD rat model via the BDNF signaling pathway of the hippocampus and amygdala

BACKGROUND

Post-traumatic stress disorder (PTSD) is associated with traumatic stress experiences. This condition can be accompanied by learning and cognitive deficits. Studies have demonstrated that ketamine can rapidly and significantly alleviate symptoms in patients with chronic PTSD. Nonetheless, the effects of ketamine on neurocognitive impairment and its mechanism of action in PTSD remain unclear.

METHODS

In this study, different concentrations of ketamine (5, 10, 15, and 20 mg/kg, i.p.) were evaluated in rat models of single prolonged stress and electrophonic shock (SPS&S). Expression levels of brain-derived neurotrophic factor (BDNF) and post-synaptic density-95 (PSD-95) in the hippocampus (HIP) and amygdala (AMG) were determined by Western blot analysis and immunohistochemistry.

RESULTS

The data showed that rats subjected to SPS&S exhibited significant PTSD-like cognitive impairment. The effect of ketamine on SPS&S-induced neurocognitive function showed a U-shaped dose effect in rats. A single administration of ketamine at a dosage of 10-15 mg/kg resulted in significant changes in behavioral outcomes. These manifestations of improvement in cognitive function and molecular changes were reversed at high doses (15-20 mg/kg).

CONCLUSION

Overall, ketamine reversed SPS&S-induced fear and spatial memory impairment and the down-regulation of BDNF and BDNF-related PSD-95 signaling in the HIP and AMG. A dose equal to 15 mg/kg rapidly reversed the behavioral and molecular changes and promoted the amelioration of cognitive dysfunction. The enhanced association of BDNF signaling with PSD-95 effects could be involved in the therapeutic efficiency of ketamine for PTSD.

Rapid-acting antidepressant drugs modulate affective bias in rats

How rapid-acting antidepressants (RAADs), such as ketamine, induce immediate and sustained improvements in mood in patients with major depressive disorder (MDD) is poorly understood. A core feature of MDD is the prevalence of cognitive processing biases associated with negative affective states, and the alleviation of negative affective biases may be an index of response to drug treatment. Here, we used an affective bias behavioral test in rats, based on an associative learning task, to investigate the effects of RAADs. To generate an affective bias, animals learned to associate two different digging substrates with a food reward in the presence or absence of an affective state manipulation. A choice between the two reward-associated digging substrates was used to quantify the affective bias generated. Acute treatment with the RAADs ketamine, scopolamine, or psilocybin selectively attenuated a negative affective bias in the affective bias test. Low, but not high, doses of ketamine and psilocybin reversed the valence of the negative affective bias 24 hours after RAAD treatment. Only treatment with psilocybin, but not ketamine or scopolamine, led to a positive affective bias that was dependent on new learning and memory formation. The relearning effects of ketamine were dependent on protein synthesis localized to the rat medial prefrontal cortex and could be modulated by cue reactivation, consistent with experience-dependent neural plasticity. These findings suggest a neuropsychological mechanism that may explain both the acute and sustained effects of RAADs, potentially linking their effects on neural plasticity with affective bias modulation in a rodent model.

Myelin-associated oligodendrocytic basic protein-dependent myelin repair confers the long-lasting antidepressant effect of ketamine

Ketamine exhibits rapid and sustained antidepressant effects. As decreased myelination has been linked to depression pathology, changes in myelination may be a pivotal mechanism underlying ketamine's long-lasting antidepressant effects. Although ketamine has a long-lasting facilitating effect on myelination, the precise roles of myelination in ketamine's sustained antidepressant effects remain unknown. In this study, we employed spatial transcriptomics (ST) to examine ketamine's lasting effects in the medial prefrontal cortex (mPFC) and hippocampus of mice subjected to chronic social defeat stress and identified several differentially expressed myelin-related genes. Ketamine's ability to restore impaired myelination in the brain by promoting the differentiation of oligodendrocyte precursor cells (OPCs) into mature oligodendrocytes was demonstrated. Moreover, we showed that inhibiting the expression of myelin-associated oligodendrocytic basic protein (Mobp) blocked ketamine's long-lasting antidepressant effects. We also illustrated that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) signaling mediated ketamine's facilitation on myelination. In addition, we found that the (R)-stereoisomer of ketamine showed stronger effects on myelination than (S)-ketamine, which may explain its longer-lasting antidepressant effects. These findings reveal novel mechanisms underlying the sustained antidepressant effects of ketamine and the differences in antidepressant effects between (R)-ketamine and (S)-ketamine, providing new insights into the role of myelination in antidepressant mechanisms.

