5-HTT independent effects of fluoxetine on neuroplasticity

The beneficial effect of fluoxetine on behavioral and cognitive changes in chronic experimental Chagas disease unveils the role of serotonin fueling astrocyte infection by Trypanosoma cruzi

BACKGROUND

In Chagas disease (CD), a neglected tropical disease caused by the parasite Trypanosoma cruzi, the development of mental disorders such as anxiety, depression, and memory loss may be underpinned by social, psychological, and biological stressors. Here, we investigated biological factors underlying behavioral changes in a preclinical model of CD.

METHODOLOGY/PRINCIPAL FINDINGS

In T. cruzi-infected C57BL/6 mice, a kinetic study (5 to 150 days postinfection, dpi) using standardized methods revealed a sequential onset of behavioral changes: reduced innate compulsive behavior, followed by anxiety and depressive-like behavior, ending with progressive memory impairments. Hence, T. cruzi-infected mice were treated (120 to 150 dpi) with 10 mg/Kg/day of the selective serotonin reuptake inhibitor fluoxetine (Fx), an antidepressant that favors neuroplasticity. Fx therapy reversed the innate compulsive behavior loss, anxiety, and depressive-like behavior while preventing or reversing memory deficits. Biochemical, histological, and parasitological analyses of the brain tissue showed increased levels of the neurotransmitters GABA/glutamate and lipid peroxidation products and decreased expression of brain-derived neurotrophic factor in the absence of neuroinflammation at 150 dpi. Fx therapy ameliorated the neurochemical changes and reduced parasite load in the brain tissue. Next, using the human U-87 MG astroglioma cell line, we found no direct effect of Fx on parasite load. Crucially, serotonin/5-HT (Ser/5-HT) promoted parasite uptake, an effect increased by prior stimulation with IFNγ and TNF but abrogated by Fx. Also, Fx blocked the cytokine-driven Ser/5-HT-promoted increase of nitric oxide and glutamate levels in infected cells.

CONCLUSION/SIGNIFICANCE

We bring the first evidence of a sequential onset of behavioral changes in T. cruzi-infected mice. Fx therapy improves behavioral and biological changes and parasite control in the brain tissue. Moreover, in the central nervous system, cytokine-driven Ser/5-HT consumption may favor parasite persistence, disrupting neurotransmitter balance and promoting a neurotoxic environment likely contributing to behavioral and cognitive disorders.

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.

Therapeutic Strategies Aimed at Improving Neuroplasticity in Alzheimer Disease

Alzheimer disease (AD) is the most prevalent form of dementia among elderly people. Owing to its varied and multicausal etiopathology, intervention strategies have been highly diverse. Despite ongoing advances in the field, efficient therapies to mitigate AD symptoms or delay their progression are still of limited scope. Neuroplasticity, in broad terms the ability of the brain to modify its structure in response to external stimulation or damage, has received growing attention as a possible therapeutic target, since the disruption of plastic mechanisms in the brain appear to correlate with various forms of cognitive impairment present in AD patients. Several pre-clinical and clinical studies have attempted to enhance neuroplasticity via different mechanisms, for example, regulating glucose or lipid metabolism, targeting the activity of neurotransmitter systems, or addressing neuroinflammation. In this review, we first describe several structural and functional aspects of neuroplasticity. We then focus on the current status of pharmacological approaches to AD stemming from clinical trials targeting neuroplastic mechanisms in AD patients. This is followed by an analysis of analogous pharmacological interventions in animal models, according to their mechanisms of action.

Cognitive impairment after cancer treatment: mechanisms, clinical characterization, and management

Cognitive impairment is a debilitating side effect experienced by patients with cancer treated with systemically administered anticancer therapies. With around 19.3 million new cases of cancer worldwide in 2020 and the five year survival rate growing from 50% in 1970 to 67% in 2013, an urgent need exists to understand enduring side effects with severe implications for quality of life. Whereas cognitive impairment associated with chemotherapy is recognized in patients with breast cancer, researchers have started to identify cognitive impairment associated with other treatments such as immune, endocrine, and targeted therapies only recently. The underlying mechanisms are diverse and therapy specific, so further evaluation is needed to develop effective therapeutic interventions. Drug and non-drug management strategies are emerging that target mechanistic pathways or the cognitive deficits themselves, but they need to be rigorously evaluated. Clinically, consistent use of objective diagnostic tools is necessary for accurate diagnosis and clinical characterization of cognitive impairment in patients treated with anticancer therapies. This should be supplemented with clinical guidelines that could be implemented in daily practice. This review summarizes the recent advances in the mechanisms, clinical characterization, and novel management strategies of cognitive impairment associated with treatment of non-central nervous system cancers.

Recovery in Stroke Patients Treated With Fluoxetine Versus Placebo: A Pooled Analysis of 7,165 Patients

BACKGROUND

Stroke is a major cause of disability and death. Stroke recovery outcomes range from functional impairment to disability. This study was designed to compare the recovery results of stroke patients treated with fluoxetine to those treated with placebo.

