Perineuronal nets protect fast-spiking interneurons against oxidative stress

Rescue of degenerating neurons and cells by stem cell released molecules: using a physiological renormalization strategy

Evidence suggests that adult stem cell types and progenitor cells act collectively in a given tissue to maintain and heal organs, such as muscle, through a release of a multitude of molecules packaged into exosomes from the different cell types. Using this principle for the development of bioinspired therapeutics that induces homeostatic renormalization, here we show that the collection of molecules released from four cell types, including mesenchymal stem cells, fibroblast, neural stem cells, and astrocytes, rescues degenerating neurons and cells. Specifically, oxidative stress induced in a human recombinant TDP-43- or FUS-tGFP U2OS cell line by exposure to sodium arsenite was shown to be significantly reduced by our collection of molecules using in vitro imaging of FUS and TDP-43 stress granules. Furthermore, we also show that the collective secretome rescues cortical neurons from glutamate toxicity as evidenced by increased neurite outgrowth, reduced LDH release, and reduced caspase 3/7 activity. These data are the first in a series supporting the development of stem cell-based exosome systems therapeutics that uses a physiological renormalization strategy to treat neurodegenerative diseases.

Fast-Spiking Interneurons Exposed in Tumor-Associated Epilepsy

Perineuronal Nets Decrease Membrane Capacitance of Peritumoral Fast Spiking Interneurons in a Model of Epilepsy

Tewari BP, Chaunsali L, Campbell SL, Patel DC, Goode AE, and Sontheimer H. Nat Commun. 2018;9(1):4724. doi:10.1038/s41467-018-07113-0

Patients with brain tumor commonly present with epileptic seizures. We show that tumor-associated seizures are the consequence of impaired GABAergic inhibition due to an overall loss of peritumoral fast-spiking interneurons (FSNs) concomitant with a significantly reduced firing rate of those that remain. The reduced firing is due to the degradation of perineuronal nets (PNNs) that surround FSNs. We show that PNNs decrease specific membrane capacitance of FSNs permitting them to fire action potentials at supraphysiological frequencies. Tumor-released proteolytic enzymes degrade PNNs, resulting in increased membrane capacitance, reduced firing, and hence decreased GABA release. These studies uncovered a hitherto unknown role of PNNs as an electrostatic insulator that reduces specific membrane capacitance, functionally akin to myelin sheaths around axons, thereby permitting FSNs to exceed physiological firing rates. Disruption of PNNs may similarly account for excitation-inhibition imbalances in other forms of epilepsy and PNN protection through proteolytic inhibition may provide therapeutic benefits.

Quantitative changes in perineuronal nets in development and posttraumatic condition

Perineuronal net (PNN) is a highly structured portion of the CNS extracellular matrix (ECM) regulating synaptic plasticity and a range of pathologic conditions including posttraumatic regeneration and epilepsy. Here we studied Wisteria floribunda agglutinin-stained histological sections to quantify the PNN size and enrichment of chondroitin sulfates in mouse brain and spinal cord. Somatosensory cortex sections were examined during the period of PNN establishment at postnatal days 14, 21 and 28. The single cell PNN size and the chondroitin sulfate intensity were quantified for all cortex layers and specifically for the cortical layer IV which has the highest density of PNN-positive neurons. We demonstrate that the chondroitin sulfate proteoglycan staining intensity is increased between P14 and P28 while the PNN size remains unchanged. We then addressed posttraumatic changes of the PNN expression in laminae 6 and 7 of cervical spinal cord following hemisection injury. We demonstrate increase of the chondroitin sulfate content at 1.6-1.8 mm rostrally from the injury site and increase of the density of PNN-bearing cells at 0.4-1.2 mm caudally from the injury site. We further demonstrate decrease of the single cell PNN area at 0.2 mm caudally from the injury site suggesting that the PNN ECM takes part in the posttraumatic tissue rearrangement in the spinal cord. Our results demonstrate new insights on the PNN structure dynamics in the developing and posttraumatic CNS.

Structural maturation of cortical perineuronal nets and their perforating synapses revealed by superresolution imaging

Parvalbumin-positive (PV+) interneurons play a pivotal role in orchestrating windows of experience-dependent brain plasticity during development. Critical period closure is marked by the condensation of a perineuronal net (PNN) tightly enwrapping subsets of PV+ neurons, both acting as a molecular brake on plasticity and maintaining mature PV+ cell signaling. As much of the molecular organization of PNNs exists at length scales near or below the diffraction limit of light microscopy, we developed a superresolution imaging and analysis platform to visualize the structural organization of PNNs and the synaptic inputs perforating them in primary visual cortex. We identified a structural trajectory of PNN maturation featuring a range of net structures, which was accompanied by an increase in Synaptotagmin-2 (Syt2) signals on PV+ cells suggestive of increased inhibitory input between PV+ neurons. The same structural trajectory was followed by PNNs both during normal development and under conditions of critical period delay by total sensory deprivation or critical period acceleration by deletion of MeCP2, the causative gene for Rett syndrome, despite shifted maturation levels under these perturbations. Notably, superresolution imaging further revealed a decrease in Syt2 signals alongside an increase in vesicular glutamate transporter-2 signals on PV+ cells in MeCP2-deficient animals, suggesting weaker recurrent inhibitory input between PV+ neurons and stronger thalamocortical excitatory inputs onto PV+ cells. These results imply a latent imbalanced circuit signature that might promote cortical silencing in Rett syndrome before the functional regression of vision.

Metabotropic functions of the NMDA receptor and an evolving rationale for exploring NR2A-selective positive allosteric modulators for the treatment of autism spectrum disorder

NMDA receptors are widely distributed throughout the brain and major therapeutic challenges include targeting specific NMDA receptor subtypes while preserving spatial and temporal specificity during their activation. The NR2A-subunit containing NMDA receptor is implicated in regulating synchronous oscillatory output of cortical pyramidal neurons, which may be disturbed in clinical presentations of autism spectrum disorder (ASD). Because NR2A-selective positive allosteric modulators (PAMs) preserve spatial and temporal selectivity while activating this subpopulation of receptors, they represent a promising strategy to address neocortical circuit abnormalities in ASD. In addition to promoting Ca²⁺ entry and membrane depolarization, diverse metabotropic effects of NMDA receptor activation on signal transduction pathways occur within the cell, some of which depend on alignment of protein binding partners. For example, NMDA receptor agonist interventions attenuate impaired sociability in transgenic mice with 'loss-of-function' mutations of the Shank family of scaffolding proteins, which highlights the necessity of a carefully orchestrated alignment of protein binding partners in the excitatory synapse. The current Review considers metabotropic functions of the NMDA receptor that could play a role in sociability and the pathogenesis of ASD (e.g., mTOR signaling), in addition to its more familiar ionotropic functions, and provides a rationale for therapeutic exploration of NR2A-selective PAMs.

Assessing Brain Metabolism With 7-T Proton Magnetic Resonance Spectroscopy in Patients With First-Episode Psychosis

IMPORTANCE

The use of high-field magnetic resonance spectroscopy (MRS) in multiple brain regions of a large population of human participants facilitates in vivo study of localized or diffusely altered brain metabolites in patients with first-episode psychosis (FEP) compared to healthy participants.

OBJECTIVE

To compare metabolite levels in 5 brain regions between patients with FEP (evaluated within 2 years of onset) and healthy controls, and to explore possible associations between targeted metabolite levels and neuropsychological test performance.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional design used 7-T MRS at a research MR imaging facility in participants recruited from clinics at the Johns Hopkins Schizophrenia Center and the local population. Eighty-one patients who had received a DSM-IV diagnosis of FEP within the last 2 years and 91 healthy age-matched (but not sex-matched) volunteers participated.

MAIN OUTCOMES AND MEASURES

Brain metabolite levels including glutamate, glutamine, γ-aminobutyric acid (GABA), N-acetylaspartate, N-acetylaspartyl glutamate, and glutathione, as well as performance on neuropsychological tests.

RESULTS

The mean (SD) age of 81 patients with FEP was 22.3 (4.4) years and 57 were male, while the mean (SD) age of 91 healthy participants was 23.3 (3.9) years and 42 were male. Compared with healthy participants, patients with FEP had lower levels of glutamate (F1,162 = 8.63, P = .02), N-acetylaspartate (F1,161 = 5.93, P = .03), GABA (F1,163 = 6.38, P = .03), and glutathione (F1,162 = 4.79, P = .04) in the anterior cingulate (all P values are corrected for multiple comparisons); lower levels of N-acetylaspartate in the orbitofrontal region (F1,136 = 7.23, P = .05) and thalamus (F1,133 = 6.78, P = .03); and lower levels of glutathione in the thalamus (F1,135 = 7.57, P = .03). Among patients with FEP, N-acetylaspartate levels in the centrum semiovale white matter were significantly correlated with performance on neuropsychological tests, including processing speed (r = 0.48; P < .001), visual (r = 0.33; P = .04) and working (r = 0.38; P = .01) memory, and overall cognitive performance (r = 0.38; P = .01).

