Amygdala GluN2B-NMDAR dysfunction is critical in abnormal aggression of neurodevelopmental origin induced by St8sia2 deficiency

Disruption of Cdk5-GluN2B complex by a small interfering peptide attenuates social isolation-induced escalated intermale attack behavior and hippocampal oxidative stress in mice

Social isolation has emerged as a significant issue during the COVID-19 pandemic that can adversely impact human mental health and potentially lead to pathological aggression. Given the lack of effective therapeutic interventions for aggressive behavior, alternative approaches are necessary. In this study, we utilized a genetic method combined with a pharmacological approach to identify and demonstrate the crucial role of Cdk5 in escalated intermale attack behavior induced by 2-week social isolation. Moreover, we developed a small peptide that effectively disrupts the interaction between Cdk5 and GluN2B, given the known involvement of this complex in various neuropsychiatric disorders. Administration of the peptide, either systemically or via intrahippocampal injection, significantly reduced oxidative stress in the hippocampus and attenuated intermale attack behavior induced by 2-week social isolation. These findings highlight the previously unknown role of the hippocampal Cdk5-GluN2B complex in social isolation-induced aggressive behavior in mice and propose the peptide as a promising therapeutic strategy for regulating attack behavior and oxidative stress.

Two parallel medial prefrontal cortex-amygdala pathways mediate memory deficits via glutamatergic projection in surgery mice

The neural circuit mechanisms underlying postoperative cognitive dysfunction (POCD) remain elusive. We hypothesized that projections from the medial prefrontal cortex (mPFC) to the amygdala are involved in POCD. A mouse model of POCD in which isoflurane (1.5%) combined with laparotomy was used. Virally assisted tracing techniques were used to label the relevant pathways. Fear conditioning, immunofluorescence, whole-cell patch-clamp recordings, and chemogenetic and optogenetic techniques were applied to investigate the role of mPFC-amygdala projections in POCD. We find that surgery impairs memory consolidation but not retrieval of consolidated memories. In POCD mice, the glutamatergic pathway from the prelimbic cortex to the basolateral amygdala (PL-BLA) shows reduced activity, whereas the glutamatergic pathway from the infralimbic cortex to the basomedial amygdala (IL-BMA) shows enhanced activity. Our study indicates that the hypoactivity in the PL-BLA pathway interrupts memory consolidation, whereas the hyperactivity in the IL-BMA promotes memory extinction, in POCD mice.

Neurobiology of Aggression-Review of Recent Findings and Relationship with Alcohol and Trauma

Aggression can be conceptualized as any behavior, physical or verbal, that involves attacking another person or animal with the intent of causing harm, pain or injury. Because of its high prevalence worldwide, aggression has remained a central clinical and public safety issue. Aggression can be caused by several risk factors, including biological and psychological, such as genetics and mental health disorders, and socioeconomic such as education, employment, financial status, and neighborhood. Research over the past few decades has also proposed a link between alcohol consumption and aggressive behaviors. Alcohol consumption can escalate aggressive behavior in humans, often leading to domestic violence or serious crimes. Converging lines of evidence have also shown that trauma and posttraumatic stress disorder (PTSD) could have a tremendous impact on behavior associated with both alcohol use problems and violence. However, although the link between trauma, alcohol, and aggression is well documented, the underlying neurobiological mechanisms and their impact on behavior have not been properly discussed. This article provides an overview of recent advances in understanding the translational neurobiological basis of aggression and its intricate links to alcoholism and trauma, focusing on behavior. It does so by shedding light from several perspectives, including in vivo imaging, genes, receptors, and neurotransmitters and their influence on human and animal behavior.

Smaller amygdala subnuclei volume in schizophrenia patients with violent behaviors

To investigate the association between the volume of amygdala subnuclei and violent behaviors in patients with schizophrenia (SCZ). In the present study, we recruited 40 SCZ patients with violent behaviors (VS), 26 SCZ patients without violent behaviors (NVS), and 28 matched healthy controls (HC) who completed T1-weighted magnetic resonance imaging. Both the total amygdala and amygdala subnuclei volumes were estimated with FreeSurfer. When comparing the SCZ patients with HC, SCZ patients had a smaller volume of the left basal nucleus (P < 0.05, uncorrected). Further, the VS patients had a smaller volume of the left amygdala central nucleus than the NVS group (P < 0.05, Bonferroni corrected). Our study suggests that a smaller volume of the left amygdala basal nucleus may be a biomarker for SCZ and that a smaller volume of the left central nucleus may be relevant to violence risk in patients with schizophrenia.

