Scopolamine produces larger antidepressant and antianxiety effects in women than in men

Group-Based Symptom Trajectory of Intramuscular Administration of Scopolamine Augmentation in Moderate to Severe Major Depressive Disorder: A Post-Hoc Analysis

Objective

Developing new strategies for rapid and sustained relief of depressive symptom has been the focus of research in the field of major depressive disorder (MDD). Scopolamine exerts rapid antidepressant effect in recent years but is controversial. Therefore, we aimed to identify a sensitive patient who may respond to intramuscular injections of scopolamine added to antidepressants based on distinct trajectory patterns.

Methods

We analyzed longitudinal post hoc data collected from 66 MDD patients at Beijing Anding Hospital, Capital Medical University, over a 4-week period. In addition to demographics, depressive symptoms were assessed using the 16-item Quick Inventory of Depressive Symptomatology and Self-Report (QIDS-SR16) Scale and 17-item Hamilton Rating Scale for Depression (HRSD-17) following an i.m. injection of scopolamine. We explored different longitudinal patterns of depressive symptoms using a group-based trajectory model (GBTM). We used multiple logistic regression models to help identify predictors of different depressive symptom trajectories.

Results

A two-class GBTM was identified as optimal for classifying depressive symptoms: high/rapidly declining (39.4%) and moderate/gradually declining depression trajectories (60.6%) were distinguished based on the HRSD-17. The high/rapidly declining depression trajectory was characterized by high initial depression followed by a rapid decrease at the end of the study. The moderate/gradual decline trajectory was dominated by moderate depression and gradual decline over 4 weeks. There were no significant associations of age, gender, education, or age of onset with the two trajectory groups.

Conclusion

Scopolamine added to antidepressants can effectively relieve the symptoms of patients with severe depression, and it decreases faster than patients with moderate depression.

Modulation of Muscarinic Signalling in the Central Nervous System by Steroid Hormones and Neurosteroids

Muscarinic acetylcholine receptors expressed in the central nervous system mediate various functions, including cognition, memory, or reward. Therefore, muscarinic receptors represent potential pharmacological targets for various diseases and conditions, such as Alzheimer's disease, schizophrenia, addiction, epilepsy, or depression. Muscarinic receptors are allosterically modulated by neurosteroids and steroid hormones at physiologically relevant concentrations. In this review, we focus on the modulation of muscarinic receptors by neurosteroids and steroid hormones in the context of diseases and disorders of the central nervous system. Further, we propose the potential use of neuroactive steroids in the development of pharmacotherapeutics for these diseases and conditions.

Rapid-acting antidepressants targeting modulation of the glutamatergic system: clinical and preclinical evidence and mechanisms

Major depressive disorder (MDD) is a devastating mental illness that affects approximately 20% of the world's population. It is a major disease that leads to disability and suicide, causing a severe burden among communities. Currently available medications for treating MDD target the monoaminergic systems. The most prescribed medications include selective serotonin reuptake inhibitors and selective norepinephrine reuptake inhibitors. However, these medications have serious drawbacks, such as a delayed onset requiring weeks or months to reach efficacy and drug resistance, as one-third of patients are unresponsive to the medications. Therefore, it is imperative to develop novel therapies with rapid action, high efficacy and few adverse effects. The discovery of the rapid antidepressant effect of ketamine has triggered tremendous enthusiasm for studying new antidepressants that target the glutamatergic system in the central nervous system. Many agents that directly or indirectly modulate the glutamatergic system have been shown to provide rapid and lasting antidepressant action. Among these agents, ketamine, an antagonist of metabotropic glutamate 2/3 receptors, and scopolamine, an unspecific muscarinic acetylcholine receptor antagonist, have been extensively studied. In this review, we discuss the clinical and preclinical evidence supporting the antidepressant efficacy of these agents and the current understanding of the underlying mechanisms.

Rapid antidepressant-like effects of muscarinic receptor antagonists require BDNF-dependent signaling in the ventrolateral periaqueductal gray

RATIONALE

Clinical reports reveal that scopolamine, an acetylcholine muscarinic receptor antagonist, exerts rapid antidepressant effects in depressed patients, but the mechanisms underlying the therapeutic effects have not been fully identified.

OBJECTIVES

The present study examines the cellular mechanisms by which scopolamine produces antidepressant-like effects through its action in the ventrolateral midbrain periaqueductal gray (vlPAG).

METHODS

We used a well-established mouse model of depression induced by chronic restraint stress (CRS) exposure for 14 days. Behaviors were tested using the forced swim test (FST), tail suspension test (TST), female urine sniffing test (FUST), novelty-suppressed feeding test (NSFT), and locomotor activity (LMA). Synaptic transmission in the vlPAG was measured by whole-cell patch-clamp recordings. IntravlPAG microinjection was used to pharmacologically verify the signaling cascades of scopolamine in the vlPAG.

RESULTS

The results demonstrated that intraperitoneal injection of scopolamine produced antidepressant-like effects in a dose-dependent manner without affecting locomotor activity. CRS elicited depression-like behaviors, whereas intraperitoneal injection of scopolamine alleviated CRS-induced depression-like behaviors. CRS diminished glutamatergic transmission in the vlPAG, while scopolamine reversed the above effects. Moreover, intravlPAG microinjection of the L-type voltage-dependent calcium channel (VDCC) blocker verapamil, tropomyosin-related kinase B (TrkB) receptor antagonist ANA-12, mammalian target of rapamycin complex 1 (mTORC1) inhibitor rapamycin, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA) antagonist CNQX prevented scopolamine-induced antidepressant-like effects.

CONCLUSIONS

Scopolamine ameliorated CRS-elicited depression-like behavior required activation of VDCC, resulting in activity-dependent release of brain-derived neurotrophic factor (BDNF), engaging the TrkB receptor and downstream mTORC1 signaling in the vlPAG.

Basal Forebrain Cholinergic Innervation Induces Depression-Like Behaviors Through Ventral Subiculum Hyperactivation

Malfunction of the ventral subiculum (vSub), the main subregion controlling the output connections from the hippocampus, is associated with major depressive disorder (MDD). Although the vSub receives cholinergic innervation from the medial septum and diagonal band of Broca (MSDB), whether and how the MSDB-to-vSub cholinergic circuit is involved in MDD is elusive. Here, we found that chronic unpredictable mild stress (CUMS) induced depression-like behaviors with hyperactivation of vSub neurons, measured by c-fos staining and whole-cell patch-clamp recording. By retrograde and anterograde tracing, we confirmed the dense MSDB cholinergic innervation of the vSub. In addition, transient restraint stress in CUMS increased the level of ACh in the vSub. Furthermore, chemogenetic stimulation of this MSDB-vSub innervation in ChAT-Cre mice induced hyperactivation of vSub pyramidal neurons along with depression-like behaviors; and local infusion of atropine, a muscarinic receptor antagonist, into the vSub attenuated the depression-like behaviors induced by chemogenetic stimulation of this pathway and CUMS. Together, these findings suggest that activating the MSDB-vSub cholinergic pathway induces hyperactivation of vSub pyramidal neurons and depression-like behaviors, revealing a novel circuit underlying vSub pyramidal neuronal hyperactivation and its associated depression.