Chronic lithium treatment ameliorates ketamine-induced mania-like behavior via the PI3K-AKT signaling pathway

Ketamine, a rapid-acting antidepressant drug, has been used to treat major depressive disorder and bipolar disorder (BD). Recent studies have shown that ketamine may increase the potential risk of treatment-induced mania in patients. Ketamine has also been applied to establish animal models of mania. At present, however, the underlying mechanism is still unclear. In the current study, we found that chronic lithium exposure attenuated ketamine-induced mania-like behavior and c-Fos expression in the medial prefrontal cortex (mPFC) of adult male mice. Transcriptome sequencing was performed to determine the effect of lithium administration on the transcriptome of the PFC in ketamine-treated mice, showing inactivation of the phosphoinositide 3-kinase (PI3K)-protein kinase B (AKT) signaling pathway. Pharmacological inhibition of AKT signaling by MK2206 (40 mg/kg), a selective AKT inhibitor, reversed ketamine-induced mania. Furthermore, selective knockdown of AKT via AAV-AKT-shRNA-EGFP in the mPFC also reversed ketamine-induced mania-like behavior. Importantly, pharmacological activation of AKT signaling by SC79 (40 mg/kg), an AKT activator, contributed to mania in low-dose ketamine-treated mice. Inhibition of PI3K signaling by LY294002 (25 mg/kg), a specific PI3K inhibitor, reversed the mania-like behavior in ketamine-treated mice. However, pharmacological inhibition of mammalian target of rapamycin (mTOR) signaling with rapamycin (10 mg/kg), a specific mTOR inhibitor, had no effect on ketamine-induced mania-like behavior. These results suggest that chronic lithium treatment ameliorates ketamine-induced mania-like behavior via the PI3K-AKT signaling pathway, which may be a novel target for the development of BD treatment.

Assessment of Objective and Subjective Cognitive Function in Patients With Treatment-Resistant Depression Undergoing Repeated Ketamine Infusions

BACKGROUND

Subanesthetic ketamine infusions can elicit rapid and sustained antidepressant effects, yet the potential cognitive impact of ketamine has not been thoroughly examined. This study measured changes in objective and subjective cognitive function following repeated ketamine treatment.

METHODS

Thirty-eight patients with treatment-resistant depression were administered cognitive assessments before and after undergoing 7 i.v. ketamine infusions (0.5 mg/kg over 40 minutes) within a clinical trial examining the efficacy of single and repeated administrations. Depression severity and perceived concentration were evaluated with the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Quick Inventory of Depressive Symptoms Self-Report.

RESULTS

Twenty-three participants (60.5%) responded after repeated infusions (≥50% decrease in MADRS total scores). We measured significant improvements in several cognitive domains, including attention, working memory, verbal, and visuospatial memory (effect sizes ranging from Cohen d = 0.37-0.79). Cognitive changes were attributed to reduction in depressive symptoms except for improvement in verbal memory, which remained significant after adjustment for change in MADRS total score (P = .029, η p2 = 0.13). Only responders reported improvement in subjective cognitive function with repeated ketamine administration (MADRS item 6, P < .001, d = 2.00; Quick Inventory of Depressive Symptoms Self-Report item 10, P < .001, d = 1.36).

CONCLUSION

A short course of repeated ketamine infusions did not impair neurocognitive function in patients with treatment-resistant depression. Further research is required to understand the potential mediating role of response and remission on improved cognitive function accompanying ketamine treatment as well as to examine longer-term safety outcomes. ClinicalTrials.gov identifier NCT01945047.

Toward asleep DBS: cortico-basal ganglia spectral and coherence activity during interleaved propofol/ketamine sedation mimics NREM/REM sleep activity

Deep brain stimulation (DBS) is currently a standard procedure for advanced Parkinson's disease. Many centers employ awake physiological navigation and stimulation assessment to optimize DBS localization and outcome. To enable DBS under sedation, asleep DBS, we characterized the cortico-basal ganglia neuronal network of two nonhuman primates under propofol, ketamine, and interleaved propofol-ketamine (IPK) sedation. Further, we compared these sedation states in the healthy and Parkinsonian condition to those of healthy sleep. Ketamine increases high-frequency power and synchronization while propofol increases low-frequency power and synchronization in polysomnography and neuronal activity recordings. Thus, ketamine does not mask the low-frequency oscillations used for physiological navigation toward the basal ganglia DBS targets. The brain spectral state under ketamine and propofol mimicked rapid eye movement (REM) and Non-REM (NREM) sleep activity, respectively, and the IPK protocol resembles the NREM-REM sleep cycle. These promising results are a meaningful step toward asleep DBS with nondistorted physiological navigation.

