Chronic fluoxetine treatment induces structural plasticity and selective changes in glutamate receptor subunits in the rat cerebral cortex

AMPA receptor diffusional trapping machinery as an early therapeutic target in neurodegenerative and neuropsychiatric disorders

Over the past two decades, there has been a growing recognition of the physiological importance and pathological implications surrounding the surface diffusion of AMPA receptors (AMPARs) and their diffusional trapping at synapses. AMPAR surface diffusion entails the thermally powered random Brownian lateral movement of these receptors within the plasma membrane, facilitating dynamic exchanges between synaptic and extrasynaptic compartments. This process also enables the activity-dependent diffusional trapping and accumulation of AMPARs at synapses through transient binding to synaptic anchoring slots. Recent research highlights the critical role of synaptic recruitment of AMPARs via diffusional trapping in fundamental neural processes such as the development of the early phases of long-term potentiation (LTP), contextual fear memory, memory consolidation, and sensory input-induced cortical remapping. Furthermore, studies underscore that regulation of AMPAR diffusional trapping is altered across various neurological disease models, including Huntington's disease (HD), Alzheimer's disease (AD), and stress-related disorders like depression. Notably, pharmacological interventions aimed at correcting deficits in AMPAR diffusional trapping have demonstrated efficacy in restoring synapse numbers, LTP, and memory functions in these diverse disease models, despite their distinct pathogenic mechanisms. This review provides current insights into the molecular mechanisms underlying the dysregulation of AMPAR diffusional trapping, emphasizing its role as a converging point for multiple pathological signaling pathways. We propose that targeting AMPAR diffusional trapping represents a promising early therapeutic strategy to mitigate synaptic plasticity and memory deficits in a spectrum of brain disorders, encompassing but not limited to HD, AD, and stress-related conditions. This approach underscores an integrated therapeutic target amidst the complexity of these neurodegenerative and neuropsychiatric diseases.

Mirtazapine decreased cocaine-induced c-fos expression and dopamine release in rats

Introduction

Chronic cocaine exposure induces an increase in dopamine release and an increase in the expression of the Fos protein in the rat striatum. It has been suggested that both are necessary for the expression of cocaine-induced alterations in behavior and neural circuitry. Mirtazapine dosing attenuated the cocaine-induced psychomotor and reinforcer effects.

Methods

The study evaluates the effect of chronic dosing of mirtazapine on cocaine-induced extracellular dopamine levels and Fos protein expression in rats. Male Wistar rats received cocaine (10 mg/Kg; i.p.) during the induction and expression of locomotor sensitization. The mirtazapine (30 mg/Kg; MIR), was administered 30 minutes before cocaine during the cocaine withdrawal. After each treatment, the locomotor activity was recorded for 30 minutes. Animals were sacrificed after treatment administration. Dopamine levels were determined by high-performance liquid chromatographic (HPLC) in the ventral striatum, the prefrontal cortex (PFC), and the ventral tegmental area (VTA) in animals treated with mirtazapine and cocaine. The quantification of c-fos immunoreactive cells was carried out by stereology analysis.

Results

Mirtazapine generated a decrease in cocaine-induced locomotor activity. In addition, mirtazapine decreased the amount of cocaine-induced dopamine and the number of cells immunoreactive to the Fos protein in the striatum, PFC, and VTA.

Discussion

These data suggest that mirtazapine could prevent the consolidation of changes in behavior and the cocaine-induced reorganization of neuronal circuits. It would explain the mirtazapine-induced effects on cocaine behavioral sensitization. Thus, these data together could support its possible use for the treatment of patients with cocaine use disorder.

The multifaceted effects of fluoxetine treatment on cognitive functions

Fluoxetine, the prototypical selective serotonin reuptake inhibitor (SSRI), is widely used to treat major depressive disorder (MDD) and a variety of other central nervous system conditions, primarily due to its established clinical safety profile. Although its efficacy in treating depression is well-recognized, the impact of fluoxetine on cognitive functions remains inconsistent and elusive. In this review, we first examine the well-substantiated biological mechanisms underlying fluoxetine's antidepressant effects, which include serotonin reuptake inhibition and activation of TrkB receptors-key to brain-derived neurotrophic factor (BDNF) signaling. Subsequently, we delve into the cognitive side effects observed in both preclinical and clinical studies, affecting domains such as memory, attention, and executive functions. While certain studies indicate cognitive improvements in patients with underlying disorders, there is also evidence of negative effects, influenced by variables like gender, duration of treatment, age, disease pathology, and the specifics of cognitive testing. Significantly, the negative cognitive outcomes reported in preclinical research often involve healthy, non-diseased animals. This review underscores the necessity for heightened caution in fluoxetine prescription and further investigation into its potentially detrimental cognitive effects, even when used prophylactically.

Perineuronal net structure as a non-cellular mechanism contributing to affective state: A scoping review

Affective state encompasses emotional responses to our physiology and influences how we perceive and respond within our environment. In affective disorders such as depression, cognitive adaptability is challenged, and structural and functional brain changes have been identified. However, an incomplete understanding persists of the molecular and cellular mechanisms at play in affective state. An exciting area of newly appreciated importance is perineuronal nets (PNNs); a specialised component of extracellular matrix playing a critical role in neuroprotection and synaptic plasticity. A scoping review found 24 studies demonstrating that PNNs are still a developing field of research with a promising general trend for stress in adulthood to increase the intensity of PNNs, whereas stress in adolescence reduced (potentially developmentally delayed) PNN numbers and intensity, while antidepressants correlated with reduced PNN numbers. Despite promising trends, limited research underscores the need for further exploration, emphasizing behavioral outcomes for validating affective states. Understanding PNNs' role may offer therapeutic insights for depression and inform biomarker development, advancing precision medicine and enhancing well-being.

Antidepressant-like effects of the Punica granatum and citalopram combination are associated with structural changes in dendritic spines of granule cells in the dentate gyrus of rats

Introduction: Natural products such as phytoestrogens-enriched foods or supplements have been considered as an alternative therapy to reduce depressive symptoms associated with menopause. It is known that the aqueous extract of Punica granatum (AE-PG) exerts antidepressant-like effects by activating β-estrogen receptors and facilitates the antidepressant response of the clinical drug citalopram (CIT). However, the effects on neuroplasticity are unknown. Objectvie investigated the antidepressant-like response of combining AE-PG and CIT at sub-optimal doses, analyzing their effects on the formation and maturation of dendrite spines in granule cells as well as on the dendrite complexity. Methods: Ovariectomized Wistar rats (3-month-old) were randomly assigned to one of the following groups: A) control (saline solution as vehicle of CIT and AE-PG, B) AE-PG at a sub-threshold dose (vehicle of CIT plus AE-PG at 0.125 mg/kg), C) CIT at a sub-threshold dose (0.77 mg/kg plus vehicle of AE-PG), and D) a combination of CIT plus AE-PG (0.125 mg/kg and 0.77 mg/kg, respectively). All rats were treated intraperitoneally for 14 days. Antidepressant-like effects were evaluated using the force swimming test test (FST). The complexity of dendrites and the number and morphology of dendrite spines of neurons were assessed in the dentate gyrus after Golgi-Cox impregnation. The expressions of the mature brain-derived neurotrophic factor (mBDNF) in plasma and of mBDNF and synaptophysin in the hippocampus, as markers of synaptogenesis, were also determined. Results: Administration of CIT combined with AE-PG, but not alone, induced a significant antidepressant-like effect in the FST with an increase in the dendritic complexity and the number of dendritic spines in the dentate gyrus (DG) of the hippocampus, revealed by the thin and stubby categories of neurons at the granular cell layer. At the same time, an increase of mBDNF and synaptophysin expression was observed in the hippocampus of rats that received the combination of AE-PG and CIT.

SNS alleviates depression-like behaviors in CUMS mice by regluating dendritic spines via NCOA4-mediated ferritinophagy

ETHNOPHARMACOLOGICAL RELEVANCE

Depression is one of the most common mood disturbances worldwide. The Si-ni-san formula (SNS) is a famous classic Traditional Chinese Medicine (TCM) widely used to treat depression for thousands of years in clinics. However, the mechanism underlying the therapeutic effect of SNS in improving depression-like behaviors following chronic unpredictable mild stress (CUMS) remains unknown.

