Reversal of hippocampal neuronal maturation by serotonergic antidepressants

Role of desmoplakin in supporting neuronal activity, neurogenic processes, and emotional-related behaviors in the dentate gyrus

Desmoplakin (Dsp) is a component of desmosomal cell-cell junctions that interacts with the cadherin complex and cytoskeletal intermediate filaments. In addition to its function as an adhesion component, Dsp is involved in various biological processes, such as gene expression, differentiation, and migration. Dsp is specifically expressed in the hippocampal dentate gyrus (DG) in the central nervous system. However, it is unclear how Dsp impacts hippocampal function and its related behaviors. Using an adeno-associated virus knockdown system in mice, we provide evidence that Dsp in the DG maintains hippocampal functions, including neuronal activity and adult neurogenesis, and contributes to anxiolytic-like effects. Dsp protein is mostly localized in mature granule cells in the adult DG. Dsp knockdown in the DG resulted in a lowered expression of an activity-dependent transcription factor FosB, and an increased expression of mature neuronal markers, such as calbindin. In addition, the suppression of Dsp decreases serotonin responsiveness at the DG output mossy fiber synapses and alters adult neurogenic processes in the subgranular zone of the DG. Moreover, DG-specific Dsp knockdown mice showed an increase in anxiety-like behaviors. Taken together, this research uncovers an unexplored function for Dsp in the central nervous system and suggests that Dsp in the DG may function as a regulator to maintain proper neuronal activation and adult neurogenesis, and contribute to the adaptation of emotion-related behavior.

The Serotonin 4 Receptor Subtype: A Target of Particular Interest, Especially for Brain Disorders

In recent years, particular attention has been paid to the serotonin 4 receptor, which is well expressed in the brain, but also peripherally in various organs. The cerebral distribution of this receptor is well conserved across species, with high densities in the basal ganglia, where they are expressed by GABAergic neurons. The 5-HT4 receptor is also present in the cerebral cortex, hippocampus, and amygdala, where they are carried by glutamatergic or cholinergic neurons. Outside the central nervous system, the 5-HT4 receptor is notably expressed in the gastrointestinal tract. The wide distribution of the 5-HT4 receptor undoubtedly contributes to its involvement in a plethora of functions. In addition, the modulation of this receptor influences the release of serotonin, but also the release of other neurotransmitters such as acetylcholine and dopamine. This is a considerable asset, as the modulation of the 5-HT4 receptor can therefore play a direct or indirect beneficial role in various disorders. One of the main advantages of this receptor is that it mediates a much faster antidepressant and anxiolytic action than classical selective serotonin reuptake inhibitors. Another major benefit of the 5-HT4 receptor is that its activation enhances cognitive performance, probably via the release of acetylcholine. The expression of the 5-HT4 receptor is also altered in various eating disorders, and its activation by the 5-HT4 agonist negatively regulates food intake. Additionally, although the cerebral expression of this receptor is modified in certain movement-related disorders, it is still yet to be determined whether this receptor plays a key role in their pathophysiology. Finally, there is no longer any need to demonstrate the value of 5-HT4 receptor agonists in the pharmacological management of gastrointestinal disorders.

Effects of electroconvulsive shock on the function, circuitry, and transcriptome of dentate gyrus granule neurons

Therapeutic use of electroconvulsive shock (ECS) is 75% effective for the remission of treatment-resistant depression. Like other more common forms of antidepressant treatment such as fluoxetine, ECS has been shown to increase neurogenesis in the hippocampal dentate gyrus of rodent models. Yet the question of how ECS-induced neurogenesis supports improvement of depressive symptoms remains unknown. Here, we show that ECS-induced neurogenesis is necessary to improve depressive-like behavior of mice exposed to chronic corticosterone (Cort). We then use slice electrophysiology to show that optogenetic stimulation of adult-born neurons produces a greater hyperpolarization in mature granule neurons after ECS vs Sham treatment. We identify that this hyperpolarization requires the activation of metabotropic glutamate receptor 2 (mGluR2). Consistent with this finding, we observe reduced expression of the immediate early gene cFos in the granule cell layer of ECS vs Sham subjects. We then show that mGluR2 knockdown specifically in ventral granule neurons blunts the antidepressant-like behavioral effects of ECS. Using single nucleus RNA sequencing, we reveal major transcriptomic shifts in granule neurons after treatment with ECS+Cort or fluoxetine+Cort vs Cort alone. We identify a population of immature cells which has greater representation in both ECS+Cort and fluoxetine+Cort treated samples vs Cort alone. We also find global differences in ECS-vs fluoxetine-induced transcriptomic shifts. Together, these findings highlight a critical role for immature granule cells and mGluR2 signaling in the antidepressant action of ECS.

Hippocampal CA1 Pyramidal Neurons Display Sublayer and Circuitry Dependent Degenerative Expression Profiles in Aged Female Down Syndrome Mice

Background

Individuals with Down syndrome (DS) have intellectual disability and develop Alzheimer's disease (AD) pathology during midlife, particularly in the hippocampal component of the medial temporal lobe memory circuit. However, molecular and cellular mechanisms underlying selective vulnerability of hippocampal CA1 neurons remains a major knowledge gap during DS/AD onset. This is compounded by evidence showing spatial (e.g., deep versus superficial) localization of pyramidal neurons (PNs) has profound effects on activity and innervation within the CA1 region.

Objective

We investigated whether there is a spatial profiling difference in CA1 PNs in an aged female DS/AD mouse model. We posit dysfunction may be dependent on spatial localization and innervation patterns within discrete CA1 subfields.

Methods

Laser capture microdissection was performed on trisomic CA1 PNs in an established mouse model of DS/AD compared to disomic controls, isolating the entire CA1 pyramidal neuron layer and sublayer microisolations of deep and superficial PNs from the distal CA1 (CA1a) region.

Results

RNA sequencing and bioinformatic inquiry revealed dysregulation of CA1 PNs based on spatial location and innervation patterns. The entire CA1 region displayed the most differentially expressed genes (DEGs) in trisomic mice reflecting innate DS vulnerability, while trisomic CA1a deep PNs exhibited fewer but more physiologically relevant DEGs, as evidenced by bioinformatic inquiry.

Conclusions

CA1a deep neurons displayed numerous DEGs linked to cognitive functions whereas CA1a superficial neurons, with approximately equal numbers of DEGs, were not linked to pathways of dysregulation, suggesting the spatial location of vulnerable CA1 PNs plays an important role in circuit dissolution.

Functional Dimerization of Serotonin Receptors: Role in Health and Depressive Disorders

Understanding the neurobiological underpinnings of depressive disorder constitutes a pressing challenge in the fields of psychiatry and neurobiology. Depression represents one of the most prevalent forms of mental and behavioral disorders globally. Alterations in dimerization capacity can influence the functional characteristics of serotonin receptors and may constitute a contributing factor to the onset of depressive disorders. The objective of this review is to consolidate the current understanding of interactions within the 5-HT receptor family and between 5-HT receptors and members of other receptor families. Furthermore, it aims to elucidate the role of such complexes in depressive disorders and delineate the mechanisms through which antidepressants exert their effects.

A complex relation between levels of adult hippocampal neurogenesis and expression of the immature neuron marker doublecortin

We investigated the mechanisms underlying the effects of the antidepressant fluoxetine on behavior and adult hippocampal neurogenesis (AHN). After confirming our earlier report that the signaling molecule β-arrestin-2 (β-Arr2) is required for the antidepressant-like effects of fluoxetine, we found that the effects of fluoxetine on proliferation of neural progenitors and survival of adult-born granule cells are absent in the β-Arr2 knockout (KO) mice. To our surprise, fluoxetine induced a dramatic upregulation of the number of doublecortin (DCX)-expressing cells in the β-Arr2 KO mice, indicating that this marker can be increased even though AHN is not. We discovered two other conditions where a complex relationship occurs between the number of DCX-expressing cells compared to levels of AHN: a chronic antidepressant model where DCX is upregulated and an inflammation model where DCX is downregulated. We concluded that assessing the number of DCX-expressing cells alone to quantify levels of AHN can be complex and that caution should be applied when label retention techniques are unavailable.

