Molecular Mechanism and Clinical Relevance of Ketamine as Rapid-Acting Antidepressant

Cognitive Considerations in Major Depression: Evaluating the Effects of Pharmacotherapy and ECT on Mood and Executive Control Deficits

Deficits in the executive control of attention greatly impact the quality of life of patients diagnosed with major depressive disorder (MDD). However, attentional deficits are often underemphasized in clinical contexts compared with mood-based symptoms, and a comprehensive approach for specifically evaluating and treating them has yet to be developed. The present study evaluates the efficacy of bifrontal electroconvulsive therapy (ECT) combined with drug therapy (DT) in alleviating mood-related symptomatology and executive control deficits in drug-refractory MDD patients and compares these effects with those observed in MDD patients undergoing DT only. The Hamilton Rating Scale for Depression and the Lateralized Attentional Network Test-Revised were administered across two test sessions to assess treatment-related changes in mood-based symptoms and conflict processing, respectively, in patients undergoing ECT + DT (n = 23), patients undergoing DT (n = 33), and healthy controls (n = 40). Although both groups showed an improvement in mood-based symptoms following treatment and a deficit in conflict processing estimated on error rate, a post-treatment reduction of an executive control deficit estimated on RT was solely observed in the ECT + DT patient group. Furthermore, Bayesian correlational analyses confirmed the dissociation of mood-related symptoms and of executive control measures, supporting existing literature proposing that attentional deficits and mood symptoms are independent aspects of MDD. The cognitive profile of MDD includes executive control deficits, and while both treatments improved mood-based symptoms, only ECT + DT exerted an effect on both measures of the executive control deficit. Our findings highlight the importance of considering the improvement in both mood and cognitive deficits when determining the efficacy of therapeutic approaches for MDD.

Antidepressant Actions of Ketamine: Potential Role of L-Type Calcium Channels

Recently, the United States Food and Drug Administration approved esketamine, the S-enantiomer of ketamine, as a fast-acting therapeutic drug for treatment-resistant depression. Although ketamine is known as an N-methyl-d-aspartate (NMDA) receptor antagonist, the underlying mechanisms of how it elicits an antidepressant effect, specifically at subanesthetic doses, are not clear and remain an advancing field of research interest. On the other hand, high-dose (more than the anesthetic dose) ketamine-induced neurotoxicity in animal models has been reported. There has been progress in understanding the potential pathways involved in ketamine-induced antidepressant effects, some of which include NMDA-receptor antagonism, modulation of voltage-gated calcium channels, and brain-derived neurotrophic factor (BDNF) signaling. Often these pathways have been shown to be linked. Voltage-gated L-type calcium channels have been shown to mediate the rapid-acting antidepressant effects of ketamine, especially involving induction of BDNF synthesis downstream, while BDNF deficiency decreases the expression of L-type calcium channels. This review focuses on the reported studies linking ketamine's rapid-acting antidepressant actions to L-type calcium channels with an objective to present a perspective on the importance of the modulation of intracellular calcium in mediating the effects of subanesthetic (antidepressant) versus high-dose ketamine (anesthetic and potential neurotoxicant), the latter having the ability to reduce intracellular calcium by blocking the calcium-permeable NMDA receptors, which is implicated in potential neurotoxicity.

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.

Assessment of Ketamine and Its Enantiomers in an Organophosphate-Based Rat Model for Features of Gulf War Illness

Approximately 33% of U.S. soldiers from the first Gulf War suffer from a multi-system disorder known as the Gulf War Illness (GWI). GW veterans suffer from a cluster of symptoms that prominently include fatigue and can include mood-related symptoms. Compared to traditional antidepressants, ketamine (KET) produces a fast-onset and long-lasting antidepressant response, but assessments of KET for GWI-related depression are lacking. The etiology of GWI is multi-factorial and exposure to organophosphates (OP) during deployment is one of the factors underlying GWI development. Here, male Sprague-Dawley rats were repeatedly exposed to an OP DFP and three months later these rats, when assessed on a battery of rodent behavioral assays, displayed signs consistent with aspects of GWI characteristics. When treated with a sub-anesthetic dose of KET (3, 5, or 10 mg/kg, i.p.), DFP-treated rats exhibited a significant improvement in immobility time, open-arm exploration, and sucrose consumption as early as 1 h and much of these effects persisted at 24-h post-KET injection. KET's stereoisomers, R-KET and S-KET, also exhibited such effects in DFP rats, with R-KET being the more potent isomer. Our studies provide a starting point for further assessment of KET for GWI depression.

