Alterations in cortical interneurons and cognitive function in schizophrenia

NARP-related alterations in the excitatory and inhibitory circuitry of socially isolated mice: developmental insights and implications for autism spectrum disorder

Background

Social isolation during critical periods of development is associated with alterations in behavior and neuronal circuitry. This study aimed to investigate the immediate and developmental effects of social isolation on firing properties, neuronal activity-regulated pentraxin (NARP) and parvalbumin (PV) expression in the prefrontal cortex (PFC), social behavior in juvenile socially isolated mice, and the biological relevance of NARP expression in autism spectrum disorder (ASD).

Methods

Mice were subjected to social isolation during postnatal days 21-35 (P21-P35) and were compared with group-housed control mice. Firing properties in the PFC pyramidal neurons were altered in P35 socially isolated mice, which might be associated with alterations in NARP and PV expression.

Results

In adulthood, mice that underwent juvenile social isolation exhibited difficulty distinguishing between novel and familiar mice during a social memory task, while maintaining similar levels of social interaction as the control mice. Furthermore, a marked decrease in NARP expression in lymphoblastoid cell lines derived from adolescent humans with ASD as compared to typically developing (TD) humans was found.

Conclusion

Our study highlights the role of electrophysiological properties, as well as NARP and PV expression in the PFC in mediating the developmental consequences of social isolation on behavior.

CCK+ Interneurons Contribute to Thalamus-Evoked Feed-Forward Inhibition in the Prelimbic Prefrontal Cortex

Interneurons in the medial prefrontal cortex (PFC) regulate local neural activity to influence cognitive, motivated, and emotional behaviors. Parvalbumin-expressing (PV+) interneurons are the primary mediators of thalamus-evoked feed-forward inhibition across the mouse cortex, including the anterior cingulate cortex, where they are engaged by inputs from the mediodorsal (MD) thalamus. In contrast, in the adjacent prelimbic (PL) cortex, we find that PV+ interneurons are scarce in the principal thalamorecipient layer 3 (L3), suggesting distinct mechanisms of inhibition. To identify the interneurons that mediate MD-evoked inhibition in PL, we combine slice physiology, optogenetics, and intersectional genetic tools in mice of both sexes. We find interneurons expressing cholecystokinin (CCK+) are abundant in L3 of PL, with cells exhibiting fast-spiking (fs) or non-fast-spiking (nfs) properties. MD inputs make stronger connections onto fs-CCK+ interneurons, driving them to fire more readily than nearby L3 pyramidal cells and other interneurons. CCK+ interneurons in turn make inhibitory, perisomatic connections onto L3 pyramidal cells, where they exhibit cannabinoid 1 receptor (CB1R) mediated modulation. Moreover, MD-evoked feed-forward inhibition, but not direct excitation, is also sensitive to CB1R modulation. Our findings indicate that CCK+ interneurons contribute to MD-evoked inhibition in PL, revealing a mechanism by which cannabinoids can modulate MD-PFC communication.

Transcranial alternating current stimulation in affecting cognitive impairment in psychiatric disorders: a review

Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation method that, through its manipulation of endogenous oscillations, can affect cognition in healthy adults. Given the fact that both endogenous oscillations and cognition are impaired in various psychiatric diagnoses, tACS might represent a suitable intervention. We conducted a search of Pubmed and Web of Science databases and reviewed 27 studies where tACS is used in psychiatric diagnoses and cognition change is evaluated. TACS is a safe and well-tolerated intervention method, suitable for multiple-sessions protocols. It can be administered at home, individualized according to the patient''s anatomical and functional characteristics, or used as a marker of disease progression. The results are varying across diagnoses and applied protocols, with some protocols showing a long-term effect. However, the overall number of studies is small with a great variety of diagnoses and tACS parameters, such as electrode montage or used frequency. Precise mechanisms of tACS interaction with pathophysiological processes are only partially described and need further research. Currently, tACS seems to be a feasible method to alleviate cognitive impairment in psychiatric patients; however, a more robust confirmation of efficacy of potential protocols is needed to introduce it into clinical practise.

Short-latency prepulse inhibition of the trigeminal blink reflex

Prepulse inhibition (PPI) is a well-established phenomenon wherein a weak sensory stimulus attenuates the startle reflex triggered by a subsequent strong stimulus. Within the circuit, variations in target responses observed for PPI paradigms represent prepulse-induced excitability changes. However, little is known about the mechanism of PPI. Here, we focused on short-latency PPI of the trigeminal blink reflex R1 signal with an oligosynaptic reflex arc through the principal sensory trigeminal nucleus and the facial nucleus. As the facial nucleus is facilitatory to any input, R1 PPI is the phenomenon in the former nucleus. Considering that GABAergic modulation may be involved in PPI, this study investigated whether the PPI mechanism includes GABA-A equivalent inhibition, which peaks at approximately 30 ms in humans. In 12 healthy volunteers, the reflex was elicited by electrical stimulation of the supraorbital nerve, and recorded at the ipsilateral lower eyelid by accelerometer. Stimulus intensity was 1.5 times the R1 threshold for test stimulus and 0.9 times for the prepulse. The prepulse-test interval (PTI) was 5-150 ms. Results showed significant inhibition at 40-and 80-150-ms PTIs but not at 20-, 30-, 50-, 60-, and 70-ms PTIs, yielding two distinct inhibitions of different time scales. This corresponds well to the early and late components of inhibitory post synaptic potentials by GABA-A and GABA-B receptor activation. Thus, the data support the contribution of inhibitory post synaptic potentials elicited by the prepulse to the observed PPI. As inhibitory function-related diseases may impair the different inhibition components to varying degrees, methods deconvoluting each inhibitory component contribution are of clinical importance.

Parvalbumin interneuron cell-to-network plasticity: mechanisms and therapeutic avenues

Alzheimer's disease (AD) and schizophrenia (SCZ) represent two major neuropathological conditions with a high disease burden. Despite their distinct etiologies, patients suffering from AD or SCZ share a common burden of disrupted memory functions unattended by current therapies. Recent preclinical analyses highlight cell-type-specific contributions of parvalbumin interneurons (PVIs), particularly the plasticity of their cellular excitability, towards intact neuronal network function (cell-to-network plasticity) and memory performance. Here we argue that deficits of PVI cell-to-network plasticity may underlie memory deficits in AD and SCZ, and we explore two therapeutic avenues: the targeting of PVI-specific neuromodulation, including by neuropeptides, and the recruitment of network synchrony in the gamma frequency range (40 Hz) by external stimulation. We finally propose that these approaches be merged under consideration of recent insights into human brain physiology.

Effects of psoralidin on the expression of glutamate decarboxylases and inhibitory synapse development

Gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter required for excitation/inhibition balance is synthesized by the glutamic acid decarboxylases (GADs) in GABAergic neurons. The levels and activity of GADs are strongly correlated with GABA and neural transmission. Dysregulation of GADs and GABA is associated with various neurological disorders. The study used psoralidin, found in the seeds of Psoralea corylifolia, to investigate its effect on GAD levels and regulatory mechanisms in primary cortical neurons. Psoralidin reduced GAD67 through transcriptional regulation. The reduction was not mediated by the N-methyl-D-aspartate receptor. Additionally, psoralidin attenuated the formation of inhibitory synapses in primary hippocampal neurons.

RNA-sequencing suggests extracellular matrix and vasculature dysregulation could impair neurogenesis in schizophrenia cases with elevated inflammation

A subgroup of schizophrenia cases with elevated inflammation have reduced neurogenesis markers and increased macrophage density in the human subependymal zone (SEZ; also termed subventricular zone or SVZ) neurogenic niche. Inflammation can impair neurogenesis; however, it is unclear which other pathways are associated with reduced neurogenesis. This research aimed to discover transcriptomic differences between inflammatory subgroups of schizophrenia in the SEZ. Total RNA sequencing was performed on SEZ tissue from schizophrenia cases, designated into low inflammation (n = 13) and high inflammation (n = 14) subgroups, based on cluster analysis of inflammation marker gene expression. 718 genes were differentially expressed in high compared to low inflammation schizophrenia (FDR p < 0.05) and were most significantly over-represented in the pathway 'Hepatic Fibrosis/Hepatic Stellate-Cell Activation'. Genes in this pathway relate to extracellular matrix stability (including ten collagens) and vascular remodelling suggesting increased angiogenesis. Collagen-IV, a key element of the basement membrane and fractones, had elevated gene expression. Immunohistochemistry revealed novel collagen-IV+ fractone bulbs within the human SEZ hypocellular gap. Considering the extracellular matrix's regulatory role in SEZ neurogenesis, fibrosis-related alterations in high inflammation schizophrenia may disrupt neurogenesis. Increased angiogenesis could facilitate immune cell transmigration, potentially explaining elevated macrophages in high inflammation schizophrenia. This discovery-driven analysis sheds light on how inflammation may contribute to schizophrenia neuropathology in the neurogenic niche.