Flavonols in Action: Targeting Oxidative Stress and Neuroinflammation in Major Depressive Disorder

Major depressive disorder is one of the most common mental illnesses that highly impairs quality of life. Pharmacological interventions are mainly focused on altered monoamine neurotransmission, which is considered the primary event underlying the disease's etiology. However, many other neuropathological mechanisms that contribute to the disease's progression and clinical symptoms have been identified. These include oxidative stress, neuroinflammation, hippocampal atrophy, reduced synaptic plasticity and neurogenesis, the depletion of neurotrophic factors, and the dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis. Current therapeutic options are often unsatisfactory and associated with adverse effects. This review highlights the most relevant findings concerning the role of flavonols, a ubiquitous class of flavonoids in the human diet, as potential antidepressant agents. In general, flavonols are considered to be both an effective and safe therapeutic option in the management of depression, which is largely based on their prominent antioxidative and anti-inflammatory effects. Moreover, preclinical studies have provided evidence that they are capable of restoring the neuroendocrine control of the HPA axis, promoting neurogenesis, and alleviating depressive-like behavior. Although these findings are promising, they are still far from being implemented in clinical practice. Hence, further studies are needed to more comprehensively evaluate the potential of flavonols with respect to the improvement of clinical signs of depression.

Boophone disticha attenuates five day repeated forced swim-induced stress and adult hippocampal neurogenesis impairment in male Balb/c mice

Depression is one of the most common neuropsychiatric disorders and is associated with dysfunction of the neuroendocrine system and alterations in specific brain proteins. Boophone disticha (BD) is an indigenous psychoactive bulb that belongs to the Amaryllidacae family, which is widely used in Southern Africa to treat depression, with scientific evidence of potent antidepressant-like effects. The present study examined the antidepressant effects of BD and its mechanisms of action by measuring some behavioural parameters in the elevated plus maze, brain content of corticosterone, brain derived neurotropic factor (BDNF), and neuroblast differentiation in the hippocampus of Balb/c mice exposed to the five day repeated forced swim stress (5d-RFSS). Male Balb/c mice were subjected to the 5d-RFSS protocol to induce depressive-like behaviour (decreased swimming, increased floating, decreased open arm entry, decreased time spent in the open arms and decreased head dips in the elevated plus maze test) and treated with distilled water, fluoxetine and BD. BD treatment (10 mg/kg/p.o for 3 weeks) significantly attenuated the 5d-RFSS-induced behavioural abnormalities and the elevated serum corticosterone levels observed in stressed mice. Additionally, 5d-RFSS exposure significantly decreased the number of neuroblasts in the hippocampus and BDNF levels in the brain of Balb/c mice, while fluoxetine and BD treatment attenuated these changes. The antidepressant effects of BD were comparable to those of fluoxetine, but unlike fluoxetine, BD did not show any anxiogenic effects, suggesting better pharmacological functions. In conclusion, our study shows that BD exerted antidepressant-like effects in 5d-RFSS mice, mediated in part by normalizing brain corticosterone and BDNF levels.

Loss of sodium leak channel (NALCN) in the ventral dentate gyrus impairs neuronal activity of the glutamatergic neurons for inflammation-induced depression in male mice

BACKGROUND

The dentate gyrus (DG) has been implicated in the pathophysiology of depression. Many studies have revealed the cellular types, neural circuits, and morphological changes of the DG involved in the development of depression. However, the molecular regulating its intrinsic activity in depression is unknown.

METHODS

Utilizing the mode of depression induced by lipopolysaccharide (LPS), we investigate the involvement of the sodium leak channel (NALCN) in inflammation-induced depressive-like behaviors of male mice. The expression of NALCN was detected by immunohistochemistry and real-time polymerase chain reaction. DG microinjection of the adeno-associated virus or lentivirus was carried out using a stereotaxic instrument and followed by behavioral tests. Neuronal excitability and NALCN conductance were recorded by whole-cell patch-clamp techniques.

RESULTS

The expression and function of NALCN were reduced in both the dorsal and ventral DG in LPS-treated mice; whereas, only knocking down NALCN in the ventral pole produced depressive-like behaviors and this effect of NALCN was specific to ventral glutamatergic neurons. The excitability of ventral glutamatergic neurons was impaired by both the knockdown of NALCN and/or the treatment of LPS. Then, the overexpression of NALCN in the ventral glutamatergic neurons decreased the susceptibility of mice to inflammation-induced depression, and the intracranial injection of substance P (non-selective NALCN activator) into the ventral DG rapidly ameliorated inflammation-induced depression-like behaviors in an NALCN-dependent manner.

CONCLUSIONS

NALCN, which drives the neuronal activity of the ventral DG glutamatergic neurons, uniquely regulates depressive-like behaviors and susceptibility to depression. Therefore, the NALCN of glutamatergic neurons in the ventral DG may present a molecular target for rapid antidepressant drugs.

Dorsal Dentate Gyrus, a Key Regulator for Mood and Psychiatric Disorders

The dentate gyrus, a "gate" that controls the flow of information into the hippocampus, is critical for learning, memory, spatial navigation, and mood regulation. Several lines of evidence have demonstrated that deficits in dentate granule cells (DGCs) (e.g., loss of DGCs or genetic mutations in DGCs) contribute to the development of various psychiatric disorders, such as depression and anxiety disorders. Whereas ventral DGCs are believed to be critical for mood regulation, the functions of dorsal DGCs in this regard remain elusive. Here, we review the role of DGCs, in particular the dorsal DGCs, in the regulation of mood, their functional relationships with DGC development, and the contributions of dysfunctional DGCs to mental disorders.

Hippocampal Inflammation and Gene Expression Changes in Peripheral Lipopolysaccharide Challenged Mice Showing Sickness and Anxiety-Like Behaviors

Neuroinflammation is often associated with the development of depressive and anxiety disorders. The hippocampus is one of the brain regions affected by inflammation that is associated with these symptoms. However, the mechanism of hippocampal inflammation-induced emotional behavior remains unknown. The aim of this study was to clarify temporal changes in the neuroinflammatory responses in the hippocampus and the response of dentate gyrus (DG) neurons using peripheral lipopolysaccharide (LPS)-challenged mice. LPS administration induced anxiety-like activity in the elevated plus maze test and social interaction test after 24 h, at which time the mice had recovered from sickness behavior. We examined the hippocampal inflammation-related gene expression changes over time. The expression of interleukin-1β (Il1b) and tumor necrosis factor α (Tnfa) was rapidly enhanced and sustained until 24 h after LPS administration, whereas the expression of Il6 was transiently induced at approx. 6 h. IL-6-dependent downstream signaling of transducer and activator of transcription 3 (STAT3) was also activated approx. 3-6 h after LPS treatment. The expression of innate immune genes including interferon-induced transmembrane proteins such as interferon-induced transmembrane protein 1 (Ifitm1) and Ifitm3 and complement factors such as C1qa and C1qb started to increase approx. 6 h and showed sustained or further increase at 24 h. We also examined changes in the expression of several maturation markers in the DG and found that LPS enhanced the expression of calbindin 1 (Calb1), tryptophan-2,3-dioxigenase 2 (Tdo2), Il1rl, and neurotrophin-3 (Ntf3) at 24 h after LPS treatment. Collectively, these results demonstrate temporal changes of inflammation and gene expression in the hippocampus in LPS-induced sickness and anxiety-like behaviors.

