Immature dentate gyrus: an endophenotype of neuropsychiatric disorders

Linking mitochondrial dysfunction, neurotransmitter, neural network abnormalities and mania: Elucidating neurobiological mechanisms of the therapeutic effect of the ketogenic diet in Bipolar Disorder

There is growing interest in the ketogenic diet as a treatment for Bipolar Disorder (BD), with promising anecdotal and small case study reports of efficacy. Yet, the neurobiological mechanisms by which diet-induced ketosis might ameliorate BD symptoms remain to be determined, particularly in manic and hypomanic states - defining features of BD. Identifying these mechanisms will therefore provide new markers to guide personalized interventions and provide targets for novel treatment developments for individuals with BD. In this critical review, we describe recent findings highlighting two types of neurobiological abnormalities in BD: 1) mitochondrial dysfunction; and 2) neurotransmitter and neural network functional abnormalities. We will consequently link these abnormalities lead to mania/hypomania and depression in BD and then describe the biological underpinnings by which the ketogenic diet might have a beneficial effect in individuals with BD. We end the review by describing future approaches that can be employed to elucidate the neurobiology underlying the therapeutic effect of the ketogenic diet in BD. In so doing, this may provide marker predictors to identify individuals who will respond well to the ketogenic diet, as well as offer neural targets for novel treatment developments for BD.

The lncRNA Snhg11, a new candidate contributing to neurogenesis, plasticity, and memory deficits in Down syndrome

Down syndrome (DS) stands as the prevalent genetic cause of intellectual disability, yet comprehensive understanding of its cellular and molecular underpinnings remains limited. In this study, we explore the cellular landscape of the hippocampus in a DS mouse model, the Ts65Dn, through single-nuclei transcriptional profiling. Our findings demonstrate that trisomy manifests as a highly specific modification of the transcriptome within distinct cell types. Remarkably, we observed a significant shift in the transcriptomic profile of granule cells in the dentate gyrus (DG) associated with trisomy. We identified the downregulation of a specific small nucleolar RNA host gene, Snhg11, as the primary driver behind this observed shift in the trisomic DG. Notably, reduced levels of Snhg11 in this region were also observed in a distinct DS mouse model, the Dp(16)1Yey, as well as in human postmortem brain tissue, indicating its relevance in Down syndrome. To elucidate the function of this long non-coding RNA (lncRNA), we knocked down Snhg11 in the DG of wild-type mice. Intriguingly, this intervention alone was sufficient to impair synaptic plasticity and adult neurogenesis, resembling the cognitive phenotypes associated with trisomy in the hippocampus. Our study uncovers the functional role of Snhg11 in the DG and underscores the significance of this lncRNA in intellectual disability. Furthermore, our findings highlight the importance of DG in the memory deficits observed in Down syndrome.

Large-scale animal model study uncovers altered brain pH and lactate levels as a transdiagnostic endophenotype of neuropsychiatric disorders involving cognitive impairment

Increased levels of lactate, an end-product of glycolysis, have been proposed as a potential surrogate marker for metabolic changes during neuronal excitation. These changes in lactate levels can result in decreased brain pH, which has been implicated in patients with various neuropsychiatric disorders. We previously demonstrated that such alterations are commonly observed in five mouse models of schizophrenia, bipolar disorder, and autism, suggesting a shared endophenotype among these disorders rather than mere artifacts due to medications or agonal state. However, there is still limited research on this phenomenon in animal models, leaving its generality across other disease animal models uncertain. Moreover, the association between changes in brain lactate levels and specific behavioral abnormalities remains unclear. To address these gaps, the International Brain pH Project Consortium investigated brain pH and lactate levels in 109 strains/conditions of 2294 animals with genetic and other experimental manipulations relevant to neuropsychiatric disorders. Systematic analysis revealed that decreased brain pH and increased lactate levels were common features observed in multiple models of depression, epilepsy, Alzheimer's disease, and some additional schizophrenia models. While certain autism models also exhibited decreased pH and increased lactate levels, others showed the opposite pattern, potentially reflecting subpopulations within the autism spectrum. Furthermore, utilizing large-scale behavioral test battery, a multivariate cross-validated prediction analysis demonstrated that poor working memory performance was predominantly associated with increased brain lactate levels. Importantly, this association was confirmed in an independent cohort of animal models. Collectively, these findings suggest that altered brain pH and lactate levels, which could be attributed to dysregulated excitation/inhibition balance, may serve as transdiagnostic endophenotypes of debilitating neuropsychiatric disorders characterized by cognitive impairment, irrespective of their beneficial or detrimental nature.

Treadmill Running Regulates Adult Neurogenesis, Spatial and Non-spatial Learning, Parvalbumin Neuron Activity by ErbB4 Signaling

Exercise can promote adult neurogenesis and improve symptoms associated with schizophrenia and other mental disorders via parvalbumin (PV)-positive GABAergic interneurons in the dentate gyrus ErbB4 is the receptor of neurotrophic factor neuregulin 1, expressed mostly in PV-positive interneurons. Whether ErbB4 in PV-positive neurons mediates the beneficial effect of exercise and adult neurogenesis on mental disorder needs to be further investigation. Here, we first conducted a four-week study on the effects of AG1478, an ErbB4 inhibitor, on memory and neurogenesis. AG1478 significantly impaired the performance in several memory tasks, including the T-maze, Morris water maze, and contextual fear conditioning, downregulated the expression of total ErbB4 (T-ErbB4) and the ratio of phosphate-ErbB4 (p-ErbB4) to T-ErbB4, and associated with neurogenesis impairment. Interestingly, AG1478 also appeared to decrease intracellular calcium levels in PV neurons, which could be reversed by exercise. These results suggest exercise may regulate adult neurogenesis and PV neuron activity through ErbB4 signaling. Overall, these findings provide further evidence of the importance of exercise for neurogenesis and suggest that targeting ErbB4 may be a promising strategy for improving memory and other cognitive functions in individuals with mental disorders.

Febrile Seizure Causes Deficit in Social Novelty, Gliosis, and Proinflammatory Cytokine Response in the Hippocampal CA2 Region in Rats

Febrile seizure (FS), which occurs as a response to fever, is the most common seizure that occurs in infants and young children. FS is usually accompanied by diverse neuropsychiatric symptoms, including impaired social behaviors; however, research on neuropsychiatric disorders and hippocampal inflammatory changes following febrile seizure occurrences is very limited. Here, we provide evidence linking FS occurrence with ASD pathogenesis in rats. We developed an FS juvenile rats model and found ASD-like abnormal behaviors including deficits in social novelty, repetitive behaviors, and hyperlocomotion. In addition, FS model juvenile rats showed enhanced levels of gliosis and inflammation in the hippocampal CA2 region and cerebellum. Furthermore, abnormal levels of social and repetitive behaviors persisted in adults FS model rats. These findings suggest that the inflammatory response triggered by febrile seizures in young children could potentially serve as a mediator of social cognitive impairments.

The lncRNA Snhg11, a new candidate contributing to neurogenesis, plasticity and memory deficits in Down syndrome

Down syndrome (DS) stands as the prevalent genetic cause of intellectual disability, yet comprehensive understanding of its cellular and molecular underpinnings remains limited. In this study, we explore the cellular landscape of the hippocampus in a DS mouse model through single-nuclei transcriptional profiling. Our findings demonstrate that trisomy manifests as a highly specific modification of the transcriptome within distinct cell types. Remarkably, we observed a significant shift in the transcriptomic profile of granule cells in the dentate gyrus (DG) associated with trisomy. We identified the downregulation of a specific small nucleolar RNA host gene, Snhg11, as the primary driver behind this observed shift in the trisomic DG. Notably, reduced levels of Snhg11 in this region were also observed in a distinct DS mouse model, the Dp(16)1Yey, as well as in human postmortem tissue, indicating its relevance in Down syndrome. To elucidate the function of this long non-coding RNA (lncRNA), we knocked down Snhg11 in the DG of wild-type mice. Intriguingly, this intervention alone was sufficient to impair synaptic plasticity and adult neurogenesis, resembling the cognitive phenotypes associated with trisomy in the hippocampus. Our study uncovers the functional role of Snhg11 in the DG and underscores the significance of this lncRNA in intellectual disability. Furthermore, our findings highlight the importance of the DG in the memory deficits observed in Down syndrome.