Positive and negative symptoms in methamphetamine-induced psychosis compared to schizophrenia: A systematic review and meta-analysis

BACKGROUND

The clinical profiles of methamphetamine-induced psychosis (MIP) and schizophrenia are largely overlapping making differentiation challenging. In this systematic review and meta-analysis, we aim to compare the positive and negative symptoms of MIP and schizophrenia to better understand the differences between them.

STUDY DESIGN

In accordance with our pre-registered protocol (CRD42021286619), we conducted a search of English-language studies up to December 16th, 2022, in PubMed, EMBASE, and PsycINFO, including stable outpatients with MIP and schizophrenia. We used the Newcastle-Ottawa Scale to measure the quality of cross-sectional, case-control, and cohort studies.

STUDY RESULTS

Of the 2052 articles retrieved, we included 12 studies (6 cross-sectional, 3 case-control, and 2 cohort studies) in our meta-analysis, involving 624 individuals with MIP and 524 individuals with schizophrenia. Our analysis found no significant difference in positive symptoms between the two groups (SMD, -0.01; 95%CI, -0.13 to +0.11; p = 1). However, individuals with MIP showed significantly less negative symptoms compared to those with schizophrenia (SMD, -0.35; 95CI%, -0.54 to -0.16; p = 0.01; I2 = 54 %). Our sensitivity analysis, which included only studies with a low risk of bias, did not change the results. However, our meta-analysis is limited by its cross-sectional approach, which limits the interpretation of causal associations. Furthermore, differences in population, inclusion criteria, methodology, and drug exposure impact our findings.

CONCLUSIONS

Negative symptoms are less prominent in individuals with MIP. While both groups do not differ regarding positive symptoms, raises the possibility of shared and partly different underlying neurobiological mechanisms related to MIP and schizophrenia.

Parvalbumin interneuron deficits in schizophrenia

Parvalbumin-expressing (PV+) interneurons represent one of the most abundant subclasses of cortical interneurons. Owing to their specific electrophysiological and synaptic properties, PV+ interneurons are essential for gating and pacing the activity of excitatory neurons. In particular, PV+ interneurons are critically involved in generating and maintaining cortical rhythms in the gamma frequency, which are essential for complex cognitive functions. Deficits in PV+ interneurons have been frequently reported in postmortem studies of schizophrenia patients, and alterations in gamma oscillations are a prominent electrophysiological feature of the disease. Here, I summarise the main features of PV+ interneurons and review clinical and preclinical studies linking the developmental dysfunction of cortical PV+ interneurons with the pathophysiology of schizophrenia.

Prevention of MK-801-induced amnestic effect with combined activation of 5-HT1A and muscarinic receptors in mice

BACKGROUND

Muscarinic or 5-HT1A receptors are crucial in learning and memory processes, and their expression is evident in the brain areas involved in cognition. The administration of the activators of these receptors prevents the development of cognitive dysfunctions in animal models of schizophrenia induced by MK-801 (N-methyl-d-aspartate receptor antagonist) administration. GABAergic dysfunction is considered as one of the most important causes of MK-801-induced spatial learning deficits.

METHODS

Novel object recognition (NOR) and Morris water maze (MWM) tests were used to study the anti-amnestic effect of the biased 5-HT1A receptor agonist (F15599) alone or in combinations with VU0357017 (M1 receptor allosteric agonist), VU0152100 (M4 receptor positive allosteric modulator), and VU0238429 (M5 receptor positive allosteric modulator) on MK-801-induced dysfunctions. The compounds were administered for 5 consecutive days. Animals tested with the MWM underwent 5-day training. Western blotting was used to study the expressions of 5-HT1A receptors and the level of GAD65 in the frontal cortices (FCs) and hippocampi of the animals.

RESULTS

F15599 prevented the amnestic effect induced by MK-801 in the MWM at a dose of 0.1 mg/kg. The co-administration of the compound with muscarinic receptors activators had no synergistic effect. The additive effect of the combinations was evident in the prevention of declarative memory dysfunctions investigated in NOR. The administration of MK-801 impaired 5-HT1A expression in the hippocampi and decreased GAD65 levels in both the FCs and hippocampi. The administration of muscarinic ligands prevented these MK-801-induced deficits only in the hippocampi of MWM-trained animals. No effects of the compounds were observed in untrained mice.

CONCLUSION

Our results indicate that F15599 prevents schizophrenia-related spatial learning deficits in the MWM; however, the activity of the compound is not intensified with muscarinic receptors activators. In contrast, the combined administration of the ligands is effective in the NOR model of declarative memory. The muscarinic receptors activators reversed MK-801-induced 5-HT1A and GAD65 dysfunctions in the hippocampi of MWM-trained mice, but not in untrained mice.

Delineating mechanisms underlying parvalbumin neuron impairment in different neurological and neurodegenerative disorders: the emerging role of mitochondrial dysfunction

Given the current paucity of effective treatments in many neurological disorders, delineating pathophysiological mechanisms among the major psychiatric and neurodegenerative diseases may fuel the development of novel, potent treatments that target shared pathways. Recent evidence suggests that various pathological processes, including bioenergetic failure in mitochondria, can perturb the function of fast-spiking, parvalbumin-positive neurons (PV+). These inhibitory neurons critically influence local circuit regulation, the generation of neuronal network oscillations and complex brain functioning. Here, we survey PV+ cell vulnerability in the major neuropsychiatric, and neurodegenerative diseases and review associated cellular and molecular pathophysiological alterations purported to underlie disease aetiology.

Multidimensional analysis of cortical interneuron synaptic features reveals underlying synaptic heterogeneity

Cortical interneurons represent a diverse set of neuronal subtypes characterized in part by their striking degree of synaptic specificity. However, little is known about the extent of synaptic diversity because of the lack of unbiased methods to extract synaptic features among interneuron subtypes. Here, we develop an approach to aggregate image features from fluorescent confocal images of interneuron synapses and their post-synaptic targets, in order to characterize the heterogeneity of synapses at fine scale. We started by training a model that recognizes pre- and post-synaptic compartments and then determines the target of each genetically-identified interneuron synapse in vitro and in vivo. Our model extracts hundreds of spatial and intensity features from each analyzed synapse, constructing a multidimensional data set, consisting of millions of synapses, which allowed us to perform an unsupervised analysis on this dataset, uncovering novel synaptic subgroups. The subgroups were spatially distributed in a highly structured manner that revealed the local underlying topology of the postsynaptic environment. Dendrite-targeting subgroups were clustered onto subdomains of the dendrite along the proximal to distal axis. Soma-targeting subgroups were enriched onto different postsynaptic cell types. We also find that the two main subclasses of interneurons, basket cells and somatostatin interneurons, utilize distinct strategies to enact inhibitory coverage. Thus, our analysis of multidimensional synaptic features establishes a conceptual framework for studying interneuron synaptic diversity.

Erythropoietin restrains the inhibitory potential of interneurons in the mouse hippocampus

Severe psychiatric illnesses, for instance schizophrenia, and affective diseases or autism spectrum disorders, have been associated with cognitive impairment and perturbed excitatory-inhibitory balance in the brain. Effects in juvenile mice can elucidate how erythropoietin (EPO) might aid in rectifying hippocampal transcriptional networks and synaptic structures of pyramidal lineages, conceivably explaining mitigation of neuropsychiatric diseases. An imminent conundrum is how EPO restores synapses by involving interneurons. By analyzing ~12,000 single-nuclei transcriptomic data, we generated a comprehensive molecular atlas of hippocampal interneurons, resolved into 15 interneuron subtypes. Next, we studied molecular alterations upon recombinant human (rh)EPO and saw that gene expression changes relate to synaptic structure, trans-synaptic signaling and intracellular catabolic pathways. Putative ligand-receptor interactions between pyramidal and inhibitory neurons, regulating synaptogenesis, are altered upon rhEPO. An array of in/ex vivo experiments confirms that specific interneuronal populations exhibit reduced dendritic complexity, synaptic connectivity, and changes in plasticity-related molecules. Metabolism and inhibitory potential of interneuron subgroups are compromised, leading to greater excitability of pyramidal neurons. To conclude, improvement by rhEPO of neuropsychiatric phenotypes may partly owe to restrictive control over interneurons, facilitating re-connectivity and synapse development.