REVIEW SUMMARY

Seventeen randomized clinical trials were identified by searching PubMed, Cochrane, Scopus, and Web of Science until June 2021. Fluoxetine enhances the National Institutes of Health Stroke Scale (NIHSS) score [mean difference (MD)=-0.67, 95% confidence interval (CI) (-1.19 to -0.15)] and the Fugl-Meyer Motor Scale (FMMS) score [MD=17.36, 95% CI (12.12-22.61)] at the 3-month follow up. However, the NIHSS score showed no significant difference between the 2 groups at 2 weeks [MD=-0.32, 95% CI (-0.72 to 0.07)] or at 6 months [MD=-0.17, 95% CI (-0.47 to 0.14)]. Fluoxetine-treated and placebo-treated patients had the same overall impact on FMMS scores at 1 month ( P =0.41). Barthel index showed no significant difference between the 2 arms at 3 months ( P =0.21) or 6 months ( P =0.68). Fluoxetine-treated patients were at a higher risk of broken bone [risk ratios (RR)=2.30, 95% CI (1.59-3.32)] and hyponatremia [RR=2.12, 95% CI (1.19-3.76)], and at lower risk of new depression [RR=0.72, 95% CI (0.61-0.84)] in comparison with placebo.

CONCLUSION

The efficacy of fluoxetine on the NIHSS and FMMS is likely to take time to emerge and is expected to be transient. The Barthel index score did not differ between the fluoxetine and placebo groups. The use of fluoxetine increased the incidence of hyponatremia and bone fractures while decreasing the risk of new-onset depression.

Neuroprotective effects of aripiprazole in stress-induced depressive-like behavior: Possible role of CACNA1C

BACKGROUND

Depression is the most common psychiatric disorder. Recently, aripiprazole, a novel antipsychotic drug, has been approved as the adjunctive therapy for the Treatment-Resistant Depression (TRD). However, the mechanisms underlying the antidepressant effects of aripiprazole are not fully known. Besides the involvement of calcium signaling dysregulations in the pathophysiology of depression, there is some evidence of overexpressed CACNA1C (the gene encoding the Cav1.2 channels) following chronic stress in the brain regions, which involved in emotional and stress responses. Based on the data indicating the aripiprazole's effects on intracellular calcium levels, this study aimed to investigate the mechanisms of therapeutic effects of aripiprazole, by a focus on the modulation of CACNA1C expression, in the rat stress-induced model of depression.

METHODS

Using Chronic Unpredictable Mild Stress (CUMS) model of depression, we examined the effects of aripiprazole on depressive and anxiety-like behaviors (by forced swimming test and elevated plus maze), serum IL-6 (Elisa), and cell survival (Nissl staining). In addition, CACNA1C, BDNF, and TrkB expression in the PFC and hippocampus (RT-qPCR), as well as BDNF and GAP-43 protein levels in the hippocampus (Immunohistofluorescence), have been assayed.

RESULTS

Our data indicated that aripiprazole could improve anxiety and depressive-like behaviors, decrease the serum levels of IL-6 and hippocampal cell death following CUMS. In addition, we showed the significant modulation on overexpressed CACNA1C, as well as downregulated BDNF and GAP-43 expression DISCUSSION: These results demonstrate that aripiprazole may promote synaptic plasticity by improving the expression of BDNF and gap-43. In addition, inflammation reduction and CACNA1C expression downregulation may be some of mechanisms by which aripiprazole alleviates chronic stress-induced hippocampal cell death and play its pivotal antidepressant role.

Brief Maternal Separation Promotes Resilience to Anxiety-like and Depressive-like Behaviors in Female C57BL/6J Offspring with Imiquimod-Induced Psoriasis

Background: Psoriasis is a common chronic inflammatory skin disease that often causes depression. Early life experience affects brain development and relates to depression. Whether the effect of different MS protocols in early life on anxiety-like and depressive-like behaviors in female offspring with imiquimod (IMQ)-induced psoriasis is unknown. Methods: C57BL/6J mice were subjected to no separation (NMS), brief MS (15 min/day, MS15) or long MS (180 min/day, MS180) from postpartum days (PPD) 1 to PPD21. Then, 5% imiquimod cream was applied for 8 days in adults. Behavioral tests, skin lesions and hippocampal protein expression were also assessed. Results: We found significant psoriasis-like skin lesions in female mice following IMQ application, and mice showed anxiety-like and depressive-like behaviors. Further, increased microglial activation and decreased expression of neuroplasticity were detected in mice following IMQ application. However, after MS15 in early life, mice showed decreased anxiety-like and depressive-like behaviors, indicating resilience. Further, inhibited hippocampal neuroinflammation and increased neuroplasticity were detected. Conclusions: Collectively, this study confirms that brief MS confers resilience to the behavior deficits in female offspring with IMQ-induced psoriasis and reverses the activation of neuroinflammation and the damage of neuroplasticity injury.