AIM OF THE STUDY

This study aimed to investigate whether SNS alleviates depression-like behaviors in CUMS mice by regulating dendritic spines via NCOA4-mediated ferritinophagy in vitro and in vivo.

STUDY DESIGN AND METHODS

In vivo, mice were exposed to CUMS for 42 days, and SNS (4.9, 9.8, 19.6 g/kg/d), fluoxetine (10 mg/kg/d), 3-methyladenine (3-MA) (30 mg/kg/d), rapamycin(1 mg/kg/d), and deferoxamine (DFO) (200 mg/kg/d) were conducted once daily during the last 3 weeks of the CUMS procedure. In vitro, a depressive model was established by culture of SH-SY5Y cells with corticosterone, followed by treatment with different concentrations of freeze-dried SNS (0.001, 0.01, 0.1 mg/mL) and rapamycin (10 nM), NCOA4-overexpression, Si-NCOA4. After the behavioral test (open-field test (OFT), sucrose preference test (SPT), forced swimming test (FST) and tail suspension test (TST), dendritic spines, GluR2 protein expression, iron concentration, and ferritinophagy-related protein levels (P62, FTH, NCOA4, LC3-II/LC3-I) were tested in vitro and in vivo using immunohistochemistry, golgi staining, immunofluorescence, and Western blot assays. Finally, HEK-293T cells were transfected by si-NCOA4 or GluR2-and NCOA4-overexpression plasmid and treated with corticosterone(100 μM), freeze-dried SNS(0.01 mg/mL), rapamycin(25 nM), and 3-MA(5 mM). The binding amount of GluR2, NCOA4, and LC3 was assessed by the co-immunoprecipitation (CO-IP) assay.

RESULTS

3-MA, SNS, and DFO promoted depressive-like behaviors in CUMS mice during OFT, SPT, FST and TST, improved the amount of the total, thin, mushroom spine density and enhanced GluR2 protein expression in the hippocampus. Meanwhile, treatment with SNS decreased iron concentrations and inhibited NCOA4-mediated ferritinophagy activation in vitro and in vivo. Importantly, 3-MA and SNS could prevent the binding of GluR2, NCOA4 and LC3 in corticosterone-treated HEK-293T, and rapamycin reversed this phenomenon after treatment with SNS.

CONCLUSION

SNS alleviates depression-like behaviors in CUMS mice by regulating dendritic spines via NCOA4-mediated ferritinophagy.

Tabernanthalog Reduces Motivation for Heroin and Alcohol in a Polydrug Use Model

Background

The potential use of psychedelic drugs as therapeutics for neuropsychiatric disorders has been limited by their hallucinogenic properties. To overcome this limitation, we developed and characterized tabernanthalog (TBG), a novel analogue of the indole alkaloids ibogaine and 5-methoxy-N,N-dimethyltryptamine with reduced cardiac arrhythmogenic risk and a lack of classical psychedelic drugs-induced sensory alterations. We previously demonstrated that TBG has therapeutic efficacy in a preclinical model of opioid use disorder (OUD) in rats and in a binge model of alcohol drinking in mice. Alcohol is commonly co-used in ∼35-50% of individuals with OUD, and yet, preclinical models that recapitulate this comorbidity are lacking.

Methodology

Here we employed a polydrug model of heroin and alcohol couse to screen the therapeutic efficacy of TBG on metrics of both opioid and alcohol seeking. We first exposed rats to alcohol (or control sucrose-fade solution) in the home-cage (HC), using a two-bottle binge protocol, over a period of 1 month. Rats were then split into two groups that underwent self-administration training for either intravenous heroin or oral alcohol, so that we could assess the impact of HC alcohol exposure on the self-administration of each substance separately. Thereafter, rats began self-administering both heroin and alcohol in the same sessions. Finally, we tested the effects of TBG on break points for heroin and alcohol in a progressive ratio test, where the number of lever presses required to obtain a single reward increased exponentially.

Results and Conclusion

TBG effectively reduced motivation for heroin and alcohol in this test, indicating its efficacy is preserved in animals with a history of heroin and alcohol polydrug use.

Antidepressant-induced increase in GluA2 expression does not translate in changes of AMPA receptor-mediated synaptic transmission at CA3/CA1 synapses in rats

Chronic treatment with serotonin selective reuptake inhibitors or tryciclic antidepressant drugs in rodents has been shown to increase the expression of GluA1 and/or GluA2 AMPA receptor (AMPAR) subunits in several brain areas, including the hippocampus. These changes in AMPAR composition have been suggested to result in increased glutamatergic neurotransmission and possibly underlie enhanced hippocampal synaptic plasticity through the increased availability of calcium-permeable AMPARs, specifically at CA3/CA1 synapses. However, the possibility that chronic treatment with antidepressants actually results in strengthened glutamatergic neurotransmission in CA1 has poorly been investigated. Here, we studied whether chronic treatment with the multimodal antidepressant drug trazodone mimicked the effect of paroxetine on the expression of AMPAR subunits in male wistar rat hippocampus and whether these drugs produced a parallel facilitation of field excitatory postsynaptic potentials (fEPSP) responses evoked by activation of CA3/CA1 synapses in dorsal hippocampal slices. In addition, we investigated whether the quality of glutamatergic AMPARs involved in basal neurotransmission was changed by altered subunit expression, e.g. leading to appearance of calcium-permeable AMPARs. We found a significant increase in GluA2 subunit expression following treatment with trazodone or paroxetine for twenty-one days, but not after seven-days treatment. In contrast, we did not find any significant changes in fEPSP responses supporting either a facilitation of glutamatergic neurotransmission in basal conditions or the appearance of functional calcium-permeable AMPARs at CA3/CA1 pyramidal neuron synapses. Thus, neurochemically-detected increases in the expression of AMPAR subunits cannot directly be extrapolated in increased number of functioning receptors and/or facilitated basal neurotransmission.

Could psychedelic drugs have a role in the treatment of schizophrenia? Rationale and strategy for safe implementation

Schizophrenia is a widespread psychiatric disorder that affects 0.5-1.0% of the world's population and induces significant, long-term disability that exacts high personal and societal cost. Negative symptoms, which respond poorly to available antipsychotic drugs, are the primary cause of this disability. Association of negative symptoms with cortical atrophy and cell loss is widely reported. Psychedelic drugs are undergoing a significant renaissance in psychiatric disorders with efficacy reported in several conditions including depression, in individuals facing terminal cancer, posttraumatic stress disorder, and addiction. There is considerable evidence from preclinical studies and some support from human studies that psychedelics enhance neuroplasticity. In this Perspective, we consider the possibility that psychedelic drugs could have a role in treating cortical atrophy and cell loss in schizophrenia, and ameliorating the negative symptoms associated with these pathological manifestations. The foremost concern in treating schizophrenia patients with psychedelic drugs is induction or exacerbation of psychosis. We consider several strategies that could be implemented to mitigate the danger of psychotogenic effects and allow treatment of schizophrenia patients with psychedelics to be implemented. These include use of non-hallucinogenic derivatives, which are currently the focus of intense study, implementation of sub-psychedelic or microdosing, harnessing of entourage effects in extracts of psychedelic mushrooms, and blocking 5-HT2A receptor-mediated hallucinogenic effects. Preclinical studies that employ appropriate animal models are a prerequisite and clinical studies will need to be carefully designed on the basis of preclinical and translational data. Careful research in this area could significantly impact the treatment of one of the most severe and socially debilitating psychiatric disorders and open an exciting new frontier in psychopharmacology.