Large-scale coupling of prefrontal activity patterns as a mechanism for cognitive control in health and disease: evidence from rodent models

Cognitive control of behavior is crucial for well-being, as allows subject to adapt to changing environments in a goal-directed way. Changes in cognitive control of behavior is observed during cognitive decline in elderly and in pathological mental conditions. Therefore, the recovery of cognitive control may provide a reliable preventive and therapeutic strategy. However, its neural basis is not completely understood. Cognitive control is supported by the prefrontal cortex, structure that integrates relevant information for the appropriate organization of behavior. At neurophysiological level, it is suggested that cognitive control is supported by local and large-scale synchronization of oscillatory activity patterns and neural spiking activity between the prefrontal cortex and distributed neural networks. In this review, we focus mainly on rodent models approaching the neuronal origin of these prefrontal patterns, and the cognitive and behavioral relevance of its coordination with distributed brain systems. We also examine the relationship between cognitive control and neural activity patterns in the prefrontal cortex, and its role in normal cognitive decline and pathological mental conditions. Finally, based on these body of evidence, we propose a common mechanism that may underlie the impaired cognitive control of behavior.

Multiple serum anti-glutamate receptor antibody levels in clozapine-treated/naïve patients with treatment-resistant schizophrenia

BACKGROUND

Glutamatergic function abnormalities have been implicated in the etiology of treatment-resistant schizophrenia (TRS), and the efficacy of clozapine may be attributed to its impact on the glutamate system. Recently, evidence has emerged suggesting the involvement of immune processes and increased prevalence of antineuronal antibodies in TRS. This current study aimed to investigate the levels of multiple anti-glutamate receptor antibodies in TRS and explore the effects of clozapine on these antibody levels.

METHODS

Enzyme linked immunosorbent assay (ELISA) was used to measure and compare the levels of anti-glutamate receptor antibodies (NMDAR, AMPAR, mGlur3, mGluR5) in clozapine-treated TRS patients (TRS-C, n = 37), clozapine-naïve TRS patients (TRS-NC, n = 39), and non-TRS patients (nTRS, n = 35). Clinical symptom severity was assessed using the Positive and Negative Symptom Scale (PANSS), while cognitive function was evaluated using the MATRICS Consensus Cognitive Battery (MCCB).

RESULT

The levels of all four glutamate receptor antibodies in TRS-NC were significantly higher than those in nTRS (p < 0.001) and in TRS-C (p < 0.001), and the antibody levels in TRS-C were comparable to those in nTRS. However, no significant associations were observed between antibody levels and symptom severity or cognitive function across all three groups after FDR correction.

CONCLUSION

Our findings suggest that TRS may related to increased anti-glutamate receptor antibody levels and provide further evidence that glutamatergic dysfunction and immune processes may contribute to the pathogenesis of TRS. The impact of clozapine on anti-glutamate receptor antibody levels may be a pharmacological mechanism underlying its therapeutic effects.

Resting-state EEG dynamic functional connectivity distinguishes non-psychotic major depression, psychotic major depression and schizophrenia

This study aims to identify dynamic patterns within the spatiotemporal feature space that are specific to nonpsychotic major depression (NPMD), psychotic major depression (PMD), and schizophrenia (SCZ). The study also evaluates the effectiveness of machine learning algorithms based on these network manifestations in differentiating individuals with NPMD, PMD, and SCZ. A total of 579 participants were recruited, including 152 patients with NPMD, 45 patients with PMD, 185 patients with SCZ, and 197 healthy controls (HCs). A dynamic functional connectivity (DFC) approach was employed to estimate the principal FC states within each diagnostic group. Incremental proportions of data (ranging from 10% to 100%) within each diagnostic group were used for variability testing. DFC metrics, such as proportion, mean duration, and transition number, were examined among the four diagnostic groups to identify disease-related neural activity patterns. These patterns were then used to train a two-layer classifier for the four groups (HC, NPMD, PMD, and SCZ). The four principal brain states (i.e., states 1,2,3, and 4) identified by the DFC approach were highly representative within and across diagnostic groups. Between-group comparisons revealed significant differences in network metrics of state 2 and state 3, within delta, theta, and gamma frequency bands, between healthy individuals and patients in each diagnostic group (p < 0.01, FDR corrected). Moreover, the identified key dynamic network metrics achieved an accuracy of 73.1 ± 2.8% in the four-way classification of HC, NPMD, PMD, and SCZ, outperforming the static functional connectivity (SFC) approach (p < 0.001). These findings suggest that the proposed DFC approach can identify dynamic network biomarkers at the single-subject level. These biomarkers have the potential to accurately differentiate individual subjects among various diagnostic groups of psychiatric disorders or healthy controls. This work may contribute to the development of a valuable EEG-based diagnostic tool with enhanced accuracy and assistive capabilities.

The "psychiatric" neuron: the psychic neuron of the cerebral cortex, revisited

Nearly 25 years ago, Dr. Patricia Goldman-Rakic published her review paper, "The 'Psychic' Neuron of the Cerebral Cortex," outlining the circuit-level dynamics, neurotransmitter systems, and behavioral correlates of pyramidal neurons in the cerebral cortex, particularly as they relate to working memory. In the decades since the release of this paper, the existing literature and our understanding of the pyramidal neuron have increased tremendously, and research is still underway to better characterize the role of the pyramidal neuron in both healthy and psychiatric disease states. In this review, we revisit Dr. Goldman-Rakic's characterization of the pyramidal neuron, focusing on the pyramidal neurons of the prefrontal cortex (PFC) and their role in working memory. Specifically, we examine the role of PFC pyramidal neurons in the intersection of working memory and social function and describe how deficits in working memory may actually underlie the pathophysiology of social dysfunction in psychiatric disease states. We briefly describe the cortico-cortical and corticothalamic connections between the PFC and non-PFC brain regions, as well the microcircuit dynamics of the pyramidal neuron and interneurons, and the role of both these macro- and microcircuits in the maintenance of the excitatory/inhibitory balance of the cerebral cortex for working memory function. Finally, we discuss the consequences to working memory when pyramidal neurons and their circuits are dysfunctional, emphasizing the resulting social deficits in psychiatric disease states with known working memory dysfunction.

Elevations in the Mitochondrial Matrix Protein Cyclophilin D Correlate With Reduced Parvalbumin Expression in the Prefrontal Cortex of Patients With Schizophrenia

BACKGROUND AND HYPOTHESIS

Cognitive deficits in schizophrenia are linked to dysfunctions of the dorsolateral prefrontal cortex (DLPFC), including alterations in parvalbumin (PV)-expressing interneurons (PVIs). Redox dysregulation and oxidative stress may represent convergence points in the pathology of schizophrenia, causing dysfunction of GABAergic interneurons and loss of PV. Here, we show that the mitochondrial matrix protein cyclophilin D (CypD), a critical initiator of the mitochondrial permeability transition pore (mPTP) and modulator of the intracellular redox state, is altered in PVIs in schizophrenia.

STUDY DESIGN

Western blotting was used to measure CypD protein levels in postmortem DLPFC specimens of schizophrenic patients (n = 27) and matched comparison subjects with no known history of psychiatric or neurological disorders (n = 26). In a subset of this cohort, multilabel immunofluorescent confocal microscopy with unbiased stereological sampling methods were used to quantify (1) numbers of PVI across the cortical mantle (20 unaffected comparison, 14 schizophrenia) and (2) PV and CypD protein levels from PVIs in the cortical layers 2-4 (23 unaffected comparison, 18 schizophrenia).

STUDY RESULTS

In schizophrenic patients, the overall number of PVIs in the DLPFC was not significantly altered, but in individual PVIs of layers 2-4 PV protein levels decreased along a superficial-to-deep gradient when compared to unaffected comparison subjects. These laminar-specific PVI alterations were reciprocally linked to significant CypD elevations both in PVIs and total DLPFC gray matter.

CONCLUSIONS

Our findings support previously reported PVI anomalies in schizophrenia and suggest that CypD-mediated mPTP formation could be a potential contributor to PVI dysfunction in schizophrenia.

Host brain environmental influences on transplanted medial ganglionic eminence progenitors

Interneuron progenitor transplantation can ameliorate disease symptoms in a variety of neurological disorders. The strategy is based on transplantation of embryonic medial ganglionic eminence (MGE) progenitors. Elucidating how host brain environment influences the integration of interneuron progenitors is critical for optimizing this strategy across different disease states. Here, we systematically evaluated the influence of age and brain region on survival, migration, and differentiation of transplant-derived cells. We find that early postnatal MGE transplantation yields superior survival and more extensive migratory capabilities compared to transplantation during the juvenile or adult stages. MGE progenitors migrate more widely in the cortex compared to the hippocampus. Maturation to interneuron subtypes is regulated by age and brain region. MGE progenitors transplanted into the dentate gyrus sub-region of the early postnatal hippocampus can differentiate into astrocytes. Our results suggest that the host brain environment critically regulates survival, spatial distribution, and maturation of MGE-derived interneurons following transplantation. These findings inform and enable optimal conditions for interneuron transplant therapies.