Serotonin Type 3 Receptor Is Potentially Involved in Cellular Stress Induced by Hydrogen Peroxide

Depression is a disease with several molecular mechanisms involved, such as problems in the serotonergic pathway. This disease is very complex and prevalent, and thus important to deeply study and aim to overcome high rates of relapse and therapeutic failure. In this study, two cellular lines were used (HT-22 and SH-SY5Y cells) to gain insight about the role of the serotonin type 3 (5-HT3) receptor in cellular stress induced by hydrogen peroxide and/or corticosterone. In research, these compounds are known to mimic the high levels of oxidative stress and dysfunction of the hypothalamus–hypophysis–adrenal axis by the action of glucocorticoids, usually present in depressed individuals. The receptor 5-HT3 is also known to be involved in depression, previously demonstrated in studies that highlight the role of these receptors as promising targets for antidepressant therapy. Indeed, the drugs used in this work (mirtazapine, scopolamine, and lamotrigine) interact with this serotonergic receptor. Thus, by using cell morphology, cell viability (neutral red and MTT), and HPLC assays, this work aimed to understand the role of these drugs in the stress induced by H₂O₂/corticosterone to HT-22 and SH-SY5Y cell lines. We concluded that the antagonism of the 5-HT3 receptor by these drugs may be important in the attenuation of H₂O₂-induced oxidative stress to the cells, but not in the corticosterone-induced stress.

Beneficial Effects of Snail Helix aspersa Extract in an Experimental Model of Alzheimer’s Type Dementia

Background: Alzheimer’s disease (AD) is a complex neurodegenerative disease with multifactorial etiology, unsatisfactory treatment, and a necessity for broad-spectrum active substances for cure. The mucus from Helix aspersa snail is a mixture of bioactive molecules with antimicrobial, anti-inflammatory, antioxidant, and anti-apoptotic effects. So far there are no data concerning the capacity of snail extract (SE) to affect neurodegenerative disorders. Objective: The effects of SE from Helix aspersa on learning and memory deficits in Alzheimer’s type dementia (ATD) induced by scopolamine (Sco) in male Wistar rats were examined and some mechanisms of action underlying these effects were evaluated. Methods: SE (0.5 mL/100 g) was applied orally through a food tube for 16 consecutive days: 5 days before and 11 days simultaneously with Sco (2 mg/kg, intraperitoneally). At the end of Sco treatment, using behavioral methods, we evaluated memory performance. Additionally, in cortex and hippocampus the acetylcholinesterase (AChE) activity, acetylcholine and monoamines (dopamine, noradrenaline, and serotonin) content, levels of main oxidative stress markers, and expression of brain-derived neurotrophic factor (BDNF) and cAMP response element-binding protein (CREB) were determined. Results: We demonstrated that, according to all behavioral tests used, SE significantly improved the cognitive deficits induced by Sco. Furthermore, SE possessed AChE inhibitory activity, moderate antioxidant properties and the ability to modulate monoamines content in two brain structures. Moreover, multiple SE applications not only restored the depressed by Sco expression of CREB and BDNF, but significantly upregulated it. Conclusion: Summarizing results, we conclude that complex mechanisms underlie the beneficial effects of SE on impaired memory in Alzheimer’s type dementia.

Efficacy and safety of scopolamine compared to placebo in individuals with bipolar disorder who are experiencing a depressive episode (SCOPE-BD): study protocol for a randomised double-blind placebo-controlled trial

Background

Current treatment options for the management of depressive episodes in bipolar disorder are often sub-optimal, with some treatments either noted to be only partially effective or to require long durations of treatment prior to a therapeutic response. Therefore, pharmaco-therapeutic options that reduce depressive symptoms in a more rapid manner might provide a viable therapeutic option for some people. Intravenous (IV) scopolamine, a pan muscarinic antagonist, has been demonstrated in a number of studies to confer a rapid antidepressant effect, albeit no study to date has exclusively evaluated its potential therapeutic effect in a cohort consisting solely of individuals with bipolar disorder.

Methods

Individuals with bipolar disorder who are currently experiencing a depressive episode of at least moderate severity will be included in this study. Eligible participants will undergo a screening and placebo-run in visit and will be randomised at visit 3 to the treatment or placebo group. Participants will receive the three blinded infusions over the course of 2 weeks, with two subsequent follow-up visits, 1 and 3 weeks after the last infusion visit. The total duration of the study will be approximately 6 weeks. Patients will continue their regular treatment regime in addition to study medication. Objective and subjective mood questionnaires, cognitive assessments and other psychometric instruments will be administered and recorded.

Discussion

To our knowledge, this is the first study to investigate the antidepressant effects of IV scopolamine in an exclusively bipolar disorder cohort. Trial findings will contribute to the evidence base regarding the cholinergic hypothesis of mood disorders and specifically might result in an additional safe therapeutic option for the management of depressive episodes in bipolar disorder.

Trial registration

ClinicalTrials.gov NCT04211961. December 26, 2019. EudraCT Number 2017-003112-39

Clinical Effectiveness of Muscarinic Receptor-Targeted Interventions in Neuropsychiatric Disorders: A Systematic Review

BACKGROUND

For decades, treatment of mood disorders, psychoses, anxiety and dementia have been confounded by limited efficacy and high rates of treatment resistance. Preclinical and clinical evidence have highlighted disruption of cholinergic signalling in several neuropsychiatric conditions and examined intervention strategies including acetylcholinesterase inhibitors and nicotinic receptor-targeted intervention. However, the effectiveness of these approaches is often curtailed by on-target side effects. Post mortem studies implicate muscarinic receptor dysregulation in neuropsychiatric pathophysiology; therefore, we conducted a systematic review and meta-analysis to investigate the therapeutic efficacy and safety of muscarinic receptor-targeted interventions in adults with neuropsychiatric disorders.

METHODS

PubMed, EMBASE, PsycINFO, EBSCO and Web of Science were searched using relevant keywords from database inception to 7 August 2022. Randomised, double-blind, placebo-controlled studies were included if they investigated the effect of muscarinic receptor-targeted intervention in adults with a diagnosis of a neuropsychiatric disorder and were published in English. A narrative synthesis approach was adopted to describe the findings. Wherever three or more studies with a similar intervention were available, effect sizes were calculated, and a meta-analysis was performed. Cochrane risk-of-bias-2 tool was utilised to assess the risk of bias, and sensitivity analyses were performed to identify publication bias. Certainty analysis (high, moderate, low and/or very low) was conducted using GRADE criteria.

RESULTS

Overall, 33 studies met the inclusion criteria and 5 were included in the meta-analysis. Despite a limited pool with several different interventions, we found therapeutic efficacy of xanomeline (M₁/M₄ agonist) in primary psychotic disorders plus behavioural and psychological symptoms of dementia. Scopolamine showed a significant antidepressant effect in a combined cohort of major depressive and bipolar disorders in the short-term outcome measure, but no effect following cessation of treatment. Results from bias assessments suggest "very low" certainty in the antidepressant effect of scopolamine. Critical limitations of the current literature included low power, high heterogeneity in the patient population and a lack of active comparators.

CONCLUSION

While the results are not definitive, findings on muscarinic receptor-targeted interventions in several mental disorders are promising in terms of efficacy and safety, specifically in treating schizophrenia, mood disorders, and behavioural and psychiatric symptoms of Alzheimer's disease. However, orthosteric muscarinic receptor-targeted interventions are associated with a range of peripheral adverse effects that are thought to be mediated via M₂/M₃ receptors. The orthosteric binding site of muscarinic acetylcholine receptors is remarkably conserved, posing a challenge for subtype-selective interventions; nonetheless allosteric ligands with biased signalling pathways are now in development. We conclude that adequately powered prospective studies with subtype-selective interventions are required to determine the clinical effectiveness of muscarinic-receptor targeted interventions for the treatment of neuropsychiatric disorders.

