The Role of Glutamate in Language and Language Disorders - Evidence from ERP and Pharmacologic Studies

Shedding light on subiculum's role in human brain disorders

Subiculum is a pivotal output component of the hippocampal formation, a structure often overlooked in neuroscientific research. Here, this review aims to explore the role of the subiculum in various brain disorders, shedding light on its significance within the functional-neuroanatomical perspective on neurological diseases. The subiculum's involvement in multiple brain disorders was thoroughly examined. In Alzheimer's disease, subiculum alterations precede cognitive decline, while in epilepsy, the subiculum plays a critical role in seizure initiation. Stress involves the subiculum's impact on the hypothalamic-pituitary-adrenocortical axis. Moreover, the subiculum exhibits structural and functional changes in anxiety, schizophrenia, and Parkinson's disease, contributing to cognitive deficits. Bipolar disorder is linked to subiculum structural abnormalities, while autism spectrum disorder reveals an alteration of inward deformation in the subiculum. Lastly, frontotemporal dementia shows volumetric differences in the subiculum, emphasizing its contribution to the disorder's complexity. Taken together, this review consolidates existing knowledge on the subiculum's role in brain disorders, and may facilitate future research, diagnostic strategies, and therapeutic interventions for various neurological conditions.

NMDA Receptor Antagonists: Emerging Insights into Molecular Mechanisms and Clinical Applications in Neurological Disorders

Neurodegenerative disorders (NDs) include a range of chronic conditions characterized by progressive neuronal loss, leading to cognitive, motor, and behavioral impairments. Common examples include Alzheimer's disease (AD) and Parkinson's disease (PD). The global prevalence of NDs is on the rise, imposing significant economic and social burdens. Despite extensive research, the mechanisms underlying NDs remain incompletely understood, hampering the development of effective treatments. Excitotoxicity, particularly glutamate-mediated excitotoxicity, is a key pathological process implicated in NDs. Targeting the N-methyl-D-aspartate (NMDA) receptor, which plays a central role in excitotoxicity, holds therapeutic promise. However, challenges, such as blood-brain barrier penetration and adverse effects, such as extrapyramidal effects, have hindered the success of many NMDA receptor antagonists in clinical trials. This review explores the molecular mechanisms of NMDA receptor antagonists, emphasizing their structure, function, types, challenges, and future prospects in treating NDs. Despite extensive research on competitive and noncompetitive NMDA receptor antagonists, the quest for effective treatments still faces significant hurdles. This is partly because the same NMDA receptor that necessitates blockage under pathological conditions is also responsible for the normal physiological function of NMDA receptors. Allosteric modulation of NMDA receptors presents a potential alternative, with the GluN2B subunit emerging as a particularly attractive target due to its enrichment in presynaptic and extrasynaptic NMDA receptors, which are major contributors to excitotoxic-induced neuronal cell death. Despite their low side-effect profiles, selective GluN2B antagonists like ifenprodil and radiprodil have encountered obstacles such as poor bioavailability in clinical trials. Moreover, the selectivity of these antagonists is often relative, as they have been shown to bind to other GluN2 subunits, albeit minimally. Recent advancements in developing phenanthroic and naphthoic acid derivatives offer promise for enhanced GluN2B, GluN2A or GluN2C/GluN2D selectivity and improved pharmacodynamic properties. Additional challenges in NMDA receptor antagonist development include conflicting preclinical and clinical results, as well as the complexity of neurodegenerative disorders and poorly defined NMDA receptor subtypes. Although multifunctional agents targeting multiple degenerative processes are also being explored, clinical data are limited. Designing and developing selective GluN2B antagonists/modulators with polycyclic moieties and multitarget properties would be significant in addressing neurodegenerative disorders. However, advancements in understanding NMDA receptor structure and function, coupled with collaborative efforts in drug design, are imperative for realizing the therapeutic potential of these NMDA receptor antagonists/modulators.

