Therapeutic doses of ketamine acutely attenuate the aversive effect of losses during decision-making.

The discovery of rapid-acting antidepressant, ketamine has opened a pathway to a new generation of treatments for depression, and inspired neuroscientific investigation based on a new perspective that non-adaptive changes in the intrinsic excitatory and inhibitory circuitry might underlie the pathophysiology of depression. Nevertheless, it still remains largely unknown how the hypothesized molecular and synaptic levels of changes in the circuitry might mediate behavioral and neuropsychological changes underlying depression, and how ketamine might restore adaptive behavior. Here, we used computational models to analyze behavioral changes induced by therapeutic doses of ketamine, while rhesus macaques were iteratively making decisions based on gains and losses of tokens. When administered intramuscularly or intranasally, ketamine reduced the aversiveness of undesirable outcomes such as losses of tokens without significantly affecting the evaluation of gains, behavioral perseveration, motivation, and other cognitive aspects of learning such as temporal credit assignment and time scales of choice and outcome memory. Ketamine's potentially antidepressant effect was separable from other side effects such as fixation errors, which unlike outcome evaluation, was readily countered with strong motivation to avoid errors. We discuss how the acute effect of ketamine to reduce the initial impact of negative events could potentially mediate longer-term antidepressant effects through mitigating the cumulative effect of those events produced by slowly decaying memory, and how the disruption-resistant affective memory might pose challenges in treating depression. Our study also invites future investigations on ketamine's antidepressant action over diverse mood states and with affective events exerting their impacts at diverse time scales.

Ketamine-induced prevention of SD-associated late infarct progression in experimental ischemia.

Spreading depolarizations (SDs) occur frequently in patients with malignant hemispheric stroke. In animal-based experiments, SDs have been shown to cause secondary neuronal damage and infarct expansion during the initial period of infarct progression. In contrast, the influence of SDs during the delayed period is not well characterized yet. Here, we analyzed the impact of SDs in the delayed phase after cerebral ischemia and the potential protective effect of ketamine. Focal ischemia was induced by distal occlusion of the left middle cerebral artery in C57BL6/J mice. 24 h after occlusion, SDs were measured using electrocorticography and laser-speckle imaging in three different study groups: control group without SD induction, SD induction with potassium chloride, and SD induction with potassium chloride and ketamine administration. Infarct progression was evaluated by sequential MRI scans. 24 h after occlusion, we observed spontaneous SDs with a rate of 0.33 SDs/hour which increased during potassium chloride application (3.37 SDs/hour). The analysis of the neurovascular coupling revealed prolonged hypoemic and hyperemic responses in this group. Stroke volume increased even 24 h after stroke onset in the SD-group. Ketamine treatment caused a lesser pronounced hypoemic response and prevented infarct growth in the delayed phase after experimental ischemia. Induction of SDs with potassium chloride was significantly associated with stroke progression even 24 h after stroke onset. Therefore, SD might be a significant contributor to delayed stroke progression. Ketamine might be a possible drug to prevent SD-induced delayed stroke progression.

Esketamine alleviates hypoxia/reoxygenation injury of cardiomyocytes by regulating TRPV1 expression and inhibiting intracellular Ca2+ concentration.

OBJECTIVE: This study aimed to investigate the effect of Esketamine (ESK) on the Hypoxia/Reoxygenation (H/R) injury of cardiomyocytes by regulating TRPV1 and inhibiting the concentration of intracellular Ca2+. METHODS: The H/R injury model of H9c2 cardiomyocytes was established after 4h hypoxia and 6h reoxygenation. H9c2 cells were treated with different concentrations of ESK or TRPV1 agonist capsaicin (10 µM) or TRPV1 inhibitor capsazepine (1 µM). Cell viability was detected by CCK-8 method, and apoptosis by flow cytometry. Intracellular Ca2+ concentration was evaluated by Fluo-4 AM. LDH, MDA, SOD, and GSH-Px were detected with corresponding commercial kits. TRPV1 and p-TRPV1 proteins were detected by Western blot. RESULTS: After H/R, H9c2 cell viability decreased, apoptosis increased, intracellular Ca2+ concentration increased, LDH and MDA levels increased, SOD and GSH-Px levels decreased, and p-TRPV1 expression increased. ESK treatment rescued these changes induced by H/R. After up-regulating TRPV1, the protective effect of ESK on H/R injury of H9c2 cells was weakened, while down-regulating TRPV1 could further protect against H/R injury. CONCLUSION: ESK alleviates H/R injury of cardiomyocytes by regulating TRPV1 expression and inhibiting intracellular Ca2+ concentration.