Effect of early-life stress or fluoxetine exposure on later-life conditioned taste aversion learning in Sprague-Dawley rats

In rodents, early-life exposure to environmental stress or antidepressant medication treatment has been shown to induce similar long-term consequences on memory- and depression-related behavior in adulthood. To expand on this line of work, we evaluated how juvenile exposure to chronic variable stress (CVS) or the selective serotonin reuptake inhibitor fluoxetine (FLX) influences conditioned taste aversion (CTA) learning in adulthood. To do this, in Experiment 1, we examined how adolescent CVS alone (postnatal day [PND] 35-48), or with prenatal stress (PNS) history (PNS + CVS), influenced the acquisition and extinction of CTA in adult male Sprague Dawley rats. Specifically, at PND70+ (adulthood), rats were presented with 0.15 % saccharin followed by an intraperitoneal (i.p.) injection of lithium chloride (LiCl) to induce visceral malaise. A total of four saccharin (conditioned stimulus) and LiCl (unconditioned stimulus) pairings occurred across the CTA acquisition phase. Next, saccharin was presented without aversive consequences, and intake was measured across consecutive days of the extinction phase. No differences in body weight gain across the experimental days, rate of CTA acquisition, or extinction of CTA, were observed among the experimental groups (control, n = 7; CVS, n = 12; PNS + CVS, n = 9). In Experiment 2, we evaluated if early-life FLX exposure alters CTA learning in adulthood. Specifically, adolescent stress naïve male and female rats received FLX (0 or 20 mg/kg/i.p) once daily for 15 consecutive days (PND35-49). During antidepressant exposure, FLX decreased body weight gain in both male (n = 7) and female rats (n = 7), when compared to respective controls (male control, n = 8; female control, n = 8). However, juvenile FLX exposure decreased body weight-gain in adult male, but not female, rats. Lastly, adolescent FLX history had no effect on CTA acquisition or extinction in adulthood (PND70), in neither male nor female rats. Together, the data indicate that juvenile FLX exposure results in a long-term decrease of body weight-gain in a male-specific manner. Yet, independent of sex, neither early-life stress nor FLX exposure alters CTA learning in adulthood.

Physical exercise prevents behavioral alterations in a reserpine-treated zebrafish: A putative depression model

Major depressive disorder (MDD) has increasingly reached the world population with an expressive increase in recent years due to the COVID-19 pandemic. Here we used adult zebrafish (Danio rerio) as a model to verify the effects of reserpine on behavior and neurotransmitter levels. We observed an increase in the immobile time and time spent in the bottom zone of the tank in reserpine-exposed animals. The results demonstrated a decrease in distance traveled and velocity. Reserpine exposure did not induce changes in memory and social interaction compared to the control group. We also evaluated the influence of exposure to fluoxetine, a well-known antidepressant, on the behavior of reserpine-exposed animals. We observed a reversal of behavioral alterations caused by reserpine. To verify whether behavioral alterations in the putative depression model induced by reserpine could be prevented, the animals were subjected to physical exercise for 6 weeks. The results showed a protective effect of the physical exercise against the behavioral changes caused by reserpine in zebrafish. In addition, we observed a reduction in dopamine and serotonin levels and an increase in the 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the brain. Physical exercise was able to prevent the changes in dopamine and serotonin levels, reinforcing that the preventive effect promoted by physical exercise is related to the modulation of neurotransmitter levels. Our findings showed that reserpine was effective in the induction of a putative depression model in zebrafish and that physical exercise may be an alternative to prevent the effects induced by reserpine.

Fluoxetine increases astrocytic glucose uptake and glycolysis in corticosterone-induced depression through restricting GR-TXNIP-GLUT1 Pathway

Antidepressant fluoxetine can affect cerebral glucose metabolism in clinic, but the underlying molecular mechanism remains poorly understood. Here, we examined the effect of fluoxetine on brain regional glucose metabolism in a rat model of depression induced by repeated corticosterone injection, and explored the molecular mechanism. Fluoxetine was found to recover the decrease of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) signal in prefrontal cortex (PFC), and increased 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-D-glucose (2-NBDG, a fluorescent glucose analog) uptake in an astrocyte-specific manner in ex vivo cultured PFC slices from corticosterone-induced depressive rats, which were consistent with its improvement of animal depressive behaviors. Furthermore, fluoxetine restricted nuclear translocation of glucocorticoid receptor (GR) to suppress the transcription of thioredoxin interacting protein (TXNIP). Subsequently, it promoted glucose transporter 1 (GLUT1)-mediated glucose uptake and glycolysis of PFC astrocytes through suppressing TXNIP expression under corticosterone-induced depressive state. More importantly, fluoxetine could improve glucose metabolism of corticosterone-stimulated astrocytes via TXNIP-GLUT1 pathway. These results demonstrated that fluoxetine increased astrocytic glucose uptake and glycolysis in corticosterone-induced depression via restricting GR-TXNIP-GLUT1 pathway. The modulation of astrocytic glucose metabolism by fluoxetine was suggested as a novel mechanism of its antidepressant action.

Multi-generational impacts of exposure to antidepressant fluoxetine on behaviour, reproduction, and morphology of freshwater snail Physa acuta