CONCLUSIONS AND RELEVANCE

Seven-tesla MRS offers insights into biochemical changes associated with FEP and may be a useful tool for probing brain metabolism that ranges from neurotransmission to stress-associated pathways in participants with psychosis.

Region-specific reduction of parvalbumin neurons and behavioral changes in adult mice following single exposure to cranial irradiation

PURPOSE

Ionizing irradiation has several long-term effects including progressive cognitive impairment. Cognitive deterioration generally appears to be caused by abnormalities in the hippocampal dentate gyrus, with abnormal function of parvalbumin-expressing interneurons (PV neurons) in the cerebral cortex. PV neurons are vulnerable to oxidative stress, which can be caused by ionizing irradiation. We speculated that selective impairment of specific brain regions due to ionizing irradiation may alter the degree of cognitive impairment.

METHODS

We irradiated mature mouse brains with 20 Gy-ionizing irradiation. Subsequently, we analyzed behavioral abnormalities and changes in the number of PV neurons.

RESULTS

PV neuron density was significantly lower in some cortical regions of irradiated mice than in control mice. Within 1 week of irradiation, both body weight and temperature of irradiated mice decreased. In the forced swim test, irradiated mice spent significantly less time immobile than did control mice. However, irradiated mice did not display any abnormalities in the elevated plus maze test, Y-maze test, tail suspension test, and social interaction test between 3 to 6 days after irradiation.

CONCLUSIONS

These results suggest that high-dose irradiation is less likely to cause brain dysfunction in the subacute phase. Moreover, the vulnerability of PV neurons appears to be brain-region specific.

Adult vitamin D deficiency disrupts hippocampal-dependent learning and structural brain connectivity in BALB/c mice

Converging evidence from human and animal studies support an association between vitamin D deficiency and cognitive impairment. Previous studies have shown that hippocampal volume is reduced in adults with vitamin D deficiency as well as in a range of disorders, such as schizophrenia. The aim of the current study was to examine the effect of adult vitamin D (AVD) deficiency on hippocampal-dependent spatial learning, and hippocampal volume and connectivity in healthy adult mice. Ten-week-old male BALB/c mice were fed a control (vitamin D 1500 IU/kg) or vitamin D-depleted (vitamin D 0 IU/kg) diet for a minimum of 10 weeks. The mice were then tested for hippocampal-dependent spatial learning using active place avoidance (APA) and on tests of muscle and motor coordination (rotarod and grip strength). The mice were perfused and brains collected to acquire ex vivo structural and diffusion-weighted images using a 16.4 T MRI scanner. We also performed immunohistochemistry to quantify perineuronal nets (PNNs) and parvalbumin (PV) interneurons in various brain regions. AVD-deficient mice had a lower latency to enter the shock zone on APA, compared to control mice, suggesting impaired hippocampal-dependent spatial learning. There were no differences in rotarod or grip strength, indicating that AVD deficiency did not have an impact on muscle or motor coordination. AVD deficiency did not have an impact on hippocampal volume. However, AVD-deficient mice displayed a disrupted network centred on the right hippocampus with abnormal connectomes among 29 nodes. We found a reduction in PNN positive cells, but no change in PV, centred on the hippocampus. Our results provide compelling evidence to show that AVD deficiency in otherwise healthy adult mice may play a key role in hippocampal-dependent learning and memory formation. We suggest that the spatial learning deficits could be due to the disruption of right hippocampal structural connectivity.

The Relative Contributions of Cell-Dependent Cortical Microcircuit Aging to Cognition and Anxiety

BACKGROUND

Aging is accompanied by altered thinking (cognition) and feeling (mood), functions that depend on information processing by brain cortical cell microcircuits. We hypothesized that age-associated long-term functional and biological changes are mediated by gene transcriptomic changes within neuronal cell types forming cortical microcircuits, namely excitatory pyramidal cells (PYCs) and inhibitory gamma-aminobutyric acidergic neurons expressing vasoactive intestinal peptide (Vip), somatostatin (Sst), and parvalbumin (Pvalb).

METHODS

To test this hypothesis, we assessed locomotor, anxiety-like, and cognitive behavioral changes between young (2 months of age, n = 9) and old (22 months of age, n = 12) male C57BL/6 mice, and performed frontal cortex cell type-specific molecular profiling, using laser capture microscopy and RNA sequencing. Results were analyzed by neuroinformatics and validated by fluorescent in situ hybridization.

RESULTS

Old mice displayed increased anxiety and reduced working memory. The four cell types displayed distinct age-related transcriptomes and biological pathway profiles, affecting metabolic and cell signaling pathways, and selective markers of neuronal vulnerability (Ryr3), resilience (Oxr1), and mitochondrial dynamics (Opa1), suggesting high age-related vulnerability of PYCs, and variable degree of adaptation in gamma-aminobutyric acidergic neurons. Correlations between gene expression and behaviors suggest that changes in cognition and anxiety associated with age are partly mediated by normal age-related cell changes, and that additional age-independent decreases in synaptic and signaling pathways, notably in PYCs and somatostatin neurons, further contribute to behavioral changes.

CONCLUSIONS

Our study demonstrates cell-dependent differential vulnerability and coordinated cell-specific cortical microcircuit molecular changes with age. Collectively, the results suggest intrinsic molecular links among aging, cognition, and mood-related behaviors, with somatostatin neurons contributing evenly to both behavioral conditions.

Keratan sulfate (KS)-proteoglycans and neuronal regulation in health and disease: the importance of KS-glycodynamics and interactive capability with neuroregulatory ligands

Compared to the other classes of glycosaminoglycans (GAGs), that is, chondroitin/dermatan sulfate, heparin/heparan sulfate and hyaluronan, keratan sulfate (KS), have the least known of its interactive properties. In the human body, the cornea and the brain are the two most abundant tissue sources of KS. Embryonic KS is synthesized as a linear poly-N-acetyllactosamine chain of d-galactose-GlcNAc repeat disaccharides which become progressively sulfated with development, sulfation of GlcNAc is more predominant than galactose. KS contains multi-sulfated high-charge density, monosulfated and non-sulfated poly-N-acetyllactosamine regions and thus is a heterogeneous molecule in terms of chain length and charge distribution. A recent proteomics study on corneal KS demonstrated its interactivity with members of the Slit-Robbo and Ephrin-Ephrin receptor families and proteins which regulate Rho GTPase signaling and actin polymerization/depolymerization in neural development and differentiation. KS decorates a number of peripheral nervous system/CNS proteoglycan (PG) core proteins. The astrocyte KS-PG abakan defines functional margins of the brain and is up-regulated following trauma. The chondroitin sulfate/KS PG aggrecan forms perineuronal nets which are dynamic neuroprotective structures with anti-oxidant properties and roles in neural differentiation, development and synaptic plasticity. Brain phosphacan a chondroitin sulfate, KS, HNK-1 PG have roles in neural development and repair. The intracellular microtubule and synaptic vesicle KS-PGs MAP1B and SV2 have roles in metabolite transport, storage, and export of neurotransmitters and cytoskeletal assembly. MAP1B has binding sites for tubulin and actin through which it promotes cytoskeletal development in growth cones and is highly expressed during neurite extension. The interactive capability of KS with neuroregulatory ligands indicate varied roles for KS-PGs in development and regenerative neural processes.

Experience-dependent transcriptional regulation in juvenile brain development

During brain development, once primary neural networks are formed, they are largely sculpted by environmental stimuli. The juvenile brain has a unique time window termed the critical period, in which neuronal circuits are remodeled by experience. Accumulating evidence indicates that abnormal rewiring of circuits in early life contributes to various neurodevelopmental disorders at later stages of life. Recent studies implicate two important aspects for activation of the critical period, both of which are experience-dependent: (a) proper excitatory/inhibitory (E/I) balance of neural circuit achieved during developmental trajectory of inhibitory interneurons, and (b) epigenetic regulation allowing flexible gene expression for neuronal plasticity. In this review, we discuss the molecular mechanisms of juvenile brain plasticity from the viewpoints of transcriptional and chromatin regulation, with a focus on Otx2 homeoprotein. Depending on experience, Otx2 is transported into cortical parvalbumin-positive interneurons (PV cells), where it induces PV cell maturation to activate the critical period. Understanding the unique behavior and function of Otx2 as a "messenger" of experience should therefore provide insights into mechanisms of juvenile brain development. Recently identified downstream targets of Otx2 suggest novel roles of Otx2 in homeostasis of PV cells, and, moreover, in regulation of chromatin state, which is important for neuronal plasticity. We further discuss epigenetic changes during postnatal brain development spanning the critical period. Different aspects of chromatin regulation may underlie experience-dependent neuronal development and plasticity.