Ameliorating effect offluoxetine on tamoxifen-induced memory loss: The role of corticolimbic NMDA receptors and CREB/BDNF/cFos signaling pathways in rats

Tamoxifen-induced cognitive dysfunction may lead to fluoxetine consumption in patients with breast cancer. Since the brain mechanisms are unclear in tamoxifen/fluoxetine therapy, the blockade effect of hippocampal/amygdala/prefrontal cortical NMDA receptors was examined in fluoxetine/tamoxifen-induced memory retrieval. We also assessed the corticolimbic signaling pathways in memory retrieval under the drug treatment in adult male Wistar rats. Using the Western blot technique, the expression levels of the cAMP response element-binding protein (CREB), brain-derived neurotrophic factor (BDNF), and cFos were evaluated in the corticolimbic regions. The results showed that pre-test administration of fluoxetine (3 and 5 mg/kg, i.p.) improved tamoxifen-induced memory impairment in the passive avoidance learning task. Pre-test bilateral microinjection of D-AP5, a selective NMDA receptor antagonist, into the dorsal hippocampal CA1 regions and the central amygdala (CeA), but not the medial prefrontal cortex (mPFC), inhibited the improving effect of fluoxetine on tamoxifen response. It is important to note that the microinjection of D-AP5 into the different sites by itself did not affect memory retrieval. Memory retrieval increased the signaling pathway of pCREB/CREB/BDNF/cFos in the corticolimbic regions. Tamoxifen-induced memory impairment decreased the hippocampal/PFC BDNF level and the amygdala level of pCREB/CREB/cFos. The improving effect of fluoxetine on tamoxifen significantly increased the hippocampal/PFC expression levels of BDNF, the PFC/amygdala expression levels of cFos, and the ratio of pCREB/CREB in all targeted areas. Thus, NMDA receptors' activity in the different corticolimbic regions mediates fluoxetine/tamoxifen memory retrieval. The corticolimbic synaptic plasticity changes likely accompany the improving effect of fluoxetine on tamoxifen response.

Symptomatic and neurotrophic effects of GABAA receptor positive allosteric modulation in a mouse model of chronic stress

Chronic stress is a risk factor for Major Depressive Disorder (MDD), and in rodents, it recapitulates human behavioral, cellular and molecular changes. In MDD and after chronic stress, neuronal dysfunctions and deficits in GABAergic signaling are observed and responsible for symptom severity. GABA signals predominantly through GABAA receptors (GABAA-R) composed of various subunit types that relate to downstream outcomes. Activity at α2-GABAA-Rs contributes to anxiolytic properties, α5-GABAA-Rs to cognitive functions, and α1-GABAA-Rs to sedation. Therefore, a therapy aiming at increasing α2- and α5-GABAA-Rs activity, but devoid of α1-GABAA-R activity, has potential to address several symptomologies of depression while avoiding side-effects. This study investigated the activity profiles and behavioral efficacy of two enantiomers of each other (GL-II-73 and GL-I-54), separately and as a racemic mixture (GL-RM), and potential disease-modifying effects on neuronal morphology. Results confirm GL-I-54 and GL-II-73 exert positive allosteric modulation at the α2-, α3-, α5-GABAA-Rs and α5-containing GABAA-Rs, respectively, and separately reduces immobility in the forced swim test and improves stress-induced spatial working memory deficits. Using unpredictable chronic mild stress (UCMS), we show that acute and chronic administration of GL-RM provide pro-cognitive effects, with mild efficacy on mood symptoms, although at lower doses avoiding sedation. Morphology studies showed reversal of spine density loss caused by UCMS after chronic GL-RM treatment at apical and basal dendrites of the PFC and CA1. Together, these results support using a racemic mixture with combined α2-, α3-, α5-GABAA-R profile to reverse chronic stress-induced mood symptoms, cognitive deficits, and with anti-stress neurotrophic effects.

Synaptic Mechanisms Regulating Mood State Transitions in Depression

Depression is an episodic form of mental illness characterized by mood state transitions with poorly understood neurobiological mechanisms. Antidepressants reverse the effects of stress and depression on synapse function, enhancing neurotransmission, increasing plasticity, and generating new synapses in stress-sensitive brain regions. These properties are shared to varying degrees by all known antidepressants, suggesting that synaptic remodeling could play a key role in depression pathophysiology and antidepressant function. Still, it is unclear whether and precisely how synaptogenesis contributes to mood state transitions. Here, we review evidence supporting an emerging model in which depression is defined by a distinct brain state distributed across multiple stress-sensitive circuits, with neurons assuming altered functional properties, synapse configurations, and, importantly, a reduced capacity for plasticity and adaptation. Antidepressants act initially by facilitating plasticity and enabling a functional reconfiguration of this brain state. Subsequently, synaptogenesis plays a specific role in sustaining these changes over time.

Guanosine as a promising target for fast-acting antidepressant responses

Although the rapid-onset and sustained antidepressant responses elicited by ketamine have gained considerable attention in recent years, it has some knock-on effects that limit its widespread clinical use. Therefore, ketamine is considered the prototype for the new generation of glutamate-based rapid-acting antidepressants. Within this context, it has been demonstrated that guanosine, an endogenous guanine-based purine, has overlapping mechanisms of action with ketamine and is effective in eliciting fast antidepressant-like responses and even potentiating ketamine's actions in preclinical studies. Here, we review the recent findings regarding the ability of guanosine to produce rapid-acting antidepressant-like effects and we provide an overview of the molecular mechanisms underlying its antidepressant-like actions. Moreover, the neurobiological mechanisms underpinning the ability of guanosine in boosting the antidepressant-like and pro-synaptogenic effects elicited by ketamine are also reported. Taken together, this review opens perspectives for the use of guanosine alone or in combination with ketamine for the management of treatment-resistant depression.

A low-dose combination of ketamine and guanosine counteracts corticosterone-induced depressive-like behavior and hippocampal synaptic impairments via mTORC1 signaling

Ketamine exhibits rapid and sustained antidepressant responses, but its repeated use may cause adverse effects. Augmentation strategies have been postulated to be useful for the management/reduction of ketamine's dose and its adverse effects. Based on the studies that have suggested that ketamine and guanosine may share overlapping mechanisms of action, the present study investigated the antidepressant-like effect of subthreshold doses of ketamine and guanosine in mice subjected to repeated administration of corticosterone (CORT) and the role of mTORC1 signaling for this effect. The ability of the treatment with ketamine (0.1 mg/kg, i.p.) plus guanosine (0.01 mg/kg, p.o.) to counteract the depressive-like behavior induced by CORT (20 mg/kg, p.o., for 21 days) in mice, was paralleled with the prevention of the CORT-induced reduction on BDNF levels, Akt (Ser⁴⁷³) and GSK-3β (Ser⁹) phosphorylation, and PSD-95, GluA1, and synapsin immunocontent in the hippocampus. No changes on mTORC1 and p70S6K immunocontent were found in the hippocampus and prefrontal cortex of any experimental group. No alterations on BDNF, Akt/GSK-3β, mTORC1/p70S6K, and synaptic proteins were observed in the prefrontal cortex of mice. The antidepressant-like and pro-synaptogenic effects elicited by ketamine plus guanosine were abolished by the pretreatment with rapamycin (0.2 nmol/site, i.c.v., a selective mTORC1 inhibitor). Our results showed that the combined administration of ketamine and guanosine at low doses counteracted CORT-induced depressive-like behavior and synaptogenic disturbances by activating mTORC1 signaling. This study supports the notion that the combined administration of guanosine and ketamine may be a useful therapeutic strategy for the management of MDD.

Insufficiency of ventral hippocampus to medial prefrontal cortex transmission explains antidepressant non-response

BACKGROUND

There is extensive evidence that antidepressant drugs restore normal brain function by repairing damage to ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC). While the damage is more extensive in hippocampus, the evidence of treatments, such as deep brain stimulation, suggests that functional changes in prefrontal cortex may be more critical. We hypothesized that antidepressant non-response may result from an insufficiency of transmission from vHPC to mPFC.

METHOD

Antidepressant non-responsive Wistar Kyoto (WKY) rats were subjected to chronic mild stress (CMS), then treated with chronic daily administration of the antidepressant drug venlafaxine (VEN) and/or repeated weekly optogenetic stimulation (OGS) of afferents to mPFC originating from vHPC or dorsal HPC (dHPC).

RESULTS

As in many previous studies, CMS decreased sucrose intake, open-arm entries on the elevated plus maze (EPM), and novel object recognition (NOR). Neither VEN nor vHPC-mPFC OGS alone was effective in reversing the effects of CMS, but the combination of chronic VEN and repeated OGS restored normal behaviour on all three measures. dHPC-mPFC OGS restored normal behaviour in the EPM and NOR test irrespective of concomitant VEN treatment, and had no effect on sucrose intake.

