The impact of maternal immune activation on GABAergic interneuron development: A systematic review of rodent studies and their translational implications

Mothers exposed to infections during pregnancy disproportionally birth children who develop autism and schizophrenia, disorders associated with altered GABAergic function. The maternal immune activation (MIA) model recapitulates this risk factor, with many studies also reporting disruptions to GABAergic interneuron expression, protein, cellular density and function. However, it is unclear if there are species, sex, age, region, or GABAergic subtype specific vulnerabilities to MIA. Furthermore, to fully comprehend the impact of MIA on the GABAergic system a synthesised account of molecular, cellular, electrophysiological and behavioural findings was required. To this end we conducted a systematic review of GABAergic interneuron changes in the MIA model, focusing on the prefrontal cortex and hippocampus. We reviewed 102 articles that revealed robust changes in a number of GABAergic markers that present as gestationally-specific, region-specific and sometimes sex-specific. Disruptions to GABAergic markers coincided with distinct behavioural phenotypes, including memory, sensorimotor gating, anxiety, and sociability. Findings suggest the MIA model is a valid tool for testing novel therapeutics designed to recover GABAergic function and associated behaviour.

Characterisation and automated quantification of induced seizure-related behaviours in Xenopus laevis tadpoles

Epilepsy, a clinical diagnosis characterized by paroxysmal episodes known as seizures, affects 1% of people worldwide. Safe and patient-specific treatment is vital and can be achieved by the development of rapid pre-clinical models of for identified epilepsy genes. Epilepsy can result from either brain injury or gene mutations, and can also be induced chemically. Xenopus laevis tadpoles could be a useful model for confirmation of variants of unknown significance found in epilepsy patients, and for drug re-purposing screens that could eventually lead to benefits for patients. Here, we characterise and quantify seizure-related behaviours in X. laevis tadpoles arrayed in 24-well plates. To provoke acute seizure behaviours, tadpoles were chemically induced with either pentylenetetrazole (PTZ) or 4-aminopyridine (4-AP). To test the capacity to adapt this method for drug testing, we also exposed induced tadpoles to the anti-seizure drug valproate (VPA). Four induced seizure-like behaviours were described and manually quantified, and two of these (darting, circling) could be accurately detected automatically, using the video analysis software TopScan. Additionally, we recorded swimming trajectories and mean swimming velocity. Automatic detection showed that either PTZ or 4-AP induced darting behaviour and increased mean swimming velocity compared to untreated controls. Both parameters were significantly reduced in the presence of VPA. In particular, darting behaviour was a shown to be a sensitive measure of epileptic seizure activity. While we could not automatically detect the full range of seizure behaviours, this method shows promise for future studies, since X. laevis is a well-characterised and genetically tractable model organism.

Animal Models of Neurological Disorders: Where Are We Now?

The Special Issue "Animal Models of Neurological Disorders: Where Are We Now [...].

Impact of Dysfunctional Feed-Forward Inhibition on Glutamate Decarboxylase Isoforms and γ-Aminobutyric Acid Transporters

Absence seizures are associated with generalised synchronous 2.5–4 Hz spike-wave discharges causing brief and sudden alteration of awareness during childhood, which is known as childhood absence epilepsy (CAE). CAE is also associated with impaired learning, psychosocial challenges, and physical danger. Absence seizures arise from disturbances within the cortico-thalamocortical (CTC) network, including dysfunctional feed-forward inhibition (FFI); however, the precise mechanisms remain unclear. In epileptic stargazers, a genetic mouse model of CAE with chronic seizures, levels of γ-aminobutyric acid (GABA), and expression of GABA receptors are altered within the CTC network, implicating altered GABAergic transmission in absence seizures. However, the expression of GABA synthesising enzymes (GAD65 and GAD67) and GABA transporters (GAT-1 and 3) have not yet been characterised within absence seizure models. We found a specific upregulation of GAD65 in the somatosensory cortex but not the thalamus of epileptic stargazer mice. No differences were detected in GAD67 and GAT-3 levels in the thalamus or somatosensory cortex. Then, we assessed if GAD65 upregulation also occurred in Gi-DREADD mice exhibiting acute absence seizures, but we found no change in the expression profiles of GAD65/67 or GAT-3. Thus, the upregulation of GAD65 in stargazers may be a compensatory mechanism in response to long-term dysfunctional FFI and chronic absence seizures.