Modulators of GABAA receptor-mediated inhibition in the treatment of neuropsychiatric disorders: past, present, and future

The predominant inhibitory neurotransmitter in the brain, γ-aminobutyric acid (GABA), acts at ionotropic GABAA receptors to counterbalance excitation and regulate neuronal firing. GABAA receptors are heteropentameric channels comprised from subunits derived from 19 different genes. GABAA receptors have one of the richest and well-developed pharmacologies of any therapeutic drug target, including agonists, antagonists, and positive and negative allosteric modulators (PAMs, NAMs). Currently used PAMs include benzodiazepine sedatives and anxiolytics, barbiturates, endogenous and synthetic neurosteroids, and general anesthetics. In this article, I will review evidence that these drugs act at several distinct binding sites and how they can be used to alter the balance between excitation and inhibition. I will also summarize existing literature regarding (1) evidence that changes in GABAergic inhibition play a causative role in major depression, anxiety, postpartum depression, premenstrual dysphoric disorder, and schizophrenia and (2) whether and how GABAergic drugs exert beneficial effects in these conditions, focusing on human studies where possible. Where these classical therapeutics have failed to exert benefits, I will describe recent advances in clinical and preclinical drug development. I will also highlight opportunities to advance a generation of GABAergic therapeutics, such as development of subunit-selective PAMs and NAMs, that are engendering hope for novel tools to treat these devastating conditions.

The role of cell adhesion molecule IgSF9b at the inhibitory synapse and psychiatric disease

Understanding perturbations in synaptic function between health and disease states is crucial to the treatment of neuropsychiatric illness. While genome-wide association studies have identified several genetic loci implicated in synaptic dysfunction in disorders such as autism and schizophrenia, many have not been rigorously characterized. Here, we highlight immunoglobulin superfamily member 9b (IgSF9b), a cell adhesion molecule thought to localize exclusively to inhibitory synapses in the brain. While both pre-clinical and clinical studies suggest its association with psychiatric diseases, our understanding of IgSF9b in synaptic maintenance, neural circuits, and behavioral phenotypes remains rudimentary. Moreover, these functions wield undiscovered influences on neurodevelopment. This review evaluates current literature and publicly available gene expression databases to explore the implications of IgSF9b dysfunction in rodents and humans. Through a focused analysis of one high-risk gene locus, we identify areas requiring further investigation and unearth clues related to broader mechanisms contributing to the synaptic etiology of psychiatric disorders.

Understanding the role of the NMDA receptor subunit, GluN2D, in mediating NMDA receptor antagonist-induced behavioral disruptions in male and female mice

Noncompetitive NMDA receptor (NMDAR) antagonists like phencyclidine (PCP) and ketamine cause psychosis-like symptoms in healthy humans, exacerbate schizophrenia symptoms in people with the disorder, and disrupt a range of schizophrenia-relevant behaviors in rodents, including hyperlocomotion. This is negated in mice lacking the GluN2D subunit of the NMDAR, suggesting the GluN2D subunit mediates the hyperlocomotor effects of these drugs. However, the role of GluN2D in mediating other schizophrenia-relevant NMDAR antagonist-induced behavioral disturbances, and in both sexes, is unclear. This study aimed to investigate the role of the GluN2D subunit in mediating schizophrenia-relevant behaviors induced by a range of NMDA receptor antagonists. Using both male and female GluN2D knockout (KO) mice, we examined the effects of the NMDAR antagonist's PCP, the S-ketamine enantiomer (S-ket), and the ketamine metabolite R-norketamine (R-norket) on locomotor activity, anxiety-related behavior, and recognition and short-term spatial memory. GluN2D-KO mice showed a blunted locomotor response to R-norket, S-ket, and PCP, a phenotype present in both sexes. GluN2D-KO mice of both sexes showed an anxious phenotype and S-ket, R-norket, and PCP showed anxiolytic effects that were dependent on sex and genotype. S-ket disrupted spatial recognition memory in females and novel object recognition memory in both sexes, independent of genotype. This datum identifies a role for the GluN2D subunit in sex-specific effects of NMDAR antagonists and on the differential effects of the R- and S-ket enantiomers.

Sub-Chronic Ketamine Administration Increases Dopamine Synthesis Capacity in the Mouse Midbrain: a Preclinical In Vivo PET Study

PURPOSE

There is robust evidence that people with schizophrenia show elevated dopamine (DA) synthesis capacity in the striatum. This finding comes from positron emission tomography (PET) studies using radiolabelled l-3,4-dihydroxyphenylalanine (18F-DOPA). DA synthesis capacity also appears to be elevated in the midbrain of people with schizophrenia compared to healthy controls. We therefore aimed to optimise a method to quantify 18F-DOPA uptake in the midbrain of mice, and to utilise this method to quantify DA synthesis capacity in the midbrain of the sub-chronic ketamine model of schizophrenia-relevant hyperdopaminergia.

PROCEDURES

Adult male C57Bl6 mice were treated daily with either ketamine (30 mg/kg, i.p.) or vehicle (saline) for 5 days. On day 7, animals were administered 18F-DOPA (i.p.) and scanned in an Inveon PET/CT scanner. Data from the saline-treated group were used to optimise an atlas-based template to position the midbrain region of interest and to determine the analysis parameters which resulted in the greatest intra-group consistency. These parameters were then used to compare midbrain DA synthesis capacity (KiMod) between ketamine- and saline-treated animals.

RESULTS

Using an atlas-based template to position the 3.7 mm3 midbrain ROI with a T*-Tend window of 15-140 min to estimate KiMod resulted in the lowest intra-group variability and moderate test-retest agreement. Using these parameters, we found that KiMod was elevated in the midbrain of ketamine-treated animals in comparison to saline-treated animals (t(22) = 2.19, p = 0.048). A positive correlation between DA synthesis capacity in the striatum and the midbrain was also evident in the saline-treated animals (r2 = 0.59, p = 0.005) but was absent in ketamine-treated animals (r2 = 0.004, p = 0.83).

CONCLUSIONS

Using this optimised method for quantifying 18F-DOPA uptake in the midbrain, we found that elevated striatal DA synthesis capacity in the sub-chronic ketamine model extends to the midbrain. Interestingly, the dysconnectivity between the midbrain and striatum seen in this model is also evident in the clinical population. This model may therefore be ideal for assessing novel compounds which are designed to modulate pre-synaptic DA synthesis capacity.

Review: Genes Involved in Mitochondrial Physiology Within 22q11.2 Deleted Region and Their Relevance to Schizophrenia

BACKGROUND AND HYPOTHESIS

Schizophrenia is associated with altered energy metabolism, but the cause and potential impact of these metabolic changes remain unknown. 22q11.2 deletion syndrome (22q11.2DS) represents a genetic risk factor for schizophrenia, which is associated with the loss of several genes involved in mitochondrial physiology. Here we examine how the haploinsufficiency of these genes could contribute to the emergence of schizophrenia in 22q11.2DS.

STUDY DESIGN

We characterize changes in neuronal mitochondrial function caused by haploinsufficiency of mitochondria-associated genes within the 22q11.2 region (PRODH, MRPL40, TANGO2, ZDHHC8, SLC25A1, TXNRD2, UFD1, and DGCR8). For that purpose, we combine data from 22q11.2DS carriers and schizophrenia patients, in vivo (animal models) and in vitro (induced pluripotent stem cells, IPSCs) studies. We also review the current knowledge about seven non-coding microRNA molecules located in the 22q11.2 region that may be indirectly involved in energy metabolism by acting as regulatory factors.

STUDY RESULTS

We found that the haploinsufficiency of genes of interest is mainly associated with increased oxidative stress, altered energy metabolism, and calcium homeostasis in animal models. Studies on IPSCs from 22q11.2DS carriers corroborate findings of deficits in the brain energy metabolism, implying a causal role between impaired mitochondrial function and the development of schizophrenia in 22q11.2DS.

CONCLUSIONS

The haploinsufficiency of genes within the 22q11.2 region leads to multifaceted mitochondrial dysfunction with consequences to neuronal function, viability, and wiring. Overlap between in vitro and in vivo studies implies a causal role between impaired mitochondrial function and the development of schizophrenia in 22q11.2DS.

Altered corollary discharge signaling in the auditory cortex of a mouse model of schizophrenia predisposition

The ability to distinguish sensations that are self-generated from those caused by external events is disrupted in schizophrenia patients. However, the neural circuit abnormalities underlying this sensory impairment and its relationship to the risk factors for the disease is not well understood. To address this, we examined the processing of self-generated sounds in male Df(16)A+/- mice, which model one of the largest genetic risk factors for schizophrenia, the 22q11.2 microdeletion. We find that auditory cortical neurons in Df(16)A+/- mice fail to attenuate their responses to self-generated sounds, recapitulating deficits seen in schizophrenia patients. Notably, the auditory cortex of Df(16)A+/- mice displayed weaker motor-related signals and received fewer inputs from the motor cortex, suggesting an anatomical basis underlying the sensory deficit. These results provide insights into the mechanisms by which a major genetic risk factor for schizophrenia disrupts the top-down processing of sensory information.