Cell-type-specific synaptic modulation of mAChR on SST and PV interneurons

The muscarinic acetylcholine receptor (mAChR) antagonist, scopolamine, has been shown to have a rapid antidepressant effect. And it is believed that GABAergic interneurons play a crucial role in this action. Therefore, characterizing the modulation effects of mAChR on GABAergic interneurons is crucial for understanding the mechanisms underlying scopolamine's antidepressant effects. In this study, we examined the effect of mAChR activation on the excitatory synaptic transmissions in two major subtypes of GABAergic interneurons, somatostatin (SST)- and parvalbumin (PV)-expressing interneurons, in the anterior cingulate cortex (ACC). We found that muscarine, a mAChR agonist, non-specifically facilitated the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) in both SST and PV interneurons. Scopolamine completely blocked the effects of muscarine, as demonstrated by recovery of sESPCs and mEPSCs in these two types of interneurons. Additionally, individual application of scopolamine did not affect the EPSCs of these interneurons. In inhibitory transmission, we further observed that muscarine suppressed the frequency of both spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs) in SST interneurons, but not PV interneurons. Interestingly, scopolamine directly enhanced the frequency of both sIPSCs and mIPSCs mainly in SST interneurons, but not PV interneurons. Overall, our results indicate that mAChR modulates excitatory and inhibitory synaptic transmission to SST and PV interneurons within the ACC in a cell-type-specific manner, which may contribute to its role in the antidepressant effects of scopolamine.

Muscarinic regulation of self-grooming behavior and ultrasonic vocalizations in the context of open-field habituation in rats

Laboratory rats repeatedly exposed to an open field (OF) apparatus display increasingly high levels of grooming -especially that characterized by long and complex sequences- which has been taken as an additional index of novelty habituation. We hypothesized that disrupting such a learning process by administering an amnesic drug as the antimuscarinic scopolamine (SCP) could delay the appearance of more complex grooming subtypes. Thus, rats were pretreated either with SCP (15 mg/kg or 30 mg/kg) or vehicle (VEH) upon four one-day apart OF (OF1-4). On a fifth assessment, all rats received VEH to analyze the likely carry-over effect of SCP. Finally, we measured 50-kHz and 22-kHz ultrasonic vocalizations (USVs) as reliable markers of positive and negative emotionality, respectively. We found that SCP increased locomotion during OF1 and reduced rearing on OF1-OF4, causing no disruption in habituation over tests. SCP prevented the increase of total grooming time by inhibiting complex grooming subtypes and promoting short cephalic sequences. Despite the SCP-induced alterations on grooming agreed with our hypotheses, those changes may have resulted from a motor impairment that could have also affected rearing behavior. Additionally, SCP suppressed 50-kHz USVs while marginally increased 22-kHz calls. Once SCP was withdrawn, rearing, grooming, and some 50-kHz USVs subtypes returned to VEH levels, suggesting that novelty habituation occurred despite the SCP administration. Altogether, that mixed profile of SCP-induced behavioral changes may derive from the complex interplay between the contrasting action of SCP on different brain regions and the doses here used.

Sex differences shape zebrafish performance in a battery of anxiety tests and in response to acute scopolamine treatment

Sex differences influence human and animal behavioral and pharmacological responses. The zebrafish (Danio rerio) is a powerful, popular model system in neuroscience and drug screening. However, the impact of zebrafish sex differences on their behavior and drug responses remains poorly understood. Here, we evaluate baseline anxiety-like behavior in adult male and female zebrafish, and its changes following an acute 30-min exposure to 800-μM scopolamine, a common psychoactive anticholinergic drug. Overall, we report high baseline anxiety-like behavior and more individual variability in locomotion in female zebrafish, as well as distinct, sex-specific (anxiolytic-like in females and anxiogenic-like in males) effects of scopolamine. Collectively, these findings reinforce the growing importance of zebrafish models for studying how both individual and sex differences shape behavioral and pharmacological responses.

Acetylcholine Muscarinic Receptors in Ventral Hippocampus Modulate Stress-Induced Anxiety-Like Behaviors in Mice

Chronic stress exposure increases the risk of developing various neuropsychiatric illnesses. The ventral hippocampus (vHPC) is central to affective and cognitive processing and displays a high density of acetylcholine (ACh) muscarinic receptors (mAChRs). However, the precise role of vHPC mAChRs in anxiety remains to be fully investigated. In this study, we found that chronic restraint stress (CRS) induced social avoidance and anxiety-like behaviors in mice and increased mAChR expression in the vHPC. CRS increased the vHPC ACh release in behaving mice. Moreover, CRS altered the synaptic activities and enhanced neuronal activity of the vHPC neurons. Using pharmacological and viral approaches, we showed that infusing the antagonist of mAChRs or decreasing their expression in the vHPC attenuated the anxiety-like behavior and rescued the social avoidance behaviors in mice probably due to suppression of vHPC neuronal activity and its excitatory synaptic transmission. Our results suggest that the changes of neuronal activity and synaptic transmission in the vHPC mediated by mAChRs may play an important role in stress-induced anxiety-like behavior, providing new insights into the pathological mechanism and potential pharmacological target for anxiety disorders.

Transient Stimulation with Psychoplastogens Is Sufficient to Initiate Neuronal Growth

Cortical neuron atrophy is a hallmark of depression and includes neurite retraction, dendritic spine loss, and decreased synaptic density. Psychoplastogens, small molecules capable of rapidly promoting cortical neuron growth, have been hypothesized to produce long-lasting positive effects on behavior by rectifying these deleterious structural and functional changes. Here we demonstrate that ketamine and LSD, psychoplastogens from two structurally distinct chemical classes, promote sustained growth of cortical neurons after only short periods of stimulation. Furthermore, we show that psychoplastogen-induced cortical neuron growth can be divided into two distinct epochs: an initial stimulation phase requiring TrkB activation and a growth period involving sustained mTOR and AMPA receptor activation. Our results provide important temporal details concerning the molecular mechanisms by which next-generation antidepressants produce persistent changes in cortical neuron structure, and they suggest that rapidly excreted psychoplastogens might still be effective neurotherapeutics with unique advantages over compounds like ketamine and LSD.

The antidepressant efficacy of the muscarinic antagonist scopolamine: Past findings and future directions

Scopolamine is a nonselective muscarinic antagonist that has shown relatively rapid antidepressant effects, although to date the results are from limited clinical studies. Scopolamine reportedly has downstream signaling effects thought to be linked to neuroplasticity within glutamatergic synapses and consequent antidepressant action. In psychiatry, clinically validated pathways are unusual and thus merit further research in an effort develop more effect medicines for patients with mood disorders. Thus, we are faced with a unique opportunity to build on the clinical observation associated with scopolamine through reverse translation to identify of targets that retain the clinical efficacy while reducing the side effect profile. This chapter reviews the clinical antidepressant findings with scopolamine, including discussion of differential response across patient subgroups, as well as a review of biomarkers that predict clinical outcome. The preclinical data associated with scopolamine also are reviewed and convey a vision for narrowing in on the therapeutic muscarinic receptor subtype(s) that support the antidepressant effects to guide the development of next generation antimuscarinic drug targets for depression.