The Physiology of Homeoprotein Transduction

The homeoprotein family comprises ~300 transcription factors and was long seen as primarily involved in developmental programs through cell autonomous regulation. However, recent evidence reveals that many of these factors are also expressed in the adult where they exert physiological functions not yet fully deciphered. Furthermore, the DNA-binding domain of most homeoproteins contains two signal sequences allowing their secretion and internalization, thus intercellular transfer. This review focuses on this new-found signaling in cell migration, axon guidance, and cerebral cortex physiological homeostasis and speculates on how it may play important roles in early arealization of the neuroepithelium. It also describes the use of homeoproteins as therapeutic proteins in mouse models of diseases affecting the central nervous system, in particular Parkinson disease and glaucoma.

The Circuitry of Dopamine System Regulation and its Disruption in Schizophrenia: Insights Into Treatment and Prevention

Despite evidence for a role of the dopamine system in the pathophysiology of schizophrenia, there has not been substantial evidence that this disorder originates from a pathological change within the dopamine system itself. Current data from human imaging studies and preclinical investigations instead point to a disruption in afferent regulation of the dopamine system, with a focus on the hippocampus. We found that the hippocampus in the methylazoxymethanol acetate (MAM) rodent developmental disruption model of schizophrenia is hyperactive and dysrhythmic, possibly due to loss of parvalbumin interneurons, leading to a hyperresponsive dopamine system. Whereas current therapeutic approaches target dopamine receptor blockade, treatment at the site of pathology may be a more effective therapeutic avenue. This model also provided insights into potential means for prevention of schizophrenia. Specifically, given that stress is a risk factor in schizophrenia, and that stress can damage hippocampal parvalbumin interneurons, we tested whether alleviating stress early in life can effectively circumvent transition to schizophrenia-like states. Administering diazepam prepubertally at an antianxiety dose in MAM rats was effective at preventing the emergence of the hyperdopaminergic state in the adult. Moreover, multiple stressors applied to normal rats at the same time point resulted in pathology similar to the MAM rat. These data suggest that a genetic predisposition leading to stress hyper-responsivity, or exposure to substantial stressors, could be a primary factor leading to the emergence of schizophrenia later in life, and furthermore treating stress at a critical period may be effective in circumventing this transition.

Can N-Methyl-D-Aspartate Receptor Hypofunction in Schizophrenia Be Localized to an Individual Cell Type?

Hypofunction of N-methyl-D-aspartate glutamate receptors (NMDARs), whether caused by endogenous factors like auto-antibodies or mutations, or by pharmacological or genetic manipulations, produces a wide variety of deficits which overlap with-but do not precisely match-the symptom spectrum of schizophrenia. In order to understand how NMDAR hypofunction leads to different components of the syndrome, it is necessary to take into account which neuronal subtypes are particularly affected by it in terms of detrimental functional alterations. We provide a comprehensive overview detailing findings in rodent models with cell type-specific knockout of NMDARs. Regarding inhibitory cortical cells, an emerging model suggests that NMDAR hypofunction in parvalbumin (PV) positive interneurons is a potential risk factor for this disease. PV interneurons display a selective vulnerability resulting from a combination of genetic, cellular, and environmental factors that produce pathological multi-level positive feedback loops. Central to this are two antioxidant mechanisms-NMDAR activity and perineuronal nets-which are themselves impaired by oxidative stress, amplifying disinhibition. However, NMDAR hypofunction in excitatory pyramidal cells also produces a range of schizophrenia-related deficits, in particular maladaptive learning and memory recall. Furthermore, NMDAR blockade in the thalamus disturbs thalamocortical communication, and NMDAR ablation in dopaminergic neurons may provoke over-generalization in associative learning, which could relate to the positive symptom domain. Therefore, NMDAR hypofunction can produce schizophrenia-related effects through an action on various different circuits and cell types.

Nutritional Intervention for Developmental Brain Damage: Effects of Lactoferrin Supplementation in Hypocaloric Induced Intrauterine Growth Restriction Rat Pups

Introduction: Intrauterine Growth Restriction (IUGR) refers to an impaired development of the fetus and hence results in adverse neurodevelopmental and psychiatric consequences later in life. Lactoferrin (Lf) is a glycoprotein present in milk that has already shown neuroprotective effects through its anti-inflammatory and antioxidant properties on impaired developing brains. The aim of this study was to characterize a rat model of IUGR and assess the neuroprotective effect of a nutritional supplementation with bovine Lf during pregnancy and lactation on this model. Methods: A model of 50% gestational caloric restriction (CR) was used. Three groups were designed, and pregnant rats had either ad libitum access to food (control group, CTL) or 50% of the controls' intake (restricted group, IUGR). The diet was isocaloric and supplemented with bovine Lf for the caloric restricted dams (restricted-Lf, IUGR_Lf). At postnatal day 7 and 21, advanced ex-vivo diffusion MRI techniques at 9.4T were used to investigate brain cortical and white matter microstructure. Further, genes and proteins involved in structure (synaptophysin, MBP), microglia (Iba-1), metabolism (MCT2, βCaMKII) and apoptosis (Bcl-2) were analyzed in the cortex and striatum. In the cortex, the number of parvalbumin immunoreactive interneurons and their perineuronal nets were quantified. Behavioral tests were performed at P31. Results: Effects of the CR were significant in the cortex and striatum with reduction of synaptophysin (marker of synaptogenesis) at P7 and MBP (marker of myelin) at P21 in the cortex. Indeed, MCT2 (energy metabolism), Bcl-2 (anti-apoptotic protein) and βCaMKII (synapse activity) expressions were reduced in IUGR groups at P7. In the striatum NG2 (marker of oligodendrocyte precursor cells) and Bcl-2 at P7 as well as βCaMKII at P21 were decreased following IUGR and restored by Lf. Cortical microstructure was impaired following CR with partial effect of Lf. Lf prevented oxidative stress induced parvalbumin interneurons impairments whereas striatum and external capsule showed alterations in microstructure depicted by diffusion MRI, which were also partially reversed by Lf. Discussion and Conclusion: The model of 50% caloric restriction induced mild impairment partially reversed by nutritional intervention using Lf during pregnancy and lactation.

Loss of interneurons and disruption of perineuronal nets in the cerebral cortex following hypoxia-ischaemia in near-term fetal sheep

Hypoxia-ischaemia (HI) in term infants is a common cause of brain injury and neurodevelopmental impairment. Development of gamma-aminobutyric acid (GABA)ergic circuitry in the cerebral cortex is a critical event in perinatal brain development. Perineuronal nets (PNNs) are specialised extracellular matrix structures that surround GABAergic interneurons, and are important for their function. Herein, we hypothesised that HI would reduce survival of cortical interneurons and disrupt PNNs in a near-term fetal sheep model of global cerebral ischaemia. Fetal sheep (0.85 gestation) received sham occlusion (n = 5) or 30 min of reversible cerebral ischaemia (HI group; n = 5), and were recovered for 7 days. Expression of interneurons (glutamate decarboxylase [GAD]⁺; parvalbumin [PV]⁺) and PNNs (Wisteria floribunda agglutinin, WFA) was assessed in the parasagittal cortex by immunohistochemistry. HI was associated with marked loss of both GAD⁺ and PV⁺ cortical interneurons (all layers of the parasagittal cortex and layer 6) and PNNs (layer 6). The expression and integrity of PNNs was also reduced on surviving GAD⁺ interneurons. There was a trend towards a linear correlation of the proportion of GAD⁺ neurons that were WFA⁺ with seizure burden (r² = 0.76, p = 0.0534). Overall, these data indicate that HI may cause deficits in the cortical GABAergic system involving loss of interneurons and disruption of PNNs, which may contribute to the range of adverse neurological outcomes following perinatal brain injury.

