Neural correlates of rapid antidepressant response to ketamine in bipolar disorder

Update on the assessment of resistance to antidepressant treatment: Rationale for the Antidepressant Treatment History Form: Short Form-2 (ATHF-SF2)

All definitions of treatment-resistant depression (TRD) require that patients have experienced insufficient benefit from one or more adequate antidepressant trials. Thus, identifying "failed, adequate trials" is key to the assessment of TRD. The Antidepressant Treatment History Form (ATHF) was one of the first and most widely used instruments that provided objective criteria in making these assessments. The original ATHF was updated in 2018 to the ATHF-SF, changing to a checklist format for scoring, and including specific pharmacotherapy, brain stimulation, and psychotherapy interventions as potentially adequate antidepressant treatments. The ATHF-SF2, presented here, is based on the consensus of the ATHF workgroup about the novel interventions introduced since the last revision and which should/should not be considered effective treatments for major depressive episodes. This document describes the rationale for these choices and, for each intervention, the minimal criteria for determining the adequacy of treatment administration. The Supplementary Material that accompanies this article provide the Scoring Checklist, Data Collection Forms (current episode and composite of previous episodes), and Instruction Manual for the ATHF-SF2.

Ketamine for Major Depressive Disorder

Major Depressive Disorder (MDD) is a leading cause of disability worldwide. Conventional antidepressant treatment is characterised by a significant time to onset of therapeutic action (approximately 2 weeks) and fails to achieve a stable remission of symptoms in one-third of subjects with MDD. In the last 20 years the discovery of antidepressant effects of the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine as a rapid acting (within hours) and sustained (up to 7 days) antidepressant has represented a major paradigm shift in the field.The present chapter reviews the pharmacology, safety, and efficacy of ketamine as a novel therapeutic agent for MDD and specifically for subjects who did not respond to conventional antidepressant (treatment resistant depression). The impact of ketamine on suicidal ideation, the availability of brain biomarkers of ketamine treatment response and the association of ketamine and psychotherapy are considered.

The role of NMDA receptors in bipolar disorder: A systematic review

OBJECTIVES

Glutamatergic transmission and N-methyl-D-aspartate receptors (NMDARs) have been implicated in the pathophysiology schizophrenic spectrum and major depressive disorders. Less is known about the role of NMDARs in bipolar disorder (BD). The present systematic review aimed to investigate the role of NMDARs in BD, along with its possible neurobiological and clinical implications.

METHODS

We performed a computerized literature research on PubMed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, using the following string: (("Bipolar Disorder"[Mesh]) OR (manic-depressive disorder[Mesh]) OR ("BD") OR ("MDD")) AND ((NMDA [Mesh]) OR (N-methyl-D-aspartate) OR (NMDAR[Mesh]) OR (N-methyl-D-aspartate receptor)).

RESULTS

Genetic studies yield conflicting results, and the most studied candidate for an association with BD is the GRIN2B gene. Postmortem expression studies (in situ hybridization and autoradiographic and immunological studies) are also contradictory but suggest a reduced activity of NMDARs in the prefrontal, superior temporal cortex, anterior cingulate cortex, and hippocampus.

CONCLUSIONS

Glutamatergic transmission and NMDARs do not appear to be primarily involved in the pathophysiology of BD, but they might be linked to the severity and chronicity of the disorder. Disease progression could be associated with a long phase of enhanced glutamatergic transmission, with ensuing excitotoxicity and neuronal damage, resulting into a reduced density of functional NMDARs.

Ventral prefrontal network response to alcohol in young adults with bipolar disorder: a within-subject randomized placebo-controlled alcohol administration study

Bipolar disorder co-occurs with alcohol use disorder at a rate 3-5 times higher than the general population. We recently reported that individuals with bipolar disorder differ in the positive stimulating and anxiolytic effects of alcohol compared with healthy peers. This study used a randomized, placebo-controlled, cross-over, within-subject alcohol administration design to investigate neurobiological mechanisms within ventral prefrontal cortical (vPFC) systems that may underlie altered sensitivity to alcohol in bipolar disorder (NCT04063384). Forty-seven young adults (n = 23 with bipolar disorder, 64% women) completed clinical assessment and two beverage administration sessions (alcohol and placebo, counter-balanced). Participants were dosed to 0.08 g% breath alcohol concentration during the alcohol condition and completed measures of subjective response to alcohol and an emotional processing fMRI task during the ascending limb. Timing during the placebo condition mirrored the alcohol session. Acute alcohol was associated with reduced functional connectivity between the insula - subcallosal cingulate cortex, and increased connectivity between the left nucleus accumbens - ventromedial PFC in bipolar disorder, but with no change in functional connectivity between these regions in healthy peers. Alcohol-related increases in nucleus accumbens - ventromedial PFC functional connectivity was associated with greater positive stimulating effects of alcohol in bipolar disorder and heavier recent alcohol use. Results suggest vPFC brain systems respond differently to acute alcohol during emotional processing in young adults with bipolar disorder compared with healthy peers, and that vPFC system responses relate to the subjective experience of intoxication and recent alcohol use.

Brain-based correlates of antidepressant response to ketamine: a comprehensive systematic review of neuroimaging studies

Ketamine is an effective antidepressant, but there is substantial variability in patient response and the precise mechanism of action is unclear. Neuroimaging can provide predictive and mechanistic insights, but findings are limited by small sample sizes. This systematic review covers neuroimaging studies investigating baseline (pre-treatment) and longitudinal (post-treatment) biomarkers of responses to ketamine. All modalities were included. We performed searches of five electronic databases (from inception to April 26, 2022). 69 studies were included (with 1751 participants). There was substantial methodological heterogeneity and no well replicated biomarker. However, we found convergence across some significant results, particularly in longitudinal biomarkers. Response to ketamine was associated with post-treatment increases in gamma power in frontoparietal regions in electrophysiological studies, post-treatment increases in functional connectivity within the prefrontal cortex, and post-treatment increases in the functional activation of the striatum. Although a well replicated neuroimaging biomarker of ketamine response was not identified, there are biomarkers that warrant further investigation.

Neurometabolite changes in response to antidepressant medication: A systematic review of 1H-MRS findings

Selective serotonin reuptake inhibitors (SSRIs), serotonin and noradrenaline reuptake inhibitors (SNRIs), and (es)ketamine are used to treat major depressive disorder (MDD). These different types of medication may involve common neural pathways related to glutamatergic and GABAergic neurotransmitter systems, both of which have been implicated in MDD pathology. We conducted a systematic review of pharmacological proton Magnetic Resonance Spectroscopy (1H-MRS) studies in healthy volunteers and individuals with MDD to explore the potential impact of these medications on glutamatergic and GABAergic systems. We searched PubMed, Web of Science and Embase and included randomized controlled trials or cohort studies, which assessed the effects of SSRIs, SNRIs, or (es)ketamine on glutamate, glutamine, Glx or GABA using single-voxel 1H-MRS or Magnetic Resonance Spectroscopic Imaging (MRSI). Additionally, studies were included when they used a field strength > 1.5 T, and when a comparison of metabolite levels between antidepressant treatment and placebo or baseline with post-medication metabolite levels was done. We excluded animal studies, duplicate publications, or articles with 1H-MRS data already described in another included article. Twenty-nine studies were included in this review. Fifteen studies investigated the effect of administration or treatment with SSRIs or SNRIs, and fourteen studies investigated the effect of (es)ketamine on glutamatergic and GABAergic metabolite levels. Studies on SSRIs and SNRIs were highly variable, generally underpowered, and yielded no consistent findings across brain regions or specific populations. Although studies on (es)ketamine were also highly variable, some demonstrated an increase in glutamate levels in the anterior cingulate cortex in a time-dependent manner after administration. Our findings highlight the need for standardized study and acquisition protocols. Additionally, measuring metabolites dynamically over time or combining 1H-MRS with whole brain functional imaging techniques could provide valuable insights into the effects of these medications on glutamate and GABAergic neurometabolism.