Forebrain-specific conditional calcineurin deficiency induces dentate gyrus immaturity and hyper-dopaminergic signaling in mice

Calcineurin (Cn), a phosphatase important for synaptic plasticity and neuronal development, has been implicated in the etiology and pathophysiology of neuropsychiatric disorders, including schizophrenia, intellectual disability, autism spectrum disorders, epilepsy, and Alzheimer's disease. Forebrain-specific conditional Cn knockout mice have been known to exhibit multiple behavioral phenotypes related to these disorders. In this study, we investigated whether Cn mutant mice show pseudo-immaturity of the dentate gyrus (iDG) in the hippocampus, which we have proposed as an endophenotype shared by these disorders. Expression of calbindin and GluA1, typical markers for mature DG granule cells (GCs), was decreased and that of doublecortin, calretinin, phospho-CREB, and dopamine D1 receptor (Drd1), markers for immature GC, was increased in Cn mutants. Phosphorylation of cAMP-dependent protein kinase (PKA) substrates (GluA1, ERK2, DARPP-32, PDE4) was increased and showed higher sensitivity to SKF81297, a Drd1-like agonist, in Cn mutants than in controls. While cAMP/PKA signaling is increased in the iDG of Cn mutants, chronic treatment with rolipram, a selective PDE4 inhibitor that increases intracellular cAMP, ameliorated the iDG phenotype significantly and nesting behavior deficits with nominal significance. Chronic rolipram administration also decreased the phosphorylation of CREB, but not the other four PKA substrates examined, in Cn mutants. These results suggest that Cn deficiency induces pseudo-immaturity of GCs and that cAMP signaling increases to compensate for this maturation abnormality. This study further supports the idea that iDG is an endophenotype shared by certain neuropsychiatric disorders.

Febrile Seizures Cause Depression and Anxiogenic Behaviors in Rats

Febrile seizure (FS) is a common type of seizure occurring in human during infancy and childhood. Although an epileptic seizure is associated with psychiatric disorders and comorbid diseases such as depression, anxiety, autism spectrum disorders, sleep disorders, attention deficits, cognitive impairment, and migraine, the causal relationship between FS and psychiatric disorders is poorly understood. The objective of the current study was to investigate the relationship of FS occurrence in childhood with the pathogenesis of anxiety disorder and depression using an FS rat model. We induced febrile seizures in infantile rats (11 days postnatal) using a mercury vapor lamp. At 3 weeks and 12 weeks after FS induction, we examined behaviors and recorded local field potentials (LFPs) to assess anxiety and depression disorder. Interestingly, after FS induction in infantile rats, anxiogenic behaviors and depression-like phenotypes were found in both adult and juvenile FS rats. The analysis of LFPs revealed that 4-7 Hz hippocampal theta rhythm, a neural oscillatory marker for anxiety disorder, was significantly increased in FS rats compared with their wild-type littermates. Taken together, our findings suggest that FS occurrence in infants is causally related to increased levels of anxiety-related behaviors and depression-like symptoms in juvenile and adult rodents.

Chronic fluoxetine enhances extinction therapy for PTSD by evaluating brain glucose metabolism in rats: an [18F]FDG PET study

BACKGROUND

Recent studies suggest that selective serotonin reuptake inhibitors (SSRIs) and exposure therapies have been used to reduced footshock-induced posttraumatic stress disorder (PTSD) symptoms. However, the therapeutic effect of the combination of SSRIs treatment with exposure therapy remains a matter of debate. This study aimed to evaluate these therapeutic effect through the behavioural and the neuroimaging changes by positron emission tomography (PET) in model rats.

METHODS

Pavlovian fear conditioning paradigm to establish model rats, and serial PET imaging with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) was performed during the control, fear-conditioning, and extinction-retrieval phases. The expression of c-Fos was used to identify neural activity.

RESULTS

We report that fear conditioning increased glucose metabolism in the right amygdala and left primary visual cortex but decreased glucose metabolism in the left primary somatosensory cortex. After extinction retrieval, there was increased [¹⁸F]FDG uptake in the left striatum, left cochlear nucleus and right primary visual cortex but decreased uptake in the anterior cingulate cortex in the extinction group. Fluoxetine increased [¹⁸F]FDG uptake in the left hippocampus and right primary visual cortex but decreased uptake in the bilateral primary somatosensory cortex, left primary/secondary motor cortex and cuneiform nucleus. The combined therapy increased [¹⁸F]FDG uptake in the left hippocampus, left striatum, right insular cortex, left posterior parietal cortex, and right secondary visual cortex but reduced uptake in the cerebellar lobule. c-Fos expression in the hippocampal dentate gyrus and anterior cingulate cortex in the fluoxetine and combined groups was significantly higher than that in the extinction group, with no significant difference between the two groups.

CONCLUSIONS

Chronic fluoxetine enhanced the effects of extinction training in a rat model of PTSD. In vivo PET imaging may provide a promising approach for evaluation chronic fluoxetine treatment of PTSD.

Regulation of adult-born and mature neurons in stress response and antidepressant action in the dentate gyrus of the hippocampus

The dentate gyrus (DG) of the hippocampus has been implicated in the regulation of stress responses, and in the pathophysiology and treatment of depression. This review discusses the cellular changes caused by chronic stress and the cellular role of the DG in stress-induced behavioral changes and its antidepressant-like effects. Regarding adult-born neurogenic processes in the DG, chronic stress, such as repeated social defeat, suppresses cell proliferation during and immediately after stress; however, this effect is transient. The subsequent differentiation and survival processes are differentially regulated depending on the timing and sensitivity of stress. The activation of young adult-born neurons during stress contributes to stress resilience, while the transient increase in the survival of adult-born neurons after the cessation of stress seems to promote stress susceptibility. In mature granule neurons, the predominant cells in the DG, synaptic plasticity is suppressed by chronic stress. However, a group of mature granule neurons is activated by chronic stress. Chronic antidepressant treatment can transform mature granule neurons to a phenotype resembling that of immature neurons, characterized as "dematuration". Adult-born neurons suppress the activation of mature granule neurons during stress, indicating that local neural interactions within the DG are important for the stress response. Elucidating the stress-associated context- and timing-dependent cellular changes and functions in the DG will provide insights into stress-related psychiatric diseases.

Noradrenaline activation of hippocampal dopamine D1 receptors promotes antidepressant effects

Dopamine D₁ receptors (D₁Rs) in the hippocampal dentate gyrus (DG) are essential for antidepressant effects. However, the midbrain dopaminergic neurons, the major source of dopamine in the brain, only sparsely project to DG, suggesting possible activation of DG D₁Rs by endogenous substances other than dopamine. We have examined this possibility using electrophysiological and biochemical techniques and found robust activation of D₁Rs in mouse DG neurons by noradrenaline. Noradrenaline at the micromolar range potentiated synaptic transmission at the DG output and increased the phosphorylation of protein kinase A substrates in DG via activation of D₁Rs and β adrenergic receptors. Neuronal excitation preferentially enhanced noradrenaline-induced synaptic potentiation mediated by D₁Rs with minor effects on β-receptor-dependent potentiation. Increased voluntary exercise by wheel running also enhanced noradrenaline-induced, D₁R-mediated synaptic potentiation, suggesting a distinct functional role of the noradrenaline-D₁R signaling. We then examined the role of this signaling in antidepressant effects using mice exposed to chronic restraint stress. In the stressed mice, an antidepressant acting on the noradrenergic system induced a mature-to-immature change in the DG neuron phenotype, a previously proposed cellular substrate for antidepressant action. This effect was evident only in mice subjected to wheel running and blocked by a D₁R antagonist. These results suggest a critical role of noradrenaline-induced activation of D₁Rs in antidepressant effects in DG. Experience-dependent regulation of noradrenaline-D₁R signaling may determine responsiveness to antidepressant drugs in depressive disorders.