Selective dopamine D2 receptor deletion from Nkx6.2 expressing cells causes impaired cognitive, motivation and anxiety phenotypes in mice

Abnormal dopamine neurotransmission is a common trait of some psychiatric diseases, like schizophrenia or bipolar disorder. Excessive dopaminergic tone in subcortical brain regions is associated with psychotic episodes, while reduced prefrontal dopaminergic activity is associated with impaired cognitive performance and reduced motivation, among other symptoms. Inhibitory interneurons expressing the calcium binding protein parvalbumin are particularly affected in both schizophrenia and bipolar disorder, as they set a fine-tuned physiological inhibitory/excitatory balance. Parvalbumin and somatostatin interneuron subtypes, are born from the medial ganglionic eminence and require the sequential expression of specific transcription factors for their specification, such as Nkx6.2. Here, we aimed at characterizing in detail interneuron subtypes derived from Nkx6.2 expressing progenitors by the generation of an Nkx6.2 Cre transgenic mouse line. We show that Nkx6.2 specifies over a third part of the total population of cortical somatostatin interneurons, preferentially at early developmental time points, whereas at late developmental stages, Nkx6.2 expressing progenitors shift to parvalbumin interneuron specification. Dopamine D2 receptor deletion from Nkx6.2 expressing progenitors causes abnormal phenotypes restricted to cognitive, motivation and anxiety domains. Our results show that Nkx6.2 have the potential to specify both somatostatin and parvalbumin interneurons in an opposite timed program and that DRD2 expression is required in Nkx6.2 expressing progenitors to avoid impaired phenotypes commonly associated to the pathophysiology of psychiatric diseases.

Deletions of Cacna2d3 in parvalbumin-expressing neurons leads to autistic-like phenotypes in mice

Autism spectrum disorder (ASD) is a series of highly inherited neurodevelopmental disorders. Loss-of-function (LOF) mutations in the CACNA2D3 gene are associated with ASD. However, the underlying mechanism is unknown. Dysfunction of cortical interneurons (INs) is strongly implicated in ASD. Parvalbumin-expressing (PV) INs and somatostatin-expressing (SOM) INs are the two most subtypes. Here, we characterized a mouse knockout of the Cacna2d3 gene in PV-expressing neurons (PVCre;Cacna2d3f/f mice) or in SOM-expressing neurons (SOMCre;Cacna2d3f/f mice), respectively. PVCre;Cacna2d3f/f mice showed deficits in the core ASD behavioral domains (including impaired sociability and increased repetitive behavior), as well as anxiety-like behavior and improved spatial memory. Furthermore, loss of Cacna2d3 from a subset of PV neurons results in a reduction of GAD67 and PV expression in the medial prefrontal cortex (mPFC). These may underlie the increased neuronal excitability in the mPFC, which contribute to the abnormal social behavior in PVCre;Cacna2d3f/f mice. Whereas, SOMCre;Cacna2d3f/f mice showed no obvious deficits in social, cognitive, or emotional phenotypes. Our findings provide the first evidence suggesting the causal role of Cacna2d3 insufficiency in PV neurons in autism.

Laminar pattern of adolescent development changes in working memory neuronal activity

Adolescent development is characterized by an improvement in cognitive abilities, such as working memory. Neurophysiological recordings in a nonhuman primate model of adolescence have revealed changes in neural activity that mirror improvement in behavior, including higher firing rate during the delay intervals of working memory tasks. The laminar distribution of these changes is unknown. By some accounts, persistent activity is more pronounced in superficial layers, so we sought to determine whether changes are most pronounced there. We therefore analyzed neurophysiological recordings from the young and adult stage of male monkeys, at different cortical depths. Superficial layers exhibited an increased baseline firing rate in the adult stage. Unexpectedly, we also detected substantial increases in delay period activity in the middle layers after adolescence, which was confirmed even after excluding penetrations near sulci. Finally, improved discriminability around the saccade period was most evident in the deeper layers. These results reveal the laminar pattern of neural activity maturation that is associated with cognitive improvement.NEW & NOTEWORTHY Structural brain changes are evident during adolescent development particularly in the cortical thickness of the prefrontal cortex, at a time when working memory ability increases markedly. The depth distribution of neurophysiological changes during adolescence is not known. Here, we show that neurophysiological changes are not confined to superficial layers, which have most often been implicated in the maintenance of working memory. Contrary to expectations, substantial changes were evident in intermediate layers of the prefrontal cortex.

Terminal type-specific cannabinoid CB1 receptor alterations in patients with schizophrenia: A pilot study

BACKGROUND

Individuals with schizophrenia are at elevated genetic risks for comorbid cannabis use, and often experience exacerbations of cognitive and psychotic symptoms when exposed to cannabis. These findings have led a number of investigators to examine cannabinoid CB1 receptor (CB1R) alterations in schizophrenia, though with conflicting results. We recently demonstrated the presence of CB1R in both excitatory and inhibitory boutons in the human prefrontal cortex, with differential levels of the receptor between bouton types. We hypothesized that the differential enrichment of CB1R between bouton types - a factor previously unaccounted for when examining CB1R changes in schizophrenia - may resolve prior discrepant reports and increase our insight into the effects of CB1R alterations on the pathophysiology of schizophrenia.

METHODS

Using co-labeling immunohistochemistry and fluorescent microscopy, we examined total CB1R levels and CB1R levels within excitatory (vGlut1-positive) and inhibitory (vGAT-positive) boutons of prefrontal cortex samples from ten pairs of individuals (nine male pairs and one female pair) diagnosed with schizophrenia and non-psychiatric comparisons.

RESULTS

Significantly higher total CB1R levels were found within samples from individuals with schizophrenia. Terminal type-specific analyses identified significantly higher CB1R levels within excitatory boutons in samples from individuals with schizophrenia relative to comparisons. In contrast, CB1R levels within the subset of inhibitory boutons that normally express high CB1R levels (presumptive cholecystokinin neuron boutons) were lower in samples from individuals with schizophrenia relative to comparison samples.

CONCLUSION

Given CB1R's role in suppressing neurotransmission upon activation, these results suggest an overall shift in excitatory and inhibitory balance regulation toward a net reduction of excitatory activity in schizophrenia.

Localization and Diagnostic Specificity of Glutamic Acid Decarboxylase Transcript Alterations in the Dorsolateral Prefrontal Cortex in Schizophrenia

BACKGROUND

Working memory (WM) deficits in schizophrenia are thought to reflect altered inhibition in the dorsolateral prefrontal cortex (DLPFC). This interpretation is supported by findings of lower transcript levels of the 2 enzymes, GAD67 and GAD65, which mediate basal and activity-dependent GABA (gamma-aminobutyric acid) synthesis, respectively. However, the relative magnitude, location within the depth of the DLPFC, and specificity to the disease process of schizophrenia of alterations in GAD67 and/or GAD65 remain unclear.

METHODS

Levels of GAD67 and GAD65 messenger RNAs (mRNAs) in superficial (layers 2/superficial 3) and deep (deep layer 6/white matter) zones of the DLPFC were quantified by quantitative polymerase chain reaction in subjects with schizophrenia (n = 41), major depression (n = 42), or bipolar disorder (n = 39) and unaffected comparison (n = 43) subjects.

RESULTS

Relative to the unaffected comparison group, GAD67 and GAD65 mRNA levels in the schizophrenia group were lower (p = .039, effect size = -0.69 and p = .027, effect size = -0.72, respectively) in the superficial zone but were unaltered in the deep zone. In the major depression group, only GAD67 mRNA levels were lower and only in the superficial zone (p = .089, effect size = 0.70). No differences were detected in the bipolar disorder group. Neither GAD67 nor GAD65 mRNA alterations were explained by psychosis, mood disturbance, or common comorbid factors.

CONCLUSIONS

Alterations in markers of GABA synthesis demonstrated transcript, DLPFC zone, and diagnostic specificity. Given the dependence of WM on GABA neurotransmission in the superficial DLPFC, our findings suggest that limitations to GABA synthesis in this location contribute to WM impairments in schizophrenia, especially during demanding WM tasks, when GABA synthesis requires the activity of both GAD67 and GAD65.

Laminar pattern of adolescent development changes in working memory neuronal activity

Adolescent development is characterized by an improvement in cognitive abilities, such as working memory. Neurophysiological recordings in a non-human primate model of adolescence have revealed changes in neural activity that mirror improvement in behavior, including higher firing rate during the delay intervals of working memory tasks. The laminar distribution of these changes is unknown. By some accounts, persistent activity is more pronounced in superficial layers, so we sought to determine whether changes are most pronounced there. We therefore analyzed neurophysiological recordings from neurons recorded in the young and adult stage, at different cortical depths. Superficial layers exhibited increased baseline firing rate in the adult stage. Unexpectedly, changes in persistent activity were most pronounced in the middle layers. Finally, improved discriminability of stimulus location was most evident in the deeper layers. These results reveal the laminar pattern of neural activity maturation that is associated with cognitive improvement.