Neuroimaging-Derived Biomarkers of the Antidepressant Effects of Ketamine

Major depressive disorder is a highly prevalent psychiatric disorder. Despite an extensive range of treatment options, about a third of patients still struggle to respond to available therapies. In the last 20 years, ketamine has gained considerable attention in the psychiatric field as a promising treatment of depression, particularly in patients who are treatment resistant or at high risk for suicide. At a subanesthetic dose, ketamine produces a rapid and pronounced reduction in depressive symptoms and suicidal ideation, and serial treatment appears to produce a greater and more sustained therapeutic response. However, the mechanism driving ketamine's antidepressant effects is not yet well understood. Biomarker discovery may advance knowledge of ketamine's antidepressant action, which could in turn translate to more personalized and effective treatment strategies. At the brain systems level, neuroimaging can be used to identify functional pathways and networks contributing to ketamine's therapeutic effects by studying how it alters brain structure, function, connectivity, and metabolism. In this review, we summarize and appraise recent work in this area, including 51 articles that use resting-state and task-based functional magnetic resonance imaging, arterial spin labeling, positron emission tomography, structural magnetic resonance imaging, diffusion magnetic resonance imaging, or magnetic resonance spectroscopy to study brain and clinical changes 24 hours or longer after ketamine treatment in populations with unipolar or bipolar depression. Though individual studies have included relatively small samples, used different methodological approaches, and reported disparate regional findings, converging evidence supports that ketamine leads to neuroplasticity in structural and functional brain networks that contribute to or are relevant to its antidepressant effects.

Ketamine administration in idiopathic epileptic and healthy control dogs: Can we detect differences in brain metabolite response with spectroscopy?

Introduction

In recent years ketamine has increasingly become the focus of multimodal emergency management for epileptic seizures. However, little is known about the effect of ketamine on brain metabolites in epileptic patients. Magnetic resonance spectroscopy (MRS) is a non-invasive technique to estimate brain metabolites in vivo. Our aim was to measure the effect of ketamine on thalamic metabolites in idiopathic epileptic (IE) dogs using 3 Tesla MRS. We hypothesized that ketamine would increase the glutamine-glutamate (GLX)/creatine ratio in epileptic dogs with and without antiseizure drug treatment, but not in control dogs. Furthermore, we hypothesized that no different responses after ketamine administration in other measured brain metabolite ratios between the different groups would be detected.

Methods

In this controlled prospective experimental trial IE dogs with or without antiseizure drug treatment and healthy client-owned relatives of the breeds Border Collie and Greater Swiss Mountain Dog, were included. After sedation with butorphanol, induction with propofol and maintenance with sevoflurane in oxygen and air, a single voxel MRS at the level of the thalamus was performed before and 2 min after intravenous administration of 1 mg/kg ketamine. An automated data processing spectral fitting linear combination model algorithm was used to estimate all commonly measured metabolite ratios. A mixed ANOVA with the independent variables ketamine administration and group allocation was performed for all measured metabolites. A p < 0.05 was considered statistically significant.

Results

Twelve healthy control dogs, 10 untreated IE and 12 treated IE dogs were included. No significant effects for GLX/creatine were found. However, increased glucose/creatine ratios were found (p < 0.001) with no effect of group allocation. Furthermore, increases in the GABA/creatine ratio were found in IEU dogs.

Discussion

MRS was able to detect changes in metabolite/creatine ratios after intravenous administration of 1 mg/kg ketamine in dogs and no evidence was found that excitatory effects are induced in the thalamus. Although it is beyond the scope of this study to investigate the antiseizure potential of ketamine in dogs, results of this research suggest that the effect of ketamine on the brain metabolites could be dependent on the concentrations of brain metabolites before administration.

Dose-dependent effects of esketamine on brain activity in awake mice: A BOLD phMRI study

Pharmacological magnetic resonance imaging (phMRI) is a noninvasive method used to evaluate neural circuitry involved in the behavioral effects of drugs like ketamine, independent of their specific biochemical mechanism. The study was designed to evaluate the immediate effect of esketamine, the S-isomer of (±) ketamine on brain activity in awake mice using blood oxygenation level dependent (BOLD) imaging. It was hypothesized the prefrontal cortex, hippocampus, and brain areas associated with reward and motivation would show a dose-dependent increase in brain activity. Mice were given vehicle, 1.0, 3.3, or 10 mg/kg esketamine I.P. and imaged for 10 min post-treatment. Data for each treatment were registered to a 3D MRI mouse brain atlas providing site-specific information on 134 different brain areas. There was a global change in brain activity for both positive and negative BOLD signal affecting over 50 brain areas. Many areas showed a dose-dependent decrease in positive BOLD signal, for example, cortex, hippocampus, and thalamus. The most common profile when comparing the three doses was a U-shape with the 3.3 dose having the lowest change in signal. At 1.0 mg/kg there was a significant increase in positive BOLD in forebrain areas and hippocampus. The anticipated dose-dependent increase in BOLD was not realized; instead, the lowest dose of 1.0 mg/kg had the greatest effect on brain activity. The prefrontal cortex and hippocampus were significantly activated corroborating previous imaging studies in humans and animals. The unexpected sensitivity to the 1.0 mg/kg dose of esketamine could be explained by imaging in fully awake mice without the confound of anesthesia and/or its greater affinity for the N-methyl-d-aspartate receptor (NMDAR) receptor than (±) ketamine.

Intrinsic Connectivity Networks of Glutamate-Mediated Antidepressant Response: A Neuroimaging Review

Conventional monoamine-based pharmacotherapy, considered the first-line treatment for major depressive disorder (MDD), has several challenges, including high rates of non-response. To address these challenges, preclinical and clinical studies have sought to characterize antidepressant response through monoamine-independent mechanisms. One striking example is glutamate, the brain's foremost excitatory neurotransmitter: since the 1990s, studies have consistently reported altered levels of glutamate in MDD, as well as antidepressant effects following molecular targeting of glutamatergic receptors. Therapeutically, this has led to advances in the discovery, testing, and clinical application of a wide array of glutamatergic agents, particularly ketamine. Notably, ketamine has been demonstrated to rapidly improve mood symptoms, unlike monoamine-based interventions, and the neurobiological basis behind this rapid antidepressant response is under active investigation. Advances in brain imaging techniques, including functional magnetic resonance imaging, magnetic resonance spectroscopy, and positron emission tomography, enable the identification of the brain network-based characteristics distinguishing rapid glutamatergic modulation from the effect of slow-acting conventional monoamine-based pharmacology. Here, we review brain imaging studies that examine brain connectivity features associated with rapid antidepressant response in MDD patients treated with glutamatergic pharmacotherapies in contrast with patients treated with slow-acting monoamine-based treatments. Trends in recent brain imaging literature suggest that the activity of brain regions is organized into coherent functionally distinct networks, termed intrinsic connectivity networks (ICNs). We provide an overview of major ICNs implicated in depression and explore how treatment response following glutamatergic modulation alters functional connectivity of limbic, cognitive, and executive nodes within ICNs, with well-characterized anti-anhedonic effects and the enhancement of "top-down" executive control. Alterations within and between the core ICNs could potentially exert downstream effects on the nodes within other brain networks of relevance to MDD that are structurally and functionally interconnected through glutamatergic synapses. Understanding similarities and differences in brain ICNs features underlying treatment response will positively impact the trajectory and outcomes for adults suffering from MDD and will facilitate the development of biomarkers to enable glutamate-based precision therapeutics.