Pathological alterations of chondroitin sulfate moiety in postmortem hippocampus of patients with schizophrenia

Perineuronal nets comprise chondroitin sulfate moieties and their core proteins, and their neuropathological alterations have been implicated in schizophrenia. To explore the molecular mechanism of the perineuronal net impairments in schizophrenia, we measured the immunoreactivity of chondroitin sulfate moieties, major components of perineuronal nets, in three brain regions (postmortem dorsolateral prefrontal cortex, caudate nucleus, and hippocampus) of schizophrenia patients and control subjects. Immunoblotting for chondroitin 4-sulfate and chondroitin 6-sulfate moieties revealed a significant increase in intensity of a 180 kD band of chondroitin 4-sulfate immunoreactivity in the hippocampus of patients, although we detected no significant alteration in their immunoreactivities with any other molecular sizes or in other brain regions. The levels of immunoreactivity were not correlated with postmortem interval, age, or storage time. We failed to find such an increase in a similar molecular range of the chondroitin 4-sulfate immunoreactivity in the hippocampus of the rats chronically treated with haloperidol. These results suggest that the level alteration of the chondroitin 4-sulfate moiety might contribute to the perineuronal net abnormality found in patients with schizophrenia.

Transcriptomic Evidence for Alterations in Astrocytes and Parvalbumin Interneurons in Subjects With Bipolar Disorder and Schizophrenia

BACKGROUND

High-throughput expression analyses of postmortem brain tissue have been widely used to study bipolar disorder and schizophrenia. However, despite the extensive efforts, no consensus has emerged as to the functional interpretation of the findings. We hypothesized that incorporating information on cell type-specific expression would provide new insights.

METHODS

We reanalyzed 15 publicly available bulk tissue expression datasets on schizophrenia and bipolar disorder, representing various brain regions from eight different cohorts of subjects (unique subjects: 332 control, 129 bipolar disorder, 341 schizophrenia). We studied changes in the expression profiles of cell type marker genes and evaluated whether these expression profiles could serve as surrogates for relative abundance of their corresponding cells.

RESULTS

In both bipolar disorder and schizophrenia, we consistently observed an increase in the expression profiles of cortical astrocytes and a decrease in the expression profiles of fast-spiking parvalbumin interneurons. No changes in astrocyte expression profiles were observed in subcortical regions. Furthermore, we found that many of the genes previously identified as differentially expressed in schizophrenia are highly correlated with the expression profiles of astrocytes or fast-spiking parvalbumin interneurons.

CONCLUSIONS

Our results indicate convergence of transcriptome studies of schizophrenia and bipolar disorder on changes in cortical astrocytes and fast-spiking parvalbumin interneurons, providing a unified interpretation of numerous studies. We suggest that these changes can be attributed to alterations in the relative abundance of the cells and are important for understanding the pathophysiology of the disorders.

Redox dysregulation as a link between childhood trauma and psychopathological and neurocognitive profile in patients with early psychosis

Early traumatic experiences interact with redox regulation and oxidative stress. Blood glutathione peroxidase (GPx) activity, involved in reducing peroxides, may reflect the oxidation status of the organism, thus allowing for the stratification of patients. Traumatized patients with psychosis who have a high blood oxidation status (high-GPx) have smaller hippocampal volumes (but not a smaller amygdala or intracranial volume), and this is associated with more severe clinical symptoms, while those with a lower oxidation status (low-GPx) showed better cognition and a correlated activation of the antioxidant thioredoxin/peroxiredoxin system. Thus, in patients with psychosis, traumatic experiences during childhood may interact with various redox systems, leading to long-term neuroanatomical and clinical defects. This redox profile may represent important biomarkers for patient stratification, defining treatment strategies at early stages of psychosis.

Exposure to childhood trauma (CT) increases the risk for psychosis and affects the development of brain structures, possibly through oxidative stress. As oxidative stress is also linked to psychosis, it may interact with CT, leading to a more severe clinical phenotype. In 133 patients with early psychosis (EPP), we explored the relationships between CT and hippocampal, amygdala, and intracranial volume (ICV); blood antioxidant defenses [glutathione peroxidase (GPx) and thioredoxin/peroxiredoxin (Trx/Prx)]; psychopathological results; and neuropsychological results. Nonadjusted hippocampal volume correlated negatively with GPx activity in patients with CT, but not in patients without CT. In patients with CT with high GPx activity (high-GPx+CT), hippocampal volume was decreased compared with that in patients with low-GPx+CT and patients without CT, who had similar hippocampal volumes. Patients with high-GPx+CT had more severe positive and disorganized symptoms than other patients. Interestingly, Trx and oxidized Prx levels correlated negatively with GPx only in patients with low-GPx+CT. Moreover, patients with low-GPx+CT performed better than other patients on cognitive tasks. Discriminant analysis combining redox markers, hippocampal volume, clinical scores, and cognitive scores allowed for stratification of the patients into subgroups. In conclusion, traumatized EPP with high peripheral oxidation status (high-GPx activity) had smaller hippocampal volumes and more severe symptoms, while those with lower oxidation status (low-GPx activity) showed better cognition and regulation of GPx and Trx/Prx systems. These results suggest that maintained regulation of various antioxidant systems allowed for compensatory mechanisms preventing long-term neuroanatomical and clinical impacts. The redox marker profile may thus represent important biomarkers for defining treatment strategies in patients with psychosis.

Inhibitory Projections from the Inferior Colliculus to the Medial Geniculate body Originate from Four Subtypes of GABAergic Cells

GABAergic cells constitute 20-40% of the cells that project from the inferior colliculus [(IC) a midbrain auditory hub] to the medial geniculate body [(MG) the main auditory nucleus of the thalamus]. Four subtypes of GABAergic IC cells have been identified based on their association with perineuronal nets (PNs) and dense rings of axosomatic terminals expressing vesicular glutamate transporter 2 (VGLUT2 rings). These subtypes differ in their soma size and distribution within the IC. Based on previous work emphasizing large GABAergic cells as the origin of GABAergic IC-MG projections, we hypothesized that GABAergic IC cells surrounded by PNs and VGLUT2 rings, which tend to have larger somas, were more likely to project to the MG than smaller cells lacking these extracellular markers. Here, we injected retrograde tract tracers into the MG of guinea pigs of either sex and analyzed retrogradely labeled GABAergic cells in the ipsilateral IC for soma size and association with PNs and/or VGLUT2 rings. We found a range of GABAergic soma sizes present within the IC-MG pathway, which were reflective of the full range of GABAergic soma sizes present within the IC. Further, we found that all four subtypes of GABAergic IC cells participate in the IC-MG pathway, and that GABAergic cells lacking PNs and VGLUT2 rings were more prevalent within the pathway than would be expected based on their overall prevalence in the IC. These results may provide an anatomical substrate for the multiple roles of inhibition in the IC-MG pathway, which have emerged in electrophysiological studies.

Perineuronal nets decrease membrane capacitance of peritumoral fast spiking interneurons in a model of epilepsy

Brain tumor patients commonly present with epileptic seizures. We show that tumor-associated seizures are the consequence of impaired GABAergic inhibition due to an overall loss of peritumoral fast spiking interneurons (FSNs) concomitant with a significantly reduced firing rate of those that remain. The reduced firing is due to the degradation of perineuronal nets (PNNs) that surround FSNs. We show that PNNs decrease specific membrane capacitance of FSNs permitting them to fire action potentials at supra-physiological frequencies. Tumor-released proteolytic enzymes degrade PNNs, resulting in increased membrane capacitance, reduced firing, and hence decreased GABA release. These studies uncovered a hitherto unknown role of PNNs as an electrostatic insulator that reduces specific membrane capacitance, functionally akin to myelin sheaths around axons, thereby permitting FSNs to exceed physiological firing rates. Disruption of PNNs may similarly account for excitation-inhibition imbalances in other forms of epilepsy and PNN protection through proteolytic inhibition may provide therapeutic benefits.

Impaired Cognitive Function after Perineuronal Net Degradation in the Medial Prefrontal Cortex

Perineuronal nets (PNNs) are highly organized components of the extracellular matrix that surround a subset of mature neurons in the CNS. These structures play a critical role in regulating neuronal plasticity, particularly during neurodevelopment. Consistent with this role, their presence is associated with functional and structural stability of the neurons they ensheath. A loss of PNNs in the prefrontal cortex (PFC) has been suggested to contribute to cognitive impairment in disorders such as schizophrenia. However, the direct consequences of PNN loss in medial PFC (mPFC) on cognition has not been demonstrated. Here, we examined behavior after disruption of PNNs in mPFC of Long-Evans rats following injection of the enzyme chondroitinase ABC (ChABC). Our data show that ChABC-treated animals were impaired on tests of object oddity perception. Performance in the cross-modal object recognition (CMOR) task was not significantly different for ChABC-treated rats, although ChABC-treated rats were not able to perform above chance levels whereas control rats were. ChABC-treated animals were not significantly different from controls on tests of prepulse inhibition (PPI), set-shifting (SS), reversal learning, or tactile and visual object recognition memory. Posthumous immunohistochemistry confirmed significantly reduced PNNs in mPFC due to ChABC treatment. Moreover, PNN density in the mPFC predicted performance on the oddity task, where higher PNN density was associated with better performance. These findings suggest that PNN loss within the mPFC impairs some aspects of object oddity perception and recognition and that PNNs contribute to cognitive function in young adulthood.