Chemogenetic Activation of Feed-Forward Inhibitory Parvalbumin-Expressing Interneurons in the Cortico-Thalamocortical Network During Absence Seizures

Parvalbumin-expressing (PV+) interneurons are a subset of GABAergic inhibitory interneurons that mediate feed-forward inhibition (FFI) within the cortico-thalamocortical (CTC) network of the brain. The CTC network is a reciprocal loop with connections between cortex and thalamus. FFI PV+ interneurons control the firing of principal excitatory neurons within the CTC network and prevent runaway excitation. Studies have shown that generalized spike-wave discharges (SWDs), the hallmark of absence seizures on electroencephalogram (EEG), originate within the CTC network. In the stargazer mouse model of absence epilepsy, reduced FFI is believed to contribute to absence seizure genesis as there is a specific loss of excitatory α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) at synaptic inputs to PV+ interneurons within the CTC network. However, the degree to which this deficit is directly related to seizure generation has not yet been established. Using chemogenetics and in vivo EEG recording, we recently demonstrated that functional silencing of PV+ interneurons in either the somatosensory cortex (SScortex) or the reticular thalamic nucleus (RTN) is sufficient to generate absence-SWDs. Here, we used the same approach to assess whether activating PV+ FFI interneurons within the CTC network during absence seizures would prevent or reduce seizures. To target these interneurons, mice expressing Cre recombinase in PV+ interneurons (PV-Cre) were bred with mice expressing excitatory Gq-DREADD (hM3Dq-flox) receptors. An intraperitoneal dose of pro-epileptic chemical pentylenetetrazol (PTZ) was used to induce absence seizure. The impact of activation of FFI PV+ interneurons during seizures was tested by focal injection of the “designer drug” clozapine N-oxide (CNO) into either the SScortex or the RTN thalamus. Seizures were assessed in PV^Cre/Gq-DREADD animals using EEG/video recordings. Overall, DREADD-mediated activation of PV+ interneurons provided anti-epileptic effects against PTZ-induced seizures. CNO activation of FFI either prevented PTZ-induced absence seizures or suppressed their severity. Furthermore, PTZ-induced tonic-clonic seizures were also reduced in severity by activation of FFI PV+ interneurons. In contrast, administration of CNO to non-DREADD wild-type control animals did not afford any protection against PTZ-induced seizures. These data demonstrate that FFI PV+ interneurons within CTC microcircuits could be a potential therapeutic target for anti-absence seizure treatment in some patients.

Neurological Manifestations of COVID-19 Associated Multi-system Inflammatory Syndrome in Children: A Systematic Review and Meta-analysis

BACKGROUND

Children comprise only 1-5% of COVID-19 cases. Recent studies have shown that COVID-19 associated multisystem inflammatory syndrome in children (MIS-C) can present with neurological signs and symptoms. In this systematic review and meta-analysis, we have reviewed neurological involvement in these patients.

METHODS

A comprehensive electronic literature search was done on PubMed, Google Scholar, Embase, Cochrane database, and SCOPUS for the published English language articles from December 1, 2019, to February 28, 2021. A meta-analysis of the proportion was expressed as a pooled proportion with a 95% confidence interval (CI). Representative forest plots showing individual studies and the combined effect size were generated to provide an overview of the results.

RESULTS

This systematic review and meta-analysis analyzed 15 published MIS-C studies with a total of 785 patients. Neurological manifestations in patients with MIS-C was found in 27.1%. We found that 27% developed headaches, 17.1% developed meningism/meningitis and 7.6 % developed encephalopathy. Other uncommon neurological manifestations of MIS-C includes anosmia, seizures, cerebellar ataxia, global proximal muscle weakness and bulbar palsy. In MIS-C patients with neurological feature, neuroimaging showed signal changes in the splenium of the corpus callosum. Electroencephalography showed slow wave pattern and nerve conduction studies and electromyography showed mild myopathic and neuropathic changes.

CONCLUSIONS

Our study revealed that neurological manifestations are not uncommon in patients with MIS-C. Further large prospective studies are needed to better explore the disease spectrum and to unravel the underlying pathophysiology.