Resting-state connectivity studies as a marker of the acute and delayed effects of subanaesthetic ketamine administration in healthy and depressed individuals: A systematic review

Acute ketamine administration has been widely used in neuroimaging research to mimic psychosis-like symptoms. Within the last two decades, ketamine has also emerged as a potent, fast-acting antidepressant. The delayed effects of the drug, observed 2–48 h after a single infusion, are associated with marked improvements in depressive symptoms. At the systems’ level, several studies have investigated the acute ketamine effects on brain activity and connectivity; however, several questions remain unanswered around the brain changes that accompany the drug’s antidepressant effects and how these changes relate to the brain areas that appear with altered function and connectivity in depression. This review aims to address some of these questions by focusing on resting-state brain connectivity. We summarise the studies that have examined connectivity changes in treatment-naïve, depressed individuals and those studies that have looked at the acute and delayed effects of ketamine in healthy and depressed volunteers. We conclude that brain areas that are important for emotional regulation and reward processing appear with altered connectivity in depression whereas the default mode network presents with increased connectivity in depressed individuals compared to healthy controls. This finding, however, is not as prominent as the literature often assumes. Acute ketamine administration causes an increase in brain connectivity in healthy volunteers. The delayed effects of ketamine on brain connectivity vary in direction and appear to be consistent with the drug normalising the changes observed in depression. The limited number of studies however, as well as the different approaches for resting-state connectivity analysis make it very difficult to draw firm conclusions and highlight the importance of data sharing and larger future studies.

Respiratory-gated auricular vagal afferent nerve stimulation (RAVANS) modulates brain response to stress in major depression

BACKGROUND

Negative stress significantly impacts major depressive disorder (MDD), given the shared brain circuitry between the stress response and mood. Thus, interventions that target this circuitry will have an important impact on MDD. The aim of this study was to evaluate the acute effects of a novel respiratory-gated auricular vagal afferent nerve stimulation (RAVANS) technique in the modulation of brain activity and connectivity in women with MDD in response to negative stressful stimuli.

METHODS

Twenty premenopausal women with recurrent MDD in an active episode were included in a cross-over experimental study that included two functional MRI visits within one week, randomized to receive exhalatory- (e-RAVANS) or inhalatory-gated (i-RAVANS) at each visit. Subjects were exposed to a visual stress challenge that preceded and followed RAVANS. A Factorial analysis was used to evaluate the effects of RAVANS on brain activity and connectivity and changes in depressive and anxiety symptomatology post-stress.

RESULTS

Compared with i-RAVANS, e-RAVANS was significantly associated with increased activation of subgenual anterior cingulate, orbitofrontal and ventromedial prefrontal cortices and increased connectivity between hypothalamus and dorsolateral prefrontal cortex, and from nucleus tractus solitarii to locus coeruleus and ventromedial prefrontal cortex. Changes in brain activity and connectivity after e-RAVANS were significantly associated with a reduction in depressive and anxiety symptoms.

CONCLUSIONS

Our study suggests exhalatory-gated RAVANS effectively modulates brain circuitries regulating response to negative stress and is associated with significant acute reduction of depressive and anxiety symptomatology in women with recurrent MDD. Findings suggest a potential non-pharmacologic intervention for acute relief of depressive symptomatology in MDD.

Neuropsychiatric Manifestations of Wilson Disease: Correlation with MRI and Glutamate Excitotoxicity

This study aims to identify neuropsychiatric manifestations in neurological Wilson disease (NWD), and their correlation with MRI changes and glutamate excitotoxicity. Forty-three consecutive patients with NWD from a tertiary care teaching hospital were evaluated prospectively who fulfilled the inclusion criteria. The neuropsychiatric evaluation was done using Neuropsychiatric Inventory (NPI) battery that assesses 12 domains including delusion, hallucination, agitation/aggression, dysphoria/depression, anxiety, euphoria, apathy, disinhibition, irritability, aberrant motor activity, appetite change, and abnormal nighttime behavior. Cranial MRI was done using a 3 T machine, and locations of signal changes were noted including the total number of MRI lesions. Serum glutamate level was measured by a fluorescence microplate reader. Abnormal NPI in various domains and total NPI scores were correlated with MRI lesions, serum and urinary copper, and glutamate level. The median age of the patients was 16 years. Forty-one (48.8%) patients had cognitive impairment and 37 (86%) had movement disorder. Neurobehavioral abnormality was detected in all-commonest being agitation (90.7%) followed by appetite change (81.4%), elation (74.4%), irritability (69.8%), anxiety (67.4%), depression (65.1%), apathy (44.2%), night time abnormal behavior (32.6%), aberrant motor behavior (20.9%), delusions (16.3%), and hallucination (18.6%). The thalamic lesion was associated with depression, globus pallidus with depression and anxiety, caudate with anxiety and agitation, brainstem with irritability, and frontal cortex with apathy. Serum glutamate level was higher in NWD. NPI sum score correlated with MRI load and glutamate level. Varying severity of neurobehavioral abnormalities are common in the patients with NWD and correlate with the location of MRI lesion and glutamate level.

Structural connectivity and subcellular changes after antidepressant doses of ketamine and Ro 25-6981 in the rat: an MRI and immuno-labeling study

Ketamine has rapid and robust antidepressant effects. However, unwanted psychotomimetic effects limit its widespread use. Hence, several studies examined whether GluN2B-subunit selective NMDA antagonists would exhibit a better therapeutic profile. Although preclinical work has revealed some of the mechanisms of action of ketamine at cellular and molecular levels, the impact on brain circuitry is poorly understood. Several neuroimaging studies have examined the functional changes in the brain induced by acute administration of ketamine and Ro 25-6981 (a GluN2B-subunit selective antagonist), but the changes in the microstructure of gray and white matter have received less attention. Here, the effects of ketamine and Ro 25-6981 on gray and white matter integrity in male Sprague-Dawley rats were determined using diffusion-weighted magnetic resonance imaging (DWI). In addition, DWI-based structural brain networks were estimated and connectivity metrics were computed at the regional level. Immunohistochemical analyses were also performed to determine whether changes in myelin basic protein (MBP) and neurofilament heavy-chain protein (NF200) may underlie connectivity changes. In general, ketamine and Ro 25-6981 showed some opposite structural alterations, but both compounds coincided only in increasing the fractional anisotropy in infralimbic prefrontal cortex and dorsal raphe nucleus. These changes were associated with increments of NF200 in deep layers of the infralimbic cortex (together with increased MBP) and the dorsal raphe nucleus. Our results suggest that the synthesis of NF200 and MBP may contribute to the formation of new dendritic spines and myelination, respectively. We also suggest that the increase of fractional anisotropy of the infralimbic and dorsal raphe nucleus areas could represent a biomarker of a rapid antidepressant response.

The anterior cingulate cortex as a key locus of ketamine's antidepressant action

The subdivisions of the anterior cingulate cortex (ACC) - including subgenual, perigenual and dorsal zones - are implicated in the etiology, pathogenesis and treatment of major depression. We review an emerging body of evidence which suggests that changes in ACC activity are critically important in mediating the antidepressant effects of ketamine, the prototypical member of an emerging class of rapidly acting antidepressants. Infusions of ketamine induce acute (over minutes) and post-acute (over hours to days) modulations in subgenual and perigenual activity, and importantly, these changes can correlate with antidepressant efficacy. The subgenual and dorsal zones of the ACC have been specifically implicated in ketamine's anti-anhedonic effects. We emphasize the synergistic relationship between neuroimaging studies in humans and brain manipulations in animals to understand the causal relationship between changes in brain activity and therapeutic efficacy. We conclude with circuit-based perspectives on ketamine's action: first, related to ACC function in a central network mediating affective pain, and second, related to its role as the anterior node of the default mode network.