The Neuroprotective Effects of 17β-Estradiol Pretreatment in a Model of Neonatal Hippocampal Injury Induced by Trimethyltin

Hippocampal dysfunction plays a central role in neurodevelopmental disorders, resulting in severe impairment of cognitive abilities, including memory and learning. On this basis, developmental studies represent an important tool both to understanding the cellular and molecular phenomena underlying early hippocampal damage and to study possible therapeutic interventions, that may modify the progression of neuronal death. Given the modulatory role played by 17β-estradiol (E2) on hippocampal functions and its neuroprotective properties, the present study investigates the effects of pretreatment with E2 in a model of neonatal hippocampal injury obtained by trimethyltin (TMT) administration, characterized by neuronal loss in CA1 and CA3 subfields and astroglial and microglial activation. At post-natal days (P)5 and P6 animals received E2 administration (0.2 mg/kg/die i.p.) or vehicle. At P7 they received a single dose of TMT (6.5 mg/kg i.p.) and were sacrificed 72 h (P10) or 7 days after TMT treatment (P14). Our findings indicate that pretreatment with E2 exerts a protective effect against hippocampal damage induced by TMT administration early in development, reducing the extent of neuronal death in the CA1 subfield, inducing the activation of genes involved in neuroprotection, lowering the neuroinflammatory response and restoring neuropeptide Y- and parvalbumin- expression, which is impaired in the early phases of TMT-induced damage. Our data support the efficacy of estrogen-based neuroprotective approaches to counteract early occurring hippocampal damage in the developing hippocampus.

Early life trauma increases threat response of peri-weaning rats, reduction of axo-somatic synapses formed by parvalbumin cells and perineuronal net in the basolateral nucleus of amygdala

Early life trauma is a risk factor for life-long disorders related to emotional processing, but knowledge underlying its enduring effect is incomplete. This study was motivated by the hypothesis that early life trauma increases amygdala-dependent threat responses via reduction in inhibition by parvalbumin (PV) interneurons and perineuronal nets (PNN) supporting PV cells, thus increasing excitability of the basolateral amygdala (BLA). From postnatal day (PN) 8-12, rat pups of both sexes were reared under normal bedding or under insufficient nest-building materials to induce maternal-to-infant maltreatment trauma (Scarcity-Adversity Model, SAM). At weaning age of PN23, the SAM group exhibited increased threat responses to predator odor. The SAM-induced increase in threat response was recapitulated in normally reared PN22-23 rats that were unilaterally depleted of PNN in the BLA by the enzymes, chondroitinase-ABC plus hyaluronidase at PN19-20. Light and electron microscopic analysis of the BLA revealed that anterior-to-mid levels of SAM group's BLAs exhibited decreased PNN intensity and decreased axo-somatic synapses between PV-to-principal pyramidal-like neurons and PV-to-PV. PV and PNN densities (cells/mm² ) in the BLA of both control (CON) and SAM groups were still low at PN12 and SAM delayed the ontogenetic rise of PV intensity and PNN density. Moreover, PV cell density in the anterior-to-mid BLA correlated negatively with threat response of CON animals, but not for SAM animals. Thus, reduction of PNN-supported, PV-mediated somatic inhibition of pyramidal cells provides a mechanistic support for the enduring effect of early life maltreatment manifested as increasing innate threat response at weaning.

Perineuronal nets in brain physiology and disease

Perineuronal nets (PNNs) in the brain are condensed glycosaminoglycan-rich extracellular matrix structures with heterogeneous composition yet specific organization. They typically assemble around a subset of fast-spiking interneurons that are implicated in learning and memory. Owing to their unique structural organization, PNNs have neuroprotective capacities but also participate in signal transduction and in controlling neuronal activity and plasticity. In this review, we define PNN structure in detail and describe its various biochemical and physiological functions. We further discuss the role of PNNs in brain disorders such as schizophrenia, bipolar disorder, Alzheimer disease and addictions. Lastly, we describe therapeutic approaches that target PNNs to alter brain physiology and counter brain dysfunction.

Subtypes of GABAergic cells in the inferior colliculus

The inferior colliculus occupies a central position in ascending and descending auditory pathways. A substantial proportion of its neurons are GABAergic, and these neurons contribute to intracollicular circuits as well as to extrinsic projections to numerous targets. A variety of types of evidence - morphology, physiology, molecular markers - indicate that the GABAergic cells can be divided into at least four subtypes that serve different functions. However, there has yet to emerge a unified scheme for distinguishing these subtypes. The present review discusses these criteria and, where possible, relates the different properties. In contrast to GABAergic cells in cerebral cortex, where subtypes are much more thoroughly characterized, those in the inferior colliculus contribute substantially to numerous long range extrinsic projections. At present, the best characterized subtype is a GABAergic cell with a large soma, dense perisomatic synaptic inputs and a large axon that provides rapid auditory input to the thalamus. This large GABAergic subtype projects to additional targets, and other subtypes also project to the thalamus. The eventual characterization of these subtypes can be expected to reveal multiple functions of these inhibitory cells and the many circuits to which they contribute.

Cocaine Exposure Modulates Perineuronal Nets and Synaptic Excitability of Fast-Spiking Interneurons in the Medial Prefrontal Cortex

We previously reported that perineuronal nets (PNNs) are required for cocaine-associated memories. Perineuronal nets are extracellular matrix that primarily surrounds parvalbumin (PV)-containing, GABAergic fast-spiking interneurons (FSIs) in the medial prefrontal cortex (mPFC). Here we measured the impact of acute (1 d) or repeated (5 d) cocaine exposure on PNNs and PV cells within the prelimbic and infralimbic regions of the mPFC. Adult rats were exposed to 1 or 5 d of cocaine and stained for PNNs (using Wisteria floribunda agglutinin) and PV intensity 2 or 24 h later. In the prelimbic and infralimbic PFC, PNN staining intensity decreased 2 h after 1 d of cocaine exposure but increased after 5 d of cocaine exposure. Cocaine also produced changes in PV intensity, which generally lagged behind that of PNNs. In the prelimbic PFC, both 1 and 5 d of cocaine exposure increased GAD65/67 puncta near PNN-surrounded PV cells, with an increase in the GAD65/67-to-VGluT1 puncta ratio after 5 d of cocaine exposure. In the prelimbic PFC, slice electrophysiology studies in FSIs surrounded by PNNs revealed that both 1 and 5 d of cocaine exposure reduced the number of action potentials 2 h later. Synaptic changes demonstrated that 5 d of cocaine exposure increased the inhibition of FSIs, potentially reducing the inhibition of pyramidal neurons and contributing to their hyperexcitability during relapse behavior. These early and rapid responses to cocaine may alter the network stability of PV FSIs that partially mediate the persistent and chronic nature of drug addiction.

The thalamic reticular nucleus in schizophrenia and bipolar disorder: role of parvalbumin-expressing neuron networks and oxidative stress

Growing evidence points to a disruption of cortico-thalamo-cortical circuits in schizophrenia (SZ) and bipolar disorder (BD). Clues for a specific involvement of the thalamic reticular nucleus (TRN) come from its unique neuronal characteristics and neural connectivity, allowing it to shape the thalamo-cortical information flow. A direct involvement of the TRN in SZ and BD has not been tested thus far. We used a combination of human postmortem and rodent studies to test the hypothesis that neurons expressing parvalbumin (PV neurons), a main TRN neuronal population, and associated Wisteria floribunda agglutinin-labeled perineuronal nets (WFA/PNNs) are altered in SZ and BD, and that these changes may occur early in the course of the disease as a consequence of oxidative stress. In both disease groups, marked decreases of PV neurons (immunoreactive for PV) and WFA/PNNs were observed in the TRN, with no effects of duration of illness or age at onset. Similarly, in transgenic mice with redox dysregulation, numbers of PV neurons and WFA/PNN+PV neurons were decreased in transgenic compared with wild-type mice; these changes were present at postnatal day (P) 20 for PV neurons and P40 for WFA/PNN+PV neurons, accompanied by alterations of their firing properties. These results show profound abnormalities of PV neurons in the TRN of subjects with SZ and BD, and offer support for the hypothesis that oxidative stress may play a key role in impacting TRN PV neurons at early stages of these disorders. We put forth that these TRN abnormalities may contribute to disruptions of sleep spindles, focused attention and emotion processing in these disorders.