Epigenetic histone acetylation and Bdnf dysregulation in the hippocampus of rats exposed to repeated, low-dose diisopropylfluorophosphate

AIMS

Deployment-related exposures to organophosphate (OP) compounds are implicated for Gulf War Illness (GWI) development in First GW veterans. However, reasons for the persistence of GWI are not fully understood. Epigenetic modifications to chromatin are regulatory mechanisms that can adaptively or maladaptively respond to external stimuli. These include DNA methylation and histone acetylation. DNA methylation changes have been reported in GWI but the role of histone acetylation in GWI has been less explored, despite its importance as an epigenetic mechanism for neurological disorders.

MAIN METHODS

Male Sprague-Dawley rats were exposed to OP diisopropyl fluorophosphate (DFP, 0.5 mg/kg s.c., 5-d) and 6-m later brains were dissected for hippocampus. Western blotting, activity assays and chromatin immunoprecipitation (ChIP) were utilized for epigenetic analyses. Behavior was assessed using the Forced Swim Test (FST) and the Elevated Plus Maze (EPM).

KEY FINDINGS

We observed a significant upregulation in HDAC1 protein along with a significant increase in HDAC enzyme activity in the hippocampus of DFP rats. A locus-specific ChIP study revealed decreases in H3K9ac at the brain derived neurotrophic factor (Bdnf) promoter IV coupled with a significant decrease in BDNF protein in DFP rat hippocampus. Treatment with HDAC inhibitor valproic acid reduced HDAC activity and decreased the FST immobility time in DFP rats.

SIGNIFICANCE

Our research suggests that epigenetic alterations to histone acetylation pathways and decreased BDNF expression could represent novel mechanisms for GWI symptomatology and may provide new targets for developing effective drugs for GWI treatment.

A Novel Application of Ketamine for Improving Perioperative Sleep Disturbances

Perioperative sleep disturbances are commonly observed before, during, and after surgery and can be caused by several factors, such as preoperative negative moods, general anesthetics, surgery trauma, and pain. Over the past decade, the fast-acting antidepressant effects of the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine represent one of the most attractive discoveries in the field of psychiatry, such as antidepressant and anxiolytic effects. It is also widely used as a short-acting anesthetic and analgesic. Recent research has revealed new possible applications for ketamine, such as for perioperative sleep disorders and circadian rhythm disorders. Here, we summarize the risk factors for perioperative sleep disturbances, outcomes of perioperative sleep disturbances, and mechanism of action of ketamine in improving perioperative sleep quality.

Molecular mechanisms for the antidepressant-like effects of a low-dose ketamine treatment in a DFP-based rat model for Gulf War Illness

Exposure to organophosphates (OP) during the First Gulf War is among one of the factors for Gulf War Illness (GWI) development in veterans and it has been challenging to treat GWI symptoms with existing therapies. Ketamine produces a rapid-onset and sustained antidepressant response, but there is no evidence whether ketamine treatment is effective for GWI depression. Repeated, low-dose exposure to diisopropyl fluorophosphate (DFP) mimic Gulf War related OP exposures and produces a chronic depressive state in rats. In this study, DFP-exposed rats treated with ketamine (10 mg/kg, i.p.) exhibited antidepressant-like effect on the Forced Swim Test at 1-h. This effect persisted at 24-h post ketamine, a time-point by which it is eliminated from the brain suggesting involvement of mechanisms that affect long-term synaptic plasticity. Western blot analysis showed significantly lower Brain-Derived Neurotrophic Factor (BDNF) levels in DFP rat brains. Ketamine produced a nonsignificant increase in BDNF expression at 1-h but produced a larger, significant (2.2-fold) increase at 24-h in DFP rats. We previously reported chronic hippocampal calcium elevations ([Ca2+]i) in DFP rats. Ketamine-treated DFP rats exhibited significantly lower [Ca2+]i at 1-h but not at 24-h. Interestingly, treatment with ANA-12, a TrkB-BDNF receptor antagonist, in DFP rats blunted ketamine's antidepressant-like effect at 24-h but not at 1-h. These experiments suggest that in a rat model of DFP-induced depression, inhibition of the NMDAR-Ca2+ contributes to the rapid-onset antidepressant effects of ketamine while the antidepressant actions that persisted at 24-h post ketamine administration involve upregulation of BDNF signaling.