Ketamine-50 years in use: from anesthesia to rapid antidepressant effects and neurobiological mechanisms

Over the past 50 years, ketamine has solidified its position in both human and veterinary medicine as an important anesthetic with many uses. More recently, ketamine has been studied and used for several new indications, ranging from chronic pain to drug addiction and post-traumatic stress disorder. The discovery of the rapid-acting antidepressant effects of ketamine has resulted in a surge of interest towards understanding the precise mechanisms driving its effects. Indeed, ketamine may have had the largest impact for advancements in the research and treatment of psychiatric disorders in the past few decades. While intense research efforts have been aimed towards uncovering the molecular targets underlying ketamine's effects in treating depression, the underlying neurobiological mechanisms remain elusive. These efforts are made more difficult by ketamine's complex dose-dependent effects on molecular mechanisms, multiple pharmacologically active metabolites, and a mechanism of action associated with the facilitation of synaptic plasticity. This review aims to provide a brief overview of the different uses of ketamine, with an emphasis on examining ketamine's rapid antidepressant effects spanning molecular, cellular, and network levels. Another focus of the review is to offer a perspective on studies related to the different doses of ketamine used in antidepressant research. Finally, the review discusses some of the latest hypotheses concerning ketamine's action.

Ketamine modulates fronto-striatal circuitry in depressed and healthy individuals

Ketamine improves motivation-related symptoms in depression but simultaneously elicits similar symptoms in healthy individuals, suggesting that it might have different effects in health and disease. This study examined whether ketamine affects the brain's fronto-striatal system, which is known to drive motivational behavior. The study also assessed whether inflammatory mechanisms-which are known to influence neural and behavioral motivational processes-might underlie some of these changes. These questions were explored in the context of a double-blind, placebo-controlled, crossover trial of ketamine in 33 individuals with treatment-resistant major depressive disorder (TRD) and 25 healthy volunteers (HVs). Resting-state functional magnetic resonance imaging (rsfMRI) was acquired 2 days post-ketamine (final sample: TRD n = 27, HV n = 19) and post-placebo (final sample: TRD n = 25, HV n = 18) infusions and was used to probe fronto-striatal circuitry with striatal seed-based functional connectivity. Ketamine increased fronto-striatal functional connectivity in TRD participants toward levels observed in HVs while shifting the connectivity profile in HVs toward a state similar to TRD participants under placebo. Preliminary findings suggest that these effects were largely observed in the absence of inflammatory (C-reactive protein) changes and were associated with both acute and sustained improvements in symptoms in the TRD group. Ketamine thus normalized fronto-striatal connectivity in TRD participants but disrupted it in HVs independently of inflammatory processes. These findings highlight the potential importance of reward circuitry in ketamine's mechanism of action, which may be particularly relevant for understanding ketamine-induced shifts in motivational symptoms.

Neuroanatomic and Functional Neuroimaging Findings

The search for brain morphology findings that could explain behavioral disorders has gone through a long path in the history of psychiatry. With the advance of brain imaging technology, studies have been able to identify brain morphology and neural circuits associated with the pathophysiology of mental illnesses, such as bipolar disorders (BD). Promising results have also shown the potential of neuroimaging findings in the identification of outcome predictors and response to treatment among patients with BD. In this chapter, we present brain imaging structural and functional findings associated with BD, as well as their hypothesized relationship with the pathophysiological aspects of that condition and their potential clinical applications.

Neurobiological biomarkers of response to ketamine

As a field, psychiatry is undergoing an exciting paradigm shift toward early identification and intervention that will likely minimize both the burden associated with severe mental illnesses as well as their duration. In this context, the rapid-acting antidepressant ketamine has revolutionized our understanding of antidepressant response and greatly expanded the pharmacologic armamentarium for treatment-resistant depression. Efforts to characterize biomarkers of ketamine response support a growing emphasis on early identification, which would allow clinicians to identify biologically enriched subgroups with treatment-resistant depression who are more likely to benefit from ketamine therapy. This chapter presents a broad overview of a range of translational biomarkers, including those drawn from imaging and electrophysiological studies, sleep and circadian rhythms, and HPA axis/endocrine function as well as metabolic, immune, (epi)genetic, and neurotrophic biomarkers related to ketamine response. Ketamine's unique, rapid-acting properties may serve as a model to explore a whole new class of novel rapid-acting treatments with the potential to revolutionize drug development and discovery. However, it should be noted that although several of the biomarkers reviewed here provide promising insights into ketamine's mechanism of action, most studies have focused on acute rather than longer-term antidepressant effects and, at present, none of the biomarkers are ready for clinical use.

Striatal and white matter volumes in chronic ketamine users with or without recent regular stimulant use

BACKGROUND

Previous studies found enlarged striatum and white matter in those with stimulants use disorders. Whether primarily ketamine users (Primarily-K) and ketamine users who co-used stimulants and other substances (K+PolyS) have abnormal brain volumes is unknown. This study aims to evaluate possible brain structural abnormalities, cognitive function and depressive symptoms, between Primarily-K and K+PolyS users.

METHODS

Striatal and white matter volumes were automatically segmented in 39 Primarily-K users, 41 K+PolyS users and 46 non-drug users (ND). Cognitive performance in 7 neurocognitive domains and depressive symptoms were also evaluated.

RESULTS

Ketamine users had larger caudates than ND-controls (Right: 1-way-ANCOVA-p=0.035; K+PolyS vs. ND, p=0.030; Linear trend for K+PolyS>Primarily-K>ND, p=0.011; Left: 1-way-ANCOVA-p=0.047, Primarily-K vs. ND p=0.051) and larger total white matter (1-way ANCOVA-p=0.009, Poly+K vs. Primarily-K, p=0.05; Poly+K vs. ND p=0.011; Linear trend for K+PolyS>Primarily-K >ND, p=0.004). Across all ketamine users, they performed poorer on Arithmetic, learning and memory tasks, and were more depressed than Non-users (p<0.001 to p=0.001). Greater lifetime ketamine usage correlated with more depressive symptoms (r=0.27, p=0.008). Larger white matter correlated with better learning across all participants (r=0.21, p=0.019), while larger right caudate correlated with lower depression scores in ketamine users (r=-0.28, p=0.013).

CONCLUSION

Ketamine users had larger caudates and total white matter than ND-controls. The even larger white matter in K+PolyS users suggests additive effects from co-use of ketamine and stimulants. However, across the ketamine users, since greater volumes were associated with better learning and less depressive symptom, the enlarged caudates and white matter might represent a compensatory response.

Effects of Xiaoyaosan on Depressive-Like Behaviors in Rats With Chronic Unpredictable Mild Stress Through HPA Axis Induced Astrocytic Activities

ABSTRACT

Astrocytes in the hippocampus are immediately relevant to depressive-like behavior. By regulating their activities, Xiaoyaosan (XYS), a traditional Chinese medicine compound, works in the treatment of depression.

OBJECTIVE

Chronic unpredictable mild stress (CUMS) rat model was established to observe the regulation of XYS. We investigated the behavioral changes of CUMS, the expression of corticosterone (CORT) of the hypothalamo-pituitary-adrenal (HPA) axis, the expression of Glu-NMDA receptor and astrocytes glial fibrillary acidic protein (GFAP) in the hippocampus. We also investigated whether these changes were linked to XYS.

METHODS

80 adult SD rats were randomly divided into four groups, control group, CUMS group, XYS group, and fluoxetine group. The rats in the control group and the CUMS group received 0.5 ml of deionized water once a day by intragastrically administration. Rats in the two treatment groups received XYS (2.224g/kg/d) and fluoxetine (2.0mg/kg/d) once a day, respectively. Rat hippocampus GFAP and Glu-NMDA receptor were respectively detected by real-time fluorescent quantitative PCR and western blot. The CORT of HPA axis was detected by Elisa. Body weight, food intake, and behavioral tests, such as open field tests, the sucrose preference test, and exhaustive swimming test, were used to assess depressive-like behavior in rats.