Synaptic coupling of inner ear sensory cells is controlled by brevican-based extracellular matrix baskets resembling perineuronal nets

Background

Perineuronal nets (PNNs) are specialized aggregations of extracellular matrix (ECM) molecules surrounding specific neurons in the central nervous system (CNS). PNNs are supposed to control synaptic transmission and are frequently associated with neurons firing at high rates, including principal neurons of auditory brainstem nuclei. The origin of high-frequency activity of auditory brainstem neurons is the indefatigable sound-driven transmitter release of inner hair cells (IHCs) in the cochlea.

Results

Here, we show that synaptic poles of IHCs are ensheathed by basket-like ECM complexes formed by the same molecules that constitute PNNs of neurons in the CNS, including brevican, aggreccan, neurocan, hyaluronan, and proteoglycan link proteins 1 and 4 and tenascin-R. Genetic deletion of brevican, one of the main components, resulted in a massive degradation of ECM baskets at IHCs, a significant impairment in spatial coupling of pre- and postsynaptic elements and mild impairment of hearing.

Conclusions

These ECM baskets potentially contribute to control of synaptic transmission at IHCs and might be functionally related to PNNs of neurons in the CNS.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0566-8) contains supplementary material, which is available to authorized users.

Brevican "nets" voltage-gated calcium channels at the hair cell ribbon synapse

During hearing in mammals, "sensorineural" inner hair cells convert sound wave-generated mechanical input into electrical activity, resulting in glutamate release onto type I spiral ganglion neurons (SGNs) at specialized synapses known as "ribbon synapses". New findings published here in BMC Biology by Sonntag and colleagues indicate a role for the proteoglycan Brevican in forming perineurounal net (PNN) baskets at these synapses and controlling the spatial distribution of presynaptic voltage-gated calcium channels that regulate glutamate release. These findings may provide insight into the mechanism by which individual ribbon synapses within a single hair cell can function in an independent manner to facilitate hearing within a broad dynamic range.

Alterations of GABAergic Neuron-Associated Extracellular Matrix and Synaptic Responses in Gad1-Heterozygous Mice Subjected to Prenatal Stress

Exposure to prenatal stress (PS) and mutations in Gad1, which encodes GABA synthesizing enzyme glutamate decarboxylase (GAD) 67, are the primary risk factors for psychiatric disorders associated with abnormalities in parvalbumin (PV)-positive GABAergic interneurons in the medial prefrontal cortex (mPFC). Decreased expression of extracellular matrix (ECM) glycoproteins has also been reported in patients with these disorders, raising the possibility that ECM abnormalities may play a role in their pathogenesis. To elucidate pathophysiological changes in ECM induced by the gene–environment interaction, we examined heterozygous GAD67-GFP (Knock-In KI; GAD67^+/GFP) mice subjected to PS from embryonic day 15.0 to 17.5. Consistent with our previous study, we confirmed a decrease in the density of PV neurons in the mPFC of postnatal GAD67^+/GFP mice with PS, which was concurrent with a decrease in density of PV neurons surrounded by perineuronal nets (PNNs), a specialized ECM important for the maturation, synaptic stabilization and plasticity of PV neurons. Glycosylation of α-dystroglycan (α-DG) and its putative mediator fukutin (Fktn) in the ECM around inhibitory synapses has also been suggested to contribute to disease development. We found that both glycosylated α-DG and the mRNA level of Fktn were reduced in GAD67^+/GFP mice with PS. None of these changes were detected in GAD67^+/GFP naive mice or wild type (GAD67^+/+) mice with PS, suggesting that both PS and reduced Gad1 gene expression are prerequisites for these changes. When assessing the function of interneurons in the mPFC of GAD67^+/GFP mice with PS through evoked inhibitory post-synaptic currents (eIPSCs) in layer V pyramidal neurons, we found that the threshold stimulus intensity for eIPSC events was reduced and that the eIPSC amplitude was increased without changes in the paired-pulse ratio (PPR). Moreover, the decay rate of eIPSCs was also slowed. In line with eIPSC, spontaneous IPSC (sIPSC) amplitude, frequency and decay tau were altered. Thus, our study suggests that alterations in the ECM mediated by gene-environment interactions might be linked to the enhanced and prolonged GABA action that compensates for the decreased density of PV neurons. This might be one of the causes of the excitatory/inhibitory imbalance in the mPFC of psychiatric patients.

Topological remodeling of cortical perineuronal nets in focal cerebral ischemia and mild hypoperfusion

Despite the crucial role of perineuronal nets (PNNs) in neural plasticity and neurological disorders, their ultrastructural organization remains largely unresolved. We have developed a novel approach combining superresolution structured illumination microscopy (SR-SIM) and mathematical reconstruction that allows for quantitative analysis of PNN topology. Since perineuronal matrix is capable to restrict neural plasticity but at the same time is necessary to maintain synapses, we hypothesized that a beneficial post stroke recovery requires a reversible loosening of PNNs. Our results indicated that focal cerebral ischemia induces partial depletion of PNNs and that mild hypoperfusion not associated with ischemic injury can induce ultra-structural rearrangements in visually intact meshworks. In line with the activation of neural plasticity under mild stress stimuli, we provide evidence that topological conversion of PNNs can support post stroke neural rewiring.

The Perineuronal 'Safety' Net? Perineuronal Net Abnormalities in Neurological Disorders

Perineuronal nets (PNN) are extracellular matrix (ECM) assemblies that preferentially ensheath parvalbumin (PV) expressing interneurons. Converging evidence indicates that PV cells and PNN are impaired in a variety of neurological disorders. PNN development and maintenance is necessary for a number of processes within the CNS, including regulation of GABAergic cell function, protection of neurons from oxidative stress, and closure of developmental critical period plasticity windows. Understanding PNN functions may be essential for characterizing the mechanisms of altered cortical excitability observed in neurodegenerative and neurodevelopmental disorders. Indeed, PNN abnormalities have been observed in post-mortem brain tissues of patients with schizophrenia and Alzheimer’s disease. There is impaired development of PNNs and enhanced activity of its key regulator matrix metalloproteinase-9 (MMP-9) in Fragile X Syndrome, a common genetic cause of autism. MMP-9, a protease that cleaves ECM, is differentially regulated in a number of these disorders. Despite this, few studies have addressed the interactions between PNN expression, MMP-9 activity and neuronal excitability. In this review, we highlight the current evidence for PNN abnormalities in CNS disorders associated with altered network function and MMP-9 levels, emphasizing the need for future work targeting PNNs in pathophysiology and therapeutic treatment of neurological disorders.

Hippocampal extracellular matrix alterations contribute to cognitive impairment associated with a chronic depressive-like state in rats

Patients with depression often suffer from cognitive impairments that contribute to disease burden. We used social defeat-induced persistent stress (SDPS) to induce a depressive-like state in rats and then studied long-lasting memory deficits in the absence of acute stressors in these animals. The SDPS rat model showed reduced short-term object location memory and maintenance of long-term potentiation (LTP) in CA1 pyramidal neurons of the dorsal hippocampus. SDPS animals displayed increased expression of synaptic chondroitin sulfate proteoglycans in the dorsal hippocampus. These effects were abrogated by a 3-week treatment with the antidepressant imipramine starting 8 weeks after the last defeat encounter. Next, we observed an increase in the number of perineuronal nets (PNNs) surrounding parvalbumin-expressing interneurons and a decrease in the frequency of inhibitory postsynaptic currents (IPSCs) in the hippocampal CA1 region in SDPS animals. In vivo breakdown of the hippocampus CA1 extracellular matrix by the enzyme chondroitinase ABC administered intracranially restored the number of PNNs, LTP maintenance, hippocampal inhibitory tone, and memory performance on the object place recognition test. Our data reveal a causal link between increased hippocampal extracellular matrix and the cognitive deficits associated with a chronic depressive-like state in rats exposed to SDPS.

HDAC2-dependent Antipsychotic-like Effects of Chronic Treatment with the HDAC Inhibitor SAHA in Mice

Antipsychotic drugs, including both typical such as haloperidol and atypical such as clozapine, remain the current standard for schizophrenia treatment. These agents are relatively effective in treating hallucinations and delusions. However, cognitive deficits are at present essentially either persistent or exacerbated following chronic antipsychotic drug exposure. This underlines the need of new therapeutic approaches to improve cognition in treated schizophrenia patients. Our previous findings suggested that upregulation of histone deacetylase 2 (HDAC2) expression upon chronic antipsychotic treatment may lead to negative effects on cognition and cortical synaptic structure. Here we tested different phenotypes of psychosis, synaptic plasticity, cognition and antipsychotic drug action in HDAC2 conditional knockout (HDAC2-cKO) mice and controls. Conditional depletion of HDAC2 function in glutamatergic pyramidal neurons led to a protective phenotype against behavior models induced by psychedelic and dissociative drugs, such as DOI and MK801, respectively. Immunoreactivity toward synaptophysin, which labels presynaptic terminals of functional synapses, was decreased in the frontal cortex of control mice chronically treated with clozapine - an opposite effect occurred in HDAC2-cKO mice. Chronic treatment with the class I and class II HDAC inhibitor SAHA prevented via HDAC2 the disruptive effects of MK801 on recognition memory. Additionally, chronic SAHA treatment affected transcription of numerous plasticity-related genes in the frontal cortex of control mice, an effect that was not observed in HDAC2-cKO animals. Together, these findings suggest that HDAC2 may represent a novel target to improve synaptic plasticity and cognition in treated schizophrenia patients.

