An investigation into dysfunctional feed-forward inhibition within the cortico-thalamocortical network on absence seizure generation using DREADD technology

Childhood absence epilepsy (CAE) is one of the most prevalent paediatric epilepsies, accounting for between 10-17% of all diagnosed cases of epilepsies seen in school-aged children. Absence seizures are characterized by behavioural arrest/loss of awareness and electrographic signature of spike-wave discharges (SWDs) measuring 2.5-4 Hz on an electroencephalogram (EEG). These brief episodes of impaired consciousness can occur hundreds of times a day and might increase the chance of physical injury when undertaking activities like swimming and cycling. Current treatment options are not sufficient and up to 30% of patients are pharmaco-resistant. ~60% of children with CAE have severe neuropsychiatric comorbid conditions including attention deficits, mood disorders, impairments in memory and cognition. Ethosuximide (ETX), an anti-absence epileptic drug which was first introduced almost six decades ago remains the first choice for initial monotherapy for the treatment of CAE. Large-scale clinical trials suggested that efficacy of ethosuximide is considerably lower than previous findings. Thus, safe, effective and patient specific treatment approach is imperative. For this, it is crucial first to understand the precise cellular and molecular mechanisms of absence seizures which may enable the development of novel therapeutic targets and discovery of new anti-epileptic drugs (AEDs). EEG and functional imaging evidence suggest that absence seizures are likely due to aberrant activity within the cortico-thalamocortical (CTC) network. Studies involving the genetic rodent models have shown that the cortex is the driving source for the origin of SWDs but is not capable of maintaining discharges on its own, nor is the thalamus. General consensus is that, within the CTC network, a cortical focus initiates rhythmic epileptic discharges, however, once the rhythmic oscillations are established, both the cortex and thalamus form an integrated network. Rhythmic absence-SWDs are sustained via the cortex and thalamus driving each other. Within the CTC network, feed-forward inhibition (FFI) is essential to prevent runaway excitation. FFI is mediated by fast spiking parvalbumin expressing (PV+) inhibitory interneurons in the somatosensory cortex (SScortex) and the reticular thalamic nucleus (RTN). Studies conducted in well-established stargazer mouse model of absence epilepsy with a genetic deficit in stargazin i.e. TARP [a transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor regulatory protein] have shown reduced expression of GluA4-AMPARs at excitatory synapses in feed-forward inhibitory (PV+) interneurons in the SScortex and RTN thalamus of the CTC network. However, the extent of this deficit in AMPARs expression impacting FFI and possibly contributing towards generation of absence-SWDs is not established via functional studies. Hence, this thesis was aimed at investigating the impact of dysfunctional feed-forward inhibitory PV+ interneurons within CTC network on absence seizure generation and behaviour. For this purpose, inhibitory and excitatory Designer Receptors Exclusively Activated by Designer Drug (DREADD) approach was utilized to silence/excite feed-forward inhibitory PV+ interneurons within the CTC network. DREADD mediated regional silencing of PV+ interneurons within the CTC network generated ETX-sensitive absence-like SWDs. Activating PV+ interneurons either prevented or suppressed pentylenetetrazole (PTZ)-induced absence-SWDs. Finally, impact of impaired FFI in γ-aminobutyric acid (GABA) levels by affecting its synthesizing enzymes (GADs) and transporter proteins (GATs) in stargazer animal model of absence epilepsy and CNO treated inhibitory Gi-DREADD animals was determined. Results indicate that upregulation of GAD65 in the SScortex of epileptic stargazers may be a consequence of absence seizures or this may have contribution in absence seizure generation. The work presented in this thesis provide an electrophysiological insight into the possible mechanism underlying the absence seizure generation. This work provides convincing evidence that dysfunctional feed-forward inhibitory PV+ interneurons within the CTC network is likely to be involved in altered excitation/inhibition balance resulting SWDs as activating these interneurons dramatically protected animals from PTZ induced absence seizures. The clinical relevance of this study is that it potentially uncovers the possibility of focally targeting PV+ interneurons within the CTC network to control absence seizures in human patients

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 cystathionineβ-synthase (CBS), cystathionineϒ-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.</jats:p

Phenotypic Correlation, Path Analysis, and Quantitative Trait-Based Selection of Elite Wheat Genotypes Under Heat Stress Conditions in The Terai Region of Nepal

Wheat is one of the most important cereal crops worldwide, but the production and productivity of wheat is affected by heat stress. A field experiment using an alpha lattice design with seven blocks was conducted on 35 elite wheat genotypes in the Terai region of Nepal to identify the most appropriate trait resulting in a high-yielding wheat genotype with high tolerance to heat stress. Correlation analysis revealed that booting-to-heading duration (BtoH), booting-to-anthesis duration (BtoA), plant height (Ph), spike length (SL), spike weight (SW), thousand grain weight (TGW), straw yield (SY), and total biomass yield (TY) had a significant positive correlation with grain yield (GY), whereas days to booting (DTB), days to heading (DTH), and days to anthesis (DTA) had significant negative correlations with GY (p ≤ 0.05). Path analysis revealed that DTB and DTA had a direct negative effect on the GY, whereas DTH had an indirect negative effect on yield via DTB. BtoA, Ph, SL, SW, and TGW had direct positive effects on yield, whereas BtoH had an indirect positive effect on yield via DTB. Principal component analysis demonstrated that high-yielding genotypes can be selected using DTB, DTH, DTA, BtoH, BtoA, and Ph. Taller and earlier genotype with long BtoH and BtoA would produce high yield under heat stress

Animal Models of Neurological Disorders: Where Are We Now?

The Special Issue &ldquo;Animal Models of Neurological Disorders: Where Are We Now [...

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 PVCre/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.</jats:p

Roles of nitric oxide and ethyl pyruvate after peripheral nerve injury

Abstract 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

Hydrogen sulfide, nitric oxide, and neurodegenerative disorders

Abstract 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

Correction to: Roles of nitric oxide and ethyl pyruvate after peripheral nerve injury

After publication of the original article [1], it came to our attention that Professor Junyang Jung was omitted from the authorship