The Neurochemical Effects of Prazosin Treatment on Fear Circuitry in a Rat Traumatic Stress Model

Objective

The timing of administration of pharmacologic agents is crucial in traumatic stress since they can either potentiate the original fear memory or may cause fear extinction depending on the phase of fear conditioning. Brain noradrenergic system has a role in fear conditioning. Data regarding the role of prazosin in traumatic stress are controversial.

Methods

In this study, we examined the effects of prazosin and the noradrenergic system in fear conditioning in a predator stress rat model. We evaluated the direct or indirect effects of stress and prazosin on noradrenaline (NA), gamma-aminobuytyric acid (GABA), glutamate, glycine levels and choline esterase activity in the amygdaloid complex, the dorsal hippocampus, the prefrontal cortex and the rostral pons.

Results

Our results demonstrated that prazosin might alleviate defensive behaviors and traumatic stress symptoms when given during the traumatic cue presentation in the stressed rats. However prazosin administration resulted in higher anxiety levels in non stressed rats when the neutral cue was presented.

Conclusion

Prazosin should be used in PTSD with caution because prazosin might exacerbate anxiety in non-traumatized subjects. However prazosin might as well alleviate stress responses very effectively. Stress induced changes included increased NA and GABA levels in the amygdaloid complex in our study, attributing noradrenaline a possible inhibitory role on fear acquisition. Acetylcholine also has a role in memory modulation in the brain. We also demonstrated increased choline esterase acitivity. Cholinergic modulation might be another target for indirect prazosin action which needs to be further studied.

Traditional Chinese Medicine in Depression Treatment: From Molecules to Systems

Depression is a multigenetic or multifactorial syndrome. The central neuron system (CNS)-orientated, single target, and conventional antidepressants are insufficient and far from ideal. Traditional Chinese Medicine (TCM) has historically been used to treat depression up till today, particularly in Asia. Its holistic, multidrug, multitarget nature fits well with the therapeutic idea of systems medicine in depression treatment. Over the past two decades, although efforts have been made to understand TCM herbal antidepressants at the molecular level, many fundamental questions regarding their mechanisms of action remain to be addressed at the systems level in order to better understand the complicated herbal formulations in depression treatment. In this Mini Review, we review and discuss the mechanisms of action of herbal antidepressants and their acting targets in the pathological systems in the brain, such as monoamine neurotransmissions, hypothalamic–pituitary–adrenal (HPA) axis, neurotropic factor brain-derived neurotrophic factor (BDNF) cascade, and glutamate transmission. Some herbal molecules, constituents, and formulas are highlighted as examples to discuss their mechanisms of action and future directions for comprehensive researches at the systems level. Furthermore, we discuss pharmacological approaches to integrate the mechanism of action from the molecular level into the systems level for understanding of systems pharmacology of TCM formulations. Integration of the studies at the molecular level into the systems level not only represents a trend in TCM study but also promotes our understanding of the system-wide mechanism of action of herbal antidepressant formulations.

Involvement of muscarinic receptor mechanisms in antidepressant drug action

Conventional antidepressants typically require weeks of daily dosing to achieve full antidepressant response in antidepressant responders. A newly evolving group of compounds can engender more rapid response times in depressed patients. These drugs include the newly approved antidepressant (S)-ketamine (esketamine, Spravato). A seminal study by Furey and Drevets in 2006 showed antidepressant response in patients after only a few doses with the antimuscarinic drug scopolamine. Several clinical reports have generally confirmed scopolamine as a rapid-acting antidepressant. The data with scopolamine are consistent with the adrenergic/cholinergic hypothesis of mania/depression derived from clinical reports originating in the 1970s from Janowsky and colleagues. Additional support for a role for muscarinic receptors in mood disorders comes from the greater efficacy of conventional antidepressants that have relatively high levels of muscarinic receptor blocking actions (e.g., the tricyclic antidepressant amitriptyline vs the selective serotonin reuptake inhibitor fluoxetine). There appears to be appreciable overlap in the mechanisms of action of scopolamine and other rapid-acting antidepressants (ketamine) or putative rapid-acting agents (mGlu2/3 receptor antagonists) although gaps exist in the experimental literature. Current hypotheses regarding the mechanisms underlying the rapid antidepressant response to scopolamine posit an M₁ receptor subtype-initiated cascade of biological events that involve the amplification of AMPA receptors. Consequent impact on brain-derived neurotrophic factor and mTor signaling pathways result in the induction of dendritic spines that enable augmented functional connectivity in brain areas regulating mood. Two major goals for research in this area focus on finding ways in which scopolamine might best be utilized for depressed patients and the discovery of alternative compounds that improve upon the efficacy and safety of scopolamine.

Exposure Therapy for Post-Traumatic Stress Disorder: Factors of Limited Success and Possible Alternative Treatment

Recent research indicates that there is mixed success in using exposure therapies on patients with post-traumatic stress disorder (PTSD). Our study argues that there are two major reasons for this: The first is that there are nonassociative aspects of PTSD, such as hyperactive amygdala activity, that cannot be attenuated using the exposure therapy; The second is that exposure therapy is conceptualized from the theoretical framework of Pavlovian fear extinction, which we know is heavily context dependent. Thus, reducing fear response in a therapist's office does not guarantee reduced response in other situations. This study also discusses work relating to the role of the hippocampus in context encoding, and how these findings can be beneficial for improving exposure therapies.

Hab-o Shefa, a Persian Medicine Compound for Maintenance Treatment of Opioid Dependence: Randomized Placebo-Controlled Clinical Trial

Objectives: The major problem in maintenance treatment of opioid use disorder is craving and relapse. The utilization of herbal compounds and complementary therapy for treatment of disease and addiction has been widely expanding. Considering the significant effect of Hab-o Shefa in detoxification phase, this clinical trial has explored the influence of this compound on maintenance treatment of opioid-dependent patients. This product is made of four herbs, including Datura stramonium L., Rheum palmatum L., Zingiber officinale Roscoe, and Acacia senegal L. Design: The authors conducted a two-group parallel randomized double-blind clinical trial on 81 opioid-dependent patients within 12 weeks. After medically assisted detoxification, participants were assigned randomly to Hab-o Shefa (n = 41) and placebo (n = 40). Outcome measures included craving assessed by craving beliefs questionnaire, self-reported opioid use, and lapse (any opioid-positive urine test) according to urinalysis and addiction severity index-lite questionnaire, retention in treatment, and depression and anxiety scores on the Hamilton's anxiety and depression scales. Results: Forty-one participants completed the study for 12 weeks, 21 subjects in the drug group and 20 subjects in the placebo group. The rates of opioid-positive urine tests and self-reported opioid use were significantly lower in Hab-o Shefa group (f = 8.41, p = 0.001). Hab-o Shefa also indicated a significant superiority over placebo in the effect of treatment by time interaction for craving (f = 5.91, p = 0.001), depression (f = 3.40, p = 0.01), and anxiety (f = 2.58, p = 0.035). The retention time was 66.6 days for drug group and 59.6 days for placebo one. Although the causes for dropping out in two groups were different, there was no significant difference (p = 0.623). The side effects of the two groups were not significantly different. Conclusion: Results indicated that Hab-o Shefa could be useful for opioid maintenance treatment, and it can also be considered as a new promising drug for prevention of craving and relapse.