The clinical and genetic spectrum of paediatric speech and language disorders in 52,143 individuals

Speech and language disorders are known to have a substantial genetic contribution. Although frequently examined as components of other conditions, research on the genetic basis of linguistic differences as separate phenotypic subgroups has been limited so far. Here, we performed an in-depth characterization of speech and language disorders in 52,143 individuals, reconstructing clinical histories using a large-scale data mining approach of the Electronic Medical Records (EMR) from an entire large paediatric healthcare network. The reported frequency of these disorders was the highest between 2 and 5 years old and spanned a spectrum of twenty-six broad speech and language diagnoses. We used Natural Language Processing to assess to which degree clinical diagnosis in full-text notes were reflected in ICD-10 diagnosis codes. We found that aphasia and speech apraxia could be easily retrieved through ICD-10 diagnosis codes, while stuttering as a speech phenotype was only coded in 12% of individuals through appropriate ICD-10 codes. We found significant comorbidity of speech and language disorders in neurodevelopmental conditions (30.31%) and to a lesser degree with epilepsies (6.07%) and movement disorders (2.05%). The most common genetic disorders retrievable in our EMR analysis were STXBP1 (n=21), PTEN (n=20), and CACNA1A (n=18). When assessing associations of genetic diagnoses with specific linguistic phenotypes, we observed associations of STXBP1 and aphasia (P=8.57 × 10-7, CI=18.62-130.39) and MYO7A with speech and language development delay due to hearing loss (P=1.24 × 10-5, CI=17.46-Inf). Finally, in a sub-cohort of 726 individuals with whole exome sequencing data, we identified an enrichment of rare variants in synaptic protein and neuronal receptor pathways and associations of UQCRC1 with expressive aphasia and WASHC4 with abnormality of speech or vocalization. In summary, our study outlines the landscape of paediatric speech and language disorders, confirming the phenotypic complexity of linguistic traits and novel genotype-phenotype associations. Subgroups of paediatric speech and language disorders differ significantly with respect to the composition of monogenic aetiologies.

Turning the Spotlight to Cholinergic Pharmacotherapy of the Human Language System

Even though language is essential in human communication, research on pharmacological therapies for language deficits in highly prevalent neurodegenerative and vascular brain diseases has received little attention. Emerging scientific evidence suggests that disruption of the cholinergic system may play an essential role in language deficits associated with Alzheimer's disease and vascular cognitive impairment, including post-stroke aphasia. Therefore, current models of cognitive processing are beginning to appraise the implications of the brain modulator acetylcholine in human language functions. Future work should be directed further to analyze the interplay between the cholinergic system and language, focusing on identifying brain regions receiving cholinergic innervation susceptible to modulation with pharmacotherapy to improve affected language domains. The evaluation of language deficits in pharmacological cholinergic trials for Alzheimer's disease and vascular cognitive impairment has thus far been limited to coarse-grained methods. More precise, fine-grained language testing is needed to refine patient selection for pharmacotherapy to detect subtle deficits in the initial phases of cognitive decline. Additionally, noninvasive biomarkers can help identify cholinergic depletion. However, despite the investigation of cholinergic treatment for language deficits in Alzheimer's disease and vascular cognitive impairment, data on its effectiveness are insufficient and controversial. In the case of post-stroke aphasia, cholinergic agents are showing promise, particularly when combined with speech-language therapy to promote trained-dependent neural plasticity. Future research should explore the potential benefits of cholinergic pharmacotherapy in language deficits and investigate optimal strategies for combining these agents with other therapeutic approaches.

Pharmacotherapy for post-stroke aphasia: what are the options?

INTRODUCTION

Aphasia is a common, long-lasting aftermath of stroke lesions. There is an increased integration of pharmacotherapy as an adjunctive strategy to speech and language therapy (SLT) for post-stroke aphasia (PSA). Nevertheless, more research in pharmacotherapy for acute and chronic PSA is necessary, including the election of drugs that target different neurotransmitter systems and deficits in specific language domains.