Substance specific EEG patterns in mice undergoing slow anesthesia induction.

The exact mechanisms and the neural circuits involved in anesthesia induced unconsciousness are still not fully understood. To elucidate them valid animal models are necessary. Since the most commonly used species in neuroscience are mice, we established a murine model for commonly used anesthetics/sedatives and evaluated the epidural electroencephalographic (EEG) patterns during slow anesthesia induction and emergence. Forty-four mice underwent surgery in which we inserted a central venous catheter and implanted nine intracranial electrodes above the prefrontal, motor, sensory, and visual cortex. After at least one week of recovery, mice were anesthetized either by inhalational sevoflurane or intravenous propofol, ketamine, or dexmedetomidine. We evaluated the loss and return of righting reflex (LORR/RORR) and recorded the electrocorticogram. For spectral analysis we focused on the prefrontal and visual cortex. In addition to analyzing the power spectral density at specific time points we evaluated the changes in the spectral power distribution longitudinally. The median time to LORR after start anesthesia ranged from 1080 [1st quartile: 960; 3rd quartile: 1080]s under sevoflurane anesthesia to 1541 [1455; 1890]s with ketamine. Around LORR sevoflurane as well as propofol induced a decrease in the theta/alpha band and an increase in the beta/gamma band. Dexmedetomidine infusion resulted in a shift towards lower frequencies with an increase in the delta range. Ketamine induced stronger activity in the higher frequencies. Our results showed substance-specific changes in EEG patterns during slow anesthesia induction. These patterns were partially identical to previous observations in humans, but also included significant differences, especially in the low frequencies. Our study emphasizes strengths and limitations of murine models in neuroscience and provides an important basis for future studies investigating complex neurophysiological mechanisms.

A Randomized, Double-Blind, Placebo-Controlled Pilot Trial of the Acute Antisuicidal and Antidepressant Effects of Intranasal (R,S)-Ketamine in Severe Unipolar and Bipolar Depression With and Without Comorbid Alcohol Use Disorder.

Objective: Although individuals with a family history of alcohol use disorder (AUD) have a superior antidepressant response to ketamine, outcomes in patients with current AUD remain unclear. This study sought to investigate whether intranasal (IN) racemic (R,S)-ketamine had antisuicidal and antidepressant effects in unipolar and bipolar depression and whether comorbid AUD conferred superior antisuicidal outcomes for patients.Methods: This was a double-blind, randomized, placebo-controlled trial (May 2018 to January 2022) of single administration, fixed-dose (50 mg) IN (R,S)-ketamine (or saline comparator) in unmedicated inpatients meeting Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, criteria for a current major depressive episode (bipolar or unipolar), with current suicidal ideation (SI) and past attempt. Patients with and without comorbid AUD were enrolled. Change in Scale for Suicide Ideation score was the primary outcome measure, and change in Montgomery-Åsberg Depression Rating Scale score was the secondary outcome measure.Results: No significant group × time effect was noted for SI (F = 1.1, P = .36). A statistical trend toward superior improvement in suicidality was observed in participants with comorbid AUD. The group × time interaction was significant for improvements in depression (F = 3.06, P = .03) and largely unaffected by comorbid AUD or primary mood disorder type. Within the ketamine group, a significant correlation was observed between improvement in depressive symptoms and SI for patients without comorbid AUD (r =0.927, P = .023) that was absent in patients with AUD (r = 0.39, P = .44).Conclusion: IN ketamine induced rapid antidepressant effects compared to placebo but did not significantly alter SI scores. The treatment was well tolerated. Continued investigation with IN ketamine as a practical alternative to current formulations is warranted.Trial Registration: ClinicalTrials.gov identifier: NCT03539887.

Effects of ketamine on penile tissues in an experimental priapism model in rats.