A randomised, double-blind, active placebo-controlled, parallel groups, dose-response study of scopolamine hydrobromide (4-6 μg/kg) in patients with major depressive disorder

Background

Depressive disorders are a leading cause of disability, but current behavioural and pharmacological therapies have a slow onset of response, typically taking several weeks before achieving efficacy. Prior studies using triplicate intravenous scopolamine infusions have been shown to reduce depressive symptomologies within days compared to saline placebo infusions. However, several parameters of scopolamine’s potential antidepressant effect remain unknown, such as its dose–response profile and its washout period. There is also the question as to whether the previously reported antidepressant responses were confounded by unblinding effects due to the lack of an active placebo control. Glycopyrronium bromide was selected as placebo for this trial given it has similar antimuscarinic properties to scopolamine hydrobromide but an inability to cross the blood–brain barrier, thereby hypothetically mimicking only the peripheral effects of scopolamine.

Methods/Design

A parallel group trial of single intravenous scopolamine infusions at three doses (4, 5, and 6 μg/kg) along with one glycopyrronium bromide 4 μg/kg group will be administered to 40 participants with major depressive disorder in a 1:1:1:2 ratio, respectively. The primary outcome measure will be the Montgomery–Åsberg Depression Rating Scale (MADRS) administered at baseline, 4 hours, 1 day, 3 days, 1 week, 2 weeks, 4 weeks, and 6 weeks post-infusion to determine antidepressant efficacy. As a secondary measure, the Quick Inventory of Depressive Symptomatology will be administered alongside the MADRS to further track potential antidepressant responses. Other secondary measures include electroencephalography, blood samples, and Bowdle visual acuity scales recorded at baseline, 5, 10, 15, 20, 30, 60, 120, and 240 min post-infusion to determine the pharmacokinetic-pharmacodynamic profile of scopolamine in depressed participants.

Discussion

This trial contributes to the literature surrounding the efficacy of scopolamine as an antidepressant. Determining the dose–response profile and washout period of scopolamine’s antidepressant effect will also provide important information for designing and conducting crossover trials. The use of an active placebo is important to reduce potentially confounding expectancy effects.

Trial registration

The trial was registered in the Australian New Zealand Clinical Trials Registry (registration number ACTRN12619000569101). Registered on 11 April 2019.

The effects of intramuscular administration of scopolamine augmentation in moderate to severe major depressive disorder: a randomized, double-blind, placebo-controlled trial

INTRODUCTION

Major depressive disorder (MDD) is a common affective disorder. Currently established pharmacotherapies lack rapid clinical response, thereby limiting their ability to bring instant relief to patients. A series of clinical trials has demonstrated the antidepressant effects of scopolamine, yet few have studied the effects of add-on scopolamine to currently available antidepressants. It is not known whether conventional antidepressant treatment with a 3-day scopolamine injection could speed up oral antidepressant efficacy. The main focus of this study is to detect the capacity of the rapid-onset efficacy of such a treatment option.

METHODS AND ANALYSIS

This study consisted of a single-centre, double-blind, three-arm randomized trial with a 4-week follow-up period. Sixty-six participants meeting entry criteria were randomly allocated to three treatment groups: a high-dose group, a low-dose group and a placebo control group. Psychiatric rating scales were administered at baseline and seven viewing points following the administration of intramuscular injections. The primary outcome measure was length of time from randomization (baseline) to early improvement.

RESULTS

Both primary and secondary outcome measures consistently showed no differences among the three groups. The cumulative response rate and the remission rate were 72.7% (48/66) and 47.0% (31/66). Intramuscular scopolamine treatment was relatively well tolerated. Two subjects with high-dose injections dropped out because of a drug-related side effect.

CONCLUSION

Contrary to our prediction, we found that, compared to placebo (0.9% saline i.m.), scopolamine was not associated with a significantly faster antidepressant response rate.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03131050. Registered on 18 April 2017.

Additive interaction between scopolamine and nitric oxide agents on immobility in the forced swim test but not exploratory activity in the hole-board

RATIONALE

The muscarinic cholinergic antagonist scopolamine has received an attention due to its unique antidepressant effects. However, the considerable adverse effects on nervous system limit the use of scopolamine as a psychiatric drug.

OBJECTIVE

In order to overcome the limitations and increase the therapeutic effects of scopolamine, we decided to examine the effects of joint administration of sub-effective dose of scopolamine and the sub-effective dose of a nitric oxide (NO) precursor L-Arginine or a non-selective nitric oxide synthase (NOS) inhibitor L-NAME on depression- and anxiety-related behaviors in male NMRI mice.

METHODS

To this aim, animal behavior was assessed in the forced swim test (FST) and hole-board apparatus.

RESULTS

Scopolamine (0.05 mg/kg) significantly decreased immobility time in the FST, suggesting an antidepressant-like effect. Moreover, L-Arginine (50 mg/kg) produced an antidepressant-like response in the FST and decreased head-dip counts in the hole-board apparatus, indicating an anxiety-like effect. The same doses of scopolamine and L-Arginine decreased the locomotor activity in mice. Joint administration of sub-effective dose of scopolamine (0.01 mg/kg) with a low dose of L-Arginine (25 mg/kg) or L-NAME (1 mg/kg) induced a profound antidepressant-like effect in the FST. These drug combinations did not influence on anxiety-related behaviors. Meanwhile, L-NAME alone did not alter the performance of mice in the FST and hole-board. Isobolographic analysis revealed an additive effect for scopolamine and L-Arginine or L-NAME.

CONCLUSION

Data suggests that NO agents could positively impact the therapeutic profile of scopolamine, because they might be useful for inducing antidepressant-like effect associated to scopolamine.

A Key Role for Prefrontocortical Small Conductance Calcium-Activated Potassium Channels in Stress Adaptation and Rapid Antidepressant Response

The muscarinic acetylcholine receptor antagonist scopolamine elicits rapid antidepressant activity, but its underlying mechanism is not fully understood. In a chronic stress model, a single low-dose administration of scopolamine reversed depressive-like reactivity. This antidepressant-like effect was mediated via a muscarinic M1 receptor–SKC pathway because it was mimicked by intra-medial prefrontal cortex (intra-mPFC) infusions of scopolamine, of the M1 antagonist pirenzepine or of the SKC antagonist apamin, but not by the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine. Extracellular and whole-cell recordings revealed that scopolamine and ketamine attenuate the SKC-mediated action potential hyperpolarization current and rapidly enhance mPFC neuronal excitability within the therapeutically relevant time window. The SKC agonist 1-EBIO abrogated scopolamine-induced antidepressant activity at a dose that completely suppressed burst firing activity. Scopolamine also induced a slow-onset activation of raphe serotonergic neurons, which in turn was dependent on mPFC-induced neuroplasticity or excitatory input, since mPFC transection abolished this effect. These early behavioral and mPFC activational effects of scopolamine did not appear to depend on prefrontocortical brain-derived neurotrophic factor and serotonin-1A activity, classically linked to SSRIs, and suggest a novel mechanism associated with antidepressant response onset through SKC-mediated regulation of activity-dependent plasticity.