Contamination of the environment by pharmaceutical pollutants poses an increasingly critical threat to aquatic ecosystems around the world. This is particularly true of psychoactive compounds, such as antidepressant drugs, which have become ubiquitous contaminants and have been demonstrated to modify aquatic animal behaviours at very low concentrations (i.e. ng/L). Despite raising risks to the hydrosphere, there is a notable paucity of data on the long term, multigenerational effects of antidepressants at environmentally realistic concentrations. Moreover, current research has predominantly focused on mean-level effects, with little research on variation among and within individuals when considering key behavioural traits. In this work, we used a multigenerational exposure of a freshwater snail (Physa acuta) to an environmentally relevant concentration of the antidepressant fluoxetine (mean measured concentration: 32.7 ng/L, SE: 2.3). The snails were allowed to breed freely in large mesocosm populations over 3 years. Upon completion of the exposure, we repeatedly measured the locomotory activity (624 measures total), reproductive output (234 measures total) as well as morphometric endpoints (78 measures total). While we found no mean-level differences between treatments in locomotory activities, we did find that fluoxetine exposed snails (n = 46) had significantly reduced behavioural plasticity (i.e. V_W; within-individual variation) in activity levels compared to unexposed snails (n = 32). As a result, fluoxetine exposed snails demonstrated significant behavioural repeatability, which was not the case for unexposed snails. Further, we report a reduction in egg mass production in fluoxetine exposed snails, and a marginally non-significant difference in morphology between treatment groups. These results highlight the potential detrimental effects of long-term fluoxetine exposure on non-target organisms at environmentally realistic dosages. Additionally, our findings demonstrate the underappreciated potential for psychoactive contaminants to have impacts beyond mean-level effects, with consequences for population resilience to current and future environmental challenges.

Cognitive adverse effects of chemotherapy and immunotherapy: are interventions within reach?

One in three people will be diagnosed with cancer during their lifetime. The community of cancer patients is growing, and several common cancers are becoming increasingly chronic; thus, cancer survivorship is an important part of health care. A large body of research indicates that cancer and cancer therapies are associated with cognitive impairment. This research has mainly concentrated on chemotherapy-associated cognitive impairment but, with the arrival of immunotherapies, the focus is expected to widen and the number of studies investigating the potential cognitive effects of these new therapies is rising. Meanwhile, patients with cognitive impairment and their healthcare providers are eagerly awaiting effective approaches to intervene against the cognitive effects of cancer treatment. In this Review, we take stock of the progress that has been made and discuss the steps that need to be taken to accelerate research into the biology underlying cognitive decline following chemotherapy and immunotherapy and to develop restorative and preventive interventions. We also provide recommendations to clinicians on how to best help patients who are currently experiencing cognitive impairment.

Fluoxetine inhibited the activation of A1 reactive astrocyte in a mouse model of major depressive disorder through astrocytic 5-HT2BR/β-arrestin2 pathway

Background

Fluoxetine, a selective serotonin reuptake inhibitor, has been reported to directly bind with 5-HT2B receptor (5-HT2BR), but the precise mechanisms, whereby fluoxetine confers the anti-depressive actions via 5-HT2BR is not fully understood. Although neuroinflammation-induced A1 astrocytes are involved in neurodegenerative diseases, the role of A1 astrocyte in the pathogenesis and treatment of major depressive disorder (MDD) remains unclear.

Methods

Mice were subjected to chronic mild stress (CMS) for 6 weeks and subsequently treated with fluoxetine for 4 weeks. The depressive-like and anxiety-like behaviors and the activation of A1 reactive astrocyte in hippocampus and cortex of mice were measured. Primary astrocytes were stimulated with A1 cocktail (tumor necrosis factor (TNF)-α, interleukin (IL)-1α and C1q), activated (LPS) microglia-conditioned medium (MCM) or IL-6 for 24 h and the expression of A1-special and A2-special markers were determined using RT-qPCR and western blot. The role of 5-HT2BR in the effects of fluoxetine on A1 reactive astrocyte was measured using 5-HT2BR inhibitor and siRNA in vitro and AAVs in vivo. The functions of downstream signaling Gq protein and β-arrestins in the effects of fluoxetine on the activation of A1 astrocyte were determined using pharmacological inhibitor and genetic knockout, respectively.

Results

In this study, we found that fluoxetine inhibited the activation of A1 reactive astrocyte and reduced the abnormal behaviors in CMS mice, as well as ameliorated A1 astrocyte reactivity under three different stimulators in primary astrocytes. We also showed that astrocytic 5-HT2BR was required in the inhibitory effects of fluoxetine on A1 reactive astrocyte in MDD in vivo and in vitro. We further found that the functions of fluoxetine in the activation of A1 astrocyte were independent of either Gq protein or β-arrestin1 in vitro. β-arrestin2 pathway was the downstream signaling of astrocytic 5-HT2BR mediated the inhibitory effects of fluoxetine on A1 astrocyte reactivity in primary astrocytes and CMS mice, as well as the improved roles of fluoxetine in behavioral impairments of CMS mice.

Conclusions

These data demonstrate that fluoxetine restricts reactive A1 astrocyte via astrocytic 5-HT2BR/β-arrestin2 pathway in a mouse model of MDD and provide a novel therapeutic avenue for MDD.