BACKGROUND: This study aimed to evaluate the histopathological and biochemical effects of ketamine on penile tissues following ischemia-reperfusion injury induced by priapism. METHODS: Twenty-four male rats were randomized into three groups. Group 1 served as the control group. Group 2 underwent the priapism model to induce ischemia-reperfusion injury. Group 3, the treatment group, experienced a similar ischemia-reperfusion model as Group 2; additionally, 50 mg/kg of ketamine was administered intraperitoneally just before reperfusion. Blood biochemical analyses and penile histopathological evaluations were performed. RESULTS: In Group 3, significant improvements were observed in all histopathological scores, including desquamation, edema, inflammation, and vasocongestion compared to Group 2 (p<0.001). Blood biochemical analyses showed that the malondialdehyde (MDA) levels were recorded as 10 in Group 2, with a significant decrease in Group 3 (p=0.013). Similarly, proinflammatory cytokine levels, including interleukin-1 beta (IL-1ß), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α), were found to be suppressed in Group 3 compared to Group 2 (p=0.003, p=0.022, and p=0.028, respectively). Antioxidant enzyme activities, such as glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), were higher in Group 3 compared to Group 2 (p=0.016 and p=0.024, respec-tively). CONCLUSION: Ketamine is an effective anesthetic agent in alleviating the effects of penile ischemia-reperfusion injury.

O-GlcNAcylation levels remain stable regardless of the anaesthesia in healthy rats.

Anaesthetics are used daily in human and veterinary medicine as well as in scientific research. Anaesthetics have an impact on cell homeostasis especially through modulation of protein post-translational modifications. O-GlcNAcylation, a ubiquitous post-translational modification, plays a role in many biological processes. The aims of this study were to evaluate whether (1) anaesthesia influences O-GlcNAcylation and (2) its stimulation affects physiological parameters. Male Wistar rats (n = 38) were anaesthetized with ketamine-xylazine or isoflurane. They randomly received either an intravenous injection of Ringer's lactate or NButGT (10mg/kg) in order to increase O-GlcNAcylation levels. One hour after induction of anaesthesia, haemodynamic parameters and plasmatic markers were evaluated. Heart, brain and lungs were harvested and O-GlcNAcylation levels and O-GlcNAc-related enzymes were evaluated by western blot. Cardiac and pulmonary O-GlcNAcylation levels and cardiac, cerebral and pulmonary O-GlcNAc associated enzyme expression were not impacted with anaesthesia. Compared with ketamine-xylazine, isoflurane had a lower impact on blood pressure, heart rate and glycaemia. Pharmacological stimulation of O-GlcNAcylation by NButGT did not affect the physiological parameters. This study offers unprecedented insights into the regulation of O-GlcNAcylation and O-GlcNAc related enzymes during anaesthesia. Pharmacological stimulation of O-GlcNAcylation over a 1-h period did not disrupt the physiological balance in healthy anaesthetized rats.

Ketamine induces multiple individually distinct whole-brain functional connectivity signatures.

Background: Ketamine has emerged as one of the most promising therapies for treatment-resistant depression. However, inter-individual variability in response to ketamine is still not well understood and it is unclear how ketamine's molecular mechanisms connect to its neural and behavioral effects. Methods: We conducted a single-blind placebo-controlled study, with participants blinded to their treatment condition. 40 healthy participants received acute ketamine (initial bolus 0.23 mg/kg, continuous infusion 0.58 mg/kg/hr). We quantified resting-state functional connectivity via data-driven global brain connectivity and related it to individual ketamine-induced symptom variation and cortical gene expression targets. Results: We found that: (i) both the neural and behavioral effects of acute ketamine are multi-dimensional, reflecting robust inter-individual variability; (ii) ketamine's data-driven principal neural gradient effect matched somatostatin (SST) and parvalbumin (PVALB) cortical gene expression patterns in humans, while the mean effect did not; and (iii) behavioral data-driven individual symptom variation mapped onto distinct neural gradients of ketamine, which were resolvable at the single-subject level. Conclusions: These results highlight the importance of considering individual behavioral and neural variation in response to ketamine. They also have implications for the development of individually precise pharmacological biomarkers for treatment selection in psychiatry. Funding: This study was supported by NIH grants DP5OD012109-01 (A.A.), 1U01MH121766 (A.A.), R01MH112746 (J.D.M.), 5R01MH112189 (A.A.), 5R01MH108590 (A.A.), NIAAA grant 2P50AA012870-11 (A.A.); NSF NeuroNex grant 2015276 (J.D.M.); Brain and Behavior Research Foundation Young Investigator Award (A.A.); SFARI Pilot Award (J.D.M., A.A.); Heffter Research Institute (Grant No. 1-190420) (FXV, KHP); Swiss Neuromatrix Foundation (Grant No. 2016-0111) (FXV, KHP); Swiss National Science Foundation under the framework of Neuron Cofund (Grant No. 01EW1908) (KHP); Usona Institute (2015 - 2056) (FXV). Clinical trial number: NCT03842800.