Cholinergic Receptor Blockade in the VTA Attenuates Cue-Induced Cocaine-Seeking and Reverses the Anxiogenic Effects of Forced Abstinence

Drug relapse after periods of abstinence is a common feature of substance abuse. Moreover, anxiety and other mood disorders are often co-morbid with substance abuse. Cholinergic receptors in the ventral tegmental area (VTA) are known to mediate drug-seeking and anxiety-related behavior in rodent models. However, it is unclear if overlapping VTA cholinergic mechanisms mediate drug relapse and anxiety-related behaviors associated with drug abstinence. We examined the effects of VTA cholinergic receptor blockade on cue-induced cocaine seeking and anxiety during cocaine abstinence. Male Sprague-Dawley rats were trained to self-administer intravenous cocaine (~0.5 mg/kg/infusion, FR1 schedule) for 10 days, followed by 14 days of forced abstinence. VTA infusion of the non-selective nicotinic acetylcholine receptor antagonist mecamylamine (0, 10, and 30 μg/side) or the non-selective muscarinic receptor antagonist scopolamine (0, 2.4 and 24 μg /side) significantly decreased cue-induced cocaine seeking. In cocaine naïve rats, VTA mecamylamine or scopolamine also led to dose-dependent increases in open arm time in the elevated plus maze (EPM). In contrast, rats that received I.V. cocaine, compared to received I.V. saline rats, displayed an anxiogenic response on day 14 of abstinence as reflected by decreased open arm time in the EPM. Furthermore, low doses of VTA mecamylamine (10 μg /side) or scopolamine (2.4 μg /side), that did not alter EPM behavior in cocaine naive rats, were sufficient to reverse the anxiogenic effects of cocaine abstinence. Together, these data point to an overlapping role of VTA cholinergic mechanisms to regulate relapse and mood disorder-related responses during cocaine abstinence.

DARK Classics in Chemical Neuroscience: Atropine, Scopolamine, and Other Anticholinergic Deliriant Hallucinogens

Anticholinergic drugs based on tropane alkaloids, including atropine, scopolamine, and hyoscyamine, have been used for various medicinal and toxic purposes for millennia. These drugs are competitive antagonists of acetylcholine muscarinic (M-) receptors that potently modulate the central nervous system (CNS). Currently used clinically to treat vomiting, nausea, and bradycardia, as well as alongside other anesthetics to avoid vagal inhibition, these drugs also evoke potent psychotropic effects, including characteristic delirium-like states with hallucinations, altered mood, and cognitive deficits. Given the growing clinical importance of anti-M deliriant hallucinogens, here we discuss their use and abuse, clinical importance, and the growing value in preclinical (experimental) animal models relevant to modeling CNS functions and dysfunctions.

Cholinergic regulation of mood: from basic and clinical studies to emerging therapeutics

Mood disorders are highly prevalent and are the leading cause of disability worldwide. The neurobiological mechanisms underlying depression remain poorly understood, although theories regarding dysfunction within various neurotransmitter systems have been postulated. Over 50 years ago, clinical studies suggested that increases in central acetylcholine could lead to depressed mood. Evidence has continued to accumulate suggesting that the cholinergic system has a important role in mood regulation. In particular, the finding that the antimuscarinic agent, scopolamine, exerts fast-onset and sustained antidepressant effects in depressed humans has led to a renewal of interest in the cholinergic system as an important player in the neurochemistry of major depression and bipolar disorder. Here, we synthesize current knowledge regarding the modulation of mood by the central cholinergic system, drawing upon studies from human postmortem brain, neuroimaging, and drug challenge investigations, as well as animal model studies. First, we describe an illustrative series of early discoveries which suggest a role for acetylcholine in the pathophysiology of mood disorders. Then, we discuss more recent studies conducted in humans and/or animals which have identified roles for both acetylcholinergic muscarinic and nicotinic receptors in different mood states, and as targets for novel therapies.

Emission of 22 kHz vocalizations in rats as an evolutionary equivalent of human crying: Relationship to depression

There is no clear relationship between crying and depression based on human neuropsychiatric observations. This situation originates from lack of suitable animal models of human crying. In the present article, an attempt will be made to answer the question whether emission of rat aversive vocalizations (22 kHz calls) may be regarded as an evolutionary equivalent of adult human crying. Using this comparison, the symptom of crying in depressed human patients will be reanalyzed. Numerous features and characteristics of rat 22 kHz aversive vocalizations and human crying vocalizations are equivalent. Comparing evolutionary, biological, physiological, neurophysiological, social, pharmacological, and pathological aspects have shown vast majority of common features. It is concluded that emission of rat 22 kHz vocalizations may be treated as an evolutionary vocal homolog of human crying, although emission of 22 kHz calls is not exactly the same phenomenon because of significant differences in cognitive processes between these species. It is further concluded that rat 22 kHz vocalizations and human crying vocalizations are both expressing anxiety and not depression. Analysis of the relationship between anxiety and depression reported in clinical studies supports this conclusion regardless of the nature and extent of comorbidity between these pathological states.

Scopolamine augmentation of a newly initiated escitalopram treatment for major depressive disorder: study protocol for a randomized controlled trial

Background

Major depressive disorder (MDD) is a prevalent and disabling disorder that can lead to heavy individual, familial, and societal burdens. Although pharmaceutical interventions still play an essential role in therapeutic measures, limitations, including effects that are delayed for weeks, are noteworthy. Antidepressants with rapid efficacy and acceptable tolerance have been investigated for many years; rapid antidepressant effects and promising clinical applications have been obtained with intravenous and oral scopolamine. This study aims to evaluate the efficacy of repeated intramuscular scopolamine as an add-on treatment to escitalopram.

Methods

This is a single-center, saline-controlled, double-blind, three-armed, randomized trial. Sixty-six participants diagnosed with MDD will be recruited at Beijing Anding Hospital and randomly assigned to one of three groups: a high-dose intramuscular scopolamine augmentation group; a low-dose intramuscular scopolamine augmentation group; and a placebo control group. Our primary endpoint is improvement in the 17-Item Hamilton Rating Scale for Depression (HRSD17) score from the baseline (at least a 20% reduction). Prespecified secondary endpoints include response rates and remission rates as well as changes in the total or subscale scores between the baseline and week 4.

Discussion

This study will provide the first insight regarding the rapid antidepressant efficacy and tolerability of an intramuscular scopolamine add-on to the usual treatment in Chinese MDD patients. The first discussion concerns whether augmentation can accelerate early antidepressant efficacy. A pilot study of intramuscular scopolamine is performed.

The limitations of this study include its small sample size and it being a single-center study, suggesting the need for further confirmation with trials enrolling larger populations.

Ethics and dissemination

The study protocol and all related materials have been approved by the Institutional Ethics Committee of the Beijing Anding Hospital (No. 2016–106, Beijing, China). The findings will be disseminated through peer-reviewed journals and at national and international conferences.

Trial registration

ClinicalTrials.gov, NCT03131050. Registered on 18 April 2017.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-3132-3) contains supplementary material, which is available to authorized users.

Depression as a Neuroendocrine Disorder: Emerging Neuropsychopharmacological Approaches beyond Monoamines

Depression is currently recognized as a crucial problem in everyday clinical practice, in light of ever-increasing rates of prevalence, as well as disability, morbidity, and mortality related to this disorder. Currently available antidepressant drugs are notoriously problematic, with suboptimal remission rates and troubling side-effect profiles. Their mechanisms of action focus on the monoamine hypothesis for depression, which centers on the disruption of serotonergic, noradrenergic, and dopaminergic neurotransmission in the brain. Nevertheless, views on the pathophysiology of depression have evolved notably, and the comprehension of depression as a complex neuroendocrine disorder with important systemic implications has sparked interest in a myriad of novel neuropsychopharmacological approaches. Innovative pharmacological targets beyond monoamines include glutamatergic and GABAergic neurotransmission, brain-derived neurotrophic factor, various endocrine axes, as well as several neurosteroids, neuropeptides, opioids, endocannabinoids and endovanilloids. This review summarizes current knowledge on these pharmacological targets and their potential utility in the clinical management of depression.