CONCLUSIONS

The synergism between VEN and vHPC-mPFC OGS supports the hypothesis that the antidepressant non-responsiveness of WKY rats results from a failure of antidepressant treatment fully to restore transmission in the vHPC-mPFC pathway.

SALM4 negatively regulates NMDA receptor function and fear memory consolidation

Many synaptic adhesion molecules positively regulate synapse development and function, but relatively little is known about negative regulation. SALM4/Lrfn3 (synaptic adhesion-like molecule 4/leucine rich repeat and fibronectin type III domain containing 3) inhibits synapse development by suppressing other SALM family proteins, but whether SALM4 also inhibits synaptic function and specific behaviors remains unclear. Here we show that SALM4-knockout (Lrfn3^-/-) male mice display enhanced contextual fear memory consolidation (7-day post-training) but not acquisition or 1-day retention, and exhibit normal cued fear, spatial, and object-recognition memory. The Lrfn3^-/- hippocampus show increased currents of GluN2B-containing N-methyl-D-aspartate (NMDA) receptors (GluN2B-NMDARs), but not α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors (AMPARs), which requires the presynaptic receptor tyrosine phosphatase PTPσ. Chronic treatment of Lrfn3^-/- mice with fluoxetine, a selective serotonin reuptake inhibitor used to treat excessive fear memory that directly inhibits GluN2B-NMDARs, normalizes NMDAR function and contextual fear memory consolidation in Lrfn3^-/- mice, although the GluN2B-specific NMDAR antagonist ifenprodil was not sufficient to reverse the enhanced fear memory consolidation. These results suggest that SALM4 suppresses excessive GluN2B-NMDAR (not AMPAR) function and fear memory consolidation (not acquisition).

Prenatal fluoxetine impairs non-hippocampal but not hippocampal memory in adult male rat offspring

Fluoxetine is often prescribed to treat depression during pregnancy. Rodent studies have shown that fluoxetine exposure during early development can induce persistent changes in the emotional behavior of the offspring. However, the effects of prenatal fluoxetine on memory have not been elucidated. This study evaluates the memory of adult male offspring from rat dams orally administered with a clinically relevant dose of 0.7 mg/kg fluoxetine from 9 weeks before pregnancy to 1 week before delivery. Hippocampal-dependent (Morris Water Maze, MWM) and non-hippocampal-dependent (Novel Object Recognition, NOR) memory paradigms were assessed. Anxiety- and depressive-like symptoms were also evaluated using the Open Field Test, Tail Suspension Test and Sucrose Preference Test. Male rats exposed to fluoxetine during gestation displayed NOR memory impairments during adulthood, as well as increased anxiety- and depressive-like symptoms. In the MWM, the offspring of fluoxetine-treated dams did not show learning deficits. However, a retention impairment was found on remote memory, 15 days after the end of training. Molecular analyses showed increased expression of NMDA subunit NR_2B, and a decrease in NR_2A-to- NR_2B ratio in the temporal cortex, but not in the hippocampus, suggesting changes in NMDA receptor composition. These results suggest that in utero exposure to fluoxetine induces detrimental effects on non-hippocampal memory and in remote retention of hippocampal-dependent memory, which is believed to be stored in the temporal cortex, possibly due to changes in cortical NMDA receptor subunit stoichiometry. The present results warrant the need for studies on potential remote memory deficits in human offspring exposed to fluoxetine in utero.

Is tDCS a potential first line treatment for major depression?

Transcranial direct current stimulation (tDCS) is a novel treatment option for major depression which could be provided as a first-line treatment. tDCS is a non-invasive form of transcranial stimulation which changes cortical tissue excitability by applying a weak (0.5-2 mA) direct current via scalp electrodes. Anodal and cathodal stimulation leads to depolarisation and hyperpolarisation, respectively, and cumulative effects are observed with repeated sessions. The montage in depression most often involves anodal stimulation to the left dorsolateral prefrontal cortex. Rates of clinical response, remission, and improvements in depressive symptoms following a course of active tDCS are greater in comparison to a course of placebo sham-controlled tDCS. In particular, the largest treatment effects are evident in first episode and recurrent major depression, while minimal effects have been observed in treatment-resistant depression. The proposed mechanism is neuroplasticity at the cellular and molecular level. Alterations in neural responses have been found at the stimulation site as well as subcortically in prefrontal-amygdala connectivity. A possible mediating effect could be cognitive control in emotion dysregulation. Additional beneficial effects on cognitive impairments have been reported, which would address an important unmet need. The tDCS device is portable and can be used at home. Clinical trials are required to establish the efficacy, feasibility and acceptability of home-based tDCS treatment and mechanisms.

Ganoderma lucidum polysaccharides ameliorated depression-like behaviors in the chronic social defeat stress depression model via modulation of Dectin-1 and the innate immune system

Major depressive disorder (MDD) is a prevalent, chronic, and recurrent disease. At least one-third of patients have treatment-resistant depression; therefore, there is an urgent need for novel drug development. Cumulative studies have suggested an inflammatory mechanism for the pathophysiology of MDD. Ganoderma lucidum polysaccharides (GLP) is an anti-inflammatory and immunomodulatory agent. Here, we found that an injection of GLP led to a rapid and robust antidepressant effect after 60 min in the tail suspension test. This antidepressant effect remained after 5 days of treatment with GLP in the forced swim test. Unlike psychostimulants, GLP did not show a hyperactive effect in the open field test. After 60 min or 5 days of treatment, GLP exhibited an antidepressant effect in a chronic social defeat stress (CSDS) depression animal model. Moreover, after 5 days of treatment, GLP attenuated the expression of the proinflammatory cytokines IL-1β and TNF-α, enhanced the expression of the anti-inflammatory cytokine IL-10 and the neurotrophic factor BDNF, and inhibited the activation of microglia and proliferation of astrocytes in the hippocampus of CSDS mice. In addition, after 5 days of treatment, GLP significantly enhanced GluA1 S845 phosphorylation as well as GluA1 and GluA2 expression levels in the hippocampus of CSDS mice. To determine whether the antidepressant effect was mediated by Dectin-1, we found that GLP treatment enhanced Dectin-1 expression in the hippocampus in CSDS mice, and the Dectin-1-specific inhibitor laminarin almost completely blocked the antidepressant effect of GLP. This study identified GLP, an agonist of Dectin-1, as a novel and rapid antidepressant with clinical potential and multiple beneficial mechanisms, particularly in regulating the neuroimmune system and, subsequently, AMPA receptor function.

The Influence of Acute SSRI Administration on White Matter Microstructure in Patients Suffering From Major Depressive Disorder and Healthy Controls

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are predominantly prescribed for people suffering from major depressive disorder. These antidepressants exert their effects by blocking the serotonin transporter (SERT), leading to increased levels of serotonin in the synaptic cleft and subsequently to an attenuation of depressive symptoms and elevation in mood. Although long-term studies investigating white matter (WM) alterations after exposure to antidepressant treatment exist, results on the acute effects on the brain's WM microstructure are lacking.

METHODS

In this interventional longitudinal study, 81 participants were included (33 patients and 48 healthy controls). All participants underwent diffusion weighted imaging on 2 separate days, receiving either citalopram or placebo using a randomized, double-blind, cross-over design. Fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity were calculated within the FMRIB software library and analyzed using tract-based spatial statistics.

RESULTS

The repeated-measures ANOVA model revealed significant decreases after SSRI administration in mean diffusivity, axial diffusivity, and radial diffusivity regardless of the group (P < .05, family-wise error [FWE] corrected). Results were predominantly evident in frontal WM regions comprising the anterior corona radiata, corpus callosum, and external capsule and in distinct areas of the frontal blade. No increases in diffusivity were found, and no changes in fractional anisotropy were present.

CONCLUSIONS

Our investigation provides the first evidence, to our knowledge, that fast WM microstructure adaptations within 1 hour after i.v. SSRI administration precede elevations in mood due to SSRI treatment. These results add a new facet to the complex mode of action of antidepressant therapy. This study was registered at clinicaltrials.gov with the identifier NCT02711215.