The Role of Ketamine in the Treatment of Bipolar Depression: A Scoping Review

Bipolar depression remains a clinical challenge with a quarter of patients failing to respond to initial conventional treatments. Although ketamine has been extensively studied in unipolar depression, its role in bipolar disorder remains inconclusive. The aim of our scoping review was to comprehensively synthesize the current clinical literature around ketamine use in bipolar depression. A total of 10 clinical studies (5 randomized controlled trials and 5 open label studies) were selected. The preliminary evidence, albeit weak, suggests that ketamine is a promising treatment and calls for further interest from the research community. Overall, ketamine treatment appeared to be tolerable with minimal risk for manic/hypomanic switching and showed some effectiveness across parameters of depression and suicidality. Moreover, ketamine is a potential treatment agent in patients with treatment-resistant bipolar depression with promising data extracted from extant controlled trials and real-world effectiveness studies. Future studies are needed to identify ketamine's role in acute and maintenance treatment phases of bipolar depression. Moreover, future researchers should study the recurrence prevention and anti-suicidal effects of ketamine in the treatment of bipolar depression.

Prenatal dexamethasone exposure induces anxiety- and depressive-like behavior of male offspring rats through intrauterine programming of the activation of NRG1-ErbB4 signaling in hippocampal PV interneurons

Dexamethasone is a commonly used synthetic glucocorticoid in the clinic. As a compound that can cross the placental barrier to promote fetal lung maturation, dexamethasone is extensively used in pregnant women at risk of premature delivery. However, the use of glucocorticoids during pregnancy increases the risk of neurodevelopmental disorders. In the present study, we observed anxiety- and depressive-like behavior changes and hyperexcitability of hippocampal neurons in adult rat offspring with previous prenatal dexamethasone exposure (PDE); the observed changes were related to in utero damage of parvalbumin interneurons. A programmed change in neuregulin 1 (NRG1)-Erb-b2 receptor tyrosine kinase 4 (ErbB4) signaling was the key to the damage of parvalbumin interneurons in the hippocampus of PDE offspring. Anxiety- and depressive-like behavior, NRG1-ErbB4 signaling activation, and damage of parvalbumin interneurons in PDE offspring were aggravated after chronic stress. The intervention of NRG1-ErbB4 signaling contributed to the improvement in dexamethasone-mediated injury to parvalbumin interneurons. These results suggested that PDE might cause anxiety- and depressive-like behavior changes in male rat offspring through the programmed activation of NRG1-ErbB4 signaling, resulting in damage to parvalbumin interneurons and hyperactivity of the hippocampus. Intrauterine programming of neuregulin 1 (NRG1)-Erb-b2 receptor tyrosine kinase 4 (ERBB4) overactivation by dexamethasone mediates anxiety- and depressive-like behavior in male rat offspring.

Behavioral phenotype, intestinal microbiome, and brain neuronal activity of male serotonin transporter knockout mice

The serotonin transporter (5-HTT) plays a critical role in the regulation of serotonin neurotransmission. Mice genetically deficient in 5-HTT expression have been used to study the physiological functions of 5-HTT in the brain and have been proposed as a potential animal model for neuropsychiatric and neurodevelopmental disorders. Recent studies have provided evidence for a link between the gut-brain axis and mood disorders. However, the effects of 5-HTT deficiency on gut microbiota, brain function, and behavior remain to be fully characterized. Here we investigated the effects of 5-HTT deficiency on different types of behavior, the gut microbiome, and brain c-Fos expression as a marker of neuronal activation in response to the forced swim test for assessing depression-related behavior in male 5-HTT knockout mice. Behavioral analysis using a battery of 16 different tests showed that 5-HTT-/- mice exhibited markedly reduced locomotor activity, decreased pain sensitivity, reduced motor function, increased anxiety-like and depression-related behavior, altered social behavior in novel and familiar environments, normal working memory, enhanced spatial reference memory, and impaired fear memory compared to 5-HTT+/+ mice. 5-HTT+/- mice showed slightly reduced locomotor activity and impaired social behavior compared to 5-HTT+/+ mice. Analysis of 16S rRNA gene amplicons showed that 5-HTT-/- mice had altered gut microbiota abundances, such as a decrease in Allobaculum, Bifidobacterium, Clostridium sensu stricto, and Turicibacter, compared to 5-HTT+/+ mice. This study also showed that after exposure to the forced swim test, the number of c-Fos-positive cells was higher in the paraventricular thalamus and lateral hypothalamus and was lower in the prefrontal cortical regions, nucleus accumbens shell, dorsolateral septal nucleus, hippocampal regions, and ventromedial hypothalamus in 5-HTT-/- mice than in 5-HTT+/+ mice. These phenotypes of 5-HTT-/- mice partially recapitulate clinical observations in humans with major depressive disorder. The present findings indicate that 5-HTT-deficient mice serve as a good and valid animal model to study anxiety and depression with altered gut microbial composition and abnormal neuronal activity in the brain, highlighting the importance of 5-HTT in brain function and the mechanisms underlying the regulation of anxiety and depression.

Lower circulating neuron-specific enolase concentrations in adults and adolescents with severe mental illness

BACKGROUND

Both neurodegenerative and neurodevelopmental abnormalities have been suggested to be part of the etiopathology of severe mental illness (SMI). Neuron-specific enolase (NSE), mainly located in the neuronal cytoplasm, may indicate the process as it is upregulated after neuronal injury while a switch from non-neuronal enolase to NSE occurs during neuronal maturation.

METHODS

We included 1132 adult patients with SMI [schizophrenia (SZ) or bipolar spectrum disorders], 903 adult healthy controls (HC), 32 adolescent patients with SMI and 67 adolescent HC. Plasma NSE concentrations were measured by enzyme immunoassay. For 842 adults and 85 adolescents, we used total grey matter volume (TGMV) based on T1-weighted magnetic resonance images processed in FreeSurfer v6.0. We explored NSE case-control differences in adults and adolescents separately. To investigate whether putative case-control differences in NSE were TGMV-dependent we controlled for TGMV.

RESULTS

We found significantly lower NSE concentrations in both adult (p < 0.001) and adolescent patients with SMI (p = 0.007) compared to HC. The results remained significant after controlling for TGMV. Among adults, both patients with SZ spectrum (p < 0.001) and bipolar spectrum disorders (p = 0.005) had lower NSE than HC. In both patient subgroups, lower NSE levels were associated with increased symptom severity. Among adults (p < 0.001) and adolescents (p = 0.040), females had lower NSE concentrations than males.

CONCLUSION

We found lower NSE concentrations in adult and adolescent patients with SMI compared to HC. The results suggest the lack of progressive neuronal injury, and may reflect abnormal neuronal maturation. This provides further support of a neurodevelopmental rather than a neurodegenerative mechanism in SMI.

Current advancements of modelling schizophrenia using patient-derived induced pluripotent stem cells

Schizophrenia (SZ) is a severe psychiatric disorder, with a prevalence of 1-2% world-wide and substantial health- and social care costs. The pathology is influenced by both genetic and environmental factors, however the underlying cause still remains elusive. SZ has symptoms including delusions, hallucinations, confused thoughts, diminished emotional responses, social withdrawal and anhedonia. The onset of psychosis is usually in late adolescence or early adulthood. Multiple genome-wide association and whole exome sequencing studies have provided extraordinary insights into the genetic variants underlying familial as well as polygenic forms of the disease. Nonetheless, a major limitation in schizophrenia research remains the lack of clinically relevant animal models, which in turn hampers the development of novel effective therapies for the patients. The emergence of human induced pluripotent stem cell (hiPSC) technology has allowed researchers to work with SZ patient-derived neuronal and glial cell types in vitro and to investigate the molecular basis of the disorder in a human neuronal context. In this review, we summarise findings from available studies using hiPSC-based neural models and discuss how these have provided new insights into molecular and cellular pathways of SZ. Further, we highlight different examples of how these models have shown alterations in neurogenesis, neuronal maturation, neuronal connectivity and synaptic impairment as well as mitochondrial dysfunction and dysregulation of miRNAs in SZ patient-derived cultures compared to controls. We discuss the pros and cons of these models and describe the potential of using such models for deciphering the contribution of specific human neural cell types to the development of the disease.

