Acute low-dose ketamine produces a rapid and robust increase in plasma BDNF without altering brain BDNF concentrations

The zebrafish for preclinical psilocybin research

In this review, we discuss the possible utility of zebrafish in research on psilocybin, a psychedelic drug whose recreational use as well as possible clinical application are gaining increasing interest. First, we review behavioral tests with zebrafish, focussing on anxiety and social behavior, which have particular relevance in the context of psilocybin research. Next, we briefly consider methods of genetic manipulations with which psilocybin's phenotypical effects and underlying mechanisms may be investigated in zebrafish. We briefly review the known mechanisms of psilocybin, and also discuss what we know about its safety and toxicity profile. Last, we discuss examples of how psilocybin may be employed for testing treatment efficacy in preclinical research for affective disorders in zebrafish. We conclude that zebrafish has a promising future in preclinical research on psychedelic drugs.

The effects of ketamine and classic hallucinogens on neurotrophic and inflammatory markers in unipolar treatment-resistant depression: a systematic review of clinical trials

Although results are still preliminary, ketamine and classical hallucinogens have shown promise in recent years as novel, fast-acting antidepressants, especially for the treatment of unipolar treatment-resistant depression (TRD). Depression also seems to be related to abnormal levels of peripheral inflammatory and neurotrophic biomarkers, which may one day help to diagnose of this disorder. In this context, this systematic review of clinical trials evaluated the current evidence that relates the antidepressant effects of ketamine and classical hallucinogens on TRD with changes in inflammatory and neurotrophic biomarkers. Twelve studies were found (n = 587), 2 with oral ayahuasca (1 mL/kg) and 10 with ketamine (mostly intravenous 0.5 mg/kg) administration. Results for all biomarkers assessed were contradictory and thus inconclusive. Randomized controlled trials with bigger samples and higher statistical power are warranted to clarify if peripheral biomarkers can confidently be used to indicate and measure ketamine's and classical hallucinogens' antidepressant effect. The PROSPERO ID for this study is CRD42021249089.

Effect of combination fluoxetine and exercise on prefrontal BDNF, anxiety-like behavior and fear extinction in a female rat model of post-traumatic stress disorder (PTSD): a comparison with male animals

Despite significant differences between men and women in the symptoms of PTSD and the response to therapeutic interventions, most PTSD studies have been done on male subjects. Continuing our previous study in male rats, this study aimed at better understanding the effect of a combination therapy of exercise with fluoxetine on female PTSD rats. The results were then compared with our past findings in male animals. Female adult Wistar rats subjected to PTSD were treated with moderate treadmill exercise or fluoxetine, or a combination of both. PTSD was induced by the single prolonged stress (SPS) model. Elevated plus-maze (EPM), serum and prefrontal BDNF, and fear extinctions were evaluated. The results showed that exercise plus fluoxetine decreased anxiety-like behavior, improved fear extinction, and increased BDNF changes in female rats. The effects of exercise alone were comparable with those of combination therapy except that combination therapy was more effective on OAT (open arm entry). The majority of results in female rats, except for those of prefrontal BDNF, 4th extinction, and OAT, were similar to those of male rats as shown in our previous study. According to our findings, exercise as a safe and cost-effective intervention can be considered as a complementary efficient option for PTSD treatment in both sexes. To achieve better treatment outcomes in PTSD patient, considering sex differences is recommended.

Towards an understanding of psychedelic-induced neuroplasticity

Classic psychedelics, such as LSD, psilocybin, and the DMT-containing beverage ayahuasca, show some potential to treat depression, anxiety, and addiction. Importantly, clinical improvements can last for months or years after treatment. It has been theorized that these long-term improvements arise because psychedelics rapidly and lastingly stimulate neuroplasticity. The focus of this review is on answering specific questions about the effects of psychedelics on neuroplasticity. Firstly, we review the evidence that psychedelics promote neuroplasticity and examine the cellular and molecular mechanisms behind the effects of different psychedelics on different aspects of neuroplasticity, including dendritogenesis, synaptogenesis, neurogenesis, and expression of plasticity-related genes (e.g., brain-derived neurotrophic factor and immediate early genes). We then examine where in the brain psychedelics promote neuroplasticity, particularly discussing the prefrontal cortex and hippocampus. We also examine what doses are required to produce this effect (e.g., hallucinogenic doses vs. "microdoses"), and how long purported changes in neuroplasticity last. Finally, we discuss the likely consequences of psychedelics' effects on neuroplasticity for both patients and healthy people, and we identify important research questions that would further scientific understanding of psychedelics' effects on neuroplasticity and its potential clinical applications.