Memantine in neurological disorders - schizophrenia and depression

Memantine is used in Alzheimer's disease treatment as a non-competitive modern-affinity strong voltage-dependent N-methyl-D-aspartate receptor antagonist. The fundamental role of these receptors is to bind glutamate: the main excitatory neurotransmitter in the brain, believed to play a crucial role in neuronal plasticity and learning mechanisms. Glutamate transmission plays an important role in all internal CNS structures and maintains the physiological state of the brain. Excessive glutamate transmission can lead to enlarged calcium ion current which may cause neurotoxicity; however, insufficient transmission can drastically alter the information flow in neurons and the brain, potentially causing schizophrenia-like symptoms by replacing lost information with completely new stimuli. Hence, it is possible that the modulation of NMDA activity may give rise to pathophysiological states. Available literature and clinical trials indicate that memantine is well tolerated by patients, with very few and light side effects. There is a belief that memantine may also benefit other conditions such as schizophrenia and depression.

Psychedelics in Psychiatry: Neuroplastic, Immunomodulatory, and Neurotransmitter Mechanisms

Mounting evidence suggests safety and efficacy of psychedelic compounds as potential novel therapeutics in psychiatry. Ketamine has been approved by the Food and Drug Administration in a new class of antidepressants, and 3,4-methylenedioxymethamphetamine (MDMA) is undergoing phase III clinical trials for post-traumatic stress disorder. Psilocybin and lysergic acid diethylamide (LSD) are being investigated in several phase II and phase I clinical trials. Hence, the concept of psychedelics as therapeutics may be incorporated into modern society. Here, we discuss the main known neurobiological therapeutic mechanisms of psychedelics, which are thought to be mediated by the effects of these compounds on the serotonergic (via 5-HT2A and 5-HT1A receptors) and glutamatergic [via N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors] systems. We focus on 1) neuroplasticity mediated by the modulation of mammalian target of rapamycin-, brain-derived neurotrophic factor-, and early growth response-related pathways; 2) immunomodulation via effects on the hypothalamic-pituitary-adrenal axis, nuclear factor ĸB, and cytokines such as tumor necrosis factor-α and interleukin 1, 6, and 10 production and release; and 3) modulation of serotonergic, dopaminergic, glutamatergic, GABAergic, and norepinephrinergic receptors, transporters, and turnover systems. We discuss arising concerns and ways to assess potential neurobiological changes, dependence, and immunosuppression. Although larger cohorts are required to corroborate preliminary findings, the results obtained so far are promising and represent a critical opportunity for improvement of pharmacotherapies in psychiatry, an area that has seen limited therapeutic advancement in the last 20 years. Studies are underway that are trying to decouple the psychedelic effects from the therapeutic effects of these compounds. SIGNIFICANCE STATEMENT: Psychedelic compounds are emerging as potential novel therapeutics in psychiatry. However, understanding of molecular mechanisms mediating improvement remains limited. This paper reviews the available evidence concerning the effects of psychedelic compounds on pathways that modulate neuroplasticity, immunity, and neurotransmitter systems. This work aims to be a reference for psychiatrists who may soon be faced with the possibility of prescribing psychedelic compounds as medications, helping them assess which compound(s) and regimen could be most useful for decreasing specific psychiatric symptoms.

Mechanisms Underlying the Antidepressant Effect of Acupuncture via the CaMK Signaling Pathway

The CaMK pathway has been proven to play an important role in regulating cognitive function and emotional response. Acupuncture through the CaMK pathway improves depression-like behavior and the molecular mechanism related to its antidepressant remains to be explored. In this study, we aimed to determine whether the ability of acupuncture at Baihui (GV20) and Shenting (GV24) points to treat depression is related to the regulation of key proteins in the CaMK pathway. A rat model of depression was induced by chronic unpredicted mild stress (CUMS). Model rats in the electroacupuncture group were subjected to acupuncture at the Baihui (GV20) and Shenting (GV24) acupoints once a day for 20 min. Model rats in the fluoxetine group were gavaged with fluoxetine (1.8 mg/kg). Immunohistochemistry and Western blotting assays were used to evaluate immunoreactivity for and the protein expression levels of CaMKII, CaMKIV, and CaM. The results showed that electroacupuncture had a significant effect in rats with depression. Electroacupuncture and fluoxetine regulated the expression of key proteins in the CaMK signaling pathway, which is related to depression, in the hippocampi of rats. This indicates that acupuncture at Baihui (GV20) and Shenting (GV24) may alleviate depressive symptoms and reduce work- and life-related burdens and stress by regulating the CaMK signaling pathway.

AMPA receptors mediate the pro-cognitive effects of electrical and optogenetic stimulation of the medial prefrontal cortex in antidepressant non-responsive Wistar-Kyoto rats

BACKGROUND

The chronic mild stress (CMS) procedure is a widely used animal model of depression, and its application in Wistar-Kyoto (WKY) rats has been validated as a model of antidepressant-refractory depression. While not responding to chronic treatment with antidepressant drugs, WKY rats do respond to acute deep brain stimulation (DBS) of the medial prefrontal cortex (mPFC). In antidepressant-responsive strains there is evidence suggesting a role for AMPA subtype of glutamate receptor in the action mechanism of both antidepressants and DBS.

METHODS

Animals were subjected to CMS for 6 to 8 weeks; sucrose intake was monitored weekly and novel object recognition (NOR) test was conducted following recovery from CMS. Wistars were treated chronically with venlafaxine (VEN), while WKY were treated acutely with either DBS, optogenetic stimulation (OGS) of virally-transduced (AAV5-hSyn-ChR2-EYFP) mPFC or ventral hippocampus, or acute intra-mPFC injection of the AMPA receptor positive allosteric modulator CX-516. The AMPA receptor antagonist NBQX was administered, at identical sites in mPFC, immediately following the exposure trial in the NOR.

RESULTS

Sucrose intake and NOR were suppressed by CMS, and restored by VEN in Wistars and by DBS, OGS, or CX-516 in WKY. However, OGS of the ventral hippocampal afferents to mPFC was ineffective. A low dose of NBQX selectively blocked the procognitive effect of VEN, DBS and OGS.

CONCLUSIONS

These results suggest that activation of AMPA receptors in the mPFC represents a common pathway for the antidepressant effects of both conventional (VEN) and novel (DBS, OGS) antidepressant modalities, in both antidepressant responsive (Wistar) and antidepressant-resistant (WKY) rats.

Asparagus cochinchinensis extract ameliorates menopausal depression in ovariectomized rats under chronic unpredictable mild stress

BACKGROUND

Depression is a serious and common psychiatric disorder generally affecting more women than men. A woman's risk of developing depression increases steadily with age, and higher incidence is associated with the onset of menopause. Here we evaluated the antidepressant properties of Asparagus cochinchinensis (AC) extract and investigated its underlying mechanisms in a rat menopausal depression model.

METHODS

To model this menopausal depression, we induced a menopause-like state in rats via ovariectomy and exposed them to chronic unpredictable mild stress (CUMS) for 6 weeks, which promotes the development of depression-like symptoms. During the final 4 weeks of CUMS, rats were treated with either AC extract (1000 or 2000 mg/kg, PO), which has been reported to provide antidepressant effects, or with the tricyclic antidepressant imipramine (10 mg/kg, IP).

RESULTS

We report that CUMS promotes depression-like behavior and significantly increases serum corticosterone and inflammatory cytokine levels in the serum of ovariectomized (OVX) rats. We also found that CUMS decreases the expression of brain-derived neurotrophic factor (BDNF) and its primary receptor, tropomyosin receptor kinase B (TrkB), in OVX rats, and treatment with AC extract rescues both BDNF and TrkB expression levels.

CONCLUSION

These results suggest that AC extract exerts antidepressant effects, possibly via modulation of the BDNF-TrkB pathway, in a rat model of menopausal depression.