The Association of Biochemical and Genetic Biomarkers in VEGF Pathway with Depression

VEGF is an important neurotrophic and vascular factor involved in mental disorders. The objective of this study was to verify the effect of genetic polymorphisms in the VEGF pathway on the risk for depression, symptom intensity, and suicide attempts. To examine the association between the VEGF pathway and depression, we genotyped polymorphisms and measured the plasma concentrations of VEGF, KDR, and FLT1 proteins. The participants were 160 patients with depression and 114 healthy controls. The questionnaires that assessed the clinical profile of the patients were the MINI-International Neuropsychiatric Interview, GRID-HAMD₂₁, CTQ, BSI, and the number of suicide attempts. Genotyping of participants was performed using the real-time PCR and protein measurements were performed using the enzyme-linked immunosorbent assay (ELISA). VEGF and its inhibitors were reduced in depression. Individuals with depression and displaying the homozygous AA of the rs699947 polymorphism had higher plasma concentrations of VEGF (p-value = 0.006) and were associated with a greater number of suicide attempts (p-value = 0.041). Individuals with depression that were homozygous for the G allele of the FLT1 polymorphism rs7993418 were associated with lower symptom severity (p-value = 0.040). Our results suggest that VEGF pathway polymorphisms are associated with the number of suicide attempts and the severity of depressive symptoms.

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.

Human-Induced Pluripotent Stem Cell Technology: Toward the Future of Personalized Psychiatry

The polygenic and multifactorial nature of many psychiatric disorders has hampered implementation of the personalized medicine approach in clinical practice. However, induced pluripotent stem cell (iPSC) technology has emerged as an innovative tool for patient-specific disease modeling to expand the pathophysiology knowledge and treatment perspectives in the last decade. Current technologies enable adult human somatic cell reprogramming into iPSCs to generate neural cells and direct neural cell conversion to model organisms that exhibit phenotypes close to human diseases, thereby effectively representing relevant aspects of neuropsychiatric disorders. In this regard, iPSCs reflect patient pathophysiology and pharmacological responsiveness, particularly when cultured under conditions that emulate spatial tissue organization in brain organoids. Recently, the application of iPSCs has been frequently associated with gene editing that targets the disease-causing gene to deepen the illness pathophysiology and to conduct drug screening. Moreover, gene editing has provided a unique opportunity to repair the putative causative genetic lesions in patient-derived cells. Here, we review the use of iPSC technology to model and potentially treat neuropsychiatric disorders by illustrating the key studies on a series of mental disorders, including schizophrenia, major depressive disorder, bipolar disorder, and autism spectrum disorder. Future perspectives will involve the development of organ-on-a-chip platforms that control the microenvironmental conditions so as to reflect individual pathophysiological by adjusting physiochemical parameters according to personal health data. This strategy could open new ways by which to build a disease model that considers individual variability and tailors personalized treatments.

Multiple types of navigational information are independently encoded in the population activities of the dentate gyrus neurons

In this study, we found that multiple types of information (position, speed, and motion direction in an open field and current and future location in a T-maze) are independently encoded in the overlapping, but different, populations of dentate gyrus (DG) neurons. This computational nature of the independent distribution of information in neural circuits is newly found not only in the DG, but also in other hippocampal regions.

The dentate gyrus (DG) plays critical roles in cognitive functions, such as learning, memory, and spatial coding, and its dysfunction is implicated in various neuropsychiatric disorders. However, it remains largely unknown how information is represented in this region. Here, we recorded neuronal activity in the DG using Ca²⁺ imaging in freely moving mice and analyzed this activity using machine learning. The activity patterns of populations of DG neurons enabled us to successfully decode position, speed, and motion direction in an open field, as well as current and future location in a T-maze, and each individual neuron was diversely and independently tuned to these multiple information types. Our data also showed that each type of information is unevenly distributed in groups of DG neurons, and different types of information are independently encoded in overlapping, but different, populations of neurons. In alpha-calcium/calmodulin-dependent kinase II (αCaMKII) heterozygous knockout mice, which present deficits in spatial remote and working memory, the decoding accuracy of position in the open field and future location in the T-maze were selectively reduced. These results suggest that multiple types of information are independently distributed in DG neurons.

Calcium/calmodulin-dependent protein kinase IIα heterozygous knockout mice show electroencephalogram and behavioral changes characteristic of a subpopulation of schizophrenia and intellectual impairment

Cognitive deficit remains an intractable symptom of schizophrenia, accounting for substantial disability. Despite this, little is known about the cause of cognitive dysfunction in schizophrenia. Recent studies suggest that schizophrenia patients show several changes in dentate gyrus structure and functional characteristic of immaturity. The immature dentate gyrus (iDG) has been replicated in several mouse models, most notably the αCaMKII heterozygous mouse (CaMKIIa-hKO). The current study characterizes behavioral phenotypes of CaMKIIa-hKO mice and determines their neurophysiological profile using electroencephalogram (EEG) recording from hippocampus. CaMKIIa-hKO mice were hypoactive in home-cage environment; however, they displayed less anxiety-like phenotype, suggestive of impulsivity-like behavior. In addition, severe cognitive dysfunction was evident in CaMKIIa-hKO mice as examined by novel object recognition and contextual fear conditioning. Several EEG phenomena established in both patients and relevant animal models indicate key pathological changes associated with the disease, include auditory event-related potentials and time-frequency EEG oscillations. CaMKIIa-hKO mice showed altered event-related potentials characterized by an increase in amplitude of the N40 and P80, as well as increased P80 latency. These mice also showed increased power in theta range time-frequency measures. Additionally, CaMKIIa-hKO mice showed spontaneous bursts of spike wave activity, possibly indicating absence seizures. The GABAB agonist baclofen increased, while the GABAB antagonist CGP35348 and the T-Type Ca2⁺ channel blocker Ethosuximide decreased spike wave burst frequency. None of these changes in event-related potentials or EEG oscillations are characteristic of those observed in general population of patients with schizophrenia; yet, CaMKIIa-hKO mice likely model a subpopulation of patients with schizophrenia.

Auts2 deletion involves in DG hypoplasia and social recognition deficit: The developmental and neural circuit mechanisms

The involvement of genetic risk and the underlying developmental and neural circuit mechanisms in autism-related social deficit are largely unclear. Here, we report that deletion of AUTS2, a high-susceptibility gene of ASDs, caused postnatal dentate gyrus (DG) hypoplasia, which was closely relevant to social recognition deficit. Furthermore, a previously unknown mechanism for neural cell migration in postnatal DG development was identified, in which Auts2-related signaling played a vital role as the transcription repressor. Moreover, the supramammillary nucleus (SuM)-DG-CA3 neural circuit was found to be involved in social recognition and affected in Auts2-deleted mice due to DG hypoplasia. Correction of DG-CA3 synaptic transmission by using a pharmacological approach or chemo/optogenetic activation of the SuM-DG circuit restored the social recognition deficit in Auts2-deleted mice. Our findings demonstrated the vital role of Auts2 in postnatal DG development, and this role was critical for SuM-DG-CA3 neural circuit-mediated social recognition behavior.

Acute and chronic effects of oral administration of a medium-chain fatty acid, capric acid, on locomotor activity and anxiety-like and depression-related behaviors in adult male C57BL/6J mice

Aim

Capric acid (also known as decanoic acid or C10) is one of the fatty acids in the medium‐chain triglycerides (MCTs) commonly found in dietary fats. Although dietary treatment with MCTs is recently of great interest for the potential therapeutic effects on neuropsychiatric disorders, the effects of oral administration of C10 on behavior remain to be examined. This study investigated acute and chronic effects of oral administration of C10 on locomotor activity and anxiety‐like and depression‐related behaviors in adult male C57BL/6J mice.

Methods

To explore the acute effects of C10 administration, mice were subjected to a series of behavioral tests in the following order: light/dark transition, open field, elevated plus maze, Porsolt forced swim, and tail suspension tests, 30 minutes after oral gavage of either vehicle or C10 solution (30 mmol/kg dose in Experiment 1; 0.1, 0.3, 1.0, 3.0 mmol/kg doses in Experiment 2). Next, to examine chronic effects of C10, mice repeatedly administered with either vehicle or C10 solution (0.3, 3.0 mmol/kg doses per day, for 21 days, in Experiment 3) were subjected to behavioral tests without oral administration immediately before each test.