Promises and Pitfalls of NMDA Receptor Antagonists in Treating Violent Aggression

Treatment options for chronically aggressive individuals remain limited despite recent medical advances. Traditional pharmacological agents used to treat aggression, such as atypical antipsychotics, have limited efficacy and are often replete with dangerous side effects. The non-competitive NMDAR antagonists ketamine and memantine are promising alternatives, but their effects appear to be highly dependent on dosage, context, and personal experience. Importantly, these drugs can increase aggression when combined with substances of abuse or during periods of heightened stress. This is likely due to mechanistic differences operating at specific synapses under different contexts. Previous findings from our lab and others have shown that early life stress, substance abuse, and attack experience promote aggression through NMDAR-dependent synaptic plasticity within aggression-related brain circuits. Ketamine and memantine affect these types of aggression in opposite ways. This has led us to propose that ketamine and memantine oppositely affect aggression brought on by early life stress, substance abuse, or attack experience through opposite effects on NMDAR-dependent synaptic plasticity. This would account for the persistent effects of these drugs on aggression and suggest they could be leveraged as a more long-lasting treatment option. However, a more thorough examination of the effects of ketamine and memantine on cellular and synaptic function will be necessary for responsible administration. Additionally, because the effects of ketamine and memantine are highly dependent on prior drug use, traumatic stress, or a history of aggressive behavior, we propose a more thorough medical evaluation and psychiatric assessment will be necessary to avoid possible adverse interactions with these drugs.

Nobiletin as a Neuroprotectant against NMDA Receptors: An In Silico Approach

Excitotoxicity is a type of neurodegenerative disorder. It caused by excessive glutamate receptor activation, which leads to neuronal malfunction and fatality. The N-methyl-D-aspartate (NMDA) receptors are found in glutamatergic neurons, and their excessive activation is primarily responsible for excitotoxicity. They are activated by both glutamate binding and postsynaptic depolarization, facilitating Ca²⁺ entry upon activation. Therefore, they are now widely acknowledged as being essential targets for excitotoxicity issues. Molecular docking and molecular dynamics (MD) simulation analyses have demonstrated that nobiletin efficiently targets the binding pocket of the NMDA receptor protein and exhibits stable dynamic behavior at the binding site. In this study, five potential neuroprotectants, nobiletin, silibinin, ononin, ginkgolide B, and epigallocatechin gallate (EGCG), were screened against the glutamate NMDA receptors in humans via computational methods. An in silico ADMET study was also performed, to predict the pharmacokinetics and toxicity profile for the expression of good drug-like behavior and a non-toxic nature. It was revealed that nobiletin fulfills the criteria for all of the drug-likeness rules (Veber, Lipinski, Ghose, Muegge, and Egan) and has neither PAINS nor structural alerts (Brenks). In conclusion, nobiletin demonstrated a possible promising neuroprotectant activities compared to other selected phytochemicals. Further, it can be evaluated in the laboratory for promising therapeutic approaches for in vitro and in vivo studies.

News and Views on Polysialic Acid: From Tumor Progression and Brain Development to Psychiatric Disorders, Neurodegeneration, Myelin Repair and Immunomodulation

Polysialic acid (polySia) is a sugar homopolymer consisting of at least eight glycosidically linked sialic acid units. It is a posttranslational modification of a limited number of proteins with the neural cell adhesion molecule NCAM being the most prominent. As extensively reviewed before, polySia-NCAM is crucial for brain development and synaptic plasticity but also modulates tumor growth and malignancy. Functions of polySia have been attributed to its polyanionic character, its spatial expansion into the extracellular space, and its modulation of NCAM interactions. In this mini-review, we first summarize briefly, how the modulation of NCAM functions by polySia impacts tumor cell growth and leads to malformations during brain development of polySia-deficient mice, with a focus on how the latter may be linked to altered behaviors in the mouse model and to neurodevelopmental predispositions to psychiatric disorders. We then elaborate on the implications of polySia functions in hippocampal plasticity, learning and memory of mice in light of recently described polySia changes related to altered neurogenesis in the aging human brain and in neurodegenerative disease. Furthermore, we highlight recent progress that extends the range of polySia functions across diverse fields of neurobiology such as cortical interneuron development and connectivity, myelination and myelin repair, or the regulation of microglia activity. We discuss possible common and distinct mechanisms that may underlie these seemingly divergent roles of polySia, and provide prospects for new therapeutic approaches building on our improved understanding of polySia functions.