TNF-Mediated Homeostatic Synaptic Plasticity: From in vitro to in vivo Models

Since it was first described almost 30 years ago, homeostatic synaptic plasticity (HSP) has been hypothesized to play a key role in maintaining neuronal circuit function in both developing and adult animals. While well characterized in vitro, determining the in vivo roles of this form of plasticity remains challenging. Since the discovery that the pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) mediates some forms of HSP, it has been possible to probe some of the in vivo contribution of TNF-mediated HSP. Work from our lab and others has found roles for TNF-HSP in a variety of functions, including the developmental plasticity of sensory systems, models of drug addiction, and the response to psychiatric drugs.

Effects of adolescent administration of fluoxetine on novel object recognition memory, anxiety-like behaviors, and hippocampal brain-derived neurotrophic factor level

AIMS

Fluoxetine (FLX) is a common selective serotonin reuptake inhibitor, which is used in adolescents with psychiatric disorders. Controversial results have been obtained in different studies about the effects of FLX on cognitive functions. The present study was designed to examine the effects of chronic FLX exposure during adolescence on cognitive function, anxiety-like behaviors, and hippocampal brain-derived neurotrophic factor (BDNF) mRNA expression among adult male and female rats.

MAIN METHODS

The sex-dependent effects of FLX chronic administration during adolescence (5 mg/kg/day, gavage) on short-term novel object recognition memory (NORM), anxiety-like behaviors, and BDNF mRNA expression in the hippocampus were examined. NORM and anxiety-like behaviors were assessed by novel object recognition, open field, and elevated plus-maze (EPM) tests, respectively. The expression of BDNF mRNA was also evaluated by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR).

KEY FINDINGS

The present findings revealed the dysfunction of short-term NORM among the adolescent male and female rats exposed to FLX, while the mRNA expression of BDNF was significantly higher among the males. Moreover, adolescent FLX administration had different effects on the anxiety-like behaviors of the male and female rats. Adolescent FLX treatment also decreased the body weight of the male animals.

SIGNIFICANCE

In conclusion, adolescent FLX treatment impairs cognitive functions in both sexes and increases BDNF mRNA expression in the hippocampus of the male animals. FLX administration during adolescence has sex-dependent effects on anxiety-like behaviors. These findings indicate that the impairment of cognitive functions can occur following the adolescent manipulation of the serotonergic system. Therefore, the side effects of chronic FLX administration during adolescence should be more considered.

Nucleus Reuniens Lesion and Antidepressant Treatment Prevent Hippocampal Neurostructural Alterations Induced by Chronic Mild Stress in Male Rats

The hippocampus-prefrontal cortex circuit plays a major role in stress and in the neurobiology of depression and its treatment. Disruption of this circuit by lesioning the thalamic nucleus reuniens (RE) has been shown to prevent the detrimental effects of chronic mild stress on prefrontal cortex neuroplasticity indices in male rats. However, it remains unknown whether hippocampal neurostructural response to stress is modified by RE lesion. In the present study, adult male rats were subjected to the chronic mild stress model of depression and were treated with either vehicle or an antidepressant (i.e. sertraline). Moreover, a group of animals was subjected to RE lesion before stress exposure with or without sertraline treatment. We demonstrated that chronic mild stress induced hippocampal CA1 dendritic atrophy and this was prevented by pre-stress RE lesion to the same extent that antidepressant treatment reversed it. The present findings highlight the importance of hippocampal-prefrontal cortex communication in chronic stress effects on hippocampal neuroplasticity and contribute to the elucidation of the role of RE in neurostructural changes underlying stress-driven depression and its treatment.

Paroxetine ameliorates prodromal emotional dysfunction and late-onset memory deficit in Alzheimer's disease mice

Background

Neuropsychiatric symptoms (NPS) such as depression, anxiety, apathy, and irritability occur in prodromal phases of clinical Alzheimer’s disease (AD), which might be an increased risk for later developing AD. Here we treated young APP/PS1 AD model mice prophylactically with serotonin-selective re-uptake inhibitor (SSRI) paroxetine and investigated the protective role of anti-depressant agent in emotional abnormalities and cognitive defects during disease progress.

Methods

To investigate the protective role of paroxetine in emotional abnormalities and cognitive defects during disease progress, we performed emotional behaviors of 3 months old APP/PS1 mouse following oral administration of paroxetine prophylactically starting at 1 month of age. Next, we tested the cognitive, biochemical and pathological, effects of long term administration of paroxetine at 6 months old.

Results

Our results showed that AD mice displayed emotional dysfunction in the early stage. Prophylactic administration of paroxetine ameliorated the initial emotional abnormalities and preserved the eventual memory function in AD mice.

Conclusion

Our data indicate that prophylactic administration of paroxetine ameliorates the emotional dysfunction and memory deficit in AD mice. These neuroprotective effects are attributable to functional restoration of glutamate receptor (GluN2A) in AD mice.

Psychedelics, but Not Ketamine, Produce Persistent Antidepressant-like Effects in a Rodent Experimental System for the Study of Depression

Psilocybin shows efficacy to alleviate depression in human clinical trials for six or more months after only one or two treatments. Another hallucinogenic drug, esketamine, has recently been U.S. Food and Drug Administration (FDA)-approved as a rapid-acting antidepressant. The mechanistic basis for the antidepressant effects of psilocybin and ketamine appear to be conserved. The efficacy of these two medications has not, however, been directly compared either clinically or preclinically. Further, whether or not a profound subjective existential experience is necessary for psilocybin to have antidepressant effects is unknown. To address these questions, we tested psilocybin, lysergic acid diethylamide (LSD), and ketamine in a rat model for depression. As in humans, a single administration of psilocybin or LSD produced persistent antidepressant-like effects in our model. In contrast, ketamine produced only a transient antidepressant-like effect. Our results indicate that classic psychedelics may have therapeutic efficacy that is more persistent than that of ketamine, and also suggest that a subjective existential experience may not be necessary for therapeutic effects.

Experience-Dependent Changes in Myelin Basic Protein Expression in Adult Visual and Somatosensory Cortex

An experience-driven increase in oligodendrocytes and myelin in the somatosensory cortex (S1) has emerged as a new marker of adult cortical plasticity. That finding contrasts with the view that myelin is a structural brake on plasticity, and that contributes to ending the critical period (CP) in the visual cortex (V1). Despite the evidence that myelin-derived signaling acts to end CP in V1, there is no information about myelin changes during adult plasticity in V1. To address this, we quantified the effect of three manipulations that drive adult plasticity (monocular deprivation (MD), fluoxetine treatment or the combination of MD and fluoxetine) on the expression of myelin basic protein (MBP) in adult rat V1. In tandem, we validated that environmental enrichment (EE) increased cortical myelin by measuring MBP in adult S1. For comparison with the MBP measurements, three plasticity markers were also quantified, the spine markers drebrin E and drebrin A, and a plasticity maintenance marker Ube3A. First, we confirmed that EE increased MBP in S1. Next, that expression of the plasticity markers was affected in S1 by EE and in V1 by the visual manipulations. Finally, we found that after adult MD, MBP increased in the non-deprived V1 hemisphere, but it decreased in the deprived hemisphere, and those changes were not influenced by fluoxetine. Together, the findings suggest that modulation of myelin expression in adult V1 may reflect the levels of visually driven activity rather than synaptic plasticity caused by adult plasticity.

Targeting the Neuronal Activity of Prefrontal Cortex: New Directions for the Therapy of Depression

Depression is one of the prevalent psychiatric illnesses with a comprehensive performance such as low self-esteem, lack of motivation, anhedonia, poor appetite, low energy, and uncomfortableness without a specific cause. So far, the cause of depression is not very clear, but it is certain that many aspects of biological psychological and social environment are involved in the pathogenesis of depression. Recently, the prefrontal cortex (PFC) has been indicated to be a pivotal brain region in the pathogenesis of depression. And increasing evidence showed that the abnormal activity of the PFC neurons is linked with depressive symptoms. Unveiling the molecular and cellular, as well as the circuit properties of the PFC neurons will help to find out how abnormalities in PFC neuronal activity are associated with depressive disorders. In addition, concerning many antidepressant drugs, in this review, we concluded the effect of several antidepressants on PFC neuronal activity to better understand its association with depression.