Subanesthetic ketamine exerts antidepressant-like effects in adult rats exposed to juvenile stress

Juvenile stress, like that caused by childhood maltreatment, is a significant risk factor for psychiatric disorders such as depression later in life. Recently, the antidepressant effect of ketamine, a noncompetitive N-methyl-d-aspartate receptor antagonist, has been widely investigated. However, little is known regarding its efficacy against depressive-like alterations caused by juvenile stress, which is clinically relevant in human depression. In the present study, we evaluated the antidepressant-like effect of ketamine in adult rats that had been subjected to juvenile stress. Depressive-like behavior was assessed using the forced swim test (FST), and electrophysiological and morphological alterations in the layer V pyramidal cells of the prelimbic cortex were examined using whole-cell patch-clamp recordings and subsequent recording-cell specific fluorescence imaging. We demonstrated that ketamine (10 mg/kg) attenuated the increased immobility time caused by juvenile stress in the FST, restored the diminished excitatory postsynaptic currents, and caused atrophic changes in the apical dendritic spines. Ketamine's effects reversing impaired excitatory/inhibitory ratio of postsynaptic currents were also revealed. These results indicated that ketamine could be effective in reversing the depression-like alterations caused by juvenile stress.

Chronic stress pathology and ketamine-induced alterations in functional connectivity in major depressive disorder: An abridged review of the clinical evidence

A paradigm shift in the conceptualization of the neurobiology of depression and the serendipitous discovery of ketamine's rapid-acting antidepressant (RAAD) effects has ushered in a new era of innovative research and novel drug development. Since the initial discovery of ketamine's RAAD effects, multiple studies have supported its short-term efficacy for fast-tracked improvements in treatment-resistant depression. Evidence from MRI studies have repeatedly demonstrated functional connectivity alterations in stress- and trauma-related disorders suggesting this may be a viable biomarker of chronic stress pathology (CSP). Human mechanistic studies further support this by coupling functional connectivity to ketamine's RAAD effects including connectivity to glutamate neurotransmission, ketamine to normalized connectivity, and these advantageous normalizations to symptom improvement/ketamine response. This review provides an abridged discussion of the suspected neurobiological underpinnings of ketamine's RAAD effects, highlighting ketamine-induced alterations in prefrontal, striatal, and anterior cingulate cortex functional connectivity in major depressive disorder. We present a model of CSP underscoring the role of synaptic loss and dysconnectivity and discuss how ketamine may be used both as (1) a treatment to restore and normalize these stress-induced neural alterations and (2) a tool to study potential biomarkers of CSP and treatment response. We conclude by noting challenges and future directions including heterogeneity, sex differences, the role of early life stress, and the need for proliferation of new methods, paradigms, and tools that will optimize signal and allow analyses at different levels of complexity, according to the needs of the question at hand, perhaps by thinking hierarchically about both clinical and biological phenotypes.

Ketamine as an antidepressant: overview of its mechanisms of action and potential predictive biomarkers

Ketamine, a drug introduced in the 1960s as an anesthetic agent and still used for that purpose, has garnered marked interest over the past two decades as an emerging treatment for major depressive disorder. With increasing evidence of its efficacy in treatment-resistant depression and its potential anti-suicidal action, a great deal of investigation has been conducted on elucidating ketamine's effects on the brain. Of particular interest and therapeutic potential is the ability of ketamine to exert rapid antidepressant properties as early as several hours after administration. This is in stark contrast to the delayed effects observed with traditional antidepressants, often requiring several weeks of therapy for a clinical response. Furthermore, ketamine appears to have a unique mechanism of action involving glutamate modulation via actions at the N-methyl-D-aspartate (NMDA) and α -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, as well as downstream activation of brain-derived neurotrophic factor (BDNF) and mechanistic target of rapamycin (mTOR) signaling pathways to potentiate synaptic plasticity. This paper provides a brief overview of ketamine with regard to pharmacology/pharmacokinetics, toxicology, the current state of clinical trials on depression, postulated antidepressant mechanisms and potential biomarkers (biochemical, inflammatory, metabolic, neuroimaging sleep-related and cognitive) for predicting response to and/or monitoring of therapeutic outcome with ketamine.

Rapid anti-depressant-like effects of ketamine and other candidates: Molecular and cellular mechanisms

Major depressive disorder takes at least 3 weeks for clinical anti‐depressants, such as serotonin selective reuptake inhibitors, to take effect, and only one‐third of patients remit. Ketamine, a kind of anaesthetic, can alleviate symptoms of major depressive disorder patients in a short time and is reported to be effective to treatment‐resistant depression patients. The rapid and strong anti‐depressant‐like effects of ketamine cause wide concern. In addition to ketamine, caloric restriction and sleep deprivation also elicit similar rapid anti‐depressant‐like effects. However, mechanisms about the rapid anti‐depressant‐like effects remain unclear. Elucidating the mechanisms of rapid anti‐depressant effects is the key to finding new therapeutic targets and developing therapeutic patterns. Therefore, in this review we summarize potential molecular and cellular mechanisms of rapid anti‐depressant‐like effects based on the pre‐clinical and clinical evidence, trying to provide new insight into future therapy.