Compromised mammillary body connectivity and psychotic symptoms in mice with di- and mesencephalic ablation of ST8SIA2

Altered long-range connectivity is a common finding across neurodevelopmental psychiatric disorders, but causes and consequences are not well understood. Genetic variation in ST8SIA2 has been associated with schizophrenia, autism, and bipolar disorder, and St8sia2^-/- mice show a number of related neurodevelopmental and behavioral phenotypes. In the present study, we use conditional knockout (cKO) to dissect neurodevelopmental defects and behavioral consequences of St8sia2 deficiency in cortical interneurons, their cortical environment, or in the di- and mesencephalon. Neither separate nor combined cortical and diencephalic ablation of St8sia2 caused the disturbed thalamus-cortex connectivity observed in St8sia2^-/- mice. However, cortical ablation reproduced hypoplasia of corpus callosum and fornix and mice with di- and mesencephalic ablation displayed smaller mammillary bodies with a prominent loss of parvalbumin-positive projection neurons and size reductions of the mammillothalamic tract. In addition, the mammillotegmental tract and the mammillary peduncle, forming the reciprocal connections between mammillary bodies and Gudden's tegmental nuclei, as well as the size of Gudden's ventral tegmental nucleus were affected. Only mice with these mammillary deficits displayed enhanced MK-801-induced locomotor activity, exacerbated impairment of prepulse inhibition in response to apomorphine, and hypoanxiety in the elevated plus maze. We therefore propose that compromised mammillary body connectivity, independent from hippocampal input, leads to these psychotic-like responses of St8sia2-deficient mice.

Targeting GluN2B/NO Pathway Ameliorates Social Isolation-Induced Exacerbated Attack Behavior in Mice

Exacerbated attack behavior has a profound socioeconomic impact and devastating social consequences; however, there is no satisfactory clinical management available for an escalated attack behavior. Social isolation (SI) is widespread during this pandemic and may exert detrimental effects on mental health, such as causing heightened attack behavior. To explore the therapeutic approaches that alleviate the SI-induced heightened attack behavior, we utilized pharmacological methods targeting the GluN2B/NO signaling pathway during the attack behavior. Ifenprodil and TAT-9C peptide targeting GluN2B showed that the inhibition of GluN2B mitigated the SI-induced escalated attack behavior and the SI-induced aberrant nitric oxide (NO) level in the brain. Additionally, the potentiation of the NO level by L-arginine reversed the effects of the inhibition of GluN2B. Moreover, we showed that high doses of L-NAME and 7-NI and subeffective doses of L-NAME in combination with ifenprodil or TAT-9C or subeffective doses of 7-NI plus ifenprodil or TAT-9C all decreased the SI-induced escalated attack behavior and reduced the NO level, further supporting the idea that GluN2B/NO signaling is a crucial modulator of the escalated attack behavior.

Neuronal Nitric Oxide Synthase Knockdown Within Basolateral Amygdala Induces Autistic-Related Phenotypes and Decreases Excitatory Synaptic Transmission in Mice

Autism spectrum disorder (ASD) is a heterogeneous group of neurodevelopmental disorders characterized by deficits in communication, impaired social interaction, and repetitive or restricted interests and behaviors. We have recently shown that neuronal nitric oxide synthase (nNOS) expression was reduced in the basolateral amygdala of mice after postnatal valproic acid exposure. However, the specific role of nNOS downregulation in mice remains to be elucidated. Herein, we investigated the behavioral alternations of naive mice with a recombinant adeno-associated virus (rAAV)-mediated knockdown of nNOS in a comprehensive test battery, including the social interaction, marble burying, self-grooming, and open field tests. Further, the electrophysiological and surface expression changes induced by nNOS deficiency of the basolateral amygdala in these animals were examined. Our results show that nNOS knockdown displayed typical symptoms of ASD-like behaviors, such as reduced social interaction and communication, elevated stereotypes, and anxiety in mice. Surprisingly, we found that nNOS knockdown exhibited greatly reduced excitatory synaptic transmission concomitant with the lower surface expression of GluN2B-containing N-methyl-D-aspartate receptors and postsynaptic density protein 95 in mice. These findings support a notion that dysregulation of nNOS might contribute to ASD-associated phenotypes, with disease pathogenesis most likely resulting from deficits in excitatory synaptic transmission.