NEW AND NOTEWORTHY

Structural brain changes are evident during adolescent development particularly in the cortical thickness of the prefrontal cortex, at a time when working memory ability increases markedly. The depth distribution of neurophysiological changes during adolescence is not known. Here we show that neurophysiological changes are not confined to superficial layers, which have most often been implicated in the maintenance of working memory. Contrary to expectations, greatest changes were evident in intermediate layers of the prefrontal cortex.

Maternal immune activation and role of placenta in the prenatal programming of neurodevelopmental disorders

Maternal infection during pregnancy, leading to maternal immune activation (mIA) and cytokine release, increases the offspring risk of developing a variety of neurodevelopmental disorders (NDDs), including schizophrenia. Animal models have provided evidence to support these mechanistic links, with placental inflammatory responses and dysregulation of placental function implicated. This leads to changes in fetal brain cytokine balance and altered epigenetic regulation of key neurodevelopmental pathways. The prenatal timing of such mIA-evoked changes, and the accompanying fetal developmental responses to an altered in utero environment, will determine the scope of the impacts on neurodevelopmental processes. Such dysregulation can impart enduring neuropathological changes, which manifest subsequently in the postnatal period as altered neurodevelopmental behaviours in the offspring. Hence, elucidation of the functional changes that occur at the molecular level in the placenta is vital in improving our understanding of the mechanisms that underlie the pathogenesis of NDDs. This has notable relevance to the recent COVID-19 pandemic, where inflammatory responses in the placenta to SARS-CoV-2 infection during pregnancy and NDDs in early childhood have been reported. This review presents an integrated overview of these collective topics and describes the possible contribution of prenatal programming through placental effects as an underlying mechanism that links to NDD risk, underpinned by altered epigenetic regulation of neurodevelopmental pathways.

Increased Central Auditory Gain and Decreased Parvalbumin-Positive Cortical Interneuron Density in the Df1/+ Mouse Model of Schizophrenia Correlate With Hearing Impairment

Background

Hearing impairment is a risk factor for schizophrenia. Patients with 22q11.2 deletion syndrome have a 25% to 30% risk of schizophrenia, and up to 60% also have varying degrees of hearing impairment, primarily from middle-ear inflammation. The Df1/+ mouse model of 22q11.2 deletion syndrome recapitulates many features of the human syndrome, including schizophrenia-relevant brain abnormalities and high interindividual variation in hearing ability. However, the relationship between brain abnormalities and hearing impairment in Df1/+ mice has not been examined.

Methods

We measured auditory brainstem responses, cortical auditory evoked potentials, and/or cortical parvalbumin-positive (PV+) interneuron density in over 70 adult mice (32 Df1/+, 39 wild-type). We also performed longitudinal auditory brainstem response measurements in an additional 20 animals (13 Df1/+, 7 wild-type) from 3 weeks of age.

Results

Electrophysiological markers of central auditory excitability were elevated in Df1/+ mice. PV+ interneurons, which are implicated in schizophrenia pathology, were reduced in density in the auditory cortex but not the secondary motor cortex. Both auditory brain abnormalities correlated with hearing impairment, which affected approximately 60% of adult Df1/+ mice and typically emerged before 6 weeks of age.

Conclusions

In the Df1/+ mouse model of 22q11.2 deletion syndrome, abnormalities in central auditory excitability and auditory cortical PV+ immunoreactivity correlate with hearing impairment. This is the first demonstration of cortical PV+ interneuron abnormalities correlating with hearing impairment in a mouse model of either schizophrenia or middle-ear inflammation.

VIP interneuron impairment promotes in vivo circuit dysfunction and autism-related behaviors in Dravet syndrome

Dravet syndrome (DS) is a severe neurodevelopmental disorder caused by loss-of-function variants in SCN1A, which encodes the voltage-gated sodium channel subunit Nav1.1. We recently showed that neocortical vasoactive intestinal peptide interneurons (VIP-INs) express Nav1.1 and are hypoexcitable in DS (Scn1a+/-) mice. Here, we investigate VIP-IN function at the circuit and behavioral level by performing in vivo 2-photon calcium imaging in awake wild-type (WT) and Scn1a+/- mice. VIP-IN and pyramidal neuron activation during behavioral transition from quiet wakefulness to active running is diminished in Scn1a+/- mice, and optogenetic activation of VIP-INs restores pyramidal neuron activity to WT levels during locomotion. VIP-IN selective Scn1a deletion reproduces core autism-spectrum-disorder-related behaviors in addition to cellular- and circuit-level deficits in VIP-IN function, but without epilepsy, sudden death, or avoidance behaviors seen in the global model. Hence, VIP-INs are impaired in vivo, which may underlie non-seizure cognitive and behavioral comorbidities in DS.

Epigenetic regulation of metabotropic glutamate 2/3 receptors: Potential role for ultra-resistant schizophrenia?

Schizophrenia is a severe and debilitating psychiatric disorder characterized by early cognitive deficits, emotional and behavioral abnormalities resulted by a dysfunctional gene x environment interaction. Genetic and epigenetic abnormalities in cortical parvalbumin-positive GABAergic interneurons lead to alterations in glutamate-mediated excitatory neurotransmission, synaptic plasticity, and neuronal development. Epigenetic alterations during pregnancy or early phases of postnatal life are associated with schizophrenia vulnerability as well as inflammatory processes which are at the basis of brain pathology. An epigenetic animal model of schizophrenia showed specific changes in promoter DNA methylation activity of genes related to schizophrenia such as reelin, BDNF and GAD67, and altered expression and function of mGlu2/3 receptors in the frontal cortex. Although antipsychotic medications represent the main treatment for schizophrenia and generally show an optimal efficacy profile for positive symptoms and relatively poor efficacy for negative or cognitive symptoms, a considerable percentage of individuals show poor response, do not achieve a complete remission, and approximately 30 % of patients show treatment-resistance. Here, we explore the potential role of epigenetic abnormalities linked to metabotropic glutamate 2/3 receptors changes in expression and function as key molecular factors underlying the difference in response to antipsychotics.

Potassium channel modulators and schizophrenia: an overview of investigational drugs

INTRODUCTION

Schizophrenia is severe mental illness comprised of positive, negative, and cognitive symptoms. Existing pharmacologic options exert their actions on the dopamine receptor but are largely ineffective at treating negative and cognitive symptoms. Alternative pharmacologic options that do not act directly on the dopamine receptor are being investigated, including potassium channel modulators. It has been hypothesized that dysfunctional fast-spiking parvalbumin-positive GABA interneurons, regulated by Kv 3.1 and Kv 3.2 potassium channels, contribute to the symptoms of schizophrenia, making potassium channels an area of clinical interest.

AREAS COVERED

This review will highlight potassium channel modulators for the treatment of schizophrenia, with a focus on AUT00206. Background on Kv3.1 and Kv3.2 potassium channels will be explored. Our search strategy included a literature review utilizing PubMed, Clinicaltrials.gov, and sources available on the manufacturer's website.

EXPERT OPINION

Initial data on potassium channel modulators is promising, however, further study is needed, and existing evidence is limited. Early data suggests that dysfunctional GABA interneurons can be ameliorated through modulators of Kv3.1 and Kv3.2 channels. AUT00206 has been shown to improve dopaminergic dysfunction induced by ketamine and PCP, improve resting gamma power in patients with schizophrenia, impact dopamine synthesis capacity in a subgroup of individuals with schizophrenia, and affect reward anticipation-related neural activation.

Brain-Derived Neurotrophic Factor Val66Met Genotype Modulates Latent Inhibition: Relevance for Schizophrenia

BACKGROUND AND HYPOTHESIS

Latent inhibition (LI) is a measure of selective attention and learning relevant to Schizophrenia (SZ), with 2 abnormality poles: Disrupted LI in acute SZ, thought to underlie positive symptoms, and persistent LI (PLI) in schizotypy and chronic SZ under conditions where normal participants fail to show LI. We hypothesized that Brain-Derived Neurotrophic Factor (BDNF)-Met genotype shifts LI toward the PLI pole.

STUDY DESIGN

We investigated the role of BDNF-Val66Met polymorphism and neural activation in regions involved in LI in mice, and the interaction between the BDNF and CHL1, a gene associated with SZ.

STUDY RESULTS

No LI differences occurred between BDNF-wild-type (WT) (Val/Val) and knock-in (KI) (Met/Met) mice after weak conditioning. Chronic stress or stronger conditioning disrupted LI in WT but not KI mice. Behavior correlated with activation in infralimbic and orbitofrontal cortices, and nucleus accumbens. Examination of LI in CHL1-KO mice revealed no LI with no Met alleles (BDNF-WTs), PLI in CHL1-WT mice with 1 Met allele (BDNF-HETs), and PLI in both CHL1-WTs and CHL1-KOs with 2 Met alleles (BDNF-KIs), suggesting a shift to LI persistence with the number of BDNF-Met alleles in the CHL1 model of acute SZ.