The impact of silencing feed-forward parvalbumin-expressing inhibitory interneurons in the cortico-thalamocortical network on seizure generation and behaviour

Feed-forward inhibition (FFI) is an essential mechanism within the brain, to regulate neuronal firing and prevent runaway excitation. In the cortico-thalamocortical (CTC) network, fast spiking parvalbumin-expressing (PV+) inhibitory interneurons regulate the firing of pyramidal cells in the cortex and relay neurons in the thalamus. PV+ interneuron dysfunction has been implicated in several neurological disorders, including epilepsy. Previously, we demonstrated that loss of excitatory AMPA-receptors, specifically at synapses on PV+ interneurons in CTC feedforward microcircuits, occurs in the stargazer mouse model of absence epilepsy. These mice present with absence seizures characterized by spike and wave discharges (SWDs) on electroencephalogram (EEG) and concomitant behavioural arrest, similar to childhood absence epilepsy. The aim of the current study was to investigate the impact of loss of FFI within the CTC on absence seizure generation and behaviour using new Designer Receptor Exclusively Activated by Designer Drug (DREADD) technology. We crossed PV-Cre mice with Cre-dependent hM4Di DREADD strains of mice, which allowed Cre-recombinase-mediated restricted expression of inhibitory G_i-DREADDs in PV+ interneurons. We then tested the impact of global and focal (within the CTC network) silencing of PV+ interneurons. CNO mediated silencing of all PV+ interneurons by intraperitoneal injection caused the impairment of motor control, decreased locomotion and increased anxiety in a dose-dependent manner. Such silencing generated pathological oscillations similar to absence-like seizures. Focal silencing of PV+ interneurons within cortical or thalamic feedforward microcircuits, induced SWD-like oscillations and associated behavioural arrest. Epileptiform activity on EEG appeared significantly sooner after focal injection compared to peripheral injection of CNO. However, the mean duration of each oscillatory burst and spike frequency was similar, irrespective of mode of CNO delivery. No significant changes were observed in vehicle-treated or non-DREADD wild-type control animals. These data suggest that dysfunctional feed-forward inhibition in CTC microcircuits may be an important target for future therapy strategies for some patients with absence seizures. Additionally, silencing of PV+ interneurons in other brain regions may contribute to anxiety related neurological and psychiatric disorders.

Hydrogen sulfide, nitric oxide, and neurodegenerative disorders

Hydrogen Sulfide (H2S) and Nitric Oxide (NO) have become recognized as important gaseous signaling molecules with enormous pharmacological effects, therapeutic value, and central physiological roles. NO is one of the most important regulators of the pathophysiological condition in central nervous system (CNS). It is critical in the various functioning of the brain; however, beyond certain concentration/level, it is toxic. H2S was regarded as toxic gas with the smell like rotten egg. But, it is now regarded as emerging neuroprotectant and neuromodulator. Recently, the use of donors and inhibitors of these signaling molecules have helped us to identify their accurate and precise biological effects. The most abundant neurotransmitter of CNS (glutamate) is the initiator of the reaction that forms NO, and H2S is highly expressed in brain. These molecules are shedding light on the pathogenesis of various neurological disorders. This review is mainly focused on the importance of H2S and NO for normal functioning of CNS.

Roles of nitric oxide and ethyl pyruvate after peripheral nerve injury

Short-lived reactive nitrogen species and reactive oxygen species have acquired significant attention in the field of biomedical science. Nitric oxide (NO), which was thought to be an unstable gas and pollutant, is now regarded as a gas transmitter like H2S and CO. NO is synthesized inside the mammalian body by l-arginine via three different isoforms of NO synthase whereas pyruvate is a glycolysis product and substrate for TCA cycle. Due to poor solubility and stability, therapeutic potential of pyruvate is limited. Ethyl pyruvate (EP) is now considered as a suitable replacement of pyruvate. In this paper, we will try to focus the effect of NO and EP in Schwann cell dedifferentiation, proliferation, nerve degeneration, and regeneration during Wallerian degeneration (WD) of peripheral nerve injury along with their neuroprotective effects, cardiovascular functioning, support in hepatic complication, etc.