LPA1 receptor and chronic stress: Effects on behaviour and the genes involved in the hippocampal excitatory/inhibitory balance

The LPA₁ receptor, one of the six characterized G protein-coupled receptors (LPA_1-6) through which lysophosphatidic acid acts, is likely involved in promoting normal emotional behaviours. Current data suggest that the LPA-LPA_1-receptor pathway may be involved in mediating the negative consequences of stress on hippocampal function. However, to date, there is no available information regarding the mechanisms whereby the LPA₁ receptor mediates this adaptation. To gain further insight into how the LPA-LPA₁ pathway may prevent the negative consequences of chronic stress, we assessed the effects of the continuous delivery of LPA on depressive-like behaviours induced by a chronic restraint stress protocol. Because a proper excitatory/inhibitory balance seems to be key for controlling the stress response system, the gene expression of molecular markers of excitatory and inhibitory neurotransmission was also determined. In addition, the hippocampal expression of mineralocorticoid receptor genes and glucocorticoid receptor genes and proteins as well as plasma corticosterone levels were determined. Contrary to our expectations, the continuous delivery of LPA in chronically stressed animals potentiated rather than inhibited some (e.g., anhedonia, reduced latency to the first immobility period), though not all, behavioural effects of stress. Furthermore, this treatment led to an alteration in the genes coding for proteins involved in the excitatory/inhibitory balance in the ventral hippocampus and to changes in corticosterone levels. In conclusion, the results of this study reinforce the assumption that LPA is involved in emotional regulation, mainly through the LPA₁ receptor, and regulates the effects of stress on hippocampal gene expression and hippocampus-dependent behaviour.

The Role of the N-Methyl-D-Aspartate Receptors in Social Behavior in Rodents

The appropriate display of social behaviors is essential for the well-being, reproductive success and survival of an individual. Deficits in social behavior are associated with impaired N-methyl-D-aspartate (NMDA) receptor-mediated neurotransmission. In this review, we describe recent studies using genetically modified mice and pharmacological approaches which link the impaired functioning of the NMDA receptors, especially of the receptor subunits GluN1, GluN2A and GluN2B, to abnormal social behavior. This abnormal social behavior is expressed as impaired social interaction and communication, deficits in social memory, deficits in sexual and maternal behavior, as well as abnormal or heightened aggression. We also describe the positive effects of pharmacological stimulation of the NMDA receptors on these social deficits. Indeed, pharmacological stimulation of the glycine-binding site either by direct stimulation or by elevating the synaptic glycine levels represents a promising strategy for the normalization of genetically-induced, pharmacologically-induced or innate deficits in social behavior. We emphasize on the importance of future studies investigating the role of subunit-selective NMDA receptor ligands on different types of social behavior to provide a better understanding of the underlying mechanisms, which might support the development of selective tools for the optimized treatment of disorders associated with social deficits.

Effects of the Genetic Depletion of Polysialyltransferases on the Structure and Connectivity of Interneurons in the Adult Prefrontal Cortex

Polysialic acid (polySia) is a complex sugar that in the nervous system appears mainly as a posttranslational modification of the neural cell adhesion molecule (NCAM). PolySia plays important roles during brain development, but also in its plasticity during adulthood. Two polysialyltransferases (polyST), ST8SIA2 and ST8SIA4, are involved in the synthesis and attachment of polySia. Both polyST are relevant for developmental migration of cortical interneurons and their establishment in the prefrontal cortex (PFC). In contrast, only ST8SIA4 appears to be important for the structural plasticity of a subpopulation of cortical interneurons in the adult. Interestingly, ST8SIA2 and NCAM are candidate genes for schizophrenia, a disorder in which interneuronal circuits are altered. However, there is still no data on the effects of polyST depletion on the dendritic structure or the connectivity of cortical interneurons. Here, we studied the contribution of each polyST on these parameters in the medial PFC (mPFC) of polyST knock-out mice with GAD67-GFP-labeled interneurons. Genetic depletion of ST8SIA4, but not ST8SIA2, resulted in a decrease in the complexity of the dendritic arbor of interneurons. In contrast, ablation of either of the two polyST induced a decrease in the density of parvalbumin (PV) expressing perisomatic puncta on pyramidal neurons. Thus, the depletion of each polyST results in similar impairments of not only developmental migration but also efferent synaptic connectivity of interneurons. In contrast, the loss of ST8SIA4 has a unique effect on dendritic structure, hence on afferent connectivity, suggesting differential and independent contributions of each polyST to neuritogenesis and synaptogenesis.