Protective effects of Rosemary extract and/or Fluoxetine on Monosodium Glutamate-induced hippocampal neurotoxicity in rat

The use of Monosodium Glutamate (MSG) as a food flavor enhancer is increasing worldwide despite its neurotoxic effects. Fluoxetine (FLX) and Rosemary extract (RE) are known to have beneficial neuroprotective properties. Rats were divided into five groups: control group; MSG group, rats received 2 g/kg/day intraperitoneal (i.p.) injections of MSG for seven days; RE/MSG group, rats received 50 mg/kg/day of oral RE for 28 days starting prior to MSG; FLX/MSG group, rats received 10 mg/kg/day of oral FLX for 28 days beginning before MSG; and RE/FLX/MSG group, received combined treatments as mentioned above. Rats underwent the Barnes maze test, in addition to histopathological, immunohistochemical, morphometric and ultrastructural evaluations for their hippocampi. MSG increased the number of errors and escaped latency in the Barnes maze test that was significantly minimized in the three treatment groups. The MSG group exhibited pyramidal cell (PC) degeneration, shrunken glial cells and massive vascular dilatation that were improved with RE and/or FLX treatment. The number of glial fibrillary acidic protein (GFAP)-immunopositive cells were increased, and the number of PCs was decreased in the MSG group, while these values were significantly reversed with the three treatment groups with the most significant improvement at RE/FLX/MSG one. Ultrastructurally, PCs were shrunken with degenerated nuclei, dilated endoplasmic reticulum, swollen mitochondria, and vacuolations in the MSG group that were improved with RE and/or FLX. In conclusion, the combined RE and FLX treatment can ameliorate the toxic effect of MSG on rat hippocampus probably through its antioxidant and anti-inflammatory effects.

Effects of the Selective Serotonin Reuptake Inhibitor Fluoxetine on Developing Neural Circuits in a Model of the Human Fetal Cortex

The developing prenatal brain is particularly susceptible to environmental disturbances. During prenatal brain development, synapses form between neurons, resulting in neural circuits that support complex cognitive functions. In utero exposure to environmental factors such as pharmaceuticals that alter the process of synapse formation increases the risk of neurodevelopmental abnormalities. However, there is a lack of research into how specific environmental factors directly impact the developing neural circuitry of the human brain. For example, selective serotonin reuptake inhibitors are commonly used throughout pregnancy to treat depression, yet their impact on the developing fetal brain remains unclear. Recently, human brain models have provided unprecedented access to the critical window of prenatal brain development. In the present study, we used human neurons and cortical spheroids to determine whether the selective serotonin reuptake inhibitor fluoxetine alters neurite and synapse formation and the development of spontaneous activity within neural circuits. We demonstrate that cortical spheroids express serotonin transporter, thus recapitulating the early developmental expression of serotonin transporter associated with cortical pyramidal neurons. Cortical spheroids also appropriately express serotonin receptors, such as synaptic 5-HT2A and glial 5-HT5A. To determine whether fluoxetine can affect developing neural circuits independent of serotonergic innervation from the dorsal and medial raphe nuclei, we treated cortical neurons and spheroids with fluoxetine. Fluoxetine alters neurite formation in a dose-dependent fashion. Intriguingly, in cortical spheroids, neither acute nor chronic fluoxetine significantly altered excitatory synapse formation. However, only acute, but not chronic fluoxetine exposure altered inhibitory synaptogenesis. Finally, fluoxetine reversibly suppresses neuronal activity in a dose-dependent manner. These results demonstrate that fluoxetine can acutely alter synaptic function in developing neural circuits, but the effects were not long-lasting. This work provides a foundation for future studies to combine serotonergic innervation with cortical spheroids and assess the contributions of fluoxetine-induced alterations in serotonin levels to brain development.

Exercise ameliorates aberrant synaptic plasticity without enhancing adult-born cell survival in the hippocampus of serotonin transporter knockout mice

Deficits in hippocampal cellular and synaptic plasticity are frequently associated with cognitive and mood disorders, and indeed common mechanisms of antidepressants are thought to involve neuroplastic processes. Here, we investigate hippocampal adult-born cell survival and synaptic plasticity (long-term potentiation, LTP, and long-term depression, LTD) in serotonin transporter (5-HTT) knockout (KO) mice. From 8 weeks of age, mice either continued in standard-housing conditions or were given access to voluntary running wheels for 1 month. Electrophysiology was performed on hippocampal slices to measure LTP and LTD, and immunohistochemistry was used to assess cell proliferation and subsequent survival in the dentate gyrus. The results revealed a reduced LTP in 5-HTT KO mice that was restored to wild-type (WT) levels after chronic exercise. While LTD appeared normal in 5-HTT KO, exercise decreased the magnitude of LTD in both WT and 5-HTT KO mice. Furthermore, although 5-HTT KO mice had normal hippocampal adult-born cell survival, they did not benefit from the pro-proliferative effects of exercise observed in WT animals. Taken together, these findings suggest that reduced 5-HTT expression is associated with significant alterations to functional neuroplasticity. Interestingly, 5-HTT appeared necessary for exercise-induced augmentation of adult-born hippocampal cell survival, yet exercise corrected the LTP impairment displayed by 5-HTT KO mice. Together, our findings further highlight the salience of serotonergic signalling in mediating the neurophysiological benefits of exercise.