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.

A Review of Nonanesthetic Uses of Ketamine

Ketamine, a nonselective NMDA receptor antagonist, is used widely in medicine as an anesthetic agent. However, ketamine's mechanisms of action lead to widespread physiological effects, some of which are now coming to the forefront of research for the treatment of diverse medical disorders. This paper aims at reviewing recent data on key nonanesthetic uses of ketamine in the current literature. MEDLINE, CINAHL, and Google Scholar databases were queried to find articles related to ketamine in the treatment of depression, pain syndromes including acute pain, chronic pain, and headache, neurologic applications including neuroprotection and seizures, and alcohol and substance use disorders. It can be concluded that ketamine has a potential role in the treatment of all of these conditions. However, research in this area is still in its early stages, and larger studies are required to evaluate ketamine's efficacy for nonanesthetic purposes in the general population.

Ketamine sensitization: Influence of dose, environment, social isolation and treatment interval

Ketamine is a dissociative anesthetic first developed in the 1960s but is increasingly used at subanesthetic doses for both clinical and non-clinical purposes. There is evidence from human recreational users of compulsive use and addiction. Sensitization is an increase in an effect of a drug with repeated use that is thought to be important in the development of addiction. Research on psychomotor stimulants has shown the development of sensitization in laboratory animals to be modified by factors that influence addiction. In the current paper we describe four experiments on the development of sensitization in laboratory rats aimed at determining if ketamine sensitization is also influenced by factors thought to be important in addiction. Adult, male Sprague-Dawley rats received ketamine (5, 10, 20 or 50 mg/kg i.p.) for five or more days and the development of locomotor sensitization was followed. Experiment 1 examined the ability of low doses of ketamine to produce sensitization and found sensitization at 5, 10 and 20 mg/kg. Experiment 2 examined the influence of environmental context and found that ketamine sensitization (20 mg/kg) was greater when administration occurred in a novel environment (the experimental apparatus) than in home cages. Experiment 3 found that ketamine sensitization (20 mg/kg) did not occur when animals were housed in social isolation but occurred readily in pair-housed animals. Finally, Experiment 4 found that ketamine sensitization (20 or 50 mg/kg) was similar whether drug was administered daily or at 3-day intervals. Together, the results demonstrate that ketamine sensitization is robust and reliable, occurring under a variety of circumstances. Moreover, ketamine sensitization is influenced by factors that influence the development of addiction in humans. The current results may lead to a better understanding of ketamine abuse and addiction and may help inform clinical use of the drug.

Acth-induced model of depression resistant to tricyclic antidepressants: Neuroendocrine and behavioral changes and influence of long-term magnesium administration

Magnesium (Mg), is not only a modulator of the glutamatergic NMDA receptors' affinity, it also prevents HPA axis hyperactivity, thus possibly being implicated in neurobiological features of mood disorders. Further uncovering of molecular mechanisms underlying magnesium's proposed effects is needed due to the recent shift in research of treatment resistant depression (TRD) towards glutamatergic pathways. Here, we applied Mg via drinking water for 28 days (50 mg/kg/day), in ACTH-treated rats, an established animal model of depression resistant to tricyclic antidepressants. Using this model in male rats we measured (1) changes in hippocampal neurogenesis and behavioral alterations, (2) adrenal hormones response to acute stress challenge and (3) levels of biometals involved in regulation of monoamines turnover in rat prefrontal cortex. Our results support beneficial behavioral impact of Mg in TRD model together with increased hippocampal neurogenesis and BDNF expression. Furthermore, Mg prevented ACTH-induced disruption in HPA axis function, by normalizing the levels of plasma ACTH, corticosterone and interleukin-6, and by increasing the peripheral release of adrenaline, noradrenaline and serotonin after the acute stress challenge. Finally, the influence on copper/zinc ratio suggested probable magnesium's involvement in monoamine turnover in PFC. Our findings provide further insights into the possible pathways implicated in the behavioral modulation effects of Mg, as well as its central and peripheral effects in ACTH-induced TRD model. Thus, further investigation of molecular signaling related to the glutamatergic transmission and role of Mg, could reveal prospects to novel treatment strategies that could be of particular importance for patients suffering from TRD.