Exercise more efficiently regulates the maturation of newborn neurons and synaptic plasticity than fluoxetine in a CUS-induced depression mouse model

Depression, a common and important cause of morbidity and mortality worldwide, is commonly treated with antidepressants, electric shock and psychotherapy. Recently, increasing evidence has shown that exercise can effectively alleviate depression. To determine the difference in efficacy between exercise and the classic antidepressant fluoxetine in treating depression, we established four groups: the Control, chronic unpredictable stress (CUS/STD), running (CUS/RUN) and fluoxetine (CUS/FLX) groups. The sucrose preference test (SPT), the forced swimming test (FST), the tail suspension test (TST), immunohistochemistry, immunofluorescence and stereological analyses were used to clarify the difference in therapeutic efficacy and mechanism between exercise and fluoxetine in the treatment of depression. In the seventh week, the sucrose preference of the CUS/RUN group was significantly higher than that of the CUS/STD group, while the sucrose preference of the CUS/FLX group did not differ from that of the CUS/STD group until the eighth week. Exercise reduced the immobility time in the FST and TST, while fluoxetine only reduced immobility time in the TST. Hippocampal structure analysis showed that the CUS/STD group exhibited an increase in immature neurons and a decrease in mature neurons. Exercise reduced the number of immature neurons and increased the number of mature neurons, but no increase in the number of mature neurons was observed after fluoxetine treatment. In addition, both running and fluoxetine reversed the decrease in the number of MAP2+ dendrites in depressed mice. Exercise increased the number of spinophilin-positive (Sp+) dendritic spines in the hippocampal CA1, CA3, and dentate gyrus (DG) regions, whereas fluoxetine only increased the number of SP+ spines in the DG. In summary, exercise promoted newborn neuron maturation in the DG and regulated neuronal plasticity in three hippocampal subregions, which might explain why running exerts earlier and more comprehensive antidepressant effects than fluoxetine.

The role of social isolation stress in escalated aggression in rodent models

Anti-social behavior and violence are major public health concerns. Globally, violence contributes to more than 1.6 million deaths each year. Previous studies have reported that social rejection or neglect exacerbates aggression. In rodent models, social isolation stress is used to demonstrate the adverse effects of social deprivation on physiological, endocrinological, immunological, and behavioral parameters, including aggressive behavior. This review summarizes recent rodent studies on the effect of social isolation stress during different developmental periods on aggressive behavior and the underlying neural mechanisms. Social isolation during adulthood affects the levels of neurosteroids and neuropeptides and increases aggressive behavior. These changes are ethologically relevant for the adaptation to changes in local environmental conditions in the natural habitats. Chronic deprivation of social interaction after weaning, especially during the juvenile to adolescent periods, leads to the disruption of the development of appropriate social behavior and the maladaptive escalation of aggressive behavior. The understanding of neurobiological mechanisms underlying social isolation-induced escalated aggression will aid in the development of therapeutic interventions for escalated aggression.

How Staying Negative Is Good for the (Adult) Brain: Maintaining Chloride Homeostasis and the GABA-Shift in Neurological Disorders

Excitatory-inhibitory (E-I) imbalance has been shown to contribute to the pathogenesis of a wide range of neurodevelopmental disorders including autism spectrum disorders, epilepsy, and schizophrenia. GABA neurotransmission, the principal inhibitory signal in the mature brain, is critically coupled to proper regulation of chloride homeostasis. During brain maturation, changes in the transport of chloride ions across neuronal cell membranes act to gradually change the majority of GABA signaling from excitatory to inhibitory for neuronal activation, and dysregulation of this GABA-shift likely contributes to multiple neurodevelopmental abnormalities that are associated with circuit dysfunction. Whilst traditionally viewed as a phenomenon which occurs during brain development, recent evidence suggests that this GABA-shift may also be involved in neuropsychiatric disorders due to the "dematuration" of affected neurons. In this review, we will discuss the cell signaling and regulatory mechanisms underlying the GABA-shift phenomenon in the context of the latest findings in the field, in particular the role of chloride cotransporters NKCC1 and KCC2, and furthermore how these regulatory processes are altered in neurodevelopmental and neuropsychiatric disorders. We will also explore the interactions between GABAergic interneurons and other cell types in the developing brain that may influence the GABA-shift. Finally, with a greater understanding of how the GABA-shift is altered in pathological conditions, we will briefly outline recent progress on targeting NKCC1 and KCC2 as a therapeutic strategy against neurodevelopmental and neuropsychiatric disorders associated with improper chloride homeostasis and GABA-shift abnormalities.

CRMP4 is required for the positioning and maturation of newly generated neurons in adult mouse hippocampus

Adult neurogenesis is a phenomenon in which neural stem cells differentiate and mature to generate new neurons in the adult brain. In mammals, the sites where adult neurogenesis occurs are limited to the subgranular zone (SGZ) of the hippocampal dentate gyrus and the subventricular zone. In the hippocampus, newly generated neurons migrate into the granule cell layer (GCL) and are integrated into neural circuits. Previous studies have revealed that CRMP4, a member of the CRMP family, is expressed in immature neurons in the hippocampal SGZ of the adult brain. However, the role of CRMP4 in adult neurogenesis is unknown. To study the role of CRMP4 in hippocampal adult neurogenesis, we compared adult neurogenesis between wild type and CRMP4-/- mice. In CRMP4-/- mice, the number of doublecortin (DCX)-positive cells was comparable to that in wild-type mice, and some DCX-positive cells were ectopically located in the granule cell layer, suggesting that CRMP4 is involved in the migration of adult neurogenesis. In addition, the number of calretinin-positive new neurons in the SGZ was significantly increased, whereas the number of EdU/NeuN-double positive neurons was decreased in CRMP4-/- mice, suggesting that CRMP4 plays an important role in neuronal maturation. Because CRMP4 is expressed in immature neurons, its expression may regulate the migration from the SGZ to the GCL during neuronal maturation in hippocampal adult neurogenesis.

Semen Sojae Praeparatum alters depression-like behaviors in chronic unpredictable mild stress rats via intestinal microbiota

A large number of Chinese medical books present that Semen Sojae Praeparatum, a fermented food, possesses antidepressant effect, but the mechanism of this antidepressant effect remains largely unknown. This study aimed to explore the effect of Semen Sojae Praeparatum on rats with chronic unpredictable mild stress (CUMS)-induced depression. The results showed that Semen Sojae Praeparatum improved depression-like behaviors (negative preference of sugar water and increased swimming immobility time and time spent in the dark zone) and effectively reduced cell morphological changes in the dentate gyrus of the hippocampus in CUMS rats. In addition, Semen Sojae Praeparatum significantly promoted the contents of norepinephrine (NE), 5-hydroxytryptamine (5-HT), brain-derived neurotrophic factor (BDNF), and gamma-aminobutyric acid (GABA) in the hippocampus and the content of BDNF in the serum (p < 0.05). 16S rRNA sequencing analysis results showed that Semen Sojae Praeparatum increased the abundance of genus Ruminococcaceae_UCG-008 and decreased those of genera Lactobacillus and Bacteroides. Genus Ruminococcaceae_UCG-008 was positively correlated with GABA and BDNF levels in the hippocampus; genus Lactobacillus had a positive correlation with 5-HT; and genus Bacteroides had negative correlations with 5-HT, BDNF, and NE. In addition, Semen Sojae Praeparatum considerably decreased the concentration of short-chain fatty acids (SCFAs). These results indicated that Semen Sojae Praeparatum fermented by Rhizopus chinensis 12 and Bacillus sp. DU-106 alleviated the neurotransmitter levels and structural changes in the neuronal morphology of the hippocampus associated with the modulation of gut microbiota and SCFAs. Therefore, this study confirmed that Semen Sojae Praeparatum could alter depression and provide a theoretical basis for the investigation of the relationship between the microbiota-gut-brain axis and antidepressant.