Results

The mice administrated with the high dose of C10 (30 mmol/kg) showed lower body weights, shorter distance traveled, and more anxiety‐like behavior than vehicle‐treated mice, and the results reached study‐wide statistical significance. The C10 administration at a lower dose of 0.3 mmol/kg had no significant effects on body weights and induced nominally significantly longer distance traveled than vehicle administration. Repeated administration of C10 at a dose of 3.0 mmol/kg for more than 21 days caused lower body weights and decreased depression‐related behavior, although the behavioral differences did not reach study‐wide significance.

Conclusions

Although these results suggest dose‐dependent effects of oral administration of capric acid on locomotor activity and anxiety‐like and depression‐related behaviors, further study will be needed to replicate the findings and explore the underlying brain mechanisms.

Repeated oral administration of the medium‐chain fatty acid, capric acid, decreased depression‐related behavior in C57BL/6J mice. This study suggests that capric acid exerts an antidepressant effect.

Lower plasma total tau in adolescent psychosis: Involvement of the orbitofrontal cortex

Schizophrenia is thought to be a neurodevelopmental disorder with neuronal migration, differentiation and maturation disturbances. Tau is a microtubule-associated protein with a crucial role in these processes. Lower circulating tau levels have been reported in adults with schizophrenia, but this association has not been investigated in adolescent psychosis. We aimed to test the hypotheses that a) adolescents with early-onset psychosis (EOP; age of onset <18 years) display lower plasma tau concentrations compared to healthy controls, and b) among patients with psychosis, tau levels are linked to structural brain measures associated with the microtubule-associated tau (MAPT) gene and psychosis. We included 37 adolescent patients with EOP (mean age 16.4 years) and 59 adolescent healthy controls (mean age 16.2 years). We investigated putative patient-control differences in plasma total tau concentrations measured by a Single molecule array (Simoa) immunoassay. We explored the correlations between tau and selected structural brain measures based on T1-weighted MRI scans processed in FreeSurfer v6.0. We found significantly lower plasma tau concentrations in patients compared to healthy controls (p = 0.017, partial eta-squared = 0.061). Tau was not associated with antipsychotic use or the antipsychotic dosage. Among patients but not healthy controls, tau levels were positively correlated with the cortical orbitofrontal surface area (p = 0.013, R-squared = 0.24). The results are suggestive of a tau-related neurodevelopmental disturbance in adolescent psychosis.

Maternal immune activation primes deficiencies in adult hippocampal neurogenesis

Neurogenesis, the process in which new neurons are generated, occurs throughout life in the mammalian hippocampus. Decreased adult hippocampal neurogenesis (AHN) is a common feature across psychiatric disorders, including schizophrenia, depression- and anxiety-related behaviours, and is highly regulated by environmental influences. Epidemiological studies have consistently implicated maternal immune activation (MIA) during neurodevelopment as a risk factor for psychiatric disorders in adulthood. The extent to which the reduction of hippocampal neurogenesis in adulthood may be driven by early life exposures, such as MIA, is however unclear. We therefore reviewed the literature for evidence of the involvement of MIA in disrupting AHN. Consistent with our hypothesis, data from both in vivo murine and in vitro human models of AHN provide evidence for key roles of specific cytokines induced by MIA in the foetal brain in disrupting hippocampal neural progenitor cell proliferation and differentiation early in development. The precise molecular mechanisms however remain unclear. Nonetheless, these data suggest a potential latent vulnerability mechanism, whereby MIA primes dysfunction in the unique hippocampal pool of neural stem/progenitor cells. This renders offspring potentially more susceptible to additional environmental exposures later in life, such as chronic stress, resulting in the unmasking of psychopathology. We highlight the need for studies to test this hypothesis using validated animal models of MIA, but also to test the relevance of such data for human pathology at a molecular basis through the use of patient-derived induced pluripotent stem cells (hiPSC) differentiated into hippocampal progenitor cells.

Lipopolysaccharide-induced maternal immune activation modulates microglial CX3CR1 protein expression and morphological phenotype in the hippocampus and dentate gyrus, resulting in cognitive inflexibility during late adolescence

Inflammation during pregnancy can disturb brain development and lead to disorders in the progeny, including autism spectrum disorder and schizophrenia. However, the mechanism by which a prenatal, short-lived increase of cytokines results in adverse neurodevelopmental outcomes remains largely unknown. Microglia-the brain's resident immune-cells-stand as fundamental cellular mediators, being highly sensitive and responsive to immune signals, which also play key roles during normal development. The fractalkine signaling axis is a neuron-microglia communication mechanism used to regulate neurogenesis and network formation. Previously, we showed hippocampal reduction of fractalkine receptor (Cx3cr1) mRNA at postnatal day (P) 15 in male offspring exposed to maternal immune activation induced with lipopolysaccharide (LPS) during late gestation, which was concomitant to an increased dendritic spine density in the dentate gyrus, a neurogenic niche. The current study sought to evaluate the origin and impact of this reduced hippocampal Cx3cr1 mRNA expression on microglia and cognition. We found that microglial total cell number and density are not affected in the dorsal hippocampus and dentate gyrus, respectively, but that the microglial CX3CR1 protein is decreased in the hippocampus of LPS-male offspring at P15. Further characterization of microglial morphology in the dentate gyrus identified a more ameboid phenotype in LPS-exposed offspring, predominantly in males, at P15. We thus explored maternal plasma and fetal brain cytokines to understand the mechanism behind microglial priming, showing a robust immune activation in the mother at 2 and 4 hrs after LPS administration, while only IL-10 tended towards upregulation at 2 hrs after LPS in fetal brains. To evaluate the functional long-term consequences, we assessed learning and cognitive flexibility behavior during late adolescence, finding that LPS affects only the latter with a male predominance on perseveration. A CX3CR1 gene variant in humans that results in disrupted fractalkine signaling has been recently associated with an increased risk for neurodevelopmental disorders. We show that an acute immune insult during late gestation can alter fractalkine signaling by reducing the microglial CX3CR1 protein expression, highlighting neuron-microglial fractalkine signaling as a relevant target underlying the outcomes of environmental risk factors on neurodevelopmental disorders.

Adult Neural Stem Cells as Promising Targets in Psychiatric Disorders

The development of new therapies for psychiatric disorders is of utmost importance, given the enormous toll these disorders pose to society nowadays. This should be based on the identification of neural substrates and mechanisms that underlie disease etiopathophysiology. Adult neural stem cells (NSCs) have been emerging as a promising platform to counteract brain damage. In this perspective article, we put forth a detailed view of how NSCs operate in the adult brain and influence brain homeostasis, having profound implications at both behavioral and functional levels. We appraise evidence suggesting that adult NSCs play important roles in regulating several forms of brain plasticity, particularly emotional and cognitive flexibility, and that NSC dynamics are altered upon brain pathology. Furthermore, we discuss the potential therapeutic value of utilizing adult endogenous NSCs as vessels for regeneration, highlighting their importance as targets for the treatment of multiple mental illnesses, such as affective disorders, schizophrenia, and addiction. Finally, we speculate on strategies to surpass current challenges in neuropsychiatric disease modeling and brain repair.

Cytomegalovirus infection associated with smaller dentate gyrus in men with severe mental illness

Cytomegalovirus (CMV) infection is usually inapparent in healthy adults but persists for life. Neural progenitor/stem cells are main CMV targets, and dentate gyrus (DG) a major neurogenic niche. Smaller DG volume has been repeatedly reported in severe mental illness (SMI). Considering the suggested immune system, blood-brain barrier and DG disturbances in SMI, we hypothesized that CMV exposure is associated with smaller DG volume in patients, but not healthy controls (HC). Due to the differential male and female immune response to CMV, we hypothesized sex-dependent associations. 381 adult patients with SMI (schizophrenia spectrum or bipolar spectrum disorders) and 396 HC were included. MRI scans were obtained with 1.5T Siemens MAGNETOM Sonata scanner or 3T General Electric Signa HDxt scanner, and processed with FreeSurfer v6.0. CMV immunoglobulin G antibody concentrations were measured by solid phase immunoassay. We investigated main and interaction effects of CMV status (antibody positivity/CMV + vs. negativity/CMV-) and sex on DG in patients and HC. Among patients, there was a significant CMV-by-sex interaction on DG (p = 0.009); CMV + male patients had significantly smaller DG volume than CMV- male patients (p = 0.001, 39 mm³ volume difference) whereas no CMV-DG association was found in female patients. Post-hoc analysis among male patients showed that the CMV-DG association was present in both hemispheres and in both patients with schizophrenia spectrum and bipolar spectrum disorders, and further, that higher CMV antibody titers were associated with smaller DG. No CMV-DG association was found in HC. The results indicate a DG vulnerability to CMV infection in men with SMI.