Long-term effects of early treatment with SSRIs on cognition and brain development in individuals with 22q11.2 deletion syndrome

Cognitive deficits in individuals at risk of psychosis represent a significant challenge for research, as current strategies for symptomatic treatment are often ineffective. Recent studies showed that atypical cognitive development predicts the occurrence of psychotic symptoms. Additionally, abnormal brain development is known to predate clinical manifestations of psychosis. Therefore, critical developmental stages may be the best period for early interventions expected to prevent cognitive decline and protect brain maturation. However, it is challenging to identify and treat individuals at risk of psychosis in the general population before the onset of the first psychotic symptoms. 22q11.2 deletion syndrome (22q11DS), the neurogenetic disorder with the highest genetic risk for schizophrenia, provides the opportunity to prospectively study the development of subjects at risk for psychosis. In this retrospective cohort study, we aimed to establish if early treatment with SSRIs in children and adolescents with 22q11DS was associated with long-term effects on cognition and brain development. We included 98 participants with a confirmed diagnosis of 22q11DS followed up 2-4 times (age range: 10-32). Thirty subjects without psychiatric disorders never received psychotropic medications, thirty had psychotic symptoms but were not treated with SSRIs, and 38 received SSRIs treatment. An increase in IQ scores characterized the developmental trajectories of participants receiving treatment with SSRIs, even those with psychotic symptoms. The thickness of frontal regions and hippocampal volume were also relatively increased. The magnitude of the outcomes was inversely correlated to the age at the onset of the treatment. We provide preliminary evidence that early long-term treatment with SSRIs may attenuate the cognitive decline associated with psychosis in 22q11DS and developmental brain abnormalities.

Membrane molecules for mood

According to the decades-old neurotrophic hypothesis of depression, the delayed actions of antidepressants are purported to be due to their downstream effects on neuronal plasticity. In a recent study, Casarotto et al. reveal that antidepressants can in fact directly bind to the neurotrophin TRKB receptor and exert their effects through this mechanism.

Neuroplastic effects of a selective serotonin reuptake inhibitor in relearning and retrieval

Animal studies using selective serotonin reuptake inhibitors (SSRIs) and learning paradigms have demonstrated that serotonin is important for flexibility in executive functions and learning. SSRIs might facilitate relearning through neuroplastic processes and thus exert their clinical effects in psychiatric diseases where cognitive functioning is affected. However, translation of these mechanisms to humans is missing. In this randomized placebo-controlled trial, we assessed functional brain activation during learning and memory retrieval in healthy volunteers performing associative learning tasks aiming to translate facilitated relearning by SSRIs.

To this extent, seventy-six participants underwent three MRI scanning sessions: (1) at baseline, (2) after three weeks of daily associative learning and subsequent retrieval (face-matching or Chinese character–noun matching) and (3) after three weeks of relearning under escitalopram (10 mg/day) or placebo. Associative learning and retrieval tasks were performed during each functional MRI (fMRI) session. Statistical modeling was done using a repeated-measures ANOVA, to test for content-by-treatment-by-time interaction effects.

During the learning task, a significant substance-by-time interaction was found in the right insula showing a greater deactivation in the SSRI cohort after 21 days of relearning compared to the learning phase. In the retrieval task, there was a significant content-by-time interaction in the left angular gyrus (AG) with an increased activation in face-matching compared to Chinese-character matching for both learning and relearning phases. A further substance-by-time interaction was found in task performance after 21 days of relearning, indicating a greater decrease of performance in the placebo group.

Our findings that escitalopram modulate insula activation demonstrates successful translation of relearning as a mechanism of SSRIs in human. Furthermore, we show that the left AG is an active component of correct memory retrieval, which coincides with previous literature. We extend the function of this region by demonstrating its activation is not only stimulus dependent but also time constrained. Finally, we were able to show that escitalopram aids in relearning, irrespective of content.

Fluoxetine regulates eEF2 activity (phosphorylation) via HDAC1 inhibitory mechanism in an LPS-induced mouse model of depression

BACKGROUND

Selective serotonin reuptaker inhibitors, including fluoxetine, are widely studied and prescribed antidepressants, while their exact molecular and cellular mechanism are yet to be defined. We investigated the involvement of HDAC1 and eEF2 in the antidepressant mechanisms of fluoxetine using a lipopolysaccharide (LPS)-induced depression-like behavior model.

METHODS

For in vivo analysis, mice were treated with LPS (2 mg/kg BW), fluoxetine (20 mg/kg BW), HDAC1 activator (Exifone: 54 mg/kg BW) and NH125 (1 mg/kg BW). Depressive-like behaviors were confirmed via behavior tests including OFT, FST, SPT, and TST. Cytokines were measured by ELISA while Iba-1 and GFAP expression were determined by immunofluorescence. Further, the desired gene expression was measured by immunoblotting. For in vitro analysis, BV2 cell lines were cultured; treated with LPS, exifone, and fluoxetine; collected; and analyzed.

RESULTS

Mice treated with LPS displayed depression-like behaviors, pronounced neuroinflammation, increased HDAC1 expression, and reduced eEF2 activity, as accompanied by altered synaptogenic factors including BDNF, SNAP25, and PSD95. Fluoxetine treatment exhibited antidepressant effects and ameliorated the molecular changes induced by LPS. Exifone, a selective HDAC1 activator, reversed the antidepressant and anti-inflammatory effects of fluoxetine both in vivo and in vitro, supporting a causing role of HDAC1 in neuroinflammation allied depression. Further molecular mechanisms underlying HDAC1 were explored with NH125, an eEF2K inhibitor, whose treatment reduced immobility time, altered pro-inflammatory cytokines, and NLRP3 expression. Moreover, NH125 treatment enhanced eEF2 and GSK3β activities, BDNF, SNAP25, and PSD95 expression, but had no effects on HDAC1.