Pharmacological targeting of cognitive impairment in depression: recent developments and challenges in human clinical research

Impaired cognition is often overlooked in the clinical management of depression, despite its association with poor psychosocial functioning and reduced clinical engagement. There is an outstanding need for new treatments to address this unmet clinical need, highlighted by our consultations with individuals with lived experience of depression. Here we consider the evidence to support different pharmacological approaches for the treatment of impaired cognition in individuals with depression, including treatments that influence primary neurotransmission directly as well as novel targets such as neurosteroid modulation. We also consider potential methodological challenges in establishing a strong evidence base in this area, including the need to disentangle direct effects of treatment on cognition from more generalised symptomatic improvement and the identification of sensitive, reliable and objective measures of cognition.

Brain polar phenol content, behavioural and neurochemical effects of Corinthian currant in a rotenone rat model of Parkinson's disease

OBJECTIVE

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of nigral dopaminergic neurons, leading to reduced motor control. A contributing factor for the nigrostriatal degeneration is known to be oxidative stress, while antioxidant/anti-inflammatory properties of natural polyphenols have been suggested to show beneficial effects. The present study questioned the potential neuroprotective effects of supplementary diet with Corinthian currant, using a rat rotenone PD model.

METHODS

The alterations in motor activity, brain Corinthian currant polar phenols' accumulation, expression patterns of tyrosine hydroxylase (TH), dopamine transporter (DAT) and brain-derived neurotrophic factor (BDNF) in the nigrostriatal dopaminergic system were determined in rotenone-treated, currant-diet rats and matching controls.

RESULTS

Rotenone treatment resulted in motor deficits and TH expression decreases in the nigrostriatal pathway, exhibiting PD-like behavioural motor and neurochemical phenotypes. Interestingly, 38 days Corinthian currant consumption resulted in differential accumulation of polar phenols in mesencephalon and striatum and had a significant effect on attenuating motor deficits and dopaminergic cell loss in substantia nigra pars compacta. In addition, it induced up-regulation of BDNF expression in the nigrostriatal dopaminergic system.

DISCUSSION

Taken all together, evidence is provided for the potential neuroprotective influences of Corinthian currant consumption, involving the neurotrophic factor BDNF, in rescuing aspects of PD-like phenotype.

Effect of treadmill exercise on serum corticosterone, serum and hippocampal BDNF, hippocampal apoptosis and anxiety behavior in an ovariectomized rat model of post-traumatic stress disorder (PTSD)

There is a sex difference in vulnerability to PTSD and in response to therapeutic interventions. Since relation between gonadal hormones and PTSD has been revealed, this study aimed to understand the severity of PTSD-induced impairments after ovarian hormone deficiency and the influence of exercise on PTSD accompanied by ovarian hormone deficiency. Female adult Wistar rats were subjected to ovariectomy, PTSD, or combination ovariectomy plus PTSD. Twenty days after ovariectomy, PTSD was induced by single prolonged stress (SPS) model. The exercise started 14 days after SPS and continued for 4 weeks. Thirty minutes moderate treadmill exercise was planned for 5 days per week. On day 65, after assessing rats using the elevated plus-maze (EPM) test, corticosterone, BDNF, and apoptotic markers were tested. p < 0.05 was considered as significant level. The results showed that ovariectomy worsened the effect of SPS on hippocampal BDNF and led to greater increase in serum corticosterone and hippocampal caspase 3 and BAX in SPS rats. Also, ovariectomy exacerbated anxiety-like behavior in SPS rats. Exercise improved the alterations of hippocampal BDNF, corticosterone, caspase 3, and BAX in SPS ovariectomized rats. However, exercise had no statistically significant effect on anxiety-like behavior in this group. According to the results, exercise is effective to attenuate SPS-induced impairments in molecular and cellular responses even when the condition becomes more complicated due to ovarian hormone deficiency. However, exercise alone cannot help to improve behavior impairments in PTSD combined with an ovarian hormone deficiency. Therefore, exercise could likely be considered as a complementary intervention to strengthen other treatments.