Ketamine is a widely used anesthetic as well as a popular illegal recreational drug. Recently, it has also gained attention as a potential treatment for depression, particularly in cases that don't respond to conventional therapies. However, individuals can vary in their response to ketamine. For example, the drug can alter some people's perception, such as seeing objects as larger or small than they are, while other individuals are unaffected. Although a single dose of ketamine was shown to improve depression symptoms in approximately 65% of patients, the treatment does not work for a significant portion of patients. Understanding why ketamine does not work for everyone could help to identify which patients would benefit most from the treatment. Previous studies investigating ketamine as a treatment for depression have typically included a group of individuals given ketamine and a group given a placebo drug. Assuming people respond similarly to ketamine, the responses in each group were averaged and compared to one another. However, this averaging of results may have masked any individual differences in response to ketamine. As a result, Moujaes et al. set out to investigate whether individuals show differences in brain activity and behavior in response to ketamine. Moujaes et al. monitored the brain activity and behavior of 40 healthy individuals that were first given a placebo drug and then ketamine. The results showed that brain activity and behavior varied significantly between individuals after ketamine administration. Genetic analysis revealed that different gene expression patterns paired with differences in ketamine response in individuals ­ an effect that was hidden when the results were averaged. Ketamine also caused greater differences in brain activity and behavior between individuals than other drugs, such as psychedelics, suggesting ketamine generates a particularly complex response in people. In the future, extending these findings in healthy individuals to those with depression will be crucial for determining whether differences in response to ketamine align with how effective ketamine treatment is for an individual.

Combining brief recall and ketamine treatment prevents stress-primed methamphetamine memory reinstatement via heightening mPFC GABA activity.

This study aimed to assess whether brief recall of methamphetamine (MA) memory, when combined with ketamine (KE) treatment, may prevent stress-primed MA memory reinstatement. Combining 3-min recall and KE facilitated MA memory extinction and resistance to subsequent stress-primed reinstatement. Such combination also produced glutamate metabotropic receptor 5 (mGluR5) upregulation in animals' medial prefrontal cortex (mPFC) γ-amino-butyric acid (GABA) neuron. Accordingly, chemogenetic methods were employed to bi-directionally modulate mPFC GABA activity. Following brief recall and KE-produced MA memory extinction, intra-mPFC mDlx-Gi-coupled-human-muscarinic-receptor 4 (hM4Di)-infused mice receiving compound 21 (C21) treatment showed eminent stress-primed reinstatement, while their GABA mGluR5 expression seemed to be unaltered. Intra-mPFC mDlx-Gq-coupled-human-muscarinic-receptor 3 (hM3Dq)-infused mice undergoing C21 treatment displayed MA memory extinction and resistance to stress-provoked reinstatement. These results suggest that combining a brief recall and KE treatment and exciting mPFC GABA neuron may facilitate MA memory extinction and resistance to stress-primed recall. mPFC GABA neuronal activity plays a role in mediating brief recall/KE-produced effects on curbing the stress-provoked MA seeking.

Acute Dissociation and Ketamine's Antidepressant and Anti-Suicidal Ideation Effects in a Midazolam-Controlled Trial.