Deficient LEF1 expression is associated with lithium resistance and hyperexcitability in neurons derived from bipolar disorder patients

Bipolar disorder (BD) is a psychiatric condition characterized by depressive and manic episodes that affect 2% of the world population. The first-line long-term treatment for mood stabilization is lithium (Li). Induced pluripotent stem cell modeling of BD using hippocampal dentate gyrus-like neurons derived from Li-responsive (LR) and Li-non-responsive (NR) patients previously showed neuronal hyperexcitability. Li treatment reversed hyperexcitability only on the LR neurons. In this study we searched for specific targets of Li resistance in NR neurons and found that the activity of Wnt/β-catenin signaling pathway was severely affected, with a significant decrease in expression of LEF1. Li targets the Wnt/β-catenin signaling pathway by inhibiting GSK-3β and releasing β-catenin that forms a nuclear complex with TCF/LEF1, activating the Wnt/β-catenin transcription program. Therefore, we propose that downregulation of LEF1 may account for Li resistance in NR neurons. Our results show that valproic acid (VPA), a drug used to treat NR patients that also acts downstream of GSK-3β, upregulated LEF1 and Wnt/β-catenin gene targets, increased transcriptional activity of complex β-catenin/TCF/LEF1, and reduced excitability in NR neurons. In addition, decreasing LEF1 expression in control neurons using shLEF1 caused hyperexcitability, confirming that the impact of VPA on excitability in NR neurons was connected to changes in LEF1 and in the Wnt/β-catenin pathway. Our results suggest that LEF1 may be a useful target for the discovery of new drugs for BD treatment.

A method for the expression of fibroblast growth factor 14 and assessment of its neuroprotective effect in an Alzheimer's disease model

Background

Fibroblast growth factor (FGF) 14 is a member of the FGF family that is mainly expressed in the central nervous system. FGF14 has a close association with the occurrence of neurodegenerative conditions; however, its significance in Alzheimer’s disease (AD) has yet to be evaluated. Therefore, we sought to obtain a large amount of exogenous FGF14 protein and explore its effect in a cellular model of AD.

Methods

FGF14 protein was expressed in an Escherichia coli system using gene recombination technology. Purified protein was obtained through washing and renaturation of inclusion bodies combined with nickel column affinity chromatography. The AD model was established via Aβ25-35-induced injury in PC12 cells. Changes in the levels of lactate dehydrogenase and malondialdehyde were detected, and the neuroprotective effect of recombinant human FGF14 (rhFGF14) was evaluated through double-fluorescence staining and flow cytometry apoptosis detection. For further exploration of rhFGF14-mediated regulation of mitogen-activated protein kinase (MAPK) signaling, western blot was employed.

Results

We successfully induced large amounts of insoluble rhFGF14. Following solubilization and refolding of the rhFGF14 from inclusion bodies, high purity rhFGF14 was purified by Nickel affinity column chromatography. The results showed that rhFGF14 alleviated Aβ25-3-induced PC12 cell injury by inhibiting the phosphorylation of p38, extracellular signal-regulated kinase 1/2, and c-Jun N-terminal kinase, thus suppressing the MAPK signaling pathway.

Conclusions

FGF14 performed a neuroprotective role in our in vitro AD model via its inhibition of MAPK signaling, highlighting its potential as a therapeutic drug for neurodegenerative conditions.

Vangl2 in the Dentate Network Modulates Pattern Separation and Pattern Completion

The organization of spatial information, including pattern completion and pattern separation processes, relies on the hippocampal circuits, yet the molecular and cellular mechanisms underlying these two processes are elusive. Here, we find that loss of Vangl2, a core PCP gene, results in opposite effects on pattern completion and pattern separation processes. Mechanistically, we show that Vangl2 loss maintains young postmitotic granule cells in an immature state, providing increased cellular input for pattern separation. The genetic ablation of Vangl2 disrupts granule cell morpho-functional maturation and further prevents CaMKII and GluA1 phosphorylation, disrupting the stabilization of AMPA receptors. As a functional consequence, LTP at lateral perforant path-GC synapses is impaired, leading to defects in pattern completion behavior. In conclusion, we show that Vangl2 exerts a bimodal regulation on young and mature GCs, and its disruption leads to an imbalance in hippocampus-dependent pattern completion and separation processes.

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Vangl2-dependent PCP signaling controls granule cell maturation and network integration

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Vangl2 stabilizes GluA1-containing receptors at the surface of dendritic spines

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Granule cells require Vangl2-dependent signaling to elicit LTP

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Vangl2 loss has opposite functional effects on pattern completion/separation processes

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.

The Rac-GEF Tiam1 Promotes Dendrite and Synapse Stabilization of Dentate Granule Cells and Restricts Hippocampal-Dependent Memory Functions

The dentate gyrus (DG) controls information flow into the hippocampus and is critical for learning, memory, pattern separation, and spatial coding, while DG dysfunction is associated with neuropsychiatric disorders. Despite its importance, the molecular mechanisms regulating DG neural circuit assembly and function remain unclear. Here, we identify the Rac-GEF Tiam1 as an important regulator of DG development and associated memory processes. In the hippocampus, Tiam1 is predominantly expressed in the DG throughout life. Global deletion of Tiam1 in male mice results in DG granule cells with simplified dendritic arbors, reduced dendritic spine density, and diminished excitatory synaptic transmission. Notably, DG granule cell dendrites and synapses develop normally in Tiam1 KO mice, resembling WT mice at postnatal day 21 (P21), but fail to stabilize, leading to dendrite and synapse loss by P42. These results indicate that Tiam1 promotes DG granule cell dendrite and synapse stabilization late in development. Tiam1 loss also increases the survival, but not the production, of adult-born DG granule cells, possibly because of greater circuit integration as a result of decreased competition with mature granule cells for synaptic inputs. Strikingly, both male and female mice lacking Tiam1 exhibit enhanced contextual fear memory and context discrimination. Together, these results suggest that Tiam1 is a key regulator of DG granule cell stabilization and function within hippocampal circuits. Moreover, based on the enhanced memory phenotype of Tiam1 KO mice, Tiam1 may be a potential target for the treatment of disorders involving memory impairments.SIGNIFICANCE STATEMENT The dentate gyrus (DG) is important for learning, memory, pattern separation, and spatial navigation, and its dysfunction is associated with neuropsychiatric disorders. However, the molecular mechanisms controlling DG formation and function remain elusive. By characterizing mice lacking the Rac-GEF Tiam1, we demonstrate that Tiam1 promotes the stabilization of DG granule cell dendritic arbors, spines, and synapses, whereas it restricts the survival of adult-born DG granule cells, which compete with mature granule cells for synaptic integration. Notably, mice lacking Tiam1 also exhibit enhanced contextual fear memory and context discrimination. These findings establish Tiam1 as an essential regulator of DG granule cell development, and identify it as a possible therapeutic target for memory enhancement.

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.

Dentate gyrus volume deficit in schizophrenia

BACKGROUND

Schizophrenia is associated with robust hippocampal volume deficits but subregion volume deficits, their associations with cognition, and contributing genes remain to be determined.

METHODS

Hippocampal formation (HF) subregion volumes were obtained using FreeSurfer 6.0 from individuals with schizophrenia (n = 176, mean age ± s.d. = 39.0 ± 11.5, 132 males) and healthy volunteers (n = 173, mean age ± s.d. = 37.6 ± 11.3, 123 males) with similar mean age, gender, handedness, and race distributions. Relationships between the HF subregion volume with the largest between group difference, neuropsychological performance, and single-nucleotide polymorphisms were assessed.