Short Daily Exposure to Environmental Enrichment, Fluoxetine, or Their Combination Reverses Deterioration of the Coat and Anhedonia Behaviors with Differential Effects on Hippocampal Neurogenesis in Chronically Stressed Mice

Depression is a neuropsychiatric disorder with a high impact on the worldwide population. To overcome depression, antidepressant drugs are the first line of treatment. However, pre-clinical studies have pointed out that antidepressants are not entirely efficacious and that the quality of the living environment after stress cessation may play a relevant role in increasing their efficacy. As it is unknown whether a short daily exposure to environmental enrichment during chronic stress and antidepressant treatment will be more effective than just the pharmacological treatment, this study analyzed the effects of fluoxetine, environmental enrichment, and their combination on depressive-associated behavior. Additionally, we investigated hippocampal neurogenesis in mice exposed to chronic mild stress. Our results indicate that fluoxetine reversed anhedonia. Besides, fluoxetine reversed the decrement of some events of the hippocampal neurogenic process caused by chronic mild stress. Conversely, short daily exposure to environmental enrichment changed the deterioration of the coat and anhedonia. Although, this environmental intervention did not produce significant changes in the neurogenic process affected by chronic mild stress, fluoxetine plus environmental enrichment showed similar effects to those caused by environmental enrichment to reverse depressive-like behaviors. Like fluoxetine, the combination reversed the declining number of Ki67, doublecortin, calretinin cells and mature newborn neurons. Finally, this study suggests that short daily exposure to environmental enrichment improves the effects of fluoxetine to reverse the deterioration of the coat and anhedonia in chronically stressed mice. In addition, the combination of fluoxetine with environmental enrichment produces more significant effects than those caused by fluoxetine alone on some events of the neurogenic process. Thus, environmental enrichment improves the benefits of pharmacological treatment by mechanisms that need to be clarified.

Stress-Related Dysfunction of Adult Hippocampal Neurogenesis-An Attempt for Understanding Resilience?

Newborn neurons in the adult hippocampus are regulated by many intrinsic and extrinsic cues. It is well accepted that elevated glucocorticoid levels lead to downregulation of adult neurogenesis, which this review discusses as one reason why psychiatric diseases, such as major depression, develop after long-term stress exposure. In reverse, adult neurogenesis has been suggested to protect against stress-induced major depression, and hence, could serve as a resilience mechanism. In this review, we will summarize current knowledge about the functional relation of adult neurogenesis and stress in health and disease. A special focus will lie on the mechanisms underlying the cascades of events from prolonged high glucocorticoid concentrations to reduced numbers of newborn neurons. In addition to neurotransmitter and neurotrophic factor dysregulation, these mechanisms include immunomodulatory pathways, as well as microbiota changes influencing the gut-brain axis. Finally, we discuss recent findings delineating the role of adult neurogenesis in stress resilience.

Activation of the p11/SMARCA3/Neurensin-2 pathway in parvalbumin interneurons mediates the response to chronic antidepressants

The delayed behavioral response to chronic antidepressants depends on dynamic changes in the hippocampus. It was suggested that the antidepressant protein p11 and the chromatin remodeling factor SMARCA3 mediate this delayed response by inducing transcriptional changes in hippocampal neurons. However, what target genes are regulated by the p11/SMARCA3 complex to mediate the behavioral response to antidepressants, and what cell type mediates these molecular changes remain unknown. Here we report that the p11/SMARCA3 complex represses Neurensin-2 transcription in hippocampal parvalbumin-expressing interneurons after chronic treatment with Selective Serotonin Reuptake Inhibitors (SSRI). The behavioral response to antidepressants requires upregulation of p11, accumulation of SMARCA3 in the cell nucleus, and a consequent repression of Neurensin-2 transcription in these interneurons. We elucidate a functional role for p11/SMARCA3/Neurensin-2 pathway in regulating AMPA-receptor signaling in parvalbumin-expressing interneurons, a function that is enhanced by chronic treatment with SSRIs. These results link SSRIs to dynamic glutamatergic changes and implicate p11/SMARCA3/Neurensin-2 pathway in the development of more specific and efficient therapeutic strategies for neuropsychiatric disorders.

The Molecular Basis of Depression: Implications of Sex-Related Differences in Epigenetic Regulation

Major depressive disorder (MDD) is a leading cause of disability worldwide. Although the etiology and pathophysiology of MDD remain poorly understood, aberrant neuroplasticity mediated by the epigenetic dysregulation of gene expression within the brain, which may occur due to genetic and environmental factors, may increase the risk of this disorder. Evidence has also been reported for sex-related differences in the pathophysiology of MDD, with female patients showing a greater severity of symptoms, higher degree of functional impairment, and more atypical depressive symptoms. Males and females also differ in their responsiveness to antidepressants. These clinical findings suggest that sex-dependent molecular and neural mechanisms may underlie the development of depression and the actions of antidepressant medications. This review discusses recent advances regarding the role of epigenetics in stress and depression. The first section presents a brief introduction of the basic mechanisms of epigenetic regulation, including histone modifications, DNA methylation, and non-coding RNAs. The second section reviews their contributions to neural plasticity, the risk of depression, and resilience against depression, with a particular focus on epigenetic modulators that have causal relationships with stress and depression in both clinical and animal studies. The third section highlights studies exploring sex-dependent epigenetic alterations associated with susceptibility to stress and depression. Finally, we discuss future directions to understand the etiology and pathophysiology of MDD, which would contribute to optimized and personalized therapy.

Effect of citalopram on hippocampal volume in first-episode schizophrenia: Structural MRI results from the DECIFER trial

Hippocampal volume loss is prominent in first episode schizophrenia (FES) and has been associated with poor clinical outcomes and with BDNF genotype; antidepressants are believed to reverse hippocampal volume loss via release of BDNF. In a 12-month, placebo-controlled add-on trial of the antidepressant, citalopram, during the maintenance phase of FES, negative symptoms were improved with citalopram. We now report results of structural brain imaging at baseline and 6 months in 63 FES patients (34 in citalopram group) from the trial to assess whether protection against hippocampal volume loss contributed to improved negative symptoms with citalopram. Hippocampal volumetric integrity (HVI) did not change significantly in the citalopram or placebo group and did not differ between treatment groups, whereas citalopram was associated with greater volume loss of the right CA1 subfield. Change in cortical thickness was associated with SANS change in 4 regions (left rostral anterior cingulate, right frontal pole, right cuneus, and right transverse temporal) but none differed between treatment groups. Our findings suggest that minimal hippocampal volume loss occurs after stabilization on antipsychotic treatment and that citalopram's potential benefit for negative symptoms is unlikely to result from protection against hippocampal volume loss or cortical thinning.

Deciphering the synergistic network regulation of active components from SiNiSan against irritable bowel syndrome via a comprehensive strategy: Combined effects of synephrine, paeoniflorin and naringin

BACKGROUND

SiNiSan (SNS) is an ancient Chinese herbal prescription, and the current clinical treatment of irritable bowel syndrome (IBS) is effective. In the previous study of the research team, the multi-functional co-synergism of SNS against IBS was presented. Some potential drug targets and candidate ligands were predicted.

PURPOSE

This study attempts to explore the crucial ingredient combinations from SNS formula and reveal their synergistic mechanism for IBS therapy.

MATERIALS AND METHODS

In present study, a comprehensive strategy was performed to reveal IBS related pathways and biological modules, and explore synergistic effects of the ingredients, including ADME (absorption, distribution, metabolism, excretion) screening, Text mining, Venn analysis, Gene ontology (GO) analysis, Pathway cluster analysis, Molecular docking, Network construction and Experimental verification in visceral hypersensitivity (VHS) rats.

RESULTS

Three compressed IBS signal pathways were derived from ClueGO KEGG analysis of 63 IBS genes, including Neuroactive ligand-receptor interaction, Inflammatory mediator regulation of TRP (transient receptor potential) channels and Serotonergic synapse. A multi-module network, composed of four IBS therapeutic modules (psychological, inflammation, neuroendocrine and cross-talk modules), was revealed by Target-Pathway network. Nine kernel targets were considered closely associated with the IBS pathways, including ADRA2A, HTR2A, F2RL1, F2RL3, TRPV1, PKC, PKA, IL-1Β and NGF. In silico analysis revealed that three crucial ingredients (synephrine, paeoniflorin and naringin) were assumed to coordinate the network of those IBS therapeutic modules by acting on these kernel targets in the important pathways. In vivo experimental results showed that the crucial ingredient combinations synergistically affected the expressions of the kernel biological molecules, and improved the minimum capacity threshold of AWR in VHS rats.