OBJECTIVE: We sought to explore relationships of acute dissociative effects of intravenous ketamine with change in depression and suicidal ideation and with plasma metabolite levels in a randomized, midazolam-controlled trial. METHODS: Data from a completed trial in suicidal, depressed participants (n = 40) randomly assigned to ketamine was used to examine relationships between ketamine treatment-emergent dissociative and psychotomimetic symptoms with pre/post-infusion changes in suicidal ideation and depression severity. Nonparametric correlational statistics were used. These methods were also used to explore associations between dissociative or psychotomimetic symptoms and blood levels of ketamine and metabolites in a subset of participants (n = 28) who provided blood samples immediately post-infusion. RESULTS: Neither acute dissociative nor psychotomimetic effects of ketamine were associated with changes in suicidal ideation or depressive symptoms from pre- to post-infusion. Norketamine had a trend-level, moderate inverse correlation with dissociative symptoms on Day 1 post-injection (P = .064; P =.013 removing 1 outlier). Dehydronorketamine correlated with Clinician-Administered Dissociative States Scale scores at 40 minutes (P = .034), 230 minutes (P = .014), and Day 1 (P = .012). CONCLUSION: We did not find evidence that ketamine's acute, transient dissociative, or psychotomimetic effects are associated with its antidepressant or anti-suicidal ideation actions. The correlation of higher plasma norketamine with lower dissociative symptoms on Day 1 post-treatment suggests dissociation may be more an effect of the parent drug.

Analgesic Mechanism of Dexmedetomidine and Esketamine in Rats with Spinal Cord Injury.

BACKGROUND: Spinal cord injury (SCI) is usually caused by external direct or indirect factors, and with a high morbidity and mortality rate. The aim of this study was to observe the effects of Dexmedetomidine (DEX) combined with Esketamine (ESK) on pain behavior and potential analgesic mechanisms in rats with SCI. The goal was to provide a reliable multimodal analgesic medication regimen for SCI. METHODS: Thirty rats were divided into five groups with six rats in each group: Sham group, SCI group, DEX group, ESK group, and DEX+ESK group. The SCI model in rats was constructed, and the motor function of hind limbs of rats was measured using Basso Beattie Bresnahan (BBB) locomotor rating scale and inclined plate test. The levels of interleukin 18 (IL-18), interleukin 1ß (IL-1ß), and tumor necrosis factor-α (TNF-α) in the spinal cord were determined by enzyme-linked immunosorbent assay (ELISA). The expressions of substance P (SP), neurokinin-1 receptor (NK-1R), B cell lymphoma-2 (Bcl-2), and Bcl2-associated X protein (Bax) in the rats' spinal cord were measured by Western blot assay. The viability of spinal astrocytes was evaluated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. RESULTS: After 7 days, the BBB scores were significantly higher in the DEX, ESK, and DEX+ESK groups compared to the SCI group (p < 0.01). Additionally, the DEX+ESK group had significantly higher scores than both the DEX and ESK groups (p < 0.01). The maximum angle of the DEX (p < 0.05), ESK (p < 0.05), and DEX+ESK groups (p < 0.01) were higher than the SCI group, and the maximum angle of DEX+ESK group was higher than DEX and ESK groups (p < 0.05). The levels of IL-18, IL-1ß, and TNF-α in the DEX, ESK, and DEX+ESK groups were lower than the SCI group (p < 0.01), while the DEX+ESK group had significantly lower IL-18, IL-1ß, and TNF-α levels than the DEX and ESK groups (p < 0.01). The levels of SP (p < 0.01) and NK-1R (p < 0.05) were lower in the DEX, ESK, and DEX+ESK groups compared to the SCI group, and the levels of SP and NK-1R were lower in the DEX+ESK group compared to the DEX and ESK groups (p < 0.01). The DEX and ESK groups suppressed the activity of spinal astrocytes (p < 0.01), however, the DEX+ESK group had larger effects on spinal astrocytes than the ESK group (p < 0.05). CONCLUSIONS: Treatment using DEX combined with ESK improves the motor function, inhibits inflammation and astrocyte activity, and exerts analgesic effects on rats with SCI. These findings can serve as a reference for the selection of multi-modal analgesics.

Effects of (2R,6R)-hydroxynorketamine in assays of acute pain-stimulated and pain-depressed behaviors in mice.