CONCLUSIONS

Results support a role for BDNF polymorphisms in gene-gene and gene-environment interactions relevant to SZ. BDNF-Met allele may reduce expression of some acute SZ symptoms, and may increase expression of negative symptoms in individuals with chronic SZ. Evaluation of (screening for) SZ phenotypes associated with mutations at a particular locus (eg, CHL1), may be masked by strong effects at different loci (eg, BDNF).

Long-range inhibition synchronizes and updates prefrontal task activity

Changes in patterns of activity within the medial prefrontal cortex enable rodents, non-human primates and humans to update their behaviour to adapt to changes in the environment-for example, during cognitive tasks^1-5. Parvalbumin-expressing inhibitory neurons in the medial prefrontal cortex are important for learning new strategies during a rule-shift task^6-8, but the circuit interactions that switch prefrontal network dynamics from maintaining to updating task-related patterns of activity remain unknown. Here we describe a mechanism that links parvalbumin-expressing neurons, a new callosal inhibitory connection, and changes in task representations. Whereas nonspecifically inhibiting all callosal projections does not prevent mice from learning rule shifts or disrupt the evolution of activity patterns, selectively inhibiting only callosal projections of parvalbumin-expressing neurons impairs rule-shift learning, desynchronizes the gamma-frequency activity that is necessary for learning⁸ and suppresses the reorganization of prefrontal activity patterns that normally accompanies rule-shift learning. This dissociation reveals how callosal parvalbumin-expressing projections switch the operating mode of prefrontal circuits from maintenance to updating by transmitting gamma synchrony and gating the ability of other callosal inputs to maintain previously established neural representations. Thus, callosal projections originating from parvalbumin-expressing neurons represent a key circuit locus for understanding and correcting the deficits in behavioural flexibility and gamma synchrony that have been implicated in schizophrenia and related conditions^9,10.

Terminal type-specific cannabinoid CB1 receptor alterations in patients with schizophrenia: a pilot study

Background

Individuals with schizophrenia are at elevated genetic risks for comorbid cannabis use, and often experience exacerbations of cognitive and psychotic symptoms when exposed to cannabis. These findings have led a number of investigators to examine cannabinoid CB1 receptor (CB1R) alterations in schizophrenia, though with conflicting results. We recently demonstrated the presence of CB1R in both excitatory and inhibitory boutons in the human prefrontal cortex, with differential levels of the receptor between bouton types. We hypothesized that the differential enrichment of CB1R between bouton types - a factor previously unaccounted for when examining CB1R changes in schizophrenia - may resolve prior discrepant reports and increase our insight into the effects of CB1R alterations on the pathophysiology of schizophrenia.

Methods

Using co-labeling immunohistochemistry and fluorescent microscopy, we examined total CB1R levels and CB1R levels within excitatory (vGlut1-positive) and inhibitory (vGAT-positive) boutons of prefrontal cortex samples from ten pairs of individuals diagnosed with schizophrenia and non-psychiatric comparisons.

Results

Significantly higher total CB1R levels were found within samples from individuals with schizophrenia. Terminal type-specific analyses identified significantly higher CB1R levels within excitatory boutons in samples from individuals with schizophrenia relative to comparisons. In contrast, CB1R levels within the subset of inhibitory boutons that normally express high CB1R levels (presumptive cholecystokinin neuron boutons) were lower in samples from individuals with schizophrenia relative to comparison samples.

Conclusion

Given CB1R's role in suppressing neurotransmission upon activation, these results suggest an overall shift in excitatory and inhibitory balance regulation toward a net reduction of excitatory activity in schizophrenia.

Ketamine as a pharmacological tool for the preclinical study of memory deficit in schizophrenia

Schizophrenia is a serious neuropsychiatric disorder characterized by the presence of positive symptoms (hallucinations, delusions, and disorganization of thought and language), negative symptoms (abulia, alogia, and affective flattening), and cognitive impairment (attention deficit, impaired declarative memory, and deficits in social cognition). Dopaminergic hyperactivity seems to explain the positive symptoms, but it does not completely clarify the appearance of negative and cognitive clinical manifestations. Preclinical data have demonstrated that acute and subchronic treatment with NMDA receptor antagonists such as ketamine (KET) represents a useful model that resembles the schizophrenia symptomatology, including cognitive impairment. This latter has been explained as a hypofunction of NMDA receptors located on the GABA parvalbumin-positive interneurons (near to the cortical pyramidal cells), thus generating an imbalance between the inhibitory and excitatory activity in the corticomesolimbic circuits. The use of behavioral models to explore alterations in different domains of memory is vital to learn more about the neurobiological changes that underlie schizophrenia. Thus, to better understand the neurophysiological mechanisms involved in cognitive impairment related to schizophrenia, the purpose of this review is to analyze the most recent findings regarding the effect of KET administration on these processes.

Psychosis spectrum features, neurocognition and functioning in a longitudinal study of youth with 22q11.2 deletion syndrome

BACKGROUND

Neuropsychiatric disorders are common in 22q11.2 Deletion Syndrome (22q11DS) with about 25% of affected individuals developing schizophrenia spectrum disorders by young adulthood. Longitudinal evaluation of psychosis spectrum features and neurocognition can establish developmental trajectories and impact on functional outcome.

METHODS

157 youth with 22q11DS were assessed longitudinally for psychopathology focusing on psychosis spectrum symptoms, neurocognitive performance and global functioning. We contrasted the pattern of positive and negative psychosis spectrum symptoms and neurocognitive performance differentiating those with more prominent Psychosis Spectrum symptoms (PS+) to those without prominent psychosis symptoms (PS-).

RESULTS

We identified differences in the trajectories of psychosis symptoms and neurocognitive performance between the groups. The PS+ group showed age associated increase in symptom severity, especially negative symptoms and general nonspecific symptoms. Correspondingly, their level of functioning was worse and deteriorated more steeply than the PS- group. Neurocognitive performance was generally comparable in PS+ and PS- groups and demonstrated a similar age-related trajectory. However, worsening executive functioning distinguished the PS+ group from PS- counterparts. Notably, of the three executive function measures examined, only working memory showed a significant difference between the groups in rate of change. Finally, structural equation modeling showed that neurocognitive decline drove the clinical change.

CONCLUSIONS

Youth with 22q11DS and more prominent psychosis features show worsening of symptoms and functional decline driven by neurocognitive decline, most related to executive functions and specifically working memory. The results underscore the importance of working memory in the developmental progression of psychosis.

Suppressive effects of ketamine on auditory steady-state responses in intact, awake macaques: A non-human primate model of schizophrenia

Auditory steady-state responses (ASSRs) are recurrent neural activities entrained to regular cyclic auditory stimulation. ASSRs are altered in individuals with schizophrenia, and may be related to hypofunction of the N-methyl-D-aspartate (NMDA) glutamate receptor. Noncompetitive NMDA receptor antagonists, including ketamine, have been used in ASSR studies of rodent models of schizophrenia. Although animal studies using non-human primates are required to complement rodent studies, the effects of ketamine on ASSRs are unknown in intact awake non-human primates. In this study, after administration of vehicle or ketamine, click trains at 20-83.3 Hz were presented to elicit ASSRs during recording of electroencephalograms in intact, awake macaque monkeys. The results indicated that ASSRs quantified by event-related spectral perturbation and inter-trial coherence were maximal at 83.3 Hz after vehicle administration, and that ketamine reduced ASSRs at 58.8 and 83.3 Hz, but not at 20 and 40 Hz. The present results demonstrated a reduction of ASSRs by the NMDA receptor antagonist at optimal frequencies with maximal responses in intact, awake macaques, comparable to ASSR reduction in patients with schizophrenia. These findings suggest that ASSR can be used as a neurophysiological biomarker of the disturbance of gamma-oscillatory neural circuits in this ketamine model of schizophrenia using intact, awake macaques. Thus, this model with ASSRs would be useful in the investigation of human brain pathophysiology as well as in preclinical translational research.

Enhancing the resolution of behavioral measures: Key observations during a forty year career in behavioral neuroscience

This manuscript reviews several key observations from the research program of Professor John P. Bruno that are believed to have significantly advanced our understanding of the brain's mediation of behavior. This review focuses on findings within several important research areas in behavioral neuroscience, including a) age-dependent neurobehavioral plasticity following brain damage; b) the role of the cortical cholinergic system in attentional processing and cognitive flexibility; and c) the design and validation of animal models of cognitive deficits in schizophrenia. In selecting these observations, emphasis was given to examples in which the heuristic potency was increased by maximizing the resolution and microanalysis of behavioral assays in the same fashion as one typically refines neuronal manipulations. Professor Bruno served the International Behavioral Neuroscience Society (IBNS) as an IBNS Fellow (1995-present) and President of the IBNS (2001-02).