AREAS COVERED

This article updates the role of pharmacotherapy for PSA, focusing the spotlight on some already investigated drugs and candidate agents deserving of future research. Refining the precision of drug election would require using multimodal biomarkers to develop personalized treatment approaches. There is a solid need to devise feasible randomized controlled trials adapted to the particularities of the PSA population. The emergent role of multimodal interventions combining one or two drugs with noninvasive brain stimulation to augment SLT is emphasized.

EXPERT OPINION

Pharmacotherapy can improve language deficits not fully alleviated by SLT. In addition, the 'drug-only' approach can also be adopted when administering SLT is not possible. The primary goal of pharmacotherapy is reducing the overall aphasia severity, although targeting language-specific deficits (i.e. naming, spoken output) also contributes to improving functional communication. Unfortunately, there is still little information for recommending a drug for specific language deficits.

Glutamatergic neurotransmission: A potential pharmacotherapeutic target for the treatment of cognitive disorders

In the mammalian brain, glutamate is regarded to be the primary excitatory neurotransmitter due to its widespread distribution and wide range of metabolic functions. Glutamate plays key roles in regulating neurogenesis, synaptogenesis, neurite outgrowth, and neuron survival in the brain. Ionotropic and metabotropic glutamate receptors, neurotransmitters, neurotensin, neurosteroids, and others co-ordinately formulate a complex glutamatergic network in the brain that maintains optimal excitatory neurotransmission. Cognitive activities are potentially synchronized by the glutamatergic activities in the brain via restoring synaptic plasticity. Dysfunctional glutamate receptors and other glutamatergic components are responsible for the aberrant glutamatergic activity in the brain that cause cognitive impairments, loss of synaptic plasticity, and neuronal damage. Thus, controlling the brain's glutamatergic transmission and modifying glutamate receptor function could be a potential therapeutic strategy for cognitive disorders. Certain drugs that regulate glutamate receptor activities have shown therapeutic promise in improving cognitive functions in preclinical and clinical studies. However, several issues regarding precise functional information of glutamatergic activity are yet to be comprehensively understood. The present article discusses the scope of developing glutamatergic systems as prospective pharmacotherapeutic targets to treat cognitive disorders. Special attention has been given to recent developments, challenges, and future prospects.

Possible Effects of Acupuncture in Poststroke Aphasia

Neural plasticity promotes the reorganization of language networks and is an essential recovery mechanism for poststroke aphasia (PSA). Neuroplasticity may be a pivotal bridge to elucidate the potential recovery mechanisms of acupuncture for aphasia. Therefore, understanding the neuroplasticity mechanism of acupuncture in PSA is crucial. However, the underlying therapeutic mechanism of neuroplasticity in PSA after acupuncture needs to be explored. Excitotoxicity after brain injury affects the activity of neurotransmitters and disrupts the transmission of normal neuron information. Thus, a helpful strategy of acupuncture might be to improve PSA by affecting the availability of these neurotransmitters and glutamate receptors at synapses. In addition, the regulation of neuroplasticity by acupuncture may also be related to the regulation of astrocytes. Considering the guiding significance of acupuncture for clinical treatment, it is necessary to carry out further study about the influence of acupuncture on the recovery of aphasia after stroke. This study summarizes the current research on the neural mechanism of acupuncture in treating PSA. It seeks to elucidate the potential effect of acupuncture on the recovery of PSA from the perspective of synaptic plasticity and integrity of gray and white matter.