Ketamine has been shown to produce analgesia in various acute and chronic pain states; however, abuse liability concerns have limited its utility. The ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) has been shown to produce antidepressant-like effects similar to ketamine without abuse liability concerns. (2R,6R)-HNK produces sustained analgesia in models of chronic pain, but has yet to be evaluated in models of acute pain. The present study evaluated the efficacy of acute (2R,6R)-HNK administration (one injection) in assays of pain-stimulated (52- and 56-degree hot plate test and acetic acid writhing) and pain-depressed behavior (locomotor activity and rearing) in male and female C57BL/6 mice. In assays of pain-stimulated behaviors, (2R,6R)-HNK (1-32 mg/kg) failed to produce antinociception in the 52- and 56-degree hot plate and acetic acid writhing assays. In assays of pain-depressed behaviors, 0.56% acetic acid produced a robust depression of locomotor activity and rearing that was not blocked by pretreatment of (2R,6R)-HNK (3.2-32 mg/kg). The positive controls morphine (hot plate test) and ketoprofen (acetic acid writhing, locomotor activity, and rearing) blocked pain-stimulated and pain-depressed behaviors. Finally, the effects of intermittent (2R,6R)-HNK administration were evaluated in 52-degree hot plate and pain-depressed locomotor activity and rearing. Intermittent administration of (2R,6R)-HNK also did not produce antinociceptive effects in the hot plate or pain-depressed locomotor activity assays. These results suggest that (2R,6R)-HNK is unlikely to have efficacy in treating acute pain; however, the efficacy of (2R,6R)-HNK in chronic pain states should continue to be evaluated.

Spectral signatures of psilocybin, lysergic acid diethylamide (LSD) and ketamine in healthy volunteers and persons with major depressive disorder and treatment-resistant depression: A systematic review.

BACKGROUND: Electrophysiologic measures provide an opportunity to inform mechanistic models and possibly biomarker prediction of response. Serotonergic psychedelics (SPs) (i.e., psilocybin, lysergic acid diethylamide (LSD)) and ketamine represent new investigational and established treatments in mood disorders respectively. There is a need to better characterize the mechanism of action of these agents. METHODS: We conducted a systematic review investigating the spectral signatures of psilocybin, LSD, and ketamine in persons with major depressive disorder (MDD), treatment-resistant depression (TRD), and healthy controls. RESULTS: Ketamine and SPs are associated with increased theta power in persons with depression. Ketamine and SPs are also associated with decreased spectral power in the alpha, beta and delta bands in healthy controls and persons with depression. When administered with SPs, theta power was increased in persons with MDD when administered with SPs. Ketamine is associated with increased gamma band power in both healthy controls and persons with MDD. LIMITATIONS: The studies included in our review were heterogeneous in their patient population, exposure, dosing of treatment and devices used to evaluate EEG and MEG signatures. Our results were extracted entirely from persons who were either healthy volunteers or persons with MDD or TRD. CONCLUSIONS: Extant literature evaluating EEG and MEG spectral signatures indicate that ketamine and SPs have reproducible effects in keeping with disease models of network connectivity. Future research vistas should evaluate whether observed spectral signatures can guide further discovery of therapeutics within the psychedelic and dissociative classes of agents, and its prediction capability in persons treated for depression.

Current concepts in ketamine therapy in the emergency department.

Ketamine has been in use since its development as a dissociative anesthetic in the 1960s, but it was largely confined to the operating theater or austere environments until used by emergency physicians to facilitate painful procedures in children. As the unique effects of ketamine across its dose-response curve were understood, new applications emerged. In low doses, ketamine has found an important role alongside or instead of opioids in the management of severe pain, and methods to slow its absorption allow higher, more effective doses while attenuating psychoperceptual effects. Ketamine's unique anesthetic properties have inspired its use as an induction agent for intubation without a paralytic and for the rapid, safe control of dangerously agitated patients. Emerging uses for ketamine in acute care include treatment for status epilepticus and alcohol withdrawal syndrome; however, its most important rising indication may be as an emergency treatment of depression and suicidality.

Effects of Mild Closed-Head Injury and Subanesthetic Ketamine Infusion on Microglia, Axonal Injury, and Synaptic Density in Sprague-Dawley Rats.