RESULTS

This study found a significant group by region interaction on hippocampal subregion volumes. Compared to healthy volunteers, individuals with schizophrenia had significantly smaller dentate gyrus (DG) (Cohen's d = -0.57), Cornu Ammonis (CA) 4, molecular layer of the hippocampus, hippocampal tail, and CA 1 volumes, when statistically controlling for intracranial volume; DG (d = -0.43) and CA 4 volumes remained significantly smaller when statistically controlling for mean hippocampal volume. DG volume showed the largest between group difference and significant positive associations with visual memory and speed of processing in the overall sample. Genome-wide association analysis with DG volume as the quantitative phenotype identified rs56055643 (β = 10.8, p < 5 × 10-8, 95% CI 7.0-14.5) on chromosome 3 in high linkage disequilibrium with MOBP. Gene-based analyses identified associations between SLC25A38 and RPSA and DG volume.

CONCLUSIONS

This study suggests that DG dysfunction is fundamentally involved in schizophrenia pathophysiology, that it may contribute to cognitive abnormalities in schizophrenia, and that underlying biological mechanisms may involve contributions from MOBP, SLC25A38, and RPSA.

Cerebrospinal fluid neuroplasticity-associated protein levels in patients with psychiatric disorders: a multiplex immunoassay study

To examine the role of neuroplasticity in the pathology of psychiatric disorders, we measured cerebrospinal fluid (CSF) neuroplasticity-associated protein levels. Participants were 94 patients with schizophrenia, 68 with bipolar disorder (BD), 104 with major depressive disorder (MDD), and 118 healthy controls, matched for age, sex, and ethnicity (Japanese). A multiplex immunoassay (22-plex assay) was performed to measure CSF neuroplasticity-associated protein levels. Among 22 proteins, 11 were successfully measured in the assay. CSF amyloid precursor protein (APP) and glial cell-derived neurotrophic factor (GDNF) levels were significantly lower in patients with schizophrenia, and CSF APP and neural cell adhesion molecule (NCAM)-1 levels were significantly lower in patients with BD, than in healthy controls (all p < 0.05). Positive and Negative Syndrome Scale total, positive, and general scores were significantly and positively correlated with CSF hepatocyte growth factor (HGF) (p < 0.01) and S100 calcium-binding protein B (S100B) (p < 0.05) levels in patients with schizophrenia. Young mania-rating scale score was significantly and positively correlated with CSF S100B level in patients with BD (p < 0.05). Hamilton Depression Rating Scale, core, sleep, activity, somatic anxiety, and delusion subscale scores were significantly and positively correlated with CSF HGF level, while sleep subscale score was positively correlated with CSF S100B and VEGF receptor 2 levels in patients with MDD (p < 0.05). Our results suggest that CSF APP, GDNF, and NCAM-1 levels are associated with psychiatric disorders, and that CSF HGF, S100B, and VEGF receptor 2 levels are related to psychiatric symptoms.

Modeling Psychiatric Disorder Biology with Stem Cells

PURPOSE OF REVIEW

We review the ways in which stem cells are used in psychiatric disease research, including the related advances in gene editing and directed cell differentiation.

RECENT FINDINGS

The recent development of induced pluripotent stem cell (iPSC) technologies has created new possibilities for the study of psychiatric disease. iPSCs can be derived from patients or controls and differentiated to an array of neuronal and non-neuronal cell types. Their genomes can be edited as desired, and they can be assessed for a variety of phenotypes. This makes them especially interesting for studying genetic variation, which is particularly useful today now that our knowledge on the genetics of psychiatric disease is quickly expanding. The recent advances in cell engineering have led to powerful new methods for studying psychiatric illness including schizophrenia, bipolar disorder, and autism. There is a wide array of possible applications as illustrated by the many examples from the literature, most of which are cited here.

The Role of BDNF on Neural Plasticity in Depression

Using behavioral, pharmacological, and molecular methods, lots of studies reveal that depression is closely related to the abnormal neural plasticity processes occurring in the prefrontal cortex and limbic system such as the hippocampus and amygdala. Meanwhile, functions of the brain-derived neurotrophic factor (BDNF) and the other neurotrophins in the pathogenesis of depression are well known. The maladaptive neuroplastic in depression may be related to alterations in the levels of neurotrophic factors, which play a central role in plasticity. Enhancement of neurotrophic factors signaling has great potential in therapy for depression. This review highlights the relevance of neurotrophic factors mediated neural plasticity and pathophysiology of depression. These studies reviewed here may suggest new possible targets for antidepressant drugs such as neurotrophins, their receptors, and relevant signaling pathways, and agents facilitating the activation of gene expression and increasing the transcription of neurotrophic factors in the brain.

Profiling gene expression in the human dentate gyrus granule cell layer reveals insights into schizophrenia and its genetic risk

Specific cell populations may have unique contributions to schizophrenia but may be missed in studies of homogenate tissue. Here laser capture microdissection followed by RNA sequencing (LCM-seq) was used to transcriptomically profile the granule cell layer of the dentate gyrus (DG-GCL) in human hippocampus and contrast these data to those obtained from bulk hippocampal homogenate. We identified widespread cell-type-enriched aging and genetic effects in the DG-GCL that were either absent or directionally discordant in bulk hippocampus data. Of the ~9 million expression quantitative trait loci identified in the DG-GCL, 15% were not detected in bulk hippocampus, including 15 schizophrenia risk variants. We created transcriptome-wide association study genetic weights from the DG-GCL, which identified many schizophrenia-associated genetic signals not found in transcriptome-wide association studies from bulk hippocampus, including GRM3 and CACNA1C. These results highlight the improved biological resolution provided by targeted sampling strategies like LCM and complement homogenate and single-nucleus approaches in human brain.

Post-weaning folate deficiency induces a depression-like state via neuronal immaturity of the dentate gyrus in mice

Folate deficiency has been suggested as a risk factor for depression in preclinical and clinical studies. Several hypotheses of mechanisms underlying folate deficiency-induced depressive symptoms have been proposed, but the detailed mechanisms are still unclear. In this study, we assessed whether post-weaning folate deficiency affect neurological and psychological function. The low folate diet-fed mice showed depression-like behavior in the forced swim test. In contrast, spontaneous locomotor activity, social behavior, coordinated motor skills, anxiety-like behavior and spatial memory did not differ between control and low folate diet-fed mice. In the dentate gyrus (DG) of the hippocampus, decreased number of newborn mature neurons and increased number of immature neurons were observed in low folate diet-fed mice. Staining with Golgi-Cox method revealed that dendritic complexity, spine density and the number of mature spines of neurons were markedly reduced in the DG of low folate diet-fed mice. Stress response of neurons indicated as c-Fos expression was also reduced in the DG of low folate diet-fed mice. These results suggest that reduction in the degree of maturation of newborn hippocampal neurons underlies folate deficiency-induced depressive symptoms.

Cognition and Reward Circuits in Schizophrenia: Synergistic, Not Separate

Schizophrenia has been studied from the perspective of cognitive or reward-related impairments, yet it cannot be wholly related to one or the other process and their corresponding neural circuits. We posit a comprehensive circuit-based model proposing that dysfunctional interactions between the brain's cognitive and reward circuits underlie schizophrenia. The model is underpinned by how the relationship between glutamatergic and dopaminergic dysfunction in schizophrenia drives interactions between cognition and reward circuits. We argue that this interaction is synergistic: that is, deficits of cognition and reward processing interact, and this interaction is a core feature of schizophrenia. In adopting this position, we undertake a focused review of animal physiology and human clinical data, and in proposing this synergistic model, we highlight dopaminergic afferents from the ventral tegmental area to nucleus accumbens (mesolimbic circuit) and frontal cortex (mesocortical circuit). We then expand on the role of glutamatergic inputs to these dopamine circuits and dopaminergic modulation of critical excitatory pathways with attention given to the role of glutamatergic hippocampal outputs onto nucleus accumbens. Finally, we present evidence for how in schizophrenia, dysfunction in the mesolimbic and mesocortical circuits and their corresponding glutamatergic inputs gives rise to clinical and cognitive phenotypes and is associated with positive and negative symptom dimensions. The synthesis attempted here provides an impetus for a conceptual shift that links cognitive and motivational aspects of schizophrenia and that can lead to treatment approaches that seek to harmonize network interactions between the brain's cognition and reward circuits with ameliorative effects in each behavioral domain.