CONCLUSIONS

Our results showed that the antidepressant effects of fluoxetine may involve HDAC1-eEF2 related neuroinflammation and synaptogenesis.

Chronic fluoxetine treatment impairs motivation and reward learning by affecting neuronal plasticity in the central amygdala

BACKGROUND AND PURPOSE

The therapeutic effects of fluoxetine are believed to be due to increasing neuronal plasticity and reversing some learning deficits. Nevertheless, a growing amount of evidence shows adverse effects of this drug on cognition and some forms of neuronal plasticity.

EXPERIMENTAL APPROACH

To study the effects of chronic fluoxetine treatment, we combine an automated assessment of motivation and learning in mice with an investigation of neuronal plasticity in the central amygdala and basolateral amygdala. We use immunohistochemistry to visualize neuronal types and perineuronal nets, along with DI staining to assess dendritic spine morphology. Gel zymography is used to test fluoxetine's impact on matrix metalloproteinase-9, an enzyme involved in synaptic plasticity.

KEY RESULTS

We show that chronic fluoxetine treatment in non-stressed mice increases perineuronal nets-dependent plasticity in the basolateral amygdala, while impairing MMP-9-dependent plasticity in the central amygdala. Further, we illustrate how the latter contributes to anhedonia and deficits of reward learning. Behavioural impairments are accompanied by alterations in morphology of dendritic spines in the central amygdala towards an immature state, most likely reflecting animals' inability to adapt. We strengthen the link between the adverse effects of fluoxetine and its influence on MMP-9 by showing that behaviour of MMP-9 knockout animals remains unaffected by the drug.

CONCLUSION AND IMPLICATIONS

Chronic fluoxetine treatment differentially affects various forms of neuronal plasticity, possibly explaining its opposing effects on brain and behaviour. These findings are of immediate clinical relevance since reported side effects of fluoxetine pose a potential threat to patients.

Delayed atomoxetine or fluoxetine treatment coupled with limited voluntary running promotes motor recovery in mice after ischemic stroke

Currently, there is an unmet need for treatments promoting post-stroke functional recovery. The aim of this study was to evaluate and compare the dose-dependent effect of delayed atomoxetine or fluoxetine therapy (starting on post-stroke day 5), coupled with limited physical exercise (2 hours daily voluntary wheel running; post-stroke days 9 to 42), on motor recovery of adult male mice after photothrombotic stroke. These drugs are selective norepinephrine or serotonin reuptake inhibitors indicated for disorders unrelated to stroke. The predetermined primary end-point for this study was motor function measured in two tasks of spontaneous motor behaviors in grid-walking and cylinder tests. Additionally, we quantified the running distance and speed throughout the study, the number of parvalbumin-positive neurons in the medial agranular cortex and infarct volumes. Both sensorimotor tests revealed that neither limited physical exercise nor a drug treatment alone significantly facilitated motor recovery in mice after stroke. However, combination of physical exercise with either of the drugs promoted restoration of motor function by day 42 post-stroke, with atomoxetine being a more potent drug. This was accompanied by a significant decrease in parvalbumin-positive inhibitory interneurons in the ipsilateral medial agranular cortex of mice with recovering motor function, while infarct volumes were comparable among experimental groups. If further validated in larger studies, our observations suggest that add-on atomoxetine or fluoxetine therapy coupled with limited, structured physical rehabilitation could offer therapeutic modality for stroke survivors who have difficulty to engage in early, high-intensity physiotherapy. Furthermore, in light of the recently completed Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) and Efficacy oF Fluoxetine-a randomisEd Controlled Trial in Stroke (EFFECTS) trials, our observations call for newly designed studies where fluoxetine or atomoxetine pharmacotherapy is evaluated in combination with structured physical rehabilitation rather than alone. This study was approved by the Texas Tech University Health Sciences Center Institutional Animal Care and Use Committee (protocol # 16019).

Erxian decoction, a famous Chinese medicine formula, antagonizes corticosterone-induced injury in PC12 cells, and improves depression-like behaviours in mice

Context: In folk medicine, erxian decoction (EXD) is used to treat perimenopausal syndrome in women. It is also used clinically to treat depression, but the mechanism remains unknown.Objectives: To investigate the neuroprotective effect of EXD, and its antidepressant potential.Materials and methods: ICR mice were treated with EXD (0.5, 1.5 and 4.5 g/kg i.g.) and fluoxetine (6.0 mg/kg i.g.) for 10 days. On day 10 of the treatment, depression-like behaviour was induced by reserpine (2.5 mg/kg injected i.p.), and after 24 h of reserpine administration, it was assessed using the tail suspension and forced swimming tests. MTT assay, lactate dehydrogenase test, flow cytometry analysis, Hoechst staining and western blotting were used to assess the apoptosis of PC12 cells. Apoptosis proteins and neurotransmitter were tested in vitro and in vivo, respectively.Results: MTT assay results showed corticosterone prevented cell growth, but EXD at concentrations of 100, 200 and 400 μg/mL restored cell viability (EC₅₀: 204.016 μg/mL). EXD decreased lactate dehydrogenase leakage from 63.48 to 43.60 U/L, and upregulated expression of Bcl-2 while the expression of Bax, caspase-3 and caspase-8 were decreased in vivo and in vitro. Moreover, EXD improved depression-like behaviour in mice, and 4.5 g/kg EXD treatment increased the secretion of serotonin, dopamine and norepinephrine by 67.44, 28.12 and 42.12 pg/mg, respectively, in hypothalamus compared to that of reserpine group.Discussion and conclusions: EXD demonstrated neuroprotective effects and improved depression-like behaviour in mice. Further research should be focussed on the mechanism of the active components in EXD.