Modulation of circuit oscillations in the rat anterior cingulate cortex (ACC) in vitro by mGlu2 metabotropic glutamate receptors and alleviation of the effects of phencyclidine-induced NMDA-receptor hypofunction

Aberrant cortical oscillations in the beta and gamma range are associated with symptoms of schizophrenia and other psychiatric conditions. We have thus investigated the ability of anterior cingulate cortex (ACC) in vitro to generate beta and gamma oscillations, and how these are affected by Group II metabotropic glutamate (mGlu) receptor activation and blockade of N-methyl-d-aspartate (NMDA) receptors. Activation of Group II mGlu receptors, and mGlu2 specifically, with orthosteric agonists reduced the power of both beta and gamma oscillations in ACC without a significant effect on oscillation peak frequencies. The NMDA receptor blocker phencyclidine (PCP), known to evoke certain schizophrenia-like symptoms in humans, elevated the power of beta oscillations in ACC and caused a shift in oscillation frequency from the gamma range to the beta range. These enhanced beta oscillations were reduced by the Group II mGlu receptor agonists. These results show that Group II mGlu receptors, and specifically mGlu2, modulate network oscillations. Furthermore, attenuation of the effect of PCP suggests that mGlu2 receptors may stabilise aberrant network activity. These results underline the importance of Group II mGlu receptors, and particularly mGlu2, as targets for the treatment of neuropsychiatric and neurodegenerative diseases.

Gene Expression and Epigenetic Regulation in the Prefrontal Cortex of Schizophrenia

Schizophrenia pathogenesis remains challenging to define; however, there is strong evidence that the interaction of genetic and environmental factors causes the disorder. This paper focuses on transcriptional abnormalities in the prefrontal cortex (PFC), a key anatomical structure that determines functional outcomes in schizophrenia. This review summarises genetic and epigenetic data from human studies to understand the etiological and clinical heterogeneity of schizophrenia. Gene expression studies using microarray and sequencing technologies reported the aberrant transcription of numerous genes in the PFC in patients with schizophrenia. Altered gene expression in schizophrenia is related to several biological pathways and networks (synaptic function, neurotransmission, signalling, myelination, immune/inflammatory mechanisms, energy production and response to oxidative stress). Studies investigating mechanisms driving these transcriptional abnormalities focused on alternations in transcription factors, gene promoter elements, DNA methylation, posttranslational histone modifications or posttranscriptional regulation of gene expression mediated by non-coding RNAs.

Biological hypotheses, risk factors, and biomarkers of schizophrenia

Both the discovery of biomarkers of schizophrenia and the verification of biological hypotheses of schizophrenia are an essential part of the process of understanding the etiology of this mental disorder. Schizophrenia has long been considered a neurodevelopmental disease whose symptoms are caused by impaired synaptic signal transduction and brain neuroplasticity. Both the onset and chronic course of schizophrenia are associated with risk factors-induced disruption of brain function and the establishment of a new homeostatic setpoint characterized by biomarkers. Different risk factors and biomarkers can converge to the same symptoms of schizophrenia, suggesting that the primary cause of the disease can be highly individual. Schizophrenia-related biomarkers include measurable biochemical changes induced by stress (elevated allostatic load), mitochondrial dysfunction, neuroinflammation, oxidative and nitrosative stress, and circadian rhythm disturbances. Here is a summary of selected valid biological hypotheses of schizophrenia formulated based on risk factors and biomarkers, neurodevelopment, neuroplasticity, brain chemistry, and antipsychotic medication. The integrative neurodevelopmental-vulnerability-neurochemical model is based on current knowledge of the neurobiology of the onset and progression of the disease and the effects of antipsychotics and psychotomimetics and reflects the complex and multifactorial nature of schizophrenia.

Using Nonhuman Primate Models to Reverse-Engineer Prefrontal Circuit Failure Underlying Cognitive Deficits in Schizophrenia

In this chapter, I review studies in nonhuman primates that emulate the circuit failure in prefrontal cortex responsible for working memory and cognitive control deficits in schizophrenia. These studies have characterized how synaptic malfunction, typically induced by blockade of NMDAR, disrupts neural function and computation in prefrontal networks to explain errors in cognitive tasks that are seen in schizophrenia. This work is finding causal relationships between pathogenic events of relevance to schizophrenia at vastly different levels of scale, from synapses, to neurons, local, circuits, distributed networks, computation, and behavior. Pharmacological manipulation, the dominant approach in primate models, has limited construct validity for schizophrenia pathogenesis, as the disease results from a complex interplay between environmental, developmental, and genetic factors. Genetic manipulation replicating schizophrenia risk is more advanced in rodent models. Nonetheless, gene manipulation in nonhuman primates is rapidly advancing, and primate developmental models have been established. Integration of large scale neural recording, genetic manipulation, and computational modeling in nonhuman primates holds considerable potential to provide a crucial schizophrenia model moving forward. Data generated by this approach is likely to fill several crucial gaps in our understanding of the causal sequence leading to schizophrenia in humans. This causal chain presents a vexing problem largely because it requires understanding how events at very different levels of scale relate to one another, from genes to circuits to cognition to social interactions. Nonhuman primate models excel here. They optimally enable discovery of causal relationships across levels of scale in the brain that are relevant to cognitive deficits in schizophrenia. The mechanistic understanding of prefrontal circuit failure they promise to provide may point the way to more effective therapeutic interventions to restore function to prefrontal networks in the disease.

Development of network oscillations through adolescence in male and female rats

The primary aim of this research was to study the developmental trajectory of oscillatory synchronization in neural networks of normal healthy rats during adolescence, corresponding to the vulnerable age of schizophrenia prodrome in human. To monitor the development of oscillatory networks through adolescence we used a "pseudo-longitudinal" design. Recordings were performed in terminal experiments under urethane anesthesia, every day from PN32 to PN52 using rats-siblings from the same mother, to reduce individual innate differences between subjects. We found that hippocampal theta power decreased and delta power in prefrontal cortex increased through adolescence, indicating that the oscillations in the two different frequency bands follow distinct developmental trajectories to reach the characteristic oscillatory activity found in adults. Perhaps even more importantly, theta rhythm showed age-dependent stabilization toward late adolescence. Furthermore, sex differences was found in both networks, more prominent in the prefrontal cortex compared with hippocampus. Delta increase was stronger in females and theta stabilization was completed earlier in females, in postnatal days PN41-47, while in males it was only completed in late adolescence. Our finding of a protracted maturation of theta-generating networks in late adolescence is overall consistent with the findings of longitudinal studies in human adolescents, in which oscillatory networks demonstrated a similar pattern of maturation.

microRNA-dependent regulation of gene expression in GABAergic interneurons

Information processing within neuronal circuits relies on their proper development and a balanced interplay between principal and local inhibitory interneurons within those circuits. Gamma-aminobutyric acid (GABA)ergic inhibitory interneurons are a remarkably heterogeneous population, comprising subclasses based on their morphological, electrophysiological, and molecular features, with differential connectivity and activity patterns. microRNA (miRNA)-dependent post-transcriptional control of gene expression represents an important regulatory mechanism for neuronal development and plasticity. miRNAs are a large group of small non-coding RNAs (21-24 nucleotides) acting as negative regulators of mRNA translation and stability. However, while miRNA-dependent gene regulation in principal neurons has been described heretofore in several studies, an understanding of the role of miRNAs in inhibitory interneurons is only beginning to emerge. Recent research demonstrated that miRNAs are differentially expressed in interneuron subclasses, are vitally important for migration, maturation, and survival of interneurons during embryonic development and are crucial for cognitive function and memory formation. In this review, we discuss recent progress in understanding miRNA-dependent regulation of gene expression in interneuron development and function. We aim to shed light onto mechanisms by which miRNAs in GABAergic interneurons contribute to sculpting neuronal circuits, and how their dysregulation may underlie the emergence of numerous neurodevelopmental and neuropsychiatric disorders.

Infections, Inflammation, and Psychiatric Illness: Review of Postmortem Evidence

While there is an abundance of epidemiological evidence implicating infectious agents in the etiology of severe mental illnesses, postmortem studies have not yet detected an increased incidence of microbial nucleic acid or proteins in the brains of people with mental illness. Nevertheless, abnormally expressed immune and inflammatory markers have consistently been found in the postmortem brain of patients with schizophrenia and mood disorders. Some of these abnormalities may be the result of an infection in utero or early in life that not only impacted the developing immune system but also the developing neurons of the brain. Some of the immune markers that are consistently found to be upregulated in schizophrenia implicate a possible viral infection and the blood brain barrier in the etiology and neuropathology of the disorder.