Neurotrophic mechanisms underlying the rapid and sustained antidepressant actions of ketamine

Clinical and preclinical studies have demonstrated that depression, one of the most common psychiatric illnesses, is associated with reduced levels of neurotrophic factors, including brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), contributing to neuronal atrophy in the prefrontal cortex (PFC) and hippocampus, and reduced hippocampal adult neurogenesis. Conventional monoaminergic antidepressants can block/reverse, at least partially, these deficits in part via induction of BDNF and/or VEGF, although these drugs have significant limitations, notably a time lag for therapeutic response and low response rates. Recent studies reveal that ketamine, an N-methyl-d-aspartate receptor antagonist produces rapid (within hours) and sustained (up to a week) antidepressant actions in both patients with treatment-resistant depression and rodent models of depression. Rodent studies also demonstrate that ketamine rapidly increases BDNF and VEGF release and/or expression in the medial PFC (mPFC) and hippocampus, leading to increase in the number and function of spine synapses in the mPFC and enhancement of hippocampal neurogenesis. These neurotrophic effects of ketamine are associated with the antidepressant effects of this drug. Together, these findings provide evidence for a neurotrophic mechanism underlying the rapid and sustained antidepressant actions of ketamine and pave the way for the development of rapid and more effective antidepressants with fewer side effects than ketamine.

Chronic Fluoxetine Treatment Induces Maturation-Compatible Changes in the Dendritic Arbor and in Synaptic Responses in the Auditory Cortex

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) used to treat mood and anxiety disorders. Chronic treatment with this antidepressant drug is thought to favor functional recovery by promoting structural and molecular changes in several forebrain areas. At the synaptic level, chronic fluoxetine induces an increased size and density of dendritic spines and an increased ratio of GluN2A over GluN2B N-methyl-D-aspartate (NMDA) receptor subunits. The "maturation"-promoting molecular changes observed after chronic fluoxetine should also induce structural remodeling of the neuronal dendritic arbor and changes in the synaptic responses. We treated adult rats with fluoxetine (0.7 mg/kg i.p. for 28 days) and performed a morphometric analysis using Golgi stain in limbic and nonlimbic cortical areas. Then, we focused especially on the auditory cortex, where we evaluated the dendritic morphology of pyramidal neurons using a 3-dimensional reconstruction of neurons expressing mRFP after in utero electroporation. With both methodologies, a shortening and decreased complexity of the dendritic arbors was observed, which is compatible with an increased GluN2A over GluN2B ratio. Recordings of extracellular excitatory postsynaptic potentials in the auditory cortex revealed an increased synaptic response after fluoxetine and were consistent with an enrichment of GluN2A-containing NMDA receptors. Our results confirm that fluoxetine favors maturation and refinement of extensive cortical networks, including the auditory cortex. The fluoxetine-induced receptor switch may decrease GluN2B-dependent toxicity and thus could be applied in the future to treat neurodegenerative brain disorders characterized by glutamate toxicity and/or by an aberrant network connectivity.

The tricyclic antidepressant clomipramine inhibits neuronal autophagic flux

Antidepressants are commonly prescribed psychotropic substances for the symptomatic treatment of mood disorders. Their primary mechanism of action is the modulation of neurotransmission and the consequent accumulation of monoamines, such as serotonin and noradrenaline. However, antidepressants have additional molecular targets that, through multiple signaling cascades, may ultimately alter essential cellular processes. In this regard, it was previously demonstrated that clomipramine, a widely used FDA-approved tricyclic antidepressant, interferes with the autophagic flux and severely compromises the viability of tumorigenic cells upon cytotoxic stress. Consistent with this line of evidence, we report here that clomipramine undermines autophagosome formation and cargo degradation in primary dissociated neurons. A similar pattern was observed in the frontal cortex and liver of treated mice, as well as in the nematode Caenorhabditis elegans exposed to clomipramine. Together, our findings indicate that clomipramine may negatively regulate the autophagic flux in various tissues, with potential metabolic and functional implications for the homeostatic maintenance of differentiated cells.

Repeated fluoxetine treatment induces long-lasting neurotrophic changes in the medial prefrontal cortex of adult rats

Fluoxetine (Flx), a selective serotonin reuptake inhibitor, is extensively used to treat mood and anxiety disorders. Previous animal studies have shown that early-life exposure to Flx results in long-lasting behavioral alterations and neuroplasticity in the hippocampus and cortex, which may persist into adulthood. It remains unclear whether repeated Flx treatment in normal adult animals can induce lasting neuroplasticity and behavioral alterations persisting long beyond the treatment period. In this study, young adult rats (about 9 weeks old) were treated with Flx (10 mg/kg body weight, twice daily) for 15 consecutive days, and the effects of Flx on medial prefrontal cortex (mPFC) neuroplasticity and mPFC-related behaviors were assessed 20 days after the last injection. It was observed that the mPFC of Flx-treated rats had significant increases in the number of 5-bromodeoxyuridine-positive (BrdU⁺) cells, dendritic complexity/spine density in layer II/III pyramidal neurons, and brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) expression levels, as well as a significant decrease in the number of parvalbumin-positive (PV⁺) interneurons. The Flx-treated rats exhibited higher motivation to explore new environments, evidenced by a significantly increased number of entries into the novel arm in the Y-maze test. However, they did not show any significant changes in the anhedonia and anxiety levels measured by sucrose preference and elevated plus maze tests respectively. In conclusion, repeated Flx treatment, with the paradigm used, induces long-lasting neuroplastic changes in the mPFC of normal adult rats; such changes and related behavioral manifestations may persist up to 20 days after the last dose.

N-Methyl D-aspartate receptor subunit signaling in fear extinction

N-Methyl D-aspartate receptors (NMDAR) are central mediators of glutamate actions underlying learning and memory processes including those required for extinction of fear and fear-related behaviors. Consistent with this view, in animal models, antagonists of NMDAR typically impair fear extinction, whereas partial agonists have facilitating effects. Promoting NMDAR function has thus been recognized as a promising strategy towards reduction of fear symptoms in patients suffering from anxiety disorders and post-traumatic disorder (PTSD). Nevertheless, application of these drugs in clinical trials has proved of limited utility. Here we summarize recent advances in our knowledge of NMDAR pharmacology relevant for fear extinction, focusing on molecular, cellular, and circuit aspects of NMDAR function as they relate to fear extinction at the level of behavior and cognition. We also discuss how these advances from animal models might help to understand and overcome the limitations of existing approaches in human anxiety disorders and how novel, more specific, and personalized approaches might help advance future therapeutic strategies.

Effects of Paroxetine on Motor and Cognitive Function Recovery in Patients with Non-Depressed Ischemic Stroke: An Open Randomized Controlled Study

Introduction: To investigate the effects of paroxetine (PAR) on motor and cognitive function recovery in patients with non-depressed ischemic stroke (nD-AIS).

Methods: One hundred sixty-seven patients hospitalized for non-depressed acute ischemic stroke were selected and divided into treatment (T) and control (C) groups using a random number table. All patients received conventional secondary ischemic stroke prevention and rehabilitation training; patients in Group T additionally received treatment with PAR (10 mg/day during week 1 and 20 mg/day thereafter) for 3 months. The follow-up observation lasted 6 months. The Fugl–Meyer motor scale (FMMS), Montreal cognitive assessment (MoCA), and Hamilton depression scale (HAMD) were used on D0, D15, D90, and D180 (T0, 1, 2, and 3, respectively; D180 = 90 days after treatment cessation) after study initiation, and scores were compared between the groups.

Results: The FMMS and MoCA scores differed significantly between Groups T and C at T2 and T3 (p < .05); by contrast, these scores did not differ significantly between the groups at T1 (p > .05). Furthermore, the HAMD scores differed significantly between the two groups at T3 (p < .05), but not at T1 and T2 (p > .05).

Conclusions: PAR treatment may improve motor and cognitive function recovery in patients with nD-AIS. Moreover, PAR may reduce the occurrence of depression after stroke.

Nucleocytoplasmic export of HDAC5 and SIRT2 downregulation: two epigenetic mechanisms by which antidepressants enhance synaptic plasticity markers

RATIONALE

Antidepressant action has been linked to increased synaptic plasticity in which epigenetic mechanisms such as histone posttranslational acetylation could be involved. Interestingly, the histone deacetylases HDAC5 and SIRT2 are oppositely regulated by stress and antidepressants in mice prefrontal cortex (PFC). Besides, the neuroblastoma SH-SY5Y line is an in vitro neuronal model reliable to study drug effects with clear advantages over animals.