Pharmacological basis of the anxiolytic and antidepressant properties of Silexan®, an essential oil from the flowers of lavender

Silexan®, a proprietary essential oil manufactured by steam distillation from Lavandula angustifolia flowers showed pronounced anxiolytic effects in patients with subthreshold anxiety disorders and was also efficacious in patients with Generalized Anxiety disorder (GAD). Moreover, evidences for antidepressant-like properties of Silexan® have been observed in anxious patients suffering from comorbid depressive symptoms and in patients with mixed anxiety-depression disorder (ICD-10 F41.2). In accordance with the clinical data Silexan® is active in several behavioral models in rodents at rather low concentrations indicating potent anxiolytic and antidepressive properties. As possible mechanism of action a moderate inhibition of voltage dependent calcium channels (VDCC) has been found showing some similarities to the anxiolytic drug pregabalin. However, while pregabalin mainly inhibits P/Q-type channels by binding to a modulatory subunit, Silexan® moderately inhibits mainly T-type and N-type channels and to some extent P/Q-type channels. Unlike pregabalin Silexan® is free of hypnotic or sedative side effects and seems to be devoid of any abuse potential. With respect to its specific antidepressant like properties Silexan® improves several aspects of neuroplasticity which seems to be the common final pathway of all antidepressant drugs. As a potential mechanism of its effects on neuroplasticity an activation of the transcription factor CREB via activation of intracellular signaling kinases like PKA and MAPK has been found. Since the concentrations of Silexan® needed to inhibit VDCC function and to improve neuroplasticity are quite similar, the effects of Silexan® on PKA or MAPK could constitute a common intracellular signaling cascade leading to VDCC modulation as well as CREB activation and improved neuroplasticity.

Inflammatory modulation of fluoxetine use in patients with depression: A systematic review and meta-analysis

There is growing evidence that there is a relationship between major depressive disorder (MDD), also simply known as "depression", and inflammatory processes. Selective serotonin inhibitors, such as fluoxetine, are used as a first-line treatment for depression, and it is hypothesized that its use can reduce levels of proinflammatory cytokines. The aim of this systematic review and meta-analysis is to enable a better understanding of how treatment with the antidepressant fluoxetine modulates inflammation, and the roles of the main cytokines in this process. Risk of bias (RoB) in the included studies was assessed using the Cochrane Risk of Bias Assessment tool for Non-randomized studies (RoBANS). In the meta-analysis, standardized mean difference (SMD) was used as a summary statistic and grouped statistics using the generic inverse variation method in RevMan 5 with random effects model. Heterogeneous changes in cytokine levels were also evaluated from the SMD forest plot of individual studies. After analysis, we observed that fluoxetine was able to decrease TNF-α levels (SMD ± 0.90, 95% CI = 0.16, 1.165, Z ± 2.40, p = 0.02), but not change IL-6 levels (SMD ± 0.37, 95% CI = 0.21, 0.95, Z ± 1.25, p = 0.21).Fluoxetine acts by modulating neuroimmunology, and not only by acting only on the independent restoration of neurotransmission and neuroinflammation pathways.

Antidepressant-like effects of ketamine in a mouse model of serotonergic dysfunction

Traditional monoaminergic treatments of depression frequently exhibit suboptimal tolerability and effectiveness. The 'short' (s) allele variant of 5-HTTLPR is known to compromise transcriptional efficacy of the serotonin transporter (5-HTT) and can reduce treatment response to traditional antidepressants (e.g. selective serotonin reuptake inhibitors or SSRIs). This study sought to establish the 5-HTT knock-out (KO) line as a mouse model of SSRI-resistant depression and assess its response to a novel glutamatergic antidepressant, ketamine, a non-competitive N-methyl-d-aspartate receptor (NMDAR) antagonist. Following acute antidepressant treatment, 5-HTT KO mice and wild-type (WT) controls were subjected to the forced-swim test (FST), one of the most widely used techniques to detect acute antidepressant response. As hypothesised, when assessed 30 min after administration in the FST, the SSRI sertraline (20 mg/kg, i.p.) produced antidepressant-like effects in WT control but not in 5-HTT KO mice. In contrast, ketamine (20 mg/kg, i.p.) induced antidepressant-like effects in both genotypes. 5-HTT KO mice also exhibited a reduced locomotor response to both MK-801 (another NMDAR antagonist) and ketamine, and reduced GluN2A protein levels in the hippocampus, suggesting glutamatergic dysfunction in this model. These results highlight the utility of 5-HTT KO mice as a relevant model of SSRI-resistant depression and demonstrate that ketamine can produce acute antidepressant-like effects in conditions of 5-HTT deficiency. These findings extend existing literature that indicates ketamine is effective in ameliorating symptoms of treatment-resistant depression and may have implications for understanding the cellular and molecular mechanisms underlying the antidepressant effects of ketamine. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.