RESULTS

In this work, significant behavioral changes and differences in expression of the CORT of HPA axis and hippocampal GFAP and Glu-NMDA receptor were presented in CUMS-exposed rats. Like fluoxetine, XYS improved CUMS-induced rat's body weight, food intake, and depressive-like behavior. The study also proved that XYS could reverse the CUMS-induced changes of the CORT of HPA axis and affect the astrocytic activities and down-regulate the NR2B subunit of NMDA receptor (NR2B) level in the hippocampus.

CONCLUSION

Changes in the hippocampus GFAP and Glu-NMDA receptor may be an essential mechanism of depression. Besides, XYS may be critical to the treatment of depression by intervention the HPA axis, GFAP and Glu-NMDA receptor.

Ketamine-Associated Brain Changes: A Review of the Neuroimaging Literature

Major depressive disorder (MDD) is one of the most prevalent conditions in psychiatry. Patients who do not respond to traditional monoaminergic antidepressant treatments have an especially difficult-to-treat type of MDD termed treatment-resistant depression. Subanesthetic doses of ketamine-a glutamatergic modulator-have shown great promise for rapidly treating patients with the most severe forms of depression. As such, ketamine represents a promising probe for understanding the pathophysiology of depression and treatment response. Through neuroimaging, ketamine's mechanism may be elucidated in humans. Here, we review 47 articles of ketamine's effects as revealed by neuroimaging studies. Some important brain areas emerge, especially the subgenual anterior cingulate cortex. Furthermore, ketamine may decrease the ability to self-monitor, may increase emotional blunting, and may increase activity in reward processing. Further studies are needed, however, to elucidate ketamine's mechanism of antidepressant action.

Increased Reactivity of the Mesolimbic Reward System after Ketamine Injection in Patients with Treatment-resistant Major Depressive Disorder

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Ketamine rapidly improves maladaptive mood states in major depressive disorder, and some of the neural substrates underlying this therapeutic effect have been identified. This study aimed to identify functional changes within neural networks that may underlie the impact of ketamine on both reward and emotional processing in patients with treatment-resistant major depression.

Methods

Ten adult patients with a Montgomery–Åsberg Depression Rating Scale score above 25 were enrolled to receive a single intravenous administration of ketamine (0.5 mg/kg). Patients’ performance along with related neural network activations were analyzed in a game-like reward task and in an emotional judgment task using functional magnetic resonance imaging 1 day before and 1 and 7 days after ketamine administration.

Results

A significant correlation (R2 = 0.46, P = 0.03) between the improvement of depression scores and the enhanced reaction time for positive items was found in the game-like reward task 1 day after ketamine administration. This enhanced sensitivity for rewarded items was accompanied by increased activity of reward-related brain regions, including the orbitofrontal cortex, ventral striatum, and the ventral tegmental area, an effect that persisted up to 1 week after ketamine injection. In the emotional judgment task, it was found that ketamine rapidly modified local brain activities in response to emotionally negative, positive, or neutral stimuli in the amygdala, insula, anterior cingulate cortex, and in the ventral tegmental area.

Conclusions

Single bolus ketamine administration rapidly triggers lasting changes in mesolimbic neural networks to improve pathologic reward and emotional processing in patients with major depressive disorder.

Functional connectivity between prefrontal cortex and subgenual cingulate predicts antidepressant effects of ketamine

Converging evidence suggests that a single sub-anesthetic dose of ketamine can produce strong and rapid antidepressant effects in patients that do not respond to standard treatment. Despite a considerable amount of research investigating ketamine's mechanisms of action, the exact neuronal targets conveying the antidepressant effects have not been identified yet. Preclinical studies suggest that molecular changes induced by ketamine bring forward large-scale network reconfigurations that might relate to ketamine's antidepressant properties. In this prospective two-site study we measured resting state fMRI in 24 depressed patients prior to, and 24 h after a single sub-anesthetic dose of ketamine. We analyzed functional connectivity (FC) at baseline and after ketamine and focused our analysis on baseline FC and FC changes directly linked to symptom reduction in order to identify neuronal targets that predict individual clinical responses to ketamine. Our results show that FC increases after ketamine between right lateral prefrontal cortex (PFC) and subgenual anterior cingulate cortex (sgACC) are positively linked to treatment response. Furthermore, low baseline FC between these regions predicts treatment outcome. We conclude that PFC-sgACC connectivity may represent a promising biomarker with both predictive and explanatory power.

The value of clinical and translational neuroscience approaches to psychiatric illness

Borsboom et al. confuse biological approaches with extreme biological reductionism and common-cause models of psychopathology. In muddling these concepts, they mistakenly throw the baby out with the bathwater. Here, we highlight recent work underscoring the unique value of clinical and translational neuroscience approaches for understanding the nature and origins of psychopathology and for developing improved intervention strategies.

An update on ketamine and its two enantiomers as rapid-acting antidepressants

Introduction: Depression is one of the most disabling diseases worldwide. Approximately one-third of depressed patients are treatment-resistant to the currently available antidepressants and there is a significant therapeutic time lag of weeks to months. There is a clear unmet need for rapid-acting and more efficacious treatments. (R,S)-ketamine, an old anesthetic drug, appears now to be going through a renaissance. Areas covered: This paper reviews recent literature describing the antidepressant effects of ketamine and its enantiomer (S)-ketamine in patients with major depressive disorder (MDD) and bipolar disorder (BD). Furthermore, the authors discuss the therapeutic potential of (R)-ketamine, another enantiomer of (R,S)-ketamine, and (S)-norketamine. Expert commentary: A number of clinical studies have demonstrated that (R,S)-ketamine has rapid-acting and sustained antidepressant activity in treatment-resistant patients with MDD, BD, and other psychiatric disorders. Off-label use of ketamine for mood disorders is proving popular in the United States. Meanwhile, preclinical data suggests that (R)-ketamine can exert longer-lasting antidepressant effects than (S)-ketamine in animal models of depression, and (R)-ketamine may have less detrimental side effects than (R,S)-ketamine and (S)-ketamine. Additionally, (S)-norketamine exhibits rapid and sustained antidepressant effects, with a potency similar to that of (S)-ketamine. Unlike (S)-ketamine, (S)-norketamine does not cause behavioral and biochemical abnormalities and could be a safer than (S)-ketamine too.

On the safety of repeated ketamine infusions for the treatment of depression: Effects of sex and developmental periods

In this review, we will discuss the safety of repeated treatments with ketamine for patients with treatment-resistant depression (TRD), a condition in which patients with major depression do not show any clinical improvements following treatments with at least two antidepressant drugs. We will discuss the effects of these treatments in both sexes at different developmental periods. Numerous small clinical studies have shown that a single, low-dose ketamine infusion can rapidly alleviate depressive symptoms and thoughts of suicidality in patients with TRD, and these effects can last for about one week. Interestingly, the antidepressant effects of ketamine can be prolonged with intermittent, repeated infusion regimens and produce more robust therapeutic effects when compared to a single infusion. The safety of such repeated treatments with ketamine has not been thoroughly investigated. Although more studies are needed, some clinical and preclinical reports indicated that repeated infusions of low doses of ketamine may have addictive properties, and suggested that adolescent and adult female subjects may be more sensitive to ketamine's addictive effects. Additionally, during ketamine infusions, many TRD patients report hallucinations and feelings of dissociation and depersonalization, and therefore the effects of repeated treatments of ketamine on cognition must be further examined. Some clinical reports indicated that, compared to women, men are more sensitive to the psychomimetic effects of ketamine. Preclinical studies extended these findings to both adolescent and adult male rodents and showed that male rodents at both developmental periods are more sensitive to ketamine's cognitive-altering effects. Accordingly, in this review we shall focus our discussion on the potential addictive and cognitive-impairing effects of repeated ketamine infusions in both sexes at two important developmental periods: adolescence and adulthood. Although more work about the safety of ketamine is warranted, we hope this review will bring some answers about the safety of treating TRD with repeated ketamine infusions.