CONCLUSION

The study proposes the important IBS associated pathways and the network regulation mechanisms of the crucial ingredients. It reveals the multi-target synergistic effect of the crucial ingredient combinations for the novel therapy on IBS.

Translating the promise of 5HT4 receptor agonists for the treatment of depression

Animal experimental studies suggest that 5-HT4 receptor activation holds promise as a novel target for the treatment of depression and cognitive impairment. 5-HT4 receptors are post-synaptic receptors that are located in striatal and limbic areas known to be involved in cognition and mood. Consistent with this, 5-HT4 receptor agonists produce rapid antidepressant effects in a number of animal models of depression, and pro-cognitive effects in tasks of learning and memory. These effects are accompanied by molecular changes, such as the increased expression of neuroplasticity-related proteins that are typical of clinically useful antidepressant drugs. Intriguingly, these antidepressant-like effects have a fast onset of their action, raising the possibility that 5-HT4 receptor agonists may be a particularly useful augmentation strategy in the early stages of SSRI treatment. Until recently, the translation of these effects to humans has been challenging. Here, we review the evidence from animal studies that the 5-HT4 receptor is a promising target for the treatment of depression and cognitive disorders, and outline a potential pathway for the efficient and cost-effective translation of these effects into humans and, ultimately, to the clinic.

Repeated fluoxetine treatment induces transient and long-term astrocytic plasticity in the medial prefrontal cortex of normal adult rats

Fluoxetine (Flx)-induced neuronal plasticity plays an important role in the effective treatment of depression and mood disorders. It is less understood whether repeated Flx treatment induces astrocytic plasticity that outlasts the presence of the drug in the body. We showed previously that Flx-induced neuronal plasticity in the medial prefrontal cortex (mPFC) persisted up to 20 days after the treatment. In this study, adult rats were subjected to a 15-day repeated Flx treatment at a daily dose of 20 mg/kg body weight. Astrocytic metabolites and markers were assessed in the mPFC at day 1 (d1) and day 20 (d20) after the treatment. Significant transient reductions in the concentrations of astrocytic metabolites taurine and myo-inositol and the expressions of glial fibrillary acidic protein (GFAP) and aquaporin-4 (AQP4) were observed in the mPFC of Flx-treated rats at d1, which recovered to the control levels at d20. Further, Flx treatment resulted in long-lasting changes in Kir4.1 expression in the mPFC, which remained downregulated at d20. The expression of 5-HT_1A receptor in the mPFC of Flx-treated rats was downregulated at d1 but became upregulated at d20. In summary, repeated Flx treatment induces both transient and long-term astrocytic plasticity in the mPFC of adult rats. The changes observed at d1 are consistent with disturbed water homeostasis and astrocytic de-maturation in the mPFC. The persistent changes in the expressions of Kir4.1 and 5-HT_1A at d20, presumably of the astrocytic origin, might have contributed to the long-term neurotrophic effects of repeated Flx treatment in the mPFC.

Forebrain-specific deficiency of the GTPase CRAG/Centaurin-γ3 leads to immature dentate gyri and hyperactivity in mice

Mouse models of various neuropsychiatric disorders, such as schizophrenia, often display an immature dentate gyrus, characterized by increased numbers of immature neurons and neuronal progenitors and a dearth of mature neurons. We previously demonstrated that the CRMP5-associated GTPase (CRAG), a short splice variant of Centaurin-γ3/AGAP3, is highly expressed in the dentate gyrus. CRAG promotes cell survival and antioxidant defense by inducing the activation of serum response factors at promyelocytic leukemia protein bodies, which are nuclear stress-responsive domains, during neuronal development. However, the physiological role of CRAG in neuronal development remains unknown. Here, we analyzed the role of CRAG using dorsal forebrain-specific CRAG/Centaurin-γ3 knockout mice. The mice revealed maturational abnormality of the hippocampal granule cells, including increased doublecortin-positive immature neurons and decreased calbindin-positive mature neurons, a typical phenotype of immature dentate gyri. Furthermore, the mice displayed hyperactivity in the open-field test, a common measure of exploratory behavior, suggesting that these mice may serve as a novel model for neuropsychiatric disorder associated with hyperactivity. Thus, we conclude that CRAG is required for the maturation of neurons in the dentate gyrus, raising the possibility that its deficiency might promote the development of psychiatric disorders in humans.

Altered hippocampal gene expression, glial cell population, and neuronal excitability in aminopeptidase P1 deficiency

Inborn errors of metabolism are often associated with neurodevelopmental disorders and brain injury. A deficiency of aminopeptidase P1, a proline-specific endopeptidase encoded by the Xpnpep1 gene, causes neurological complications in both humans and mice. In addition, aminopeptidase P1-deficient mice exhibit hippocampal neurodegeneration and impaired hippocampus-dependent learning and memory. However, the molecular and cellular changes associated with hippocampal pathology in aminopeptidase P1 deficiency are unclear. We show here that a deficiency of aminopeptidase P1 modifies the glial population and neuronal excitability in the hippocampus. Microarray and real-time quantitative reverse transcription-polymerase chain reaction analyses identified 14 differentially expressed genes (Casp1, Ccnd1, Myoc, Opalin, Aldh1a2, Aspa, Spp1, Gstm6, Serpinb1a, Pdlim1, Dsp, Tnfaip6, Slc6a20a, Slc22a2) in the Xpnpep1^−/− hippocampus. In the hippocampus, aminopeptidase P1-expression signals were mainly detected in neurons. However, deficiency of aminopeptidase P1 resulted in fewer hippocampal astrocytes and increased density of microglia in the hippocampal CA3 area. In addition, Xpnpep1^−/− CA3b pyramidal neurons were more excitable than wild-type neurons. These results indicate that insufficient astrocytic neuroprotection and enhanced neuronal excitability may underlie neurodegeneration and hippocampal dysfunction in aminopeptidase P1 deficiency.

The effects of Kctd12, an auxiliary subunit of GABAB receptor in dentate gyrus on behavioral response to chronic social defeat stress in mice

Adaptive responses to stress are critical to enhance physical and mental well-being, but excessive or prolonged stress may cause inadaptability and increase the risks of psychiatric disorders, such as depression. GABABR signaling is fundamental to brain function and has been identified in neuropsychiatric disorders. KCTD12 is a critical auxiliary subunit in GABABR signaling, but its role in mental disorders, such as depression is unclear. In the present study, we used a well-validated mice model, chronic social defeat stress (CSDS) to investigate behavioral responses to stress and explore the role of Kctd12 in stress response, as well as the relevant mechanisms. We found that CSDS increased the expression of Kctd12 in the dentate gyrus (DG), a subregion of hippocampus. Overexpression of Kctd12 in DG induced higher responsiveness to acute stress and increased vulnerability to social stress in mice, whereas knock-down of Kctd12 in DG prevented the social avoidance. Furthermore, an increased expression of GABAB receptor 2 (GB2) in the DG of CSDS-treated mice was observed, and CGP35348, an antagonist of GABABR, improved the stress-induced behavior responses along with suppressing the excess expression of Kctd12. In addition, Kctd12 regulated the excitability of granule cell in DG, and the stimulation of neuronal activity by silencing Kctd12 contributed to the antidepressant-like effect of fluoxetine. These findings identify that the Kctd12 in DG works as a critical mediator of stress responses, providing a promising therapeutic target in stress-related psychiatric disorders, including depression.