Mild traumatic brain injury (mTBI) affects millions of people in the U.S. Approximately 20-30% of those individuals develop adverse symptoms lasting at least 3 months. In a rat mTBI study, the closed-head impact model of engineered rotational acceleration (CHIMERA) produced significant axonal injury in the optic tract (OT), indicating white-matter damage. Because retinal ganglion cells project to the lateral geniculate nucleus (LGN) in the thalamus through the OT, we hypothesized that synaptic density may be reduced in the LGN of rats following CHIMERA injury. A modified SEQUIN (synaptic evaluation and quantification by imaging nanostructure) method, combined with immunofluorescent double-labeling of pre-synaptic (synapsin) and post-synaptic (PSD-95) markers, was used to quantify synaptic density in the LGN. Microglial activation at the CHIMERA injury site was determined using Iba-1 immunohistochemistry. Additionally, the effects of ketamine, a potential neuroprotective drug, were evaluated in CHIMERA-induced mTBI. A single-session repetitive (ssr-) CHIMERA (3 impacts, 1.5 joule/impact) produced mild effects on microglial activation at the injury site, which was significantly enhanced by post-injury intravenous ketamine (10 mg/kg) infusion. However, ssr-CHIMERA did not alter synaptic density in the LGN, although ketamine produced a trend of reduction in synaptic density at post-injury day 4. Further research is necessary to characterize the effects of ssr-CHIMERA and subanesthetic doses of intravenous ketamine on different brain regions and multiple time points post-injury. The current study demonstrates the utility of the ssr-CHIMERA as a rodent model of mTBI, which researchers can use to identify biological mechanisms of mTBI and to develop improved treatment strategies for individuals suffering from head trauma.

Enhancing Cognitive Functions and Neuronal Growth through NPY1R Agonist and Ketamine Co-Administration: Evidence for NPY1R-TrkB Heteroreceptor Complexes in Rats.

This study investigates the combined effects of the neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31-Pro34]NPY at a dose of 132 µg and Ketamine at 10 mg/Kg on cognitive functions and neuronal proliferation, against a backdrop where neurodegenerative diseases present an escalating challenge to global health systems. Utilizing male Sprague-Dawley rats in a physiological model, this research employed a single-dose administration of these compounds and assessed their impact 24 h after treatment on object-in-place memory tasks, alongside cellular proliferation within the dorsal hippocampus dentate gyrus. Methods such as the in situ proximity ligation assay and immunohistochemistry for proliferating a cell nuclear antigen (PCNA) and doublecortin (DCX) were utilized. The results demonstrated that co-administration significantly enhanced memory consolidation and increased neuronal proliferation, specifically neuroblasts, without affecting quiescent neural progenitors and astrocytes. These effects were mediated by the potential formation of NPY1R-TrkB heteroreceptor complexes, as suggested by receptor co-localization studies, although further investigation is required to conclusively prove this interaction. The findings also highlighted the pivotal role of brain-derived neurotrophic factor (BDNF) in mediating these effects. In conclusion, this study presents a promising avenue for enhancing cognitive functions and neuronal proliferation through the synergistic action of the NPY1R agonist and Ketamine, potentially via NPY1R-TrkB heteroreceptor complex formation, offering new insights into therapeutic strategies for neurodegenerative diseases.

Neural assemblies coordinated by cortical waves are associated with waking and hallucinatory brain states.

The relationship between sensory stimuli and perceptions is brain-state dependent: in wakefulness, suprathreshold stimuli evoke perceptions; under anesthesia, perceptions are abolished; and during dreaming and in dissociated states, percepts are internally generated. Here, we exploit this state dependence to identify brain activity associated with internally generated or stimulus-evoked perceptions. In awake mice, visual stimuli phase reset spontaneous cortical waves to elicit 3-6 Hz feedback traveling waves. These stimulus-evoked waves traverse the cortex and entrain visual and parietal neurons. Under anesthesia as well as during ketamine-induced dissociation, visual stimuli do not disrupt spontaneous waves. Uniquely, in the dissociated state, spontaneous waves traverse the cortex caudally and entrain visual and parietal neurons, akin to stimulus-evoked waves in wakefulness. Thus, coordinated neuronal assemblies orchestrated by traveling cortical waves emerge in states in which perception can manifest. The awake state is privileged in that this coordination is reliably elicited by external visual stimuli.

Evidence from preclinical and clinical metabolomics studies on the antidepressant effects of ketamine and esketamine.