Thymoquinone-rich black cumin oil attenuates ibotenic acid-induced excitotoxicity through glutamate receptors in Wistar rats

Inflammation-mediated alterations in glutamate neurotransmission constitute the most important pathway in the pathophysiology of various brain disorders. The excessive signalling of glutamate results in excitotoxicity, neuronal degeneration, and neuronal cell death. In the present study, we investigated the relative efficacy of black cumin (Nigella sativa) oil with high (5 % w/w) and low (2 % w/w) thymoquinone content (BCO-5 and BCO-2, respectively) in alleviating ibotenic acid-induced excitotoxicity and neuroinflammation in Wistar rats. It was found that BCO-5 reversed the abnormal behavioural patterns and the key inflammatory mediators (TNF-α and NF-κB) when treated at 5 mg/kg body weight. Immunohistochemical studies showed the potential of BCO-5 to attenuate the glutamate receptor subunits NMDA and GluR-2 along with increased glutamate decarboxylase levels in the brain tissues. Histopathological studies revealed the neuroprotection of BCO-5 against the inflammatory lesions, as evidenced by the normal cerebellum, astrocytes, and glial cells. BCO-2 on the other hand showed either a poor protective effect or no effect even at a 4-fold higher concentration of 20 mg/kg body weight indicating a very significant role of thymoquinone content on the neuroprotective effect of black cumin oil and its plausible clinical efficacy in counteracting the anxiety and stress-related neurological disorders under conditions such as depression and Alzheimer's disease.

Language abnormalities in schizophrenia: binding core symptoms through contemporary empirical evidence

Both the ability to speak and to infer complex linguistic messages from sounds have been claimed as uniquely human phenomena. In schizophrenia, formal thought disorder (FTD) and auditory verbal hallucinations (AVHs) are manifestations respectively relating to concrete disruptions of those abilities. From an evolutionary perspective, Crow (1997) proposed that "schizophrenia is the price that Homo sapiens pays for the faculty of language". Epidemiological and experimental evidence points to an overlap between FTD and AVHs, yet a thorough investigation examining their shared neural mechanism in schizophrenia is lacking. In this review, we synthesize observations from three key domains. First, neuroanatomical evidence indicates substantial shared abnormalities in language-processing regions between FTD and AVHs, even in the early phases of schizophrenia. Second, neurochemical studies point to a glutamate-related dysfunction in these language-processing brain regions, contributing to verbal production deficits. Third, genetic findings further show how genes that overlap between schizophrenia and language disorders influence neurodevelopment and neurotransmission. We argue that these observations converge into the possibility that a glutamatergic dysfunction in language-processing brain regions might be a shared neural basis of both FTD and AVHs. Investigations of language pathology in schizophrenia could facilitate the development of diagnostic tools and treatments, so we call for multilevel confirmatory analyses focused on modulations of the language network as a therapeutic goal in schizophrenia.

Disturbance of glutamate metabolism and inhibition of CaM-CaMKII-CREB signaling pathway in the hippocampus of mice induced by 1,2-dichloroethane exposure

1,2-Dichloroethane (1,2-DCE) is a highly toxic neurotoxicity, and the brain tissue is the main target organ. At present, long-term exposure to 1,2-DCE has been shown to cause cognitive dysfunction in some studies, but the mechanism is not clear. The results of this study showed that long-term 1,2-DCE exposure decreased learning and memory abilities in mice and impaired the structure and morphology of neurons in the hippocampal region. Moreover, except for the mRNA level of PAG, the enzymatic activities and protein levels of GS and PAG, as well as the mRNA level of GS were inhibited. With increasing dose of exposure, the protein and mRNA expression of GLAST and GLT-1 also decreased. Contrarily, there were protein and mRNA expression upregulation of GluN1, GluN2A and GluN2B in the hippocampus, as well as increased levels of extracellular Glu and intracellular Ca²⁺. In addition, 1,2-DCE exposure also downregulated the protein expression levels of CaM, CaMKII and CREB. Taken together, our results suggest that long-term 1,2-DCE exposure impairs the learning and memory capacity in mice, which may be attributed to the disruption of Glu metabolism and the inhibition of CaM- CaMKII-CREB signaling pathway in the hippocampus.