Rewiring of the Serotonin System in Major Depression

Serotonin is a key neurotransmitter that is implicated in a wide variety of behavioral and cognitive phenotypes. Originating in the raphe nuclei, 5-HT neurons project widely to innervate many brain regions implicated in the functions. During the development of the brain, as serotonin axons project and innervate brain regions, there is evidence that 5-HT plays key roles in wiring the developing brain, both by modulating 5-HT innervation and by influencing synaptic organization within corticolimbic structures. These actions are mediated by 14 different 5-HT receptors, with region- and cell-specific patterns of expression. More recently, the role of the 5-HT system in synaptic re-organization during adulthood has been suggested. The 5-HT neurons have the unusual capacity to regrow and reinnervate brain regions following insults such as brain injury, chronic stress, or altered development that result in disconnection of the 5-HT system and often cause depression, anxiety, and cognitive impairment. Chronic treatment with antidepressants that amplify 5-HT action, such as selective serotonin reuptake inhibitors (SSRIs), appears to accelerate the rewiring of the 5-HT system by mechanisms that may be critical to the behavioral and cognitive improvements induced in these models. In this review, we survey the possible 5-HT receptor mechanisms that could mediate 5-HT rewiring and assess the evidence that 5-HT-mediated brain rewiring is impacting recovery from mental illness. By amplifying 5-HT-induced rewiring processes using SSRIs and selective 5-HT agonists, more rapid and effective treatments for injury-induced mental illness or cognitive impairment may be achieved.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Inflammatory Response, a Key Pathophysiological Mechanism of Obesity-Induced Depression

In recent years, with the acceleration of life rhythm and the increase of social competition, the incidence of obesity and depression has been increasing, which has seriously affected the quality of life and health of people. Obesity and depression, two seemingly unrelated physical and psychological diseases, in fact, are closely related: obese people are more likely to have depression than nonobese ones. We have reviewed and analyzed the relevant research literature and found that the inflammatory response plays a key role in obesity-induced depression. This article will discuss in detail the inflammatory mechanisms by which obesity induces depression.

Paroxetine binding and activation of phosphofructokinase implicates energy metabolism in antidepressant mode of action

Selective serotonin reuptake inhibitors (SSRIs) are the predominant drugs prescribed for Major Depressive Disorder. The immediate pharmacological target of SSRIs is the serotonin transporter. However, the delayed therapeutic effect and high rate of patient non-response make it highly likely that SSRIs also have other molecular targets that are yet to be identified. Cellular thermal shift assay (CETSA) is a method based on thermal stabilization of target proteins upon drug binding. In the present study, we show that the SSRI paroxetine binds to phosphofructokinase (PFK) protein using CETSA. We found that mouse brain PFK and recombinant human PFK proteins are stabilized by paroxetine incubation. Chronic paroxetine treatment also significantly increased mouse brain PFK thermal stability. Paroxetine significantly elevated in vitro and in vivo PFK activity. Levels of several metabolites in glutamate- and energy metabolism-related pathways are significantly correlated with PFK activity in mouse hippocampus. Our data show that paroxetine can bind to PFK and affect its activity. Implications of these results for the antidepressant mode of action of paroxetine are discussed.

Adult Neurogenesis, Glia, and the Extracellular Matrix

In the adult mammalian hippocampus, new neurons arise from stem and progenitor cell division, in a process known as adult neurogenesis. Adult-generated neurons are sensitive to experience and may participate in hippocampal functions, including learning and memory, anxiety and stress regulation, and social behavior. Increasing evidence emphasizes the importance of new neuron connectivity within hippocampal circuitry for understanding the impact of adult neurogenesis on brain function. In this Review, we discuss how the functional consequences of new neurons arise from the collective interactions of presynaptic and postsynaptic neurons, glial cells, and the extracellular matrix, which together form the "tetrapartite synapse."

The selenocompound 1-methyl-3-(phenylselanyl)-1H-indole attenuates depression-like behavior, oxidative stress, and neuroinflammation in streptozotocin-treated mice

Major depressive disorder (MDD) is a chronic mental illness affecting a wide range of people worldwide. The pathophysiology of MDD is not completely elucidated, but it is believed that oxidative stress and neuroinflammation are involved. In light with this, the aim of the present study was to investigate whether a single administration of the antioxidant 1-methyl-3-(phenylselanyl)-1H-indole (MFSeI) was able to reverse the streptozotocin-induced depression-like behavior, oxidative stress, and neuroinflammation in mice. MFSeI (10 mg/kg) was administered intragastrically (i.g.) 24 h after the intracerebroventricular injection of STZ (0.2 mg/4 μL/per mouse). Thirty minutes after MFSeI administration, behavioral tests and neurochemical analyses were performed. Fluoxetine (10 mg/kg, i.g.) was used as a positive control. MFSeI and fluoxetine were able to reverse the STZ-induced depression-like behavior, as evidenced by decreased immobility time in the forced swimming test and increased grooming time in the splash test. Mechanistically, MFSeI reversed the increased levels of reactive species and lipid peroxidation in the prefrontal cortices and hippocampi of STZ-treated mice. Additionally, neuroinflammation (i.e. expression of NF-κB, IL-1β, and TNF-α) and the reduced mRNA levels of BDNF in the and hippocampi of depressed mice were reversed by treatment with MFSeI. Fluoxetine did not improve the STZ-induced alterations at the levels of reactive species, NF-κB and BDNF in the prefrontal cortices neither the levels of TNF-α in both brain regions. Together, these data suggest that the MFSeI may be a promising compound with antidepressant-like action, reducing oxidative stress and modulating inflammatory pathways in the brain of depressed mice.

Sox11 is an Activity-Regulated Gene with Dentate-Gyrus-Specific Expression Upon General Neural Activation

Neuronal activity initiates transcriptional programs that shape long-term changes in plasticity. Although neuron subtypes differ in their plasticity response, most activity-dependent transcription factors (TFs) are broadly expressed across neuron subtypes and brain regions. Thus, how region- and neuronal subtype-specific plasticity are established on the transcriptional level remains poorly understood. We report that in young adult (i.e., 6-8 weeks old) mice, the developmental TF SOX11 is induced in neurons within 6 h either by electroconvulsive stimulation or by exploration of a novel environment. Strikingly, SOX11 induction was restricted to the dentate gyrus (DG) of the hippocampus. In the novel environment paradigm, SOX11 was observed in a subset of c-FOS expressing neurons (ca. 15%); whereas around 75% of SOX11+ DG granule neurons were c-FOS+, indicating that SOX11 was induced in an activity-dependent fashion in a subset of neurons. Environmental enrichment or virus-mediated overexpression of SOX11 enhanced the excitability of DG granule cells and downregulated the expression of different potassium channel subunits, whereas conditional Sox11/4 knock-out mice presented the opposite phenotype. We propose that Sox11 is regulated in an activity-dependent fashion, which is specific to the DG, and speculate that activity-dependent Sox11 expression may participate in the modulation of DG neuron plasticity.

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.

Fluoxetine effects on behavior and adult hippocampal neurogenesis in female C57BL/6J mice across the estrous cycle

RATIONALE

Some mood disorders, such as major depressive disorder, are more prevalent in women than in men. However, historically preclinical studies in rodents have a lower inclusion rate of females than males, possibly due to the fact that behavior can be affected by the estrous cycle. Several studies have demonstrated that chronic antidepressant treatment can decrease anxiety-associated behaviors and increase adult hippocampal neurogenesis in male rodents.

OBJECTIVE

Very few studies have looked at the effects of antidepressants on behavior and neurogenesis across the estrous cycle in naturally cycling female rodents.

METHODS

Here, we analyze the effects of chronic treatment with the selective serotonin reuptake inhibitor (SSRI) fluoxetine (Prozac) on behavior and adult hippocampal neurogenesis in naturally cycling C57BL/6J females across all four phases of the estrous cycle.

RESULTS

In naturally cycling C57BL/6J females, fluoxetine decreases negative valence behaviors associated with anxiety in the elevated plus maze and novelty-suppressed feeding task, reduces immobility time in forced swim test, and increases adult hippocampal neurogenesis. Interestingly, the effects of fluoxetine on several negative valence behavior and adult hippocampal neurogenesis measures were mainly found within the estrus and diestrus phases of the estrous cycle.