The Mechanisms Behind Rapid Antidepressant Effects of Ketamine: A Systematic Review With a Focus on Molecular Neuroplasticity

The mechanism of action underlying ketamine's rapid antidepressant effects in patients with depression, both suffering from major depressive disorder (MDD) and bipolar disorder (BD), including treatment resistant depression (TRD), remains unclear. Of the many speculated routes that ketamine may act through, restoring deficits in neuroplasticity may be the most parsimonious mechanism in both human patients and preclinical models of depression. Here, we conducted a literature search using PubMed for any reports of ketamine inducing neuroplasticity relevant to depression, to identify cellular and molecular events, relevant to neuroplasticity, immediately observed with rapid mood improvements in humans or antidepressant-like effects in animals. After screening reports using our inclusion/exclusion criteria, 139 publications with data from cell cultures, animal models, and patients with BD or MDD were included (registered on PROSPERO, ID: CRD42019123346). We found accumulating evidence to support that ketamine induces an increase in molecules involved in modulating neuroplasticity, and that these changes are paired with rapid antidepressant effects. Molecules or complexes of high interest include glutamate, AMPA receptors (AMPAR), mTOR, BDNF/TrkB, VGF, eEF2K, p70S6K, GSK-3, IGF2, Erk, and microRNAs. In summary, these studies suggest a robust relationship between improvements in mood, and ketamine-induced increases in molecular neuroplasticity, particularly regarding intracellular signaling molecules.

Ketamine-induced changes in plasma brain-derived neurotrophic factor (BDNF) levels are associated with the resting-state functional connectivity of the prefrontal cortex

OBJECTIVES

Synaptic plasticity and brain-derived neurotrophic factor (BDNF) signalling are proposed to play key roles in antidepressant drug action. Ketamine, an N-methyl-D-aspartate receptor antagonist and putative antidepressant, may increase synaptic plasticity in prefrontal cortex through higher expression of BDNF. Furthermore, ketamine was shown to change resting-state functional connectivity (RSFC) of dorsomedial prefrontal cortex (dmPFC).

METHODS

In a randomised, placebo-controlled study, we investigated acutely (100 min) and at 24 h following subanesthetic ketamine infusion which dmPFC seeded RSFC changes are most strongly associated with plasma BDNF level changes in 53 healthy participants (21 females, age: 24.4 ± 2.9 years) using 7 T-fMRI.

RESULTS

We observed higher relative levels of BDNF 2 h and 24 h after ketamine compared to placebo. Whole-brain regression revealed that the change in BDNF after 24 h was associated with RSFC decreases from dmPFC to posterior cingulate cortex and ventromedial PFC at 24 h and exploratively also at the 100 min measurement point. Follow-up analyses revealed that RSFC reductions following ketamine were restricted to subjects showing increased BDNF levels at 24 h.

CONCLUSIONS

Our findings indicate BDNF level dynamics following ketamine are related to acute and 24 h RSFC changes. Particularly when BDNF increases are observed after ketamine infusion, a disconnection from dmPFC after 24 h is seen and may reflect synaptic plasticity effects.

Antidepressants Promote and Prevent Cancers

The review states that antidepressants (ADs) increase brain-derived neurotrophic factor (BDNF) transmission concomitantly in the brain and the blood: ADs increasing BDNF synthesis in specific areas of the central nervous system (CNS) could presumably affect megakaryocyte's production of platelets. ADs increase BDNF levels in the CNS and improve mood. In the blood, ADs increase BDNF release from platelets. The hypothesis presented here is that the release of BDNF from platelets contributes to the ADs effects on neurogenesis and on tumor growth in the cancer disease. Oncological studies indicate that chemicals ADs exert an aggravating effect on the cancer disease, possibly by promoting proplatelets formation and enhancing BDNF release from platelets in the tumor.

Safety and efficacy of extended release ketamine tablets in patients with treatment-resistant depression and anxiety: open label pilot study

BACKGROUND

Ketamine's defining side effects are dissociation and increased blood pressure/heart rate. An oral formulation with delayed absorption could minimize these effects. We recently reported safety and tolerability data for an extended release ketamine tablet in healthy volunteers.

METHODS

To assess safety, tolerability, efficacy, and pharmacokinetics of an extended release oral ketamine tablet in patients with treatment-resistant depression/anxiety. This was a multiple dose open-label flexible dose uncontrolled study in seven patients with treatment-resistant depression/anxiety, who had all previously demonstrated mood improvement to subcutaneous ketamine. Assessments included ratings of anxiety, depression and dissociation, safety and tolerability, and blood samples for ketamine pharmacokinetics and brain-derived neurotrophic factor (BDNF) concentrations.

RESULTS

Improvements in anxiety and depression ratings occurred gradually over 96 h; all patients had >50% improvements in mood ratings. Ketamine was safe and well tolerated, with no changes in vital signs, and a single brief report of dissociation. Ketamine may induce its own metabolism, as the ratio of norketamine to ketamine increased out to 96 h. Serum BDNF concentrations did not change during the study.

