Expression of GABA receptor subunits in the hippocampus and thalamus after experimental traumatic brain injury

Traumatic Brain Injury: A Comprehensive Review of Biomechanics and Molecular Pathophysiology

Traumatic brain injury (TBI) is a critical public health concern with profound consequences for affected individuals. This comprehensive literature review delves into TBI intricacies, encompassing primary injury biomechanics and the molecular pathophysiology of the secondary injury cascade. Primary TBI involves a complex interplay of forces, including impact loading, blast overpressure, and impulsive loading, leading to diverse injury patterns. These forces can be categorized into inertial (e.g., rotational acceleration causing focal and diffuse injuries) and contact forces (primarily causing focal injuries like skull fractures). Understanding their interactions is crucial for effective injury management. The secondary injury cascade in TBI comprises multifaceted molecular and cellular responses, including altered ion concentrations, dysfunctional neurotransmitter networks, oxidative stress, and cellular energy disturbances. These disruptions impair synaptic function, neurotransmission, and neuroplasticity, resulting in cognitive and behavioral deficits. Moreover, neuroinflammatory responses play a pivotal role in exacerbating damage. As we endeavor to bridge the knowledge gap between biomechanics and molecular pathophysiology, further research is imperative to unravel the nuanced interplay between mechanical forces and their consequences at the molecular and cellular levels, ultimately guiding the development of targeted therapeutic strategies to mitigate the debilitating effects of TBI. In this study, we aim to provide a concise review of the bridge between biomechanical processes causing primary injury and the ensuing molecular pathophysiology of secondary injury, while detailing the subsequent clinical course for this patient population. This knowledge is crucial for advancing our understanding of TBI and developing effective interventions to improve outcomes for those affected.

Extension domain of amyloid processor protein inhibits amyloidogenic cleavage and balances neural activity in a traumatic brain injury mouse model

BACKGROUND

Mechanisms underlying cognitive dysfunction following traumatic brain injury (TBI) partially due to abnormal amyloid processor protein (APP) cleavage and neural hyperactivity. Binding of the extension domain of APP (ExD17) to the GABAbR1 receptor results in reduced neural activity, which might play a role in the mechanisms of cognitive dysfunction caused by TBI.

METHODS

Stretch-induced injury was utilized to establish a cell injury model in HT22 cells. The TBI model was created by striking the exposed brain tissue with a free-falling weight. Topical or intraperitoneal administration of ExD17 was performed. Cell viability was assessed through a cell counting kit-8 assay, while intracellular Ca2+ was measured using Fluo-4. Western blotting was used to investigate the expression of APP amyloidogenic cleavage proteins, GABAbR1, phospholipase C (PLC), PLCB3, and synaptic proteins. ELISA was performed to analyze the levels of Aβ42. Seizures were assessed using electroencephalography (EEG). Behaviors were evaluated through the novel object recognition test, open field test, elevated plus maze test, and nest-building test.

RESULTS

ExD17 improved cell viability and reduced intracellular calcium in the cell injury model. The treatment also suppressed the increased expression of APP amyloidogenic cleavage proteins and Aβ42 in both cell injury and TBI models. ExD17 treatment reversed the abnormal expression of GABAbR1, GRIA2, p-PLCG1/PLCG1 ratio, and p-PLCB3/PLCB3 ratio. In addition, ExD17 treatment reduced neural activity, seizure events, and their duration in TBI. Intraperitoneal injection of ExD17 improved behavioral outcomes in the TBI mouse model.

CONCLUSIONS

ExD17 treatment results in a reduction of amyloidogenic APP cleavage and neuroexcitotoxicity, ultimately leading to an improvement in the behavioral deficits observed in TBI mice.

The Rehabilitation Potential of Neurostimulation for Mild Traumatic Brain Injury in Animal and Human Studies

Neurostimulation carries high therapeutic potential, accompanied by an excellent safety profile. In this review, we argue that an arena in which these tools could provide breakthrough benefits is traumatic brain injury (TBI). TBI is a major health problem worldwide, with the majority of cases identified as mild TBI (mTBI). MTBI is of concern because it is a modifiable risk factor for dementia. A major challenge in studying mTBI is its inherent heterogeneity across a large feature space (e.g., etiology, age of injury, sex, treatment, initial health status, etc.). Parallel lines of research in human and rodent mTBI can be collated to take advantage of the full suite of neuroscience tools, from neuroimaging (electroencephalography: EEG; functional magnetic resonance imaging: fMRI; diffusion tensor imaging: DTI) to biochemical assays. Despite these attractive components and the need for effective treatments, there are at least two major challenges to implementation. First, there is insufficient understanding of how neurostimulation alters neural mechanisms. Second, there is insufficient understanding of how mTBI alters neural function. The goal of this review is to assemble interrelated but disparate areas of research to identify important gaps in knowledge impeding the implementation of neurostimulation.

Identification of miRNA-mRNA regulatory network associated with the glutamatergic system in post-traumatic epilepsy rats

Background

Glutamate is one of the most important excitatory neurotransmitters in the mammalian brain and is involved in a variety of neurological disorders. Increasing evidence also shows that microRNA (miRNA) and mRNA pairs are engaged in a variety of pathophysiological processes. However, the miRNA and mRNA pairs that affect the glutamatergic system in post-traumatic epilepsy (PTE) remain unknown.