Ketamine: A Review for Clinicians

A growing series of clinical trials and case series now suggest that ketamine-originally used as an anesthetic agent-potentially offers an exciting new treatment option for severe depression. Increasing numbers of studies show that ketamine can provide prompt relief for many depressed patients, including those with severe treatment-refractory depression. Although the effects of a single treatment are commonly short-lived, multiple infusion protocols may offer sustained relief. The uniquely rapid onset of antidepressant action raises the potential for ketamine use in a variety of clinical situations, including the prevention or shortening of hospital stays, the treatment of acute suicidal ideation, and the facilitation of medication crossovers. Ketamine, in combination with other multimodal treatment approaches, including psychotherapy, may further augment response effect and duration. Promises of efficacy have led to increasingly unbridled use to treat a variety of psychiatric disorders, with diverse approaches and treatment environments, despite inadequate data demonstrating the true clinical efficacy and safety of the various protocols or a thorough understanding of mechanisms of action. This article briefly reviews the history of ketamine's development as a potential antidepressant, current hypotheses related to its mechanisms of action, and existing evidence for its safety and efficacy with a focus on clinicians' interests.

General Anesthetics to Treat Major Depressive Disorder: Clinical Relevance and Underlying Mechanisms

Major depressive disorder is a frequent and devastating psychological condition with tremendous public health impact. The underlying pathophysiological mechanisms involve abnormal neurotransmission and a relatedly impaired synaptic plasticity. Since general anesthetics are potent modulators of neuronal activity and, thereby, can exert long-term context-dependent impact on neural networks, an intriguing hypothesis is that these drugs could enhance impaired neural plasticity associated with certain psychiatric diseases. Clinical observations over the past few decades appear to confirm this possibility. Indeed, equipotency of general anesthesia alone in comparison with electroconvulsive therapy under general anesthesia has been demonstrated in several clinical trials. Importantly, in the past 15 years, intravenous administration of subanesthetic doses of ketamine have also been demonstrated to have rapid antidepressant effects. The molecular, cellular, and network mechanisms underlying these therapeutic effects have been partially identified. Although several important questions remain to be addressed, the ensemble of these experimental and clinical observations opens new therapeutic possibilities in the treatment of depressive disorders. Importantly, they also suggest a new therapeutic role for anesthetics that goes beyond their principal use in the perioperative period to facilitate surgery.

Glutamatergic Dysfunction and Glutamatergic Compounds for Major Psychiatric Disorders: Evidence From Clinical Neuroimaging Studies

Excessive glutamate release has been linked to stress and many neurodegenerative diseases. Evidence indicates abnormalities of glutamatergic neurotransmission or glutamatergic dysfunction as playing an important role in the development of many major psychiatric disorders (e.g., schizophrenia, bipolar disorder, and major depressive disorder). Recently, ketamine, an N-methyl-d-aspartate antagonist, has been demonstrated to have promisingly rapid antidepressant efficacy for treatment-resistant depression. Many compounds that target the glutamate system have also become available that possess potential in the treatment of major psychiatric disorders. In this review, we update evidence from recent human studies that directly or indirectly measured glutamatergic neurotransmission and function in major psychiatric disorders using modalities such as magnetic resonance spectroscopy, positron emission tomography/single-photon emission computed tomography, and paired-pulse transcranial magnetic stimulation. The newer generation of antidepressants that target the glutamatergic system developed in human clinical studies is also reviewed.

Glutamate and Gamma-Aminobutyric Acid Systems in the Pathophysiology of Major Depression and Antidepressant Response to Ketamine

In patients with major depressive disorder or bipolar disorder, abnormalities in excitatory and/or inhibitory neurotransmission and neuronal plasticity may lead to aberrant functional connectivity patterns within large brain networks. Network dysfunction in association with altered brain levels of glutamate and gamma-aminobutyric acid have been identified in both animal and human studies of depression. In addition, evidence of an antidepressant response to subanesthetic-dose ketamine has led to a collection of studies that have examined neurochemical (e.g., glutamatergic and gamma-aminobutyric acidergic) and functional imaging correlates associated with such an effect. Results from these studies suggest that an antidepressant response in association with ketamine occurs, in part, by reversing these neurochemical/physiological disturbances. Future studies in depression will require a combination of neuroimaging approaches from which more biologically homogeneous subgroups can be identified, particularly with respect to treatment response biomarkers of glutamatergic modulation.

Targeting glutamate signalling in depression: progress and prospects

Major depressive disorder (MDD) is severely disabling, and current treatments have limited efficacy. The glutamate N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine was recently repurposed as a rapidly acting antidepressant, catalysing the vigorous investigation of glutamate-signalling modulators as novel therapeutic agents for depressive disorders. In this Review, we discuss the progress made in the development of such modulators for the treatment of depression, and examine recent preclinical and translational studies that have investigated the mechanisms of action of glutamate-targeting antidepressants. Fundamental questions remain regarding the future prospects of this line of drug development, including questions concerning safety and tolerability, efficacy, dose-response relationships and therapeutic mechanisms.

Divergent topological architecture of the default mode network as a pretreatment predictor of early antidepressant response in major depressive disorder

Identifying a robust pretreatment neuroimaging marker would be helpful for the selection of an optimal therapy for major depressive disorder (MDD). We recruited 82 MDD patients [n = 42 treatment-responsive depression (RD) and n = 40 non-responding depression (NRD)] and 50 healthy controls (HC) for this study. Based on the thresholded partial correlation matrices of 58 specific brain regions, a graph theory approach was applied to analyse the topological properties. When compared to HC, both RD and NRD patients exhibited a lower nodal degree (D_nodal) in the left anterior cingulate gyrus; as for RD, the D_nodal of the left superior medial orbitofrontal gyrus was significantly reduced, but the right inferior orbitofrontal gyrus was increased (all P < 0.017, FDR corrected). Moreover, the nodal degree in the right dorsolateral superior frontal cortex (SFGdor) was significantly lower in RD than in NRD. Receiver operating characteristic curve analysis demonstrated that the λ and nodal degree in the right SFGdor exhibited a good ability to distinguish nonresponding patients from responsive patients, which could serve as a specific maker to predict an early response to antidepressants. The disrupted topological configurations in the present study extend the understanding of pretreatment neuroimaging predictors for antidepressant medication.

Ketamine: 50 Years of Modulating the Mind

Ketamine was introduced into clinical practice in the 1960s and continues to be both clinically useful and scientifically fascinating. With considerably diverse molecular targets and neurophysiological properties, ketamine’s effects on the central nervous system remain incompletely understood. Investigators have leveraged the unique characteristics of ketamine to explore the invariant, fundamental mechanisms of anesthetic action. Emerging evidence indicates that ketamine-mediated anesthesia may occur via disruption of corticocortical information transfer in a frontal-to-parietal (“top down”) distribution. This proposed mechanism of general anesthesia has since been demonstrated with anesthetics in other pharmacological classes as well. Ketamine remains invaluable to the fields of anesthesiology and critical care medicine, in large part due to its ability to maintain cardiorespiratory stability while providing effective sedation and analgesia. Furthermore, there may be an emerging role for ketamine in treatment of refractory depression and Post-Traumatic Stress Disorder. In this article, we review the history of ketamine, its pharmacology, putative mechanisms of action and current clinical applications.

Invited commentary: mapping the alteration in glutamate with GluCEST MRI in a mouse model of dopamine deficiency: An Editorial Highlight for 'Mapping the alterations in glutamate with GluCEST MRI in a mouse model of dopamine deficiency'

Read the highlighted article 'Mapping the alterations in glutamate with GluCEST MRI in a mouse model of dopamine deficiency' on page 432.