CONCLUSION

Ketamine's safety/tolerability may be improved with an extended release oral formulation. Onset of mood improvement is slightly delayed compared with parenteral dosing. These data support the further development of extended release ketamine tablets for treatment of resistant depression and anxiety disorders.

Effects of subanesthetic intravenous ketamine infusion on neuroplasticity-related proteins in the prefrontal cortex, amygdala, and hippocampus of Sprague-Dawley rats

Ketamine, a multimodal dissociative anesthetic, is a powerful analgesic administered following trauma due to its hemodynamic and respiratory stability. However, ketamine can cause hallucination and dissociation which may adversely impact traumatic memory after an injury. The effects of ketamine on proteins implicated in neural plasticity are unclear due to different doses, routes, and timing of drug administration in previous studies. Here, we investigated the effects of a single intravenous (IV) ketamine infusion on protein levels in three brain regions of rats. Adult male Sprague-Dawley rats with indwelling IV catheters underwent an auditory fear conditioning (three pairings of tone and mild footshock 0.8 mA, 0.5 s) and received a high dose of IV ketamine (0 or 40 mg/kg/2 h) infusion (Experiment 1). In a follow-up study, animals received a low dose of IV ketamine (0 or 10 mg/kg/2 h) infusion (Experiment 2). Two hours after the infusion, brain tissue from the medial prefrontal cortex (mPFC), hippocampus, and amygdala were collected for western blot analyses. Protein levels of a transcription factor (c-Fos), brain-derived neurotrophic factor (BDNF), and phosphorylated extracellular signal-regulated kinase (pERK) were quantified in these regions. The 40 mg/kg ketamine infusion increased c-Fos levels in the mPFC and amygdala as well as pERK levels in the mPFC and hippocampus. The 10 mg/kg ketamine infusion increased BDNF levels in the amygdala, but decreased pERK levels in the mPFC and hippocampus. These findings suggest that a clinically relevant route of ketamine administration produces dose-dependent and brain region-specific effects on proteins involved in neuroplasticity.

The effect of route of administration on the enantioselective pharmacokinetics of ketamine and norketamine in rats

BACKGROUND

Ketamine has been shown to produce a rapid and potent antidepressant response in patients with treatment-resistant depression. Currently ketamine is most commonly administered as a 40-minute intravenous infusion, though it is unknown whether this is the optimal route of administration.

AIMS

To determine the plasma concentration time course of the R- and S-enantiomers of ketamine and norketamine following administration of ketamine by four different routes of administration.

METHODS

Plasma from conscious non-anaesthetised rats was collected following administration of ketamine by either subcutaneous (SC), intramuscular (IM), intravenous infusion (IVI) or intravenous bolus (IVB) routes of administration. Concentrations of the enantiomers of ketamine and norketamine were determined by LC/MS.

RESULTS

Administration by the SC, IM and IVI routes produced an overall similar drug exposure. In contrast, administration by the IVB route produced approximately 15-fold higher peak plasma concentrations for the enantiomers of ketamine and an approximately four-fold lower AUC for the enantiomers of norketamine.

CONCLUSIONS

Route of administration can significantly influence ketamine and norketamine exposures. These differences may influence safety and tolerability, and potentially drug efficacy in humans. This knowledge adds to current research into the optimisation of the use of ketamine for the treatment of depression.

Eradicating Suicide at Its Roots: Preclinical Bases and Clinical Evidence of the Efficacy of Ketamine in the Treatment of Suicidal Behaviors

Despite the continuous advancement in neurosciences as well as in the knowledge of human behaviors pathophysiology, currently suicide represents a puzzling challenge. The World Health Organization (WHO) has established that one million people die by suicide every year, with the impressive daily rate of a suicide every 40 s. The weightiest concern about suicidal behavior is how difficult it is for healthcare professionals to predict. However, recent evidence in genomic studies has pointed out the essential role that genetics could play in influencing person's suicide risk. Combining genomic and clinical risk assessment approaches, some studies have identified a number of biomarkers for suicidal ideation, which are involved in neural connectivity, neural activity, mood, as well as in immune and inflammatory response, such as the mammalian target of rapamycin (mTOR) signaling. This interesting discovery provides the neurobiological bases for the use of drugs that impact these specific signaling pathways in the treatment of suicidality, such as ketamine. Ketamine, an N-methyl-d-aspartate glutamate (NMDA) antagonist agent, has recently hit the headlines because of its rapid antidepressant and concurrent anti-suicidal action. Here we review the preclinical and clinical evidence that lay the foundations of the efficacy of ketamine in the treatment of suicidal ideation in mood disorders, thereby also approaching the essential question of the understanding of neurobiological processes of suicide and the potential therapeutics.