Juvenile stress induces behavioral change and affects perineuronal net formation in juvenile mice

Background

Many neuropsychiatric disorders develop in early life. Although the mechanisms involved have not been elucidated, it is possible that functional abnormalities of parvalbumin-positive interneurons (PV neurons) are present. Several previous studies have shown that juvenile stress is implicated in the development of neuropsychiatric disorders. We aimed to clarify the effects of juvenile stress on behavior and on the central nervous system. We investigated behavioral abnormalities of chronically-stressed mice during juvenilehood and the effect of juvenile stress on PV neurons and WFA-positive perineuronal nets (PNNs), which are associated with vulnerability and plasticity in the mouse brain.

Results

Due to juvenile stress, mice showed neurodevelopmental disorder-like behavior. Juvenile stressed mice did not show depressive-like behaviors, but on the contrary, they showed increased activity and decreased anxiety-like behavior. In the central nervous system of juvenile stressed mice, the fluorescence intensity of WFA-positive PNNs decreased, which may signify increased vulnerability.

Conclusion

This study suggested that juvenile stressed mice showed behavioral abnormalities, resembling those seen in neuropsychiatric disorders, and increased brain vulnerability.

The Impact of Perineuronal Net Digestion Using Chondroitinase ABC on the Intrinsic Physiology of Cortical Neurons

Perineuronal nets (PNNs) are a form of aggregate Extracellular Matrix (ECM) in the brain. Recent evidence suggests that the postnatal deposition of PNNs may play an active role in regulating neuroplasticity and, potentially, neurological disorders. Observations of high levels of PNN expression around somas, proximal dendrites, and axon initial segments of a subtype of neurons have also led to proposals that PNNs may modulate the intrinsic properties of the neurons they ensheathe. While high levels of PNNs are postnatally expressed throughout the neocortex, it is still unclear how they impact the neuronal physiology of the many classes and subtypes of neurons that exist. In this study, we demonstrate that Chondroitinase ABC digestion of PNNs from acute cortical slices from juvenile mice (P28-35) resulted in neuron-specific impacts on intrinsic physiology. Fast spiking (FS) interneurons showed decreased input resistance, resting membrane potential (RMP), reduced action potential (AP) peaks and altered spontaneous synaptic inputs. Low-Threshold Spiking interneurons showed altered rebound depolarizations and decreased frequency of spontaneous synaptic inputs. Putative excitatory neurons; regular spiking, bursting, and doublet phenotypes did not demonstrate any alterations. Our data indicate that chABC-sensitive PNNs may specifically regulate the intrinsic and synaptic physiology of inhibitory interneurons.

Trajectory of Parvalbumin Cell Impairment and Loss of Cortical Inhibition in Traumatic Brain Injury

Many neuropsychiatric symptoms that follow traumatic brain injury (TBI), including mood disorders, sleep disturbance, chronic pain, and posttraumatic epilepsy (PTE) are attributable to compromised cortical inhibition. However, the temporal trajectory of cortical inhibition loss and its underlying mechanisms are not known. Using paired-pulse transcranial magnetic stimulation (ppTMS) and immunohistochemistry, we tracked functional and cellular changes of cortical inhibitory network elements after fluid-percussion injury (FPI) in rats. ppTMS revealed a progressive loss of cortical inhibition as early as 2 weeks after FPI. This profile paralleled the increasing levels of cortical oxidative stress, which was accompanied by a gradual loss of parvalbumin (PV) immunoreactivity in perilesional cortex. Preceding the PV loss, we identified a degradation of the perineuronal net (PNN)-a specialized extracellular structure enwrapping cortical PV-positive (PV+) inhibitory interneurons which binds the PV+ cell maintenance factor, Otx2. The trajectory of these impairments underlies the reduced inhibitory tone, which can contribute to posttraumatic neurological conditions, such as PTE. Taken together, our results highlight the use of ppTMS as a biomarker to track the course of cortical inhibitory dysfunction post-TBI. Moreover, the neuroprotective role of PNNs on PV+ cell function suggests antioxidant treatment or Otx2 enhancement as a promising prophylaxis for post-TBI symptoms.

NMDA-receptor inhibition and oxidative stress during hippocampal maturation differentially alter parvalbumin expression and gamma-band activity

Dysfunction of parvalbumin (PV)-expressing interneurons is thought to underlie the alterations of gamma-band oscillations observed in schizophrenia. Although the pathomechanisms of this disease remain unclear, oxidative stress induced by NMDA receptor (NMDAR) hypofunction and decreased glutathione (GSH) synthesizing capacity have been shown to lead to PV-loss and aberrant oscillatory activity. However, the individual contributions of NMDAR-inhibition and GSH-depletion to the developmental alterations observed in schizophrenia are largely unknown. We therefore investigated each condition in isolation using hippocampal slice cultures wherein interneuron maturation occurs entirely in vitro. Although both treatments caused oxidative stress, NMDAR-inhibition led to an immediate reduction in gamma oscillation frequency and a delayed loss of PV. In contrast, GSH-depletion immediately decreased PV expression and increased power, without affecting frequency. Hence, although disturbances of PV-expression and gamma oscillations coexist in schizophrenia, they can arise from separate pathological processes.

Networks of blood proteins in the neuroimmunology of schizophrenia

Levels of certain circulating cytokines and related immune system molecules are consistently altered in schizophrenia and related disorders. In addition to absolute analyte levels, we sought analytes in correlation networks that could be prognostic. We analyzed baseline blood plasma samples with a Luminex platform from 72 subjects meeting criteria for a psychosis clinical high-risk syndrome; 32 subjects converted to a diagnosis of psychotic disorder within two years while 40 other subjects did not. Another comparison group included 35 unaffected subjects. Assays of 141 analytes passed early quality control. We then used an unweighted co-expression network analysis to identify highly correlated modules in each group. Overall, there was a striking loss of network complexity going from unaffected subjects to nonconverters and thence to converters (applying standard, graph-theoretic metrics). Graph differences were largely driven by proteins regulating tissue remodeling (e.g. blood-brain barrier). In more detail, certain sets of antithetical proteins were highly correlated in unaffected subjects (e.g. SERPINE1 vs MMP9), as expected in homeostasis. However, for particular protein pairs this trend was reversed in converters (e.g. SERPINE1 vs TIMP1, being synthetical inhibitors of remodeling of extracellular matrix and vasculature). Thus, some correlation signals strongly predict impending conversion to a psychotic disorder and directly suggest pharmaceutical targets.

Effects of inhaled particulate matter on the central nervous system in mice

Little is known regarding the adverse effects of chronic particulate matter (PM) inhalation on the central nervous system (CNS). The present study aimed to examine how PM exposure impacts on oxidative stress and inflammatory processes, as well as the expression of interneurons and perineuronal nets (PNNs) in the CNS. BALB/c mice (6-week-old females, n = 32) were exposed to 1 to 5 μm size diesel-extracted particles (DEPs) (100 μg/m³, 5 d/week, 5 h/day) and categorized into the following four groups: 1) 4-week DEP (n = 8); 2) 4-week control (n = 8), 3) 8-week DEP (n = 8); and 4) 8-week control (n = 8). The olfactory bulb, prefrontal cortex, temporal cortex, striatum, and cerebellum were harvested from the animals in each group. The expression of antioxidants (heme oxygenase 1 [HO-1] and superoxide dismutase 2 [SOD-2]), and markers of the unfolded protein response (X-box binding protein [XBP]-1S), inflammation (tumor necrosis factor-alpha [TNF-α]), and proliferation (neurotrophin-3 and brain-derived neurotrophic factor [BDNF]) were measured using reverse transcription polymerase chain reaction (PCR) and Western blotting. The expression levels of HO-1, SOD-2, XBP-1S, TNF-α, neurotrophin-3, and BDNF were compared among groups using the Mann-Whitney U test. The temporal cortex was immunostained for parvalbumin (PV) and Wisteria floribunda agglutinin (WFA). The numbers of PV- and WFA-positive cells were counted using a confocal microscope and analyzed with the Mann-Whitney U test. HO-1 expression was elevated in the prefrontal cortex, temporal cortex, striatum, and cerebellum of mice in the 8-week DEP group compared with the control group. Expression of SOD-2 and XBP-1S was elevated in the prefrontal cortex and striatum of the 8-week DEP group compared with the control group. TNF-α expression was elevated in the prefrontal cortex, temporal cortex, striatum, and cerebellum in the 4- and 8-week DEP groups compared with the control group. Neurotrophin-3 expression was decreased in the olfactory bulb and striatum of the 8-week DEP group compared with the control group. WFA density was increased in the 8-week DEP group compared with the control group. The PV and PV + WFA densities were decreased in the 4-week DEP group compared with the control group. Chronic DEP inhalation activated oxidative stress and inflammation in multiple brain regions. Chronic DEP inhalation increased PNNs and decreased the number of interneurons, which may contribute to PM exposure-related CNS dysfunction.