Betaine enhances antidepressant-like, but blocks psychotomimetic effects of ketamine in mice

Ketamine is emerging as a new hope against depression, but ketamine-associated psychotomimetic effects limit its clinical use. An adjunct therapy along with ketamine to alleviate its adverse effects and even potentiate the antidepressant effects might be an alternative strategy. Betaine, a methyl derivative of glycine and a dietary supplement, has been shown to have antidepressant-like effects and to act like a partial agonist at the glycine site of N-methyl-D-aspartate receptors (NMDARs). Accordingly, betaine might have potential to be an adjunct to ketamine treatment for depression. The antidepressant-like effects of ketamine and betaine were evaluated by forced swimming test and novelty suppressed feeding test in mice. Both betaine and ketamine produced antidepressant-like effects. Furthermore, we determined the effects of betaine on ketamine-induced antidepressant-like and psychotomimetic behaviors, motor incoordination, hyperlocomotor activity, and anesthesia. The antidepressant-like responses to betaine combined with ketamine were stronger than their individual effects. In contrast, ketamine-induced impairments in prepulse inhibition, novel object recognition test, social interaction, and rotarod test were remarkably attenuated, whereas ketamine-induced hyperlocomotion and loss of righting reflex were not affected by betaine. These findings revealed that betaine could enhance the antidepressant-like effects, yet block the psychotomimetic effects of ketamine, suggesting that betaine can be considered as an add-on therapy to ketamine for treatment-resistant depression and suitable for the treatment of depressive symptoms in patients with schizophrenia.

Ketamine use in current clinical practice

After nearly half a century on the market, ketamine still occupies a unique corner in the medical armamentarium of anesthesiologists or clinicians treating pain. Over the last two decades, much research has been conducted highlighting the drug's mechanisms of action, specifically those of its enantiomers. Nowadays, ketamine is also being utilized for pediatric pain control in emergency department, with its anti-hyperalgesic and anti-inflammatory effects being revealed in acute and chronic pain management. Recently, new insights have been gained on ketamine's potential anti-depressive and antisuicidal effects. This article provides an overview of the drug's pharmacokinetics and pharmacodynamics while also discussing the potential benefits and risks of ketamine administration in various clinical settings.

Comparing the actions of lanicemine and ketamine in depression: key role of the anterior cingulate

Intravenous infusion of lanicemine (formerly AZD6765), a low trapping non-selective N-methyl-D-aspartate (NMDA) receptor antagonist, induces antidepressant effects with a similar time course to ketamine. We investigated whether a single dose lanicemine infusion would reproduce the previously reported decrease in subgenual anterior cingulate cortex (sgACC) activity evoked by ketamine, a potential mechanism of antidepressant efficacy. Sixty un-medicated adults meeting the criteria for major depressive disorder were randomly assigned to receive constant intravenous infusions of ketamine, lanicemine or saline during a 60min pharmacological magnetic resonance imaging (phMRI) scan. Both ketamine and lanicemine gradually increased the blood oxygen level dependent signal in sgACC and rostral ACC as the primary outcome measure. No decreases in signal were seen in any region. Interviewer-rated psychotic and dissociative symptoms were minimal following administration of lanicemine. There was no significant antidepressant effect of either infusion compared to saline. The previously reported deactivation of sgACC after ketamine probably reflects the rapid and pronounced subjective effects evoked by the bolus-infusion method used in the previous study. Activation of the ACC was observed following two different NMDA compounds in both Manchester and Oxford using different 3T MRI scanners, and this effect predicted improvement in mood 1 and 7 days post-infusion. These findings suggest that the initial site of antidepressant action for NMDA antagonists may be the ACC (NCT01046630. A Phase I, Multi-centre, Double-blind, Placebo-controlled Parallel Group Study to Assess the pharmacoMRI Effects of AZD6765 in Male and Female Subjects Fulfilling the Criteria for Major Depressive Disorder; http://clinicaltrials.gov/show/NCT01046630).

A pilot in vivo proton magnetic resonance spectroscopy study of amino acid neurotransmitter response to ketamine treatment of major depressive disorder

The N-methyl-D-aspartate receptor antagonist ketamine can improve major depressive disorder (MDD) within hours. To evaluate the putative role of glutamatergic and GABAergic systems in ketamine's antidepressant action, medial prefrontal cortical (mPFC) levels of glutamate+glutamine (Glx) and γ-aminobutyric acid (GABA) were measured before, during, and after ketamine administration using proton magnetic resonance spectroscopy. Ketamine (0.5 mg kg(-1) intravenously) was administered to 11 depressed patients with MDD. Glx and GABA mPFC responses were measured as ratios relative to unsuppressed voxel tissue water (W) successfully in 8/11 patients. Ten of 11 patients remitted (50% reduction in 24-item Hamilton Depression Rating Scale and total score ⩽10) within 230 min of commencing ketamine. mPFC Glx/W and GABA/W peaked at 37.8%±7.5% and 38.0%±9.1% above baseline in ~26 min. Mean areas under the curve for Glx/W (P=0.025) and GABA/W (P=0.005) increased and correlated (r=0.796; P=0.018). Clinical improvement correlated with 90-min norketamine concentration (df=6, r=-0.78, P=0.023), but no other measures.

Ketamine modulates subgenual cingulate connectivity with the memory-related neural circuit-a mechanism of relevance to resistant depression?

Background. Ketamine has been reported to have efficacy as an antidepressant in several studies of treatment-resistant depression. In this study, we investigate whether an acute administration of ketamine leads to reductions in the functional connectivity of subgenual anterior cingulate cortex (sgACC) with other brain regions.

Methods. Thirteen right-handed healthy male subjects underwent a 15 min resting state fMRI with an infusion of intravenous ketamine (target blood level = 150 ng/ml) starting at 5 min. We used a seed region centred on the sgACC and assessed functional connectivity before and during ketamine administration.

Results. Before ketamine administration, positive coupling with the sgACC seed region was observed in a large cluster encompassing the anterior cingulate and negative coupling was observed with the anterior cerebellum. Following ketamine administration, sgACC activity became negatively correlated with the brainstem, hippocampus, parahippocampal gyrus, retrosplenial cortex, and thalamus.

Discussion. Ketamine reduced functional connectivity of the sgACC with brain regions implicated in emotion, memory and mind wandering. It is possible the therapeutic effects of ketamine may be mediated via this mechanism, although further work is required to test this hypothesis.

Ameliorating treatment-refractory depression with intranasal ketamine: potential NMDA receptor actions in the pain circuitry representing mental anguish

This article reviews the antidepressant actions of ketamine, an N-methyl-D-aspartame glutamate receptor (NMDAR) antagonist, and offers a potential neural mechanism for intranasal ketamine's ultra-rapid actions based on the key role of NMDAR in the nonhuman primate prefrontal cortex (PFC). Although intravenous ketamine infusions can lift mood within hours, the current review describes how intranasal ketamine administration can have ultra-rapid antidepressant effects, beginning within minutes (5-40 minutes) and lasting hours, but with repeated treatments needed for sustained antidepressant actions. Research in rodents suggests that increased synaptogenesis in PFC may contribute to the prolonged benefit of ketamine administration, beginning hours after administration. However, these data cannot explain the relief that occurs within minutes of intranasal ketamine delivery. We hypothesize that the ultra-rapid effects of intranasal administration in humans may be due to ketamine blocking the NMDAR circuits that generate the emotional representations of pain (eg, Brodmann Areas 24 and 25, insular cortex), cortical areas that can be overactive in depression and which sit above the nasal epithelium. In contrast, NMDAR blockade in the dorsolateral PFC following systemic administration of ketamine may contribute to cognitive deficits. This novel view may help to explain how intravenous ketamine can treat the symptoms of depression yet worsen the symptoms of schizophrenia.