Rapid and simultaneous determination of histidine metabolism intermediates in human and mouse microbiota and biomatrices

Histidine metabolism is a key pathway physiologically involved in satiety, recognition memory, skin, and neural protection and allergic diseases. Microbiologically-produced imidazole propionate induces type II diabetes and interferes with glucose lowering drugs. Despite their determinant health implications, no single method simultaneously assesses histidine metabolites in urine, feces, and microbiota. The aim of this study was to develop a simple, rapid, and sensitive method for the determination of histidine and its major bioactive metabolites histamine, N-acetylhistamine, imidazole-4-acetate, cis-urocanate, trans-urocanate, glutamate and imidazole propionate, using ultrahigh-performance liquid chromatography with electrospray ionization tandem mass spectrometry. An innovative simple extraction method from small aliquots of human and mice urine, feces and microbial cell extracts was coupled to separation in a 6.5 min chromatographic run. The successful performance allowed accurate and precise quantification of all metabolites in mouse feces, suggesting broad exchange of histidine metabolites between the gut and mice. Higher urine histamine, histamine to histidine ratio, and imidazole-4-acetate pointed to an underlying inflammatory or allergic process in mice compared to human subjects. N-acetylhistamine and imidazole propionate were detected in human and mouse feces, confirming its origin from gut microbial metabolism. Our novel and robust analytical method captured histidine metabolism in a single assay that will facilitate broad and deep histidine metabolic phenotyping assessing the impact of microbiota on host health in large-scale human observational and interventional studies.

Associations between polygenic risk scores and amplitude of low-frequency fluctuation of inferior frontal gyrus in schizophrenia

Schizophrenia (SCZ) is a serious and complex mental disorder with high heritability. Polygenic risk score (PRS) is a useful tool calculating the accumulating effects of multiple common genetic variants of schizophrenia. The amplitude of low-frequency fluctuation (ALFF) is an efficient index to reflect spontaneous, intrinsic neuronal activity. Aberrant ALFF of brain regions were reported in schizophrenia frequently, but the relationship between PRS and ALFF has not been studied. In the present study, we compared PRS and ALFF in 101 schizophrenia patients and 106 age-matched healthy controls to test their associations with schizophrenia. Then, the correlation of PRS with ALFF was measured to reveal the effect of polygenic risk on brain activity in schizophrenia. We found that schizophrenia patients showed significant differences in PRS and ALFF compared with controls. Twenty-six brain regions showed significant difference of ALFF between schizophrenia cases and controls, of which left inferior frontal gyrus, triangular part (IFGtriang.L) showed increased activity in schizophrenia. PRS-SCZ was positively correlated with ALFF in IFGtriang.L in 57 non-chronic patients. Genes involved in synaptic organization and transmission, especially in glutamatergic synapse, were highly enriched in PRS-SCZ genes, suggesting the dysfunction of synapses in schizophrenia. These results help to understand the molecular mechanism underlying schizophrenia and related brain dysfunction.

Altered Brain Function in Treatment-Resistant and Non-treatment-resistant Depression Patients: A Resting-State Functional Magnetic Resonance Imaging Study

OBJECTIVE

In this study, we used amplitude of low-frequency fluctuation (ALFF) and regional homogeneity (ReHo) to observe differences in local brain functional activity and its characteristics in patients with treatment-resistant depression (TRD) and non-treatment-resistant depression (nTRD), and to explore the correlation between areas of abnormal brain functional activity and clinical symptoms.

METHOD

Thirty-seven patients with TRD, 36 patients with nTRD, and 35 healthy controls (HCs) were included in resting-state fMRI scans. ALFF and ReHo were used for image analysis and further correlation between abnormal brain regions and clinical symptoms were analyzed.