Five potential therapeutic agents as antidepressants: a brief review and future directions

Despite the availability of numerous antidepressants, many patients with depression do not show adequate response. The therapeutic lag between drug administration and onset of clinical improvement observed with conventional antidepressants has led to a need for antidepressants with a novel mechanism of action. Recently, five such agents, including acetyl-L-carnitine, scopolamine, ω-3 polyunsaturated fatty acids, ketamine, and selective 5-HT7 serotonin receptor antagonists, have gained interest as potential antidepressants with enhanced symptom control, improved tolerability, and faster onset of action compared to conventional antidepressants. This review provides an update and critical examination of these five novel therapeutic agents as potential antidepressants.

Convergent Mechanisms Underlying Rapid Antidepressant Action

Traditional pharmacological treatments for depression have a delayed therapeutic onset, ranging from several weeks to months, and there is a high percentage of individuals who never respond to treatment. In contrast, ketamine produces rapid-onset antidepressant, anti-suicidal, and anti-anhedonic actions following a single administration to patients with depression. Proposed mechanisms of the antidepressant action of ketamine include N-methyl-D-aspartate receptor (NMDAR) modulation, gamma aminobutyric acid (GABA)-ergic interneuron disinhibition, and direct actions of its hydroxynorketamine (HNK) metabolites. Downstream actions include activation of the mechanistic target of rapamycin (mTOR), deactivation of glycogen synthase kinase-3 and eukaryotic elongation factor 2 (eEF2), enhanced brain-derived neurotrophic factor (BDNF) signaling, and activation of α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors (AMPARs). These putative mechanisms of ketamine action are not mutually exclusive and may complement each other to induce potentiation of excitatory synapses in affective-regulating brain circuits, which results in amelioration of depression symptoms. We review these proposed mechanisms of ketamine action in the context of how such mechanisms are informing the development of novel putative rapid-acting antidepressant drugs. Such drugs that have undergone pre-clinical, and in some cases clinical, testing include the muscarinic acetylcholine receptor antagonist scopolamine, GluN2B-NMDAR antagonists (i.e., CP-101,606, MK-0657), (2R,6R)-HNK, NMDAR glycine site modulators (i.e., 4-chlorokynurenine, pro-drug of the glycineB NMDAR antagonist 7-chlorokynurenic acid), NMDAR agonists [i.e., GLYX-13 (rapastinel)], metabotropic glutamate receptor 2/3 (mGluR2/3) antagonists, GABAA receptor modulators, and drugs acting on various serotonin receptor subtypes. These ongoing studies suggest that the future acute treatment of depression will typically occur within hours, rather than months, of treatment initiation.

Rapid-Acting Antidepressants: Mechanistic Insights and Future Directions

PURPOSE OF REVIEW

Ketamine produces rapid (within hours) antidepressant actions, even in patients considered treatment resistant, and even shows promise for suicidal ideation. Here, we review current research on the molecular and cellular mechanisms of ketamine and other novel rapid-acting antidepressants, and briefly explore gender differences in the pathophysiology and treatment of MDD.

RECENT FINDINGS

Ketamine, an NMDA receptor antagonist, increases BDNF release and synaptic connectivity, opposing the deficits caused by chronic stress and depression. Efforts are focused on the development of novel rapid agents that produce similar synaptic and rapid antidepressant actions, but without the side effects of ketamine. The impact of gender on the response to ketamine and other rapid-acting antidepressants is in early stages of investigation.

SUMMARY

The discovery that ketamine produces rapid therapeutic actions for depression and suicidal ideation represents a major breakthrough and much needed alternative to currently available medications. However, novel fast acting agents with fewer side effects are needed, as well as elucidation of the efficacy of these rapid-acting antidepressants for depression in women.

Do psychoactive drugs have a therapeutic role in compulsivity? Studies on schedule-induced polydipsia

RATIONALE

Clinical studies have shown that some psychoactive recreational drugs have therapeutic applications in anxiety, depression, and schizophrenia. However, to date, there are few studies on the therapeutic potential efficacy of recreational drugs in compulsive neuropsychiatric disorders.

OBJECTIVES

We explored the therapeutic potential of different psychoactive and psychedelic drugs in a preclinical model of compulsive behavior.

METHODS

Outbred male Wistar rats were selected as either high (HD) or low (LD) drinkers according to their behavior in schedule-induced polydipsia (SIP). Subsequently, we assessed the effects of acute administration of scopolamine (0.125, 0.25, and 0.5 mg/kg), methamphetamine (0.25, 0.5, 1.25, and 2.5 mg/kg), ketamine (1.25, 2.5, 5, and 10 mg/kg), cannabidiol (1 and 3 mg/kg), WIN21255-2 (0.5, 075, and 1 mg/kg), and AM404 (0.25 and 0.5 mg/kg) on compulsive drinking in SIP.

RESULTS

Scopolamine reduced dose-dependent compulsive drinking in HD compared with LD rats in SIP. Methamphetamine induced a dose-dependent inverted U-curve effect in both groups, in which lower doses increased and higher doses reduced compulsive drinking in SIP. Ketamine, cannabidiol, WIN21255-2, and AM404 did not have any relevant effects in SIP.

CONCLUSIONS

These data provide new evidence that low doses of scopolamine and intermediate doses of methamphetamine might therapeutically reduce compulsive behaviors and suggest that there is not a direct participation of the endocannabinoid system in compulsive behavior on SIP. The research in the underlying neurochemical mechanisms of these psychoactive drugs might provide an additional insight on new therapeutic targets in compulsive neuropsychiatric disorders.

Circuit and synaptic mechanisms of repeated stress: Perspectives from differing contexts, duration, and development

The current review is meant to synthesize research presented as part of a symposium at the 2016 Neurobiology of Stress workshop in Irvine California. The focus of the symposium was "Stress and the Synapse: New Concepts and Methods" and featured the work of several junior investigators. The presentations focused on the impact of various forms of stress (altered maternal care, binge alcohol drinking, chronic social defeat, and chronic unpredictable stress) on synaptic function, neurodevelopment, and behavioral outcomes. One of the goals of the symposium was to highlight the mechanisms accounting for how the nervous system responds to stress and their impact on outcome measures with converging effects on the development of pathological behavior. Dr. Kevin Bath's presentation focused on the impact of disruptions in early maternal care and its impact on the timing of hippocampus maturation in mice, finding that this form of stress drove accelerated synaptic and behavioral maturation, and contributed to the later emergence of risk for cognitive and emotional disturbance. Dr. Scott Russo highlighted the impact of chronic social defeat stress in adolescent mice on the development and plasticity of reward circuity, with a focus on glutamatergic development in the nucleus accumbens and mesolimbic dopamine system, and the implications of these changes for disruptions in social and hedonic response, key processes disturbed in depressive pathology. Dr. Kristen Pleil described synaptic changes in the bed nuclei of the stria terminalis that underlie the behavioral consequences of allostatic load produced by repeated cycles of alcohol binge drinking and withdrawal. Dr. Eric Wohleb and Dr. Ron Duman provided new data associating decreased mammalian target of rapamycin (mTOR) signaling and neurobiological changes in the synapses in response to chronic unpredictable stress, and highlighted the potential for the novel antidepressant ketamine to rescue synaptic and behavioral effects. In aggregate, these presentations showcased how divergent perspectives provide new insights into the ways in which stress impacts circuit development and function, with implications for understanding emergence of affective pathology.