A New Perspective on the Anti-Suicide Effects With Ketamine Treatment: A Procognitive Effect

Available evidence indicates that a single, low-dose administration of ketamine is a robust, rapid-onset intervention capable of mitigating depressive symptoms in adults with treatment-resistant mood disorders. Additional evidence also suggests that ketamine may offer antisuicide effects. Herein, we propose that the antidepressant effects reported with ketamine administration are mediated, in part, by targeting neural circuits that subserve cognitive processing relevant to executive function and cognitive emotional processing. Empirical support for the conceptual framework of the cognitive domain as a critical target of ketamine's action is the additional observation that pretreatment cognitive function predicts treatment outcomes with ketamine administration. The proposal that beneficial effects on cognitive function may be, in some individuals, the proximate mechanism mitigating symptom relief in mood disorders exists alongside the well-established deleterious effect of ketamine on cognitive function. During the past 5 years, there have been several reviews and meta-analyses concluding that ketamine has possible clinical benefits in refractory mood disorders. We introduce the conceptual framework that ketamine's salutary effects, notably in suicidality, may in part be via procognitive mechanisms.

The effects of low-dose ketamine on the prefrontal cortex and amygdala in treatment-resistant depression: A randomized controlled study

BACKGROUND

Low-dose ketamine has been found to have robust and rapid antidepressant effects. A hypoactive prefrontal cortex (PFC) and a hyperactive amygdala have been suggested to be associated with treatment-resistant depression (TRD). However, it is unclear whether the rapid antidepressant mechanisms of ketamine on TRD involve changes in glutamatergic neurotransmission in the PFC and the amygdala.

METHODS

A group of 48 TRD patients were recruited and equally randomized into three groups (A: 0.5 kg/mg-ketamine; B: 0.2 kg/mg-ketamine; and C: normal saline [NS]). Standardized uptake values (SUV) of glucose metabolism measured by (18) F-FDG positron-emission-tomography before and immediately after a 40-min ketamine or NS infusion were used for subsequent region-of-interest (ROI) analyses (a priori regions: PFC and amygdala) and whole-brain voxel-wise analyses and were correlated with antidepressant responses, as defined by the Hamilton depression rating scale score. The (18) F-FDG signals were used as a proxy measure of glutamate neurotransmission.

RESULTS

The ROI analysis indicated that Group A and Group B, but not Group C, had increases in the SUV of the PFC (group-by-time interaction: F = 7.373, P = 0.002), whereas decreases in the SUV of the amygdala were observed in all three groups (main effect of time, P < 0.001). The voxel-wise analysis further confirmed a significant group effect on the PFC (corrected for family-wise errors, P < 0.05; post hoc analysis: Group A<Group C, Group B<Group C). The SUV differences in the PFC predicted the antidepressant responses at 40 and 240 min post-treatment. The PFC changes did not differ between those with and without side effects.

CONCLUSION

Ketamine's rapid antidepressant effects involved the facilitation of glutamatergic neurotransmission in the PFC.

Current Status of Ketamine and Related Therapies for Mood and Anxiety Disorders

Major Depressive Disorder (MDD) is a leading cause of disability worldwide. Despite a plethora of established treatments, less than one-third of individuals with MDD achieve stable remission of symptoms. Given limited efficacy and significant lag time to onset of therapeutic action among conventional antidepressants, interest has shifted to treatments that act outside of the monoamine neurotransmitter systems (e.g., serotonin, norepinephrine, and dopamine). Preclinical and clinical research on the glutamate system has been particularly promising in this regard. Accumulating evidence shows support for a rapid antidepressant effect of ketamine - a glutamate N-methyl-d-aspartate (NMDA) receptor antagonist. The present article reviews the pharmacology, safety, and efficacy of ketamine as a novel therapeutic agent for mood and anxiety disorders. The majority of clinical trials using ketamine have been conducted in patients with treatment resistant forms of MDD; recent work has begun to examine ketamine in bipolar disorder, posttraumatic stress disorder, and obsessive-compulsive disorder. The impact of ketamine on suicidal ideation is also discussed. The current status and prospects for the identification of human biomarkers of ketamine treatment response and hurdles to treatment development are considered. We conclude by considering modulators of the glutamate system other than ketamine currently in development as potential novel treatment strategies for mood and anxiety disorders.

Ketamine-an update on its clinical uses and abuses

This review highlights the recent clinical research that supports the therapeutic utility of ketamine as a multifaceted drug. After long-term use as a dissociative anesthetic, it has re-emerged as a useful agent for ameliorating pain, asthmaticus, and depression. In addition, it is also a substance of abuse. Chronic ketamine abuse over prolonged periods (weeks, months, and years) can produce toxicity to the gastrointestinal and urinary tract. In this review, we described the recent progress on its clinical uses and abuses.

Ketamine and other N-methyl-D-aspartate receptor antagonists in the treatment of depression: a perspective review

Current pharmacotherapies for major depressive disorder (MDD) and bipolar depression (BDep) have a distinct lag of onset that can generate great distress and impairment in patients. Furthermore, as demonstrated by several real-world effectiveness trials, their efficacy is limited. All approved antidepressant medications for MDD primarily act through monoaminergic mechanisms, agonists or antagonists with varying affinities for serotonin, norepinephrine and dopamine. The glutamate system has received much attention in recent years as an avenue for developing novel therapeutics. A single subanesthetic dose infusion of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist ketamine has been shown to have rapid and potent antidepressant effects in treatment-resistant MDD and BDep. In a reverse translational framework, ketamine's clinical efficacy has inspired many preclinical studies to explore glutamatergic mechanisms of antidepressant action. These studies have revealed enhanced synaptic plasticity/synaptogenesis via numerous molecular and cellular mechanisms: release of local translational inhibition of brain-derived neurotrophic factor and secretion from dendritic spines, mammalian target of rapamycin activation and glycogen synthase kinase-3 inhibition. Current efforts are focused on extending ketamine's antidepressant efficacy, uncovering the neurobiological mechanisms responsible for ketamine's antidepressant activity in biologically enriched subgroups, and identifying treatment response biomarkers to personalize antidepressant selection. Other NMDA receptor antagonists have been studied both preclinically and clinically, which have revealed relatively modest antidepressant effects compared with ketamine but potentially other favorable characteristics, for example, decreased dissociative or psychotomimetic effects; therefore, there is great interest in developing novel glutamatergic antidepressants with greater target specificity and/or decreased adverse effects.

Neural correlates of change in major depressive disorder anhedonia following open-label ketamine

Anhedonia is a cardinal symptom of major depression and is often refractory to standard treatment, yet no approved medication for this specific symptom exists. In this exploratory re-analysis, we assessed whether administration of rapid-acting antidepressant ketamine was associated specifically with reduced anhedonia in medication-free treatment-refractory patients with major depressive disorder in an open-label investigation. Additionally, participants received either oral riluzole or placebo daily beginning 4 hours post-infusion. A subgroup of patients underwent fluorodeoxyglucose positron emission tomography scans at baseline (1-3 days pre-infusion) and 2 hours post-ketamine infusion. Anhedonia rapidly decreased following a single ketamine infusion; this was sustained for up to three days, but was not altered by riluzole. Reduced anhedonia correlated with increased glucose metabolism in the hippocampus and dorsal anterior cingulate cortex (dACC) and decreased metabolism in the inferior frontal gyrus and orbitofrontal cortex (OFC). The tentative relationship between change in anhedonia and glucose metabolism remained significant in dACC and OFC, and at trend level in the hippocampus, a result not anticipated, when controlling for change in total depression score. Results, however, remain tenuous due to the lack of a placebo control for ketamine. In addition to alleviating overall depressive symptoms, ketamine could possess anti-anhedonic potential in major depressive disorder, which speculatively, may be mediated by alterations in metabolic activity in the hippocampus, dACC and OFC.