RESULTS

ANOVA revealed that the significantly different brain regions of ALFF and ReHo among the three groups were mainly concentrated in the frontal and temporal lobes. Compared with the nTRD group, the TRD group had decreased ALFF in the left/right inferior frontal triangular gyrus, left middle temporal gyrus, left cuneus and bilateral posterior lobes of the cerebellum, and increased ALFF in the left middle frontal gyrus and right superior temporal gyrus, and the TRD group had decreased ReHo in the left/right inferior frontal triangular gyrus, left middle temporal gyrus, and increased ReHo in the right superior frontal gyrus. Compared with the HC group, the TRD group had decreased ALFF/ReHo in both the right inferior frontal triangular gyrus and the left middle temporal gyrus. Pearson correlation analysis showed that both ALFF and ReHo values in these abnormal brain regions were positively correlated with HAMD-17 scores (P < 0.05).

CONCLUSION

Although the clinical symptoms were similar in the TRD and nTRD groups, abnormal neurological functional activity were present in some of the same brain regions. Compared with the nTRD group, ALFF and ReHo showed a wider range of brain area alterations and more complex neuropathological mechanisms in the TRD group, especially in the inferior frontal triangular gyrus of the frontal lobe and the middle temporal gyrus of the temporal lobe.

Cerebral Expression of Metabotropic Glutamate Receptor Subtype 5 in Idiopathic Autism Spectrum Disorder and Fragile X Syndrome: A Pilot Study

Multiple lines of evidence suggest that dysfunction of the metabotropic glutamate receptor subtype 5 (mGluR5) plays a role in the pathogenesis of autism spectrum disorder (ASD). Yet animal and human investigations of mGluR5 expression provide conflicting findings about the nature of dysregulation of cerebral mGluR5 pathways in subtypes of ASD. The demonstration of reduced mGluR5 expression throughout the living brains of men with fragile X syndrome (FXS), the most common known single-gene cause of ASD, provides a clue to examine mGluR5 expression in ASD. We aimed to (A) compare and contrast mGluR5 expression in idiopathic autism spectrum disorder (IASD), FXS, and typical development (TD) and (B) show the value of positron emission tomography (PET) for the application of precision medicine for the diagnosis and treatment of individuals with IASD, FXS, and related conditions. Two teams of investigators independently administered 3-[18F]fluoro-5-(2-pyridinylethynyl)benzonitrile ([18F]FPEB), a novel, specific mGluR5 PET ligand to quantitatively measure the density and the distribution of mGluR5s in the brain regions, to participants of both sexes with IASD and TD and men with FXS. In contrast to participants with TD, mGluR5 expression was significantly increased in the cortical regions of participants with IASD and significantly reduced in all regions of men with FXS. These results suggest the feasibility of this protocol as a valuable tool to measure mGluR5 expression in clinical trials of individuals with IASD and FXS and related conditions.

Reduced Expression of Cerebral Metabotropic Glutamate Receptor Subtype 5 in Men with Fragile X Syndrome

Glutamatergic receptor expression is mostly unknown in adults with fragile X syndrome (FXS). Favorable behavioral effects of negative allosteric modulators (NAMs) of the metabotropic glutamate receptor subtype 5 (mGluR5) in fmr1 knockout (KO) mouse models have not been confirmed in humans with FXS. Measurement of cerebral mGluR5 expression in humans with FXS exposed to NAMs might help in that effort. We used positron emission tomography (PET) to measure the mGluR5 density as a proxy of mGluR5 expression in cortical and subcortical brain regions to confirm target engagement of NAMs for mGluR5s. The density and the distribution of mGluR5 were measured in two independent samples of men with FXS (N = 9) and typical development (TD) (N = 8). We showed the feasibility of this complex study including MRI and PET, meaning that this challenging protocol can be accomplished in men with FXS with an adequate preparation. Analysis of variance of estimated mGluR5 expression showed that mGluR5 expression was significantly reduced in cortical and subcortical regions of men with FXS in contrast to age-matched men with TD.