Establishing zebrafish as a model to study the anxiolytic effects of scopolamine

Scopolamine (hyoscine) is a muscarinic acetylcholine receptor antagonist that has traditionally been used to treat motion sickness in humans. However, studies investigating depressed and bipolar populations have found that scopolamine is also effective at reducing depression and anxiety symptoms. The potential anxiety-reducing (anxiolytic) effects of scopolamine could have great clinical implications for humans; however, rats and mice administered scopolamine showed increased anxiety in standard behavioural tests. This is in direct contrast to findings in humans, and complicates studies to elucidate the specific mechanisms of scopolamine action. The aim of this study was to assess the suitability of zebrafish as a model system to test anxiety-like compounds using scopolamine. Similar to humans, scopolamine acted as an anxiolytic in individual behavioural tests (novel approach test and novel tank diving test). The anxiolytic effect of scopolamine was dose dependent and biphasic, reaching maximum effect at 800 µM. Scopolamine (800 µM) also had an anxiolytic effect in a group behavioural test, as it significantly decreased their tendency to shoal. These results establish zebrafish as a model organism for studying the anxiolytic effects of scopolamine, its mechanisms of action and side effects.

Methylene blue and its analogues as antidepressant compounds

Methylene Blue (MB) is considered to have diverse medical applications and is a well-described treatment for methemoglobinemias and ifosfamide-induced encephalopathy. In recent years the focus has shifted to MB as an antimalarial agent and as a potential treatment for neurodegenerative disorders such as Alzheimer's disease. Of interest are reports that MB possesses antidepressant and anxiolytic activity in pre-clinical models and has shown promise in clinical trials for schizophrenia and bipolar disorder. MB is a noteworthy inhibitor of monoamine oxidase A (MAO-A), which is a well-established target for antidepressant action. MB is also recognized as a non-selective inhibitor of nitric oxide synthase (NOS) and guanylate cyclase. Dysfunction of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) cascade is strongly linked to the neurobiology of mood, anxiety and psychosis, while the inhibition of NOS and/or guanylate cyclase has been associated with an antidepressant response. This action of MB may contribute significantly to its psychotropic activity. However, these disorders are also characterised by mitochondrial dysfunction and redox imbalance. By acting as an alternative electron acceptor/donor MB restores mitochondrial function, improves neuronal energy production and inhibits the formation of superoxide, effects that also may contribute to its therapeutic activity. Using MB in depression co-morbid with neurodegenerative disorders, like Alzheimer's and Parkinson's disease, also represents a particularly relevant strategy. By considering their physicochemical and pharmacokinetic properties, analogues of MB may provide therapeutic potential as novel multi-target strategies in the treatment of depression. In addition, low MAO-A active analogues may provide equal or improved response with a lower risk of adverse effects.

Molecular and Cellular Mechanisms of Rapid-Acting Antidepressants Ketamine and Scopolamine

Major depressive disorder (MDD) is a prevalent neuropsychiatric disease that causes profound social and economic burdens. The impact of MDD is compounded by the limited therapeutic efficacy and delay of weeks to months of currently available medications. These issues highlight the need for more efficacious and faster-acting treatments to alleviate the burdens of MDD. Recent breakthroughs demonstrate that certain drugs, including ketamine and scopolamine, produce rapid and long-lasting antidepressant effects in MDD patients. Moreover, preclinical work has shown that the antidepressant actions of ketamine and scopolamine in rodent models are caused by an increase of extracellular glutamate, elevated BDNF, activation of the mammalian target of rapamycin complex 1 (mTORC1) cascade, and increased number and function of spine synapses in the prefrontal cortex (PFC). Here we review studies showing that both ketamine and scopolamine elicit rapid antidepressant effects through converging molecular and cellular mechanisms in the PFC. In addition, we discuss evidence that selective antagonists of NMDA and muscarinic acetylcholine (mACh) receptor subtypes (i.e., NR2B and M1-AChR) in the PFC produce comparable antidepressant responses. Furthermore, we discuss evidence that ketamine and scopolamine antagonize inhibitory interneurons in the PFC leading to disinhibition of pyramidal neurons and increased extracellular glutamate that promotes the rapid antidepressant responses to these agents. Collectively, these studies indicate that specific NMDA and mACh receptor subtypes on GABAergic interneurons are promising targets for novel rapid-acting antidepressant therapies.

The Role of Muscarinic Receptors in the Pathophysiology of Mood Disorders: A Potential Novel Treatment?

The central cholinergic system has been implicated in the pathophysiology of mood disorders. An imbalance in central cholinergic neurotransmitter activity has been proposed to contribute to the manic and depressive episodes typical of these disorders. Neuropharmacological studies into the effects of cholinergic agonists and antagonists on mood state have provided considerable support for this hypothesis. Furthermore, recent clinical studies have shown that the pan-CHRM antagonist, scopolamine, produces rapid-acting antidepressant effects in individuals with either major depressive disorder (MDD) or bipolar disorder (BPD), such as bipolar depression, contrasting the delayed therapeutic response of conventional mood stabilisers and antidepressants. This review presents recent data from neuroimaging, post-mortem and genetic studies supporting the involvement of muscarinic cholinergic receptors (CHRMs), particularly CHRM2, in the pathophysiology of MDD and BPD. Thus, novel drugs that selectively target CHRMs with negligible effects in the peripheral nervous system might produce more rapid and robust clinical improvement in patients with BPD and MDD.

[Interest of scopolamine as a treatment of major depressive disorder]

INTRODUCTION

The number of patients with depression in the world is 350 millions according to estimates. The search for new treatments, particularly in forms of resistant depression, is necessary given the growing number of patients experiencing treatment failure and resistance. Scopolamine, an anticholinergic antimuscarinic molecule, is one of the treatments under evaluation. It falls within the assumptions of cholinergic disruption of the pathophysiology of depression, at different levels (genetic, receptorial [muscarinic and glutamate receptors], hormonal, synaptic…). In 2006, a pilot study made to evaluate the role of the cholinergic system in cognitive symptoms of depression found unexpected results regarding the antidepressant effect of scopolamine in depressive patients. Since that time other studies have been conducted to evaluate the benefits of treatment with intravenous injections of scopolamine.

OBJECTIVE

Our main objective was to evaluate the interest of scopolamine as an antidepressant treatment in depressed populations.

METHODS

We conducted a literature review with the aim of assessing the effectiveness of treatment with scopolamine in uni- and bipolar patients with depressive symptoms. The protocol consisted of two injection blocks (each block consisting of three injections spaced fifteen minutes apart within three to five days) of active ingredient or placebo crossover. The selected patients were between 18 and 45years and had the DSM-IV major depressive disorder or bipolar disorder criteria. Regarding the methods of measurement, the primary endpoint was the reduction in scores of the Montgomery Asberg Depression Rating Scale (MADRS) with a total response defined by a decrease of more than 50 % of the score and remission corresponding to a MADRS score<10. Seven sessions of evaluations were performed.

RESULTS

The published results are promising in terms of efficiency with rapid antidepressant effect, a total response rate ranging from 59-64% and a remission rate of between 37 and 55% in uni- and bipolar patients, which persists at least 15days. The treatment was well tolerated by patients with relatively mild and transient side effects the most common being the sensation of sleepiness that was also found in the placebo group. There were no serious side effects such as heart failure or confusion. In terms of mood, there was no becoming manic or hypomanic even for bipolar patients.

CONCLUSION

The results are encouraging, but there is concern for the moment because of the few studies, so to date there is little data on the subject including medium and long term.