Expression of aggrecan components in perineuronal nets in the mouse cerebral cortex

Specific regions of the cerebral cortex are highly plastic in an organism's lifetime. It is thought that perineuronal nets (PNNs) regulate plasticity, but labeling for Wisteria floribunda agglutinin (WFA), which is widely used to detect PNNs, is observed throughout the cortex. The aggrecan molecule-a PNN component-may regulate plasticity, and may also be involved in determining region-specific vulnerability to stress. To clarify cortical region-specific plasticity and vulnerability, we qualitatively analyzed aggrecan-positive and glycosylated aggrecan-positive PNNs in the mature mouse cerebral cortex. Our findings revealed the selective expression of both aggrecan-positive and glycosylated aggrecan-positive PNNs in the cortex. WFA-positive PNNs expressed aggrecan in a region-specific manner in the cortex. Furthermore, we observed variable distributions of PNNs containing WFA- and aggrecan-positive molecules. Together, our findings suggest that PNN components and their function differ depending on the cortical region, and that aggrecan molecules may be involved in determining region-specific plasticity and vulnerability in the cortex.

Brain stimulation patterns emulating endogenous thalamocortical input to parvalbumin-expressing interneurons reduce nociception in mice

BACKGROUND

The bursting pattern of thalamocortical (TC) pathway dampens nociception. Whether brain stimulation mimicking endogenous patterns can engage similar sensory gating processes in the cortex and reduce nociceptive behaviors remains uninvestigated.

OBJECTIVE

We investigated the role of cortical parvalbumin expressing (PV) interneurons within the TC circuit in gating nociception and their selective response to TC burst patterns. We then tested if transcranial magnetic stimulation (TMS) patterned on endogenous nociceptive TC bursting modulate nociceptive behaviors.

METHODS

The switching of TC neurons between tonic (single spike) and burst (high frequency spikes) firing modes may be a critical component in modulating nociceptive signals. Deep brain electrical stimulation of TC neurons and immunohistochemistry were used to examine the differential influence of each firing mode on cortical PV interneuron activity. Optogenetic stimulation of cortical PV interneurons assessed a direct role in nociceptive modulation. A new TMS protocol mimicking thalamic burst firing patterns, contrasted with conventional continuous and intermittent theta burst protocols, tested if TMS patterned on endogenous TC activity reduces nociceptive behaviors in mice.

RESULTS

Immunohistochemical evidence confirmed that burst, but not tonic, deep brain stimulation of TC neurons increased the activity of PV interneurons in the cortex. Both optogenetic activation of PV interneurons and TMS protocol mimicking thalamic burst reduced nociceptive behaviors.

CONCLUSIONS

Our findings suggest that burst firing of TC neurons recruits PV interneurons in the cortex to reduce nociceptive behaviors and that neuromodulation mimicking thalamic burst firing may be useful for modulating nociception.

Dominant-Negative DISC1 Alters the Dopaminergic Modulation of Inhibitory Interneurons in the Mouse Prefrontal Cortex

A truncated disrupted in schizophrenia 1 (Disc1) gene increases the risk of psychiatric disorders, probably affecting cortical interneurons. Here, we sought to determine whether this cell population is affected in mice carrying a truncated (Disc1) allele (DN-DISC1). We utilized whole cell recordings to assess electrophysiological properties and modulation by dopamine (DA) in two classes of interneurons: fast-spiking (FS) and low threshold-spiking (LTS) interneurons in wild-type and DN-DISC1 mice. In DN-DISC1 mice, FS interneurons, but not LTS interneurons, exhibited altered action potentials. Further, the perineuronal nets that surround FS interneurons exhibited abnormal morphology in DN-DISC1 mice, and the DA modulation of this cell type was altered in DN-DISC1 mice. We conclude that early-life manipulation of a gene associated with risk of psychiatric disease can result in dysfunction, but not loss, of specific GABAergic interneurons. The resulting alteration of excitatory-inhibitory balance is a critical element in DISC1 pathophysiology.

Parvalbumin promoter hypermethylation in postmortem brain in schizophrenia

Deficits of brain parvalbumin (PV) are a consistent finding in schizophrenia and models of psychosis. We investigated whether this is associated with abnormal PV gene (PVALB) methylation in the brain in schizophrenia. Bisulfite pyrosequencing was used to determine cytosine (CpG) methylation in a PVALB promoter sequence. Greater PVALB methylation was found in schizophrenia hippocampus, while no differences were observed in prefrontal cortex. LINE-1 methylation, a measure of global methylation, was also elevated in both regions in schizophrenia, although the PVALB change was independent of this effect. These results provide the first evidence that PVALB promoter methylation is abnormal in schizophrenia and suggest that this epigenetic finding may relate to the reduction of PV expression seen in the disease.

Consumption of a High-Fat Diet Alters Perineuronal Nets in the Prefrontal Cortex

A key factor in the development of obesity is the overconsumption of fatty foods, which, in addition to facilitating weight gain, alters neuronal structures within brain reward circuitry. Our previous work demonstrates that sustained consumption of a high-fat diet (HFD) attenuates spine density in the prefrontal cortex (PFC). Whether HFD promotes structural adaptation among inhibitory cells of the PFC is presently unknown. One structure of interest is the perineuronal net (PNN), a specialized extracellular matrix surrounding, primarily, parvalbumin-containing GABAergic interneurons. PNNs contribute to synaptic stabilization, protect against oxidative stress, regulate the ionic microenvironment within cells, and modulate regional excitatory output. To examine diet-induced changes in PNNs, we maintained rats on one of three dietary conditions for 21 days: ad libitum chow, ad libitum 60% high fat (HF-AL), or limited-access calorically matched high fat (HF-CM), which produced no significant change in weight gain or adiposity with respect to chow controls. The PNN “number” and intensity were then quantified in the prelimbic (PL-PFC), infralimbic (IL-PFC), and ventral orbitofrontal cortex (OFC) using Wisteria floribunda agglutinin (WFA). Our results demonstrated that fat exposure, independent of weight gain, induced a robust decrease in the PNN intensity in the PL-PFC and OFC and a decrease in the PNN number in the OFC.

Perineuronal Nets in Spinal Motoneurones: Chondroitin Sulphate Proteoglycan around Alpha Motoneurones

Perineuronal nets (PNNs) are extracellular matrix structures surrounding neuronal sub-populations throughout the central nervous system, regulating plasticity. Enzymatically removing PNNs successfully enhances plasticity and thus functional recovery, particularly in spinal cord injury models. While PNNs within various brain regions are well studied, much of the composition and associated populations in the spinal cord is yet unknown. We aim to investigate the populations of PNN neurones involved in this functional motor recovery. Immunohistochemistry for choline acetyltransferase (labelling motoneurones), PNNs using Wisteria floribunda agglutinin (WFA) and chondroitin sulphate proteoglycans (CSPGs), including aggrecan, was performed to characterise the molecular heterogeneity of PNNs in rat spinal motoneurones (Mns). CSPG-positive PNNs surrounded ~70–80% of Mns. Using WFA, only ~60% of the CSPG-positive PNNs co-localised with WFA in the spinal Mns, while ~15–30% of Mns showed CSPG-positive but WFA-negative PNNs. Selective labelling revealed that aggrecan encircled ~90% of alpha Mns. The results indicate that (1) aggrecan labels spinal PNNs better than WFA, and (2) there are differences in PNN composition and their associated neuronal populations between the spinal cord and cortex. Insights into the role of PNNs and their molecular heterogeneity in the spinal motor pools could aid in designing targeted strategies to enhance functional recovery post-injury.