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.

Peripheral blood metabolome predicts mood change-related activity in mouse model of bipolar disorder

Bipolar disorder is a major mental illness characterized by severe swings in mood and activity levels which occur with variable amplitude and frequency. Attempts have been made to identify mood states and biological features associated with mood changes to compensate for current clinical diagnosis, which is mainly based on patients' subjective reports. Here, we used infradian (a cycle > 24 h) cyclic locomotor activity in a mouse model useful for the study of bipolar disorder as a proxy for mood changes. We show that metabolome patterns in peripheral blood could retrospectively predict the locomotor activity levels. We longitudinally monitored locomotor activity in the home cage, and subsequently collected peripheral blood and performed metabolomic analyses. We then constructed cross-validated linear regression models based on blood metabolome patterns to predict locomotor activity levels of individual mice. Our analysis revealed a significant correlation between actual and predicted activity levels, indicative of successful predictions. Pathway analysis of metabolites used for successful predictions showed enrichment in mitochondria metabolism-related terms, such as "Warburg effect" and "citric acid cycle." In addition, we found that peripheral blood metabolome patterns predicted expression levels of genes implicated in bipolar disorder in the hippocampus, a brain region responsible for mood regulation, suggesting that the brain-periphery axis is related to mood-change-associated behaviors. Our results may serve as a basis for predicting individual mood states through blood metabolomics in bipolar disorder and other mood disorders and may provide potential insight into systemic metabolic activity in relation to mood changes.

Serotonin 5-HT4 Receptor Agonists Improve Facilitation of Contextual Fear Extinction in an MPTP-Induced Mouse Model of Parkinson's Disease

Previously, we found that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson’s disease (PD) model mice (PD mice) showed facilitation of hippocampal memory extinction via reduced cyclic adenosine monophosphate (cAMP)/cAMP-dependent response element-binding protein (CREB) signaling, which may cause cognitive impairment in PD. Serotonergic neurons in the median raphe nucleus (MnRN) project to the hippocampus, and functional abnormalities have been reported. In the present study, we investigated the effects of the serotonin 5-HT₄ receptor (5-HT₄R) agonists prucalopride and velusetrag on the facilitation of memory extinction observed in PD mice. Both 5-HT₄R agonists restored facilitation of contextual fear extinction in PD mice by stimulating the cAMP/CREB pathway in the dentate gyrus of the hippocampus. A retrograde fluorogold-tracer study showed that γ-aminobutyric acid-ergic (GABAergic) neurons in the reticular part of the substantia nigra (SNr), but not dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNpc), projected to serotonergic neurons in the MnRN, which are known to project their nerve terminals to the hippocampus. It is possible that the degeneration of the SNpc DAergic neurons in PD mice affects the SNr GABAergic neurons, and thereafter, the serotonergic neurons in the MnRN, resulting in hippocampal dysfunction. These findings suggest that 5HT4R agonists could be potentially useful as therapeutic drugs for treating cognitive deficits in PD.

Fluoxetine-induced dematuration of hippocampal neurons and adult cortical neurogenesis in the common marmoset

The selective serotonin reuptake inhibitor fluoxetine (FLX) is widely used to treat depression and anxiety disorders. Chronic FLX treatment reportedly induces cellular responses in the brain, including increased adult hippocampal and cortical neurogenesis and reversal of neuron maturation in the hippocampus, amygdala, and cortex. However, because most previous studies have used rodent models, it remains unclear whether these FLX-induced changes occur in the primate brain. To evaluate the effects of FLX in the primate brain, we used immunohistological methods to assess neurogenesis and the expression of neuronal maturity markers following chronic FLX treatment (3 mg/kg/day for 4 weeks) in adult marmosets (n = 3 per group). We found increased expression of doublecortin and calretinin, markers of immature neurons, in the hippocampal dentate gyrus of FLX-treated marmosets. Further, FLX treatment reduced parvalbumin expression and the number of neurons with perineuronal nets, which indicate mature fast-spiking interneurons, in the hippocampus, but not in the amygdala or cerebral cortex. We also found that FLX treatment increased the generation of cortical interneurons; however, significant up-regulation of adult hippocampal neurogenesis was not observed in FLX-treated marmosets. These results suggest that dematuration of hippocampal neurons and increased cortical neurogenesis may play roles in FLX-induced effects and/or side effects. Our results are consistent with those of previous studies showing hippocampal dematuration and increased cortical neurogenesis in FLX-treated rodents. In contrast, FLX did not affect hippocampal neurogenesis or dematuration of interneurons in the amygdala and cerebral cortex.

Loss of serum response factor in mature neurons in the dentate gyrus alters the morphology of dendritic spines and hippocampus-dependent behavioral tasks

Serum response factor (SRF) is a major transcription factor that regulates the expression of several plasticity-associated genes in the brain. Although the developmental expression of SRF in excitatory neurons is crucial for establishing proper hippocampal circuitry, no substantial evidence of its role in unstimulated mature neurons has been provided. The present study used time-controlled, conditional SRF knockout mice and found that the lack of SRF in adult neurons led to decreased actin levels and inactivation of the actin-severing protein cofilin 1 through its increase in phosphorylation at Ser3. The augmentation of cofilin 1 phosphorylation correlated with an alteration of dendritic spine morphology in the dentate gyrus, which was reflected by an increase in the number of spines that clustered into the long-spine category. The changes in spine morphology coincided with a lower amplitude and frequency of miniature excitatory postsynaptic currents. Moreover, SRF knockout animals were hyperactive and exhibited impairments in hippocampus-dependent behaviors, such as digging, marble burying, and nesting. Altogether, our data indicate that the adult deletion of neuronal SRF leads to alterations of spine morphology and function and hippocampus-dependent behaviors. Thus, SRF deletion in adult neurons recapitulates some aspects of morphological, electrophysiological, and behavioral changes that are observed in such psychiatric disorders as schizophrenia and autism spectrum disorders.

A Critical Period for the Development of Schizophrenia-Like Pathology by Aberrant Postnatal Neurogenesis

Schizophrenia is a complex and serious mental disorder, and patients with schizophrenia are characterized by psychological hallucinations, deregulated emotionality, and cognitive impairment. Evidence indicated that postnatal neurogenesis in the hippocampus is profoundly impaired in schizophrenic individuals but the role of such dysregulated neurodevelopmental processing in the pathophysiological progress of schizophrenia has not been well investigated. Here in this study, by using the rodent model of schizophrenia through maternal immune activation of poly (I:C) injection, we aimed to examine whether the postnatal neurogenesis might be involved in the development of schizophrenia-like pathology. Through the comprehensive behavioral analyses of multiple core symptoms of schizophrenia at different developmental stages (6-, 9-, and 12-weeks after birth) of the affected offspring, we found a delayed onset of schizophrenia-like behaviors in poly (I:C) animals through the development. Meanwhile, there is an age-dependent alteration of postnatal neurogenesis in the poly (I:C) animals along different development stages by which the aberrant dendritic elaboration functionally correlated with the schizophrenia-like symptoms in 9-week-old of age for the animals. Interestingly, increase in the neurogenesis during a critical period of neurodevelopment exacerbates the schizophrenia-like pathology. Conversely, temporal suppression of aberrant postnatal neurogenesis during the same period of neurodevelopment ameliorates the occurrence of schizophrenia-like symptoms. Together, these findings strongly suggested the aberrant dendritic growth of postnatal neurogenesis during the critical time window of development is essential for controlling the pathophysiological progression of schizophrenia-like symptoms. And pharmacological treatments that adjust these abnormalities may provide potential therapeutic benefits toward patients with schizophrenia in clinic.

Transcriptomic evidence for immaturity induced by antidepressant fluoxetine in the hippocampus and prefrontal cortex

Aims

The molecular and cellular mechanisms underlying the antidepressant effects of fluoxetine in the brain are not fully understood. Emerging evidence has led to the hypothesis that chronic fluoxetine treatment induces dematuration of certain types of mature neurons in rodents. These studies have focused on the properties of typical molecular and/or electrophysiological markers for neuronal maturation. Nevertheless, it remains unknown whether dematuration‐related phenomena are present at the genome‐wide gene expression level.