OBJECTIVES

We aimed to characterize in vitro the role of HDAC5 and SIRT2 in antidepressant regulation of neuroplasticity.

METHODS

SH-SY5Y cultures were incubated with imipramine, fluoxetine, and reboxetine (10 μM, 2 and 24 h) as well as the selective HDAC5 (MC3822, 5 μM, 24 h) or SIRT2 (33i, 5 μM, 24 h) inhibitors. The regulation of the brain-derived neurotrophic factor (BDNF), the vesicular glutamate transporter 1 (VGLUT1), the acetylated histones 3 (AcH3) and 4 (AcH4), HDAC5, and SIRT2 was studied. Comparatively, the long-term effects of these antidepressants (21 days, i.p.) in the mice (C57BL6, 8 weeks) PFC were studied.

RESULTS

Antidepressants increased both in vitro and in vivo expression of BDNF, VGLUT1, AcH3, and AcH4. Moreover, imipramine and reboxetine increased the phosphorylated form of HDAC5 (P-HDAC5), mediating its cytoplasmic export. Further, SIRT2 was downregulated by all antidepressants. Finally, specific inhibition of HDAC5 and SIRT2 increased neuroplasticity markers.

CONCLUSIONS

This study supports the validity of the SH-SY5Y model for studying epigenetic changes linked to synaptic plasticity induced by antidepressants as well as the effect of selective HDAC inhibitors. Particularly, nucleocytoplasmic export of HDAC5 and SIRT2 downregulation mediated by antidepressants could enhance synaptic plasticity markers leading to antidepressant action.

Cannabidiol Induces Rapid and Sustained Antidepressant-Like Effects Through Increased BDNF Signaling and Synaptogenesis in the Prefrontal Cortex

Currently available antidepressants have a substantial time lag to induce therapeutic response and a relatively low efficacy. The development of drugs that addresses these limitations is critical to improving public health. Cannabidiol (CBD), a non-psychotomimetic component of Cannabis sativa, is a promising compound since it shows large-spectrum therapeutic potential in preclinical models and humans. However, its antidepressant properties have not been completely investigated. Therefore, the aims of this study were to investigate in male rodents (i) whether CBD could induce rapid and sustained antidepressant-like effects after a single administration and (ii) whether such effects could be related to changes in synaptic proteins/function. Results showed that a single dose of CBD dose-dependently induced antidepressant-like effect (7-30 mg/kg) in Swiss mice submitted to the forced swim test (FST), 30 min (acute) or 7 days (sustained) following treatment. Similar effects were observed in the Flinders Sensitive and Flinders Resistant Line (FSL/FRL) rats and the learned helplessness (LH) paradigm using Wistar rats. The acute antidepressant effects (30 min) were associated with increased expression of synaptophysin and PSD95 in the medial prefrontal cortex (mPFC) and elevated BDNF levels in both mPFC and hippocampus (HPC). CBD also increased spine density in the mPFC after 30 min, but not 7 days later. Intracerebroventricular injection of the TrkB antagonist, K252a (0.05 nmol/μL), or the mTOR inhibitor, rapamycin (1 nmol/μL), abolished the behavioral effects of CBD. These results indicate that CBD induces fast and sustained antidepressant-like effect in distinct animal models relevant for depression. These effects may be related to rapid changes in synaptic plasticity in the mPFC through activation of the BDNF-TrkB signaling pathway. The data support a promising therapeutic profile for CBD as a new fast-acting antidepressant drug.

Epigenetic mechanisms of major depression: Targeting neuronal plasticity

Major depressive disorder is one of the most common mental illnesses as it affects more than 350 million people globally. Major depressive disorder is etiologically complex and disabling. Genetic factors play a role in the etiology of major depression. However, identical twin studies have shown high rates of discordance, indicating non-genetic mechanisms as well. For instance, stressful life events increase the risk of depression. Environmental stressors also induce stable changes in gene expression within the brain that may lead to maladaptive neuronal plasticity in regions implicated in disease pathogenesis. Epigenetic events alter the chromatin structure and thus modulate expression of genes that play a role in neuronal plasticity, behavioral response to stress, depressive behaviors, and response to antidepressants. Here, we review new information regarding current understanding of epigenetic events that may impact depression. In particular, we discuss the roles of histone acetylation, DNA methylation, and non-coding RNA. These novel mechanisms of action may lead to new therapeutic strategies for treating major depression.

Modeling consequences of prolonged strong unpredictable stress in zebrafish: Complex effects on behavior and physiology

Chronic stress is the major pathogenetic factor of human anxiety and depression. Zebrafish (Danio rerio) have become a novel popular model species for neuroscience research and CNS drug discovery. The utility of zebrafish for mimicking human affective disorders is also rapidly growing. Here, we present a new zebrafish model of clinically relevant, prolonged unpredictable strong chronic stress (PUCS). The 5-week PUCS induced overt anxiety-like and motor retardation-like behaviors in adult zebrafish, also elevating whole-body cortisol and proinflammatory cytokines - interleukins IL-1β and IL-6. PUCS also elevated whole-body levels of the anti-inflammatory cytokine IL-10 and increased the density of dendritic spines in zebrafish telencephalic neurons. Chronic treatment of fish with an antidepressant fluoxetine (0.1mg/L for 8days) normalized their behavioral and endocrine phenotypes, as well as corrected stress-elevated IL-1β and IL-6 levels, similar to clinical and rodent data. The CNS expression of the bdnf gene, the two genes of its receptors (trkB, p75), and the gfap gene of glia biomarker, the glial fibrillary acidic protein, was unaltered in all three groups. However, PUCS elevated whole-body BDNF levels and the telencephalic dendritic spine density (which were corrected by fluoxetine), thereby somewhat differing from the effects of chronic stress in rodents. Together, these findings support zebrafish as a useful in-vivo model of chronic stress, also calling for further cross-species studies of both shared/overlapping and distinct neurobiological responses to chronic stress.

The Aqueous Crude Extracts of Montanoa frutescens and Montanoa grandiflora Reduce Immobility Faster Than Fluoxetine Through GABAA Receptors in Rats Forced to Swim

BACKGROUND

Montanoa frutescens and Montanoa grandiflora have been indistinctly used for centuries in traditional Mexican medicine for reproductive impairments, anxiety, and mood disorders. Preclinical studies support their aphrodisiac and anxiolytic properties, but their effects on mood are still unexplored.

METHODS

The effects of 25 and 50 mg/kg of M frutescens and M grandiflora extracts were evaluated on days 1, 7, 14, 21, and 28 of treatment, and compared with fluoxetine (1 mg/kg) and Remotiv (7.14 mg/kg) in Wistar rats. The participation of GABAA receptor in the effects produced by the treatments was explored.

RESULTS

Montanoa extracts reduced immobility since day 1 of treatment, while fluoxetine and Remotiv required 14 days. The GABAA antagonism blocked the effects of Montanoa extracts, but not of fluoxetine or Remotiv.

CONCLUSIONS

Montanoa extracts prevented quickly the stress-induced behaviors in the swimming test through action at the GABAA receptor, exerting a protective effect different to the typical antidepressants drugs.

Neural Plasticity Is Involved in Physiological Sleep, Depressive Sleep Disturbances, and Antidepressant Treatments

Depression, which is characterized by a pervasive and persistent low mood and anhedonia, greatly impacts patients, their families, and society. The associated and recurring sleep disturbances further reduce patient's quality of life. However, therapeutic sleep deprivation has been regarded as a rapid and robust antidepressant treatment for several decades, which suggests a complicated role of sleep in development of depression. Changes in neural plasticity are observed during physiological sleep, therapeutic sleep deprivation, and depression. This correlation might help us to understand better the mechanism underlying development of depression and the role of sleep. In this review, we first introduce the structure of sleep and the facilitated neural plasticity caused by physiological sleep. Then, we introduce sleep disturbances and changes in plasticity in patients with depression. Finally, the effects and mechanisms of antidepressants and therapeutic sleep deprivation on neural plasticity are discussed.