Anatomical distributional defects in mutant genes associated with dominant intermediate Charcot-Marie-Tooth disease type C in an adenovirus-mediated mouse model

Dominant intermediate Charcot-Marie-Tooth disease type C (DI-CMTC) is a dominantly inherited neuropathy that has been classified primarily based on motor conduction velocity tests but is now known to involve axonal and demyelination features. DI-CMTC is linked to tyrosyl-tRNA synthetase (YARS)-associated neuropathies, which are caused by E196K and G41R missense mutations and a single de novo deletion (153-156delVKQV). It is well-established that these YARS mutations induce neuronal dysfunction, morphological symptoms involving axonal degeneration, and impaired motor performance. The present study is the first to describe a novel mouse model of YARS-mutation-induced neuropathy involving a neuron-specific promoter with a deleted mitochondrial targeting sequence that inhibits the expression of YARS protein in the mitochondria. An adenovirus vector system and in vivo techniques were utilized to express YARS fusion proteins with a Flag-tag in the spinal cord, peripheral axons, and dorsal root ganglia. Following transfection of YARS-expressing viruses, the distributions of wild-type (WT) YARS and E196K mutant proteins were compared in all expressed regions; G41R was not expressed. The proportion of Flag/green fluorescent protein (GFP) double-positive signaling in the E196K mutant-type mice did not significantly differ from that of WT mice in dorsal root ganglion neurons. All adenovirus genes, and even the empty vector without the YARS gene, exhibited GFP-positive signaling in the ventral horn of the spinal cord because GFP in an adenovirus vector is driven by a cytomegalovirus promoter. The present study demonstrated that anatomical differences in tissue can lead to dissimilar expressions of YARS genes. Thus, use of this novel animal model will provide data regarding distributional defects between mutant and WT genes in neurons, the DI-CMTC phenotype, and potential treatment approaches for this disease.

Physiological Importance of Hydrogen Sulfide: Emerging Potent Neuroprotector and Neuromodulator

Hydrogen sulfide (H2S) is an emerging neuromodulator that is considered to be a gasotransmitter similar to nitrogen oxide (NO) and carbon monoxide (CO). H2S exerts universal cytoprotective effects and acts as a defense mechanism in organisms ranging from bacteria to mammals. It is produced by the enzymes cystathionine β-synthase (CBS), cystathionine ϒ-lyase (CSE), 3-mercaptopyruvate sulfurtransferase (MST), and D-amino acid oxidase (DAO), which are also involved in tissue-specific biochemical pathways for H2S production in the human body. H2S exerts a wide range of pathological and physiological functions in the human body, from endocrine system and cellular longevity to hepatic protection and kidney function. Previous studies have shown that H2S plays important roles in peripheral nerve regeneration and degeneration and has significant value during Schwann cell dedifferentiation and proliferation but it is also associated with axonal degradation and the remyelination of Schwann cells. To date, physiological and toxic levels of H2S in the human body remain unclear and most of the mechanisms of action underlying the effects of H2S have yet to be fully elucidated. The primary purpose of this review was to provide an overview of the role of H2S in the human body and to describe its beneficial effects.

Outcome of Both Bone Forearm Fracture Fixation in Children by Rush Nails

INTRODUCTION

Forearm fractures are common upper limb injuries among children and usually treated non-operatively. Failure of non-operative treatment, open injuries and multiple fractures are the indications for surgery in paediatric both bone forearm fractures. Intramedullary nailing is considered as minimally invasive procedure with excellent to fair outcomes but it is not free of complications. We reviewed the results and evaluated the outcomes of IM fixation of forearm fractures in children by Rush nails to understand the risks and complications associated with these procedures.

METHODS

A retrospective crossectional study of all paediatric patients treated for diaphyseal forearm fractures for period of five years in a tertiary care setup. Complications were classified according to modified Clavien-Dindo complication classification system. Outcomes were graded depending upon complication grade along with range of motion of forearm.

RESULTS

A total of 25 patients were included in the study. Mean time for fracture union was 10.56 weeks. Outcomes were excellent in 16 (64%), good in 7 (28%), fair in 2 (8%) patients and no poor outcome was noted. Ten minor complications were seen.

CONCLUSION

Fixation of paediatric forearm fractures by intramedullary Rush nail is minimally invasive procedure and outcomes are excellent to fair with acceptable complication rates.