CONCLUSIONS

Taken together, these data are the first to illustrate the effects of fluoxetine on behavior and adult hippocampal neurogenesis across all four phases of the murine estrous cycle.

Predominant Role of Serotonin at the Hippocampal Mossy Fiber Synapse with Redundant Monoaminergic Modulation

The hippocampal mossy fiber (MF) synapse has been implicated in the pathophysiology and treatment of psychiatric disorders. Alterations of dopaminergic and serotonergic modulations at this synapse are candidate mechanisms underlying antidepressant and other related treatments. However, these monoaminergic modulations share the intracellular signaling pathway at the MF synapse, which implies redundancy in their functions. We here show that endogenous monoamines can potentiate MF synaptic transmission in mouse hippocampal slices by activating the serotonin 5-HT₄ receptor. Dopamine receptors were not effectively activated by endogenous agonists, suggesting that the dopaminergic modulation is latent. Electroconvulsive treatment enhanced the 5-HT₄ receptor-mediated serotonergic synaptic potentiation specifically at the MF synapse, increased the hippocampal serotonin content, and produced an anxiolytic-like behavioral effect in a 5-HT₄ receptor-dependent manner. These results suggest that serotonin plays a predominant role in monoaminergic modulations at the MF synapse. Augmentation of this serotonergic modulation may mediate anxiolytic effects of electroconvulsive treatment.

Raloxifene potentiates the effect of fluoxetine against maximal electroshock induced seizures in mice

The evidence to guide clinicians regarding rationale polytherapy with current antiepileptic drugs (AEDs) is lacking, and current practice recommendations are largely empirical.  The excessive drug loading with combinatorial therapies of existing AEDs are associated with escalated neurotoxicity, and that emergence of pharmacoresistant seizures couldn't be averted. In pursuit of judicious selection of novel AEDs in combinatorial therapies with mechanism based evidences, standardized dose of raloxifene, fluoxetine, bromocriptine and their low dose combinations, were experimentally tested for their impact on maximal electroshock (MES) induced tonic hind limb extension (THLE) in mice. Hippocampal neuropeptide Y (NPY) levels, oxidative stress and histopathological studies were undertaken. The results suggest the potentiating effect of 4 mg/kg raloxifene on 14 mg/kg fluoxetine against MES induced THLE, as otherwise monotherapy with 4 mg/kg raloxifene was unable to produce an effect. The results also depicted better efficacy than carbamazepine (20 mg/kg), standard AED. Most profoundly, MES-induced significant (P < 0.001) reduction in hippocampal NPY levels, that were escalated insignificantly with the duo-drug combination, suggesting some other mechanism in mitigation of electroshock induced seizures. These results were later corroborated with assays to assess oxidative stress and neuronal damage. In conclusion, the results demonstrated the propitious therapeutic benefit of duo-drug low dose combination of drugs; raloxifene and fluoxetine, with diverse mode of actions fetching greater effectiveness in the management of generalized tonic clonic seizures (GTCS).

Obligatory roles of dopamine D1 receptors in the dentate gyrus in antidepressant actions of a selective serotonin reuptake inhibitor, fluoxetine

Depression is a leading cause of disability. Current pharmacological treatment of depression is insufficient, and development of improved treatments especially for treatment-resistant depression is desired. Understanding the neurobiology of antidepressant actions may lead to development of improved therapeutic approaches. Here, we demonstrate that dopamine D1 receptors in the dentate gyrus act as a pivotal mediator of antidepressant actions in mice. Chronic administration of a selective serotonin reuptake inhibitor (SSRI), fluoxetine, increases D1 receptor expression in mature granule cells in the dentate gyrus. The increased D1 receptor signaling, in turn, contributes to the actions of chronic fluoxetine treatment, such as suppression of acute stress-evoked serotonin release, stimulation of adult neurogenesis and behavioral improvement. Importantly, under severely stressed conditions, chronic administration of a D1 receptor agonist in conjunction with fluoxetine restores the efficacy of fluoxetine actions on D1 receptor expression and behavioral responses. Thus, our results suggest that stimulation of D1 receptors in the dentate gyrus is a potential adjunctive approach to improve therapeutic efficacy of SSRI antidepressants.

Expression of progenitor cell/immature neuron markers does not present definitive evidence for adult neurogenesis

It is agreed upon that adult hippocampal neurogenesis (AHN) occurs in the dentate gyrus (DG) in rodents. However, the existence of AHN in humans, particularly in elderly individuals, remains to be determined. Recently, several studies reported that neural progenitor cells, neuroblasts, and immature neurons were detected in the hippocampus of elderly humans, based on the expressions of putative markers for these cells, claiming that this provides evidence of the persistence of AHN in humans. Herein, we briefly overview the phenomenon that we call "dematuration," in which mature neurons dedifferentiate to a pseudo-immature status and re-express the molecular markers of neural progenitor cells and immature neurons. Various conditions can easily induce dematuration, such as inflammation and hyper-excitation of neurons, and therefore, the markers for neural progenitor cells and immature neurons may not necessarily serve as markers for AHN. Thus, the aforementioned studies have not presented definitive evidence for the persistence of hippocampal neurogenesis throughout adult life in humans, and we would like to emphasize that those markers should be used cautiously when presented as evidence for AHN. Increasing AHN has been considered as a therapeutic target for Alzheimer's disease (AD); however, given that immature neuronal markers can be re-expressed in mature adult neurons, independent of AHN, in various disease conditions including AD, strategies to increase the expression of these markers in the DG may be ineffective or may worsen the symptoms of such diseases.

Search for factors contributing to resistance to the electroconvulsive seizure treatment model using adrenocorticotrophic hormone-treated mice

Approximately one third of patients with depression remain treatment resistant with existing antidepressants, suggesting that the currently-available antidepressants cannot induce appropriate responses in the brains of all patients. Long-term exposure to adrenocorticotrophic hormone (ACTH) has been proposed as a model that mimics at least some aspects of clinical treatment-resistant depression in rodents. The purpose of this study was to explore potential causes of antidepressant treatment resistance using the chronic ACTH-treated mouse model. We subjected ACTH-treated mice to a rodent model of electroconvulsive therapy, i.e., electroconvulsive seizure (ECS), which induces various molecular and cellular changes, including in gene expression and adult neurogenesis in the hippocampus. First, behavioral effect of repeated ECS in the forced swim test (FST) was examined. In our experimental setting, ACTH-treated mice showed resistance to the antidepressant-like effect of ECS in the FST. We then examined which cellular and molecular changes induced by ECS were attenuated by ACTH administration. Chronic ACTH treatment suppressed the increase of gene expression such as of Bdnf, Npy, and Drd1 induced by ECS in the hippocampus. In contrast, there was no difference in ECS-induced promotion of the early neurogenetic process in the hippocampus between ACTH-treated and control mice. Our results suggest the possibility that impaired neuromodulation and monoamine signaling in the hippocampus are among the factors contributing to antidepressant treatment resistance.

Fluoxetine-induced plasticity in the visual cortex outlasts the duration of the naturally occurring critical period

Heightened neuronal plasticity expressed during early postnatal life has been thought to permanently decline once critical periods have ended. For example, monocular deprivation is able to shift ocular dominance in the mouse visual cortex during the first months of life, but this effect is lost later in life. However, various treatments, such as the antidepressant fluoxetine, can reactivate a critical period‐like plasticity in the adult brain. When monocular deprivation is supplemented with chronic fluoxetine administration, a major shift in ocular dominance is produced after the critical period has ended. In the current study, we characterized the temporal patterns of fluoxetine‐induced plasticity in the adult mouse visual cortex, using in vivo optical imaging. We found that artificially induced plasticity in ocular dominance extended beyond the duration of the naturally occurring critical period and continued as long as fluoxetine was administered. However, this fluoxetine‐induced plasticity period ended as soon as the drug was not given. These features of antidepressant‐induced plasticity may be useful when designing treatment strategies involving long‐term antidepressant treatment in humans.