The antidepressant effects of ketamine and esketamine are well-documented. Nonetheless, most of the underlying molecular mechanisms have to be uncovered yet. In the last decade, metabolomics has emerged as a useful means to investigate the metabolic phenotype associated with depression as well as changes induced by antidepressant treatments. This mini-review aims at summarizing the main findings from preclinical and clinical studies that used metabolomics to investigate the metabolic effects of subanesthetic, antidepressant doses of ketamine and esketamine and their relationship with clinical response. Both animal and human studies report alterations in several metabolic pathways - including the tricarboxylic acid cycle, glycolysis, the pentose phosphate pathway, lipid metabolism, amino acid metabolism, the kynurenine pathway, and the urea cycle - following the administration of ketamine or its enantiomers. Although more research is needed to clarify commonalities and differences in molecular mechanisms of action between the racemic compound and its enantiomers, these findings comprehensively support an influence of ketamine and esketamine on mitochondrial and cellular energy production, membrane homeostasis, neurotransmission, and signaling. Metabolomics may thus represent a promising strategy to clarify molecular mechanisms underlying treatment-resistant depression and related markers of clinical response to ketamine and esketamine. This body of preclinical and clinical evidence, if further substantiated, has the potential to guide clinicians towards personalized approaches, contributing to new paradigms in the clinical management of depression.

Neither Amphetamine nor Sub-Anesthetic Ketamine Treatment during Adolescence Impairs Devaluation in Rats Tested during Adulthood.

BACKGROUND: Much of the existing animal literature on the devaluation task suggests that prior repeated exposure to drugs of abuse during adulthood can impair goal-directed action, but the literature on human drug users is mixed. Also, the initiation of drug use often occurs during adolescence, but examinations of the effects of drug exposure during adolescence on behavior in the devaluation task are lacking. METHODS: We examined whether repeated exposure during adolescence to amphetamine (3 mg/kg injections every-other day from post-natal day 27-45) or ketamine (twice daily 30 mg/kg injections from post-natal day 35-44) would impair behavior in a devaluation test when tested drug-free in adulthood. Rats were trained to press a left lever with a steady cue-light above it for one reinforcer and a right lever with a flashing cue-light above it for a different reinforcer. We tested whether any impairments in goal-directed action could be overcome by compensation between strategies by giving rats information based on lever-location and cue-lights during the test that was either congruent (allowing compensation) or incongruent (preventing compensation between strategies) with the configurations during training. RESULTS: Our results provided no evidence for impairment of goal-directed action during adulthood after adolescent amphetamine or ketamine exposure. CONCLUSIONS: We discuss possible reasons for this discrepancy with the prior literature, including (1) the age of exposure and (2) the pattern in the previous literature that most previous demonstrations of drug exposure impairing devaluation in laboratory animals may be attributed to either drug-associated cues present in the testing environment and/or accelerated habit learning in tasks that predispose laboratory animals towards habit formation with extended training (with training procedures that should resist the formation of habits in the current experiment). However, additional research is needed to examine the effects of these factors, as well a potential role for the particular doses and washout periods to determine the cause of our finding of no devaluation impairment after drug exposure.

Functional connectivity of the amygdala subregions and the antidepressant effects of repeated ketamine infusions in major depressive disorder.

BACKGROUND: Amygdala subregion-based network dysfunction has been determined to be centrally implicated in major depressive disorder (MDD). Little is known about whether ketamine modulates amygdala subarea-related networks. We aimed to investigate the relationships between changes in the resting-state functional connectivity (RSFC) of amygdala subregions and ketamine treatment and to identify important neuroimaging predictors of treatment outcomes. METHODS: Thirty-nine MDD patients received six doses of ketamine (0.5 mg/kg). Depressive symptoms were assessed, and magnetic resonance imaging (MRI) scans were performed before and after treatment. Forty-five healthy controls underwent one MRI scan. Seed-to-voxel RSFC analyses were performed on the amygdala subregions, including the centromedial amygdala (CMA), laterobasal amygdala (LBA), and superficial amygdala subregions. RESULTS: Abnormal RSFC between the left LBA and the left precuneus in MDD patients is related to the therapeutic efficacy of ketamine. There were significant differences in changes in bilateral CMA RSFC with the left orbital part superior frontal gyrus and in changes in the left LBA with the right middle frontal gyrus between responders and nonresponders following ketamine treatment. Moreover, there was a difference in the RSFC of left LBA and the right superior temporal gyrus/middle temporal gyrus (STG/MTG) between responders and nonresponders at baseline, which could predict the antidepressant effect of ketamine on Day 13. CONCLUSIONS: The mechanism by which ketamine improves depressive symptoms may be related to its regulation of RSFC in the amygdala subregion. The RSFC between the left LBA and right STG/MTG may predict the response to the antidepressant effect of ketamine.