Methods

Based on the aforementioned hypothesis, we directly compared transcriptome data between fluoxetine‐treated adult mice and those of naive infants in the hippocampus and medial prefrontal cortex (mPFC) to assess similarities and/or differences. We further investigated whether fluoxetine treatment caused dematuration in these brain regions in a hypothesis‐free manner using a weighted gene co‐expression network analysis (WGCNA).

Results

Gene expression patterns in fluoxetine‐treated mice resembled those in infants in the mPFC and, to a large extent, in the hippocampus. The gene expression patterns of fluoxetine‐treated adult mice were more similar to those of approximately 2‐week‐old infants than those of older mice. WGCNA confirmed that fluoxetine treatment was associated with maturation abnormalities, particularly in the hippocampus, and highlighted respective co‐expression modules for maturity and immaturity marker genes in the hippocampus in response to fluoxetine treatment.

Conclusions

Our results strongly support the hypothesis that chronic fluoxetine treatment induces dematuration in the adult mouse brain from a transcriptomic standpoint. Detection of discrete transcriptomic regulatory networks related to fluoxetine treatment may help to further elucidate the mechanisms of antidepressant action.

This study compares the transcriptomic profile of adult mice treated with clinically relevant dose of FLX and that of naïve infants in the hippocampus and medial prefrontal cortex (mPFC). We observed that gene expression profiles in FLX‐treated adult mice resembled those of infants in the mPFC and hippocampus. Our results provide support for the hypothesis that FLX can cause dematuration of the adult mouse brain to a more immature phenotype.

Dentate Gyrus Immaturity in Schizophrenia

Hippocampal abnormalities have been heavily implicated in the pathophysiology of schizophrenia. The dentate gyrus of the hippocampus was shown to manifest an immature molecular profile in schizophrenia subjects, as well as in various animal models of the disorder. In this position paper, we advance a hypothesis that this immature molecular profile is accompanied by an identifiable immature morphology of the dentate gyrus granule cell layer. We adduce evidence for arrested maturation of the dentate gyrus in the human schizophrenia-affected brain, as well as multiple rodent models of the disease. Implications of this neurohistopathological signature for current theory regarding the development of schizophrenia are discussed.

Sex-Specific Proteomic Changes Induced by Genetic Deletion of Fibroblast Growth Factor 14 (FGF14), a Regulator of Neuronal Ion Channels

Fibroblast growth factor 14 (FGF14) is a member of the intracellular FGFs, which is a group of proteins involved in neuronal ion channel regulation and synaptic transmission. We previously demonstrated that male Fgf14^−/− mice recapitulate the salient endophenotypes of synaptic dysfunction and behaviors that are associated with schizophrenia (SZ). As the underlying etiology of SZ and its sex-specific onset remain elusive, the Fgf14^−/− model may provide a valuable tool to interrogate pathways related to disease mechanisms. Here, we performed label-free quantitative proteomics to identify enriched pathways in both male and female hippocampi from Fgf14^+/+ and Fgf14^−/− mice. We discovered that all of the differentially expressed proteins measured in Fgf14^−/− animals, relative to their same-sex wildtype counterparts, are associated with SZ based on genome-wide association data. In addition, measured changes in the proteome were predominantly sex-specific, with the male Fgf14^−/− mice distinctly enriched for pathways associated with neuropsychiatric disorders. In the male Fgf14^−/− mouse, we found molecular characteristics that, in part, may explain a previously described neurotransmission and behavioral phenotype. This includes decreased levels of ALDH1A1 and protein kinase A (PRKAR2B). ALDH1A1 has been shown to mediate an alternative pathway for gamma-aminobutyric acid (GABA) synthesis, while PRKAR2B is essential for dopamine 2 receptor signaling, which is the basis of current antipsychotics. Collectively, our results provide new insights in the role of FGF14 and support the use of the Fgf14^−/− mouse as a useful preclinical model of SZ for generating hypotheses on disease mechanisms, sex-specific manifestation, and therapy.

Transcriptomic immaturity inducible by neural hyperexcitation is shared by multiple neuropsychiatric disorders

Biomarkers are needed to improve the diagnosis of neuropsychiatric disorders, which are often associated to excitatory/inhibitory imbalances in neural transmission and abnormal maturation. Here, we characterized different disease conditions by mapping changes in the expression patterns of maturation-related genes whose expression was altered by experimental neural hyperexcitation in published studies. This analysis revealed two gene expression patterns: decreases in maturity markers and increases in immaturity markers. These two groups of genes were characterized by the over-representation of genes related to synaptic function and chromosomal modification, respectively. Using these two groups in a transdiagnostic analysis of 87 disease datasets for eight neuropsychiatric disorders and 12 datasets from corresponding animal models, we found that transcriptomic pseudoimmaturity inducible by neural hyperexcitation is shared by multiple neuropsychiatric disorders, such as schizophrenia, Alzheimer disorders, and amyotrophic lateral sclerosis. Our results indicate that this endophenotype serves as a basis for the transdiagnostic characterization of these disorders.

Tomoyuki Murano et al. showed that neural hyperexcitation increases the expression of immaturity related genes. These changes in gene expression are shared among different neuropsychiatric and neurological conditions, hinting at their potential role as biomarkers.

Cell-Biological Requirements for the Generation of Dentate Gyrus Granule Neurons

The dentate gyrus (DG) receives highly processed information from the associative cortices functionally integrated in the trisynaptic hippocampal circuit, which contributes to the formation of new episodic memories and the spontaneous exploration of novel environments. Remarkably, the DG is the only brain region currently known to have high rates of neurogenesis in adults (Andersen et al., 1966, 1971). The DG is involved in several neurodegenerative disorders, including clinical dementia, schizophrenia, depression, bipolar disorder and temporal lobe epilepsy. The principal neurons of the DG are the granule cells. DG granule cells generated in culture would be an ideal model to investigate their normal development and the causes of the pathologies in which they are involved and as well as possible therapies. Essential to establish such in vitro models is the precise definition of the most important cell-biological requirements for the differentiation of DG granule cells. This requires a deeper understanding of the precise molecular and functional attributes of the DG granule cells in vivo as well as the DG cells derived in vitro. In this review we outline the neuroanatomical, molecular and cell-biological components of the granule cell differentiation pathway, including some growth- and transcription factors essential for their development. We summarize the functional characteristics of DG granule neurons, including the electrophysiological features of immature and mature granule cells and the axonal pathfinding characteristics of DG neurons. Additionally, we discuss landmark studies on the generation of dorsal telencephalic precursors from pluripotent stem cells (PSCs) as well as DG neuron differentiation in culture. Finally, we provide an outlook and comment critical aspects.

A gene co-expression module implicating the mitochondrial electron transport chain is associated with long-term response to lithium treatment in bipolar affective disorder

Lithium is the first-line treatment for bipolar affective disorder (BPAD) but two-thirds of patients respond only partially or not at all. The reasons for this high variability in lithium response are not well understood. Transcriptome-wide profiling, which tests the interface between genes and the environment, represents a viable means of exploring the molecular mechanisms underlying lithium response variability. Thus, in the present study we performed co-expression network analyses of whole-blood-derived RNA-seq data from n = 50 lithium-treated BPAD patients. Lithium response was assessed using the well-validated ALDA scale, which we used to define both a continuous and a dichotomous measure. We identified a nominally significant correlation between a co-expression module comprising 46 genes and lithium response represented as a continuous (i.e., scale ranging 0-10) phenotype (cor = -0.299, p = 0.035). Forty-three of these 46 genes had reduced mRNA expression levels in better lithium responders relative to poorer responders, and the central regulators of this module were all mitochondrially-encoded (MT-ND1, MT-ATP6, MT-CYB). Accordingly, enrichment analyses indicated that genes involved in mitochondrial functioning were heavily over-represented in this module, specifically highlighting the electron transport chain (ETC) and oxidative phosphorylation (OXPHOS) as affected processes. Disrupted ETC and OXPHOS activity have previously been implicated in the pathophysiology of BPAD. Our data adds to previous evidence suggesting that a normalisation of these processes could be central to lithium's mode of action, and could underlie a favourable therapeutic response.