Methods

PTE rats were induced by injecting 0.1 mol/L, 1 μL/min FeCl₂ solution. Behavioral scores and EEG monitoring were used to evaluate whether PTE was successfully induced. RNA-seq was used to obtain mRNA and miRNA expression profiles. Bioinformatics analysis was performed to screen differentially expressed mRNAs and miRNAs associated with the glutamatergic system and then predict miRNA-mRNA interaction pairs. Real-time quantitative reverse transcription PCR was used to further validate the expression of the differential miRNAs and mRNAs. The microRNA-mRNA was subject to the Pearson correlation analysis.

Results

Eight of the 91 differentially expressed mRNAs were associated with the glutamatergic system, of which six were upregulated and two were downregulated. Forty miRNAs were significantly differentially expressed, with 14 upregulated and 26 downregulated genes. The predicted miRNA-mRNA interaction network shows that five of the eight differentially expressed mRNAs associated with the glutamatergic system were targeted by multiple miRNAs, including Slc17a6, Mef2c, Fyn, Slc25a22, and Shank2, while the remaining three mRNAs were not targeted by any miRNAs. Of the 40 differentially expressed miRNAs, seven miRNAs were found to have multiple target mRNAs associated with the glutamatergic system. Real-time quantitative reverse transcription PCR validation and Pearson correlation analysis were performed on these seven targeted miRNAs-Slc17a6, Mef2c, Fyn, Slc25a22, and Shank2-and six additional miRNAs selected from the literature. Real-time quantitative reverse transcription PCR showed that the expression levels of the mRNAs and miRNAs agreed with the predictions in the study. Among them, the miR-98-5p-Slc17a6, miR-335-5p-Slc17a6, miR-30e-5p-Slc17a6, miR-1224-Slc25a22, and miR-211-5p-Slc25a22 pairs were verified to have negative correlations.

Conclusions

Our results indicate that miRNA-mRNA interaction pairs associated with the glutamatergic system are involved in the development of PTE and have potential as diagnostic biomarkers and therapeutic targets for PTE.

Macromolecular-Suppressed GABA-Edited MR Spectroscopy in the Posterior Cingulate Cortex of Patients With Acute Mild Traumatic Brain Injury

BACKGROUND

Mild traumatic brain injury (mTBI) causes a number of molecular and cellular alterations. There is evidence of an imbalance between the main excitatory (glutamate, Glu) and the main inhibitory (gamma-aminobutyric acid [GABA]) neurotransmitters following mTBI. In vivo human GABA-Glu balance studies following mTBI are sparse.

PURPOSE

To investigate the effect of acute mTBI on the GABA concentration measured in the posterior cingulate cortex (PCC) of pediatric patients by using the macromolecular (MM)-suppressed GABA J-editing technique.

STUDY TYPE

Prospective patient and phantom.

PARTICIPANTS

A total of 14 pediatric patients (mean age 16.0 ± 1.7) with acute mTBI (<3 days after trauma; Glasgow Coma Scale 15) and 16 healthy volunteers (mean age 16.9 ± 2.8). Phantom: 524 cm³ sphere containing 10 mM glycine, 10 mM GABA.

FIELD STRENGTH/SEQUENCE

A 3 T, MEGA-PRESS pulse sequence.

ASSESSMENT

GABA spectra were processed in Gannet software. MM-suppressed GABA editing efficiency was derived from the phantom study. Absolute GABA and glutamate + glutamine (Glx) concentrations were quantified using different types of correction and compared between groups. N-acetyl aspartate (NAA) and choline (Cho) levels relative to tCr were also compared.

STATISTICAL TESTS

Shapiro-Wilk test, Mann-Whitney U test, Student t-test, Pearson or Spearman correlations. P < 0.01 was considered statistically significant.

RESULTS

The MM-suppressed GABA editing efficiency was 0.63. GABA signal fit error was <16% for all participants. The GABA concentration in the PCC of the mTBI group was significantly different from that in healthy controls: GABA/tCr was higher by 27%, absolute GABA concentration with different types of correction was higher by ≈17%. No significant differences were observed in Glx concentrations (P ≥ 0.32) or in Glx/tCr (P ≥ 0.1), NAA/tCr (P = 0.55), and Cho/tCr levels (P = 0.85).

DATA CONCLUSION

We report an increase in the GABA concentration in the PCC region in acute mTBI pediatric patients. This may suggest activation of GABA synthesis and impairment of the GABAergic system after acute mTBI.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 1.

Zolpidem Profoundly Augments Spared Tonic GABAAR Signaling in Dentate Granule Cells Ipsilateral to Controlled Cortical Impact Brain Injury in Mice

Type A GABA receptors (GABA_ARs) are pentameric combinations of protein subunits that give rise to tonic (I_TonicGABA) and phasic (i.e., synaptic; I_SynapticGABA) forms of inhibitory GABA_AR signaling in the central nervous system. Remodeling and regulation of GABA_AR protein subunits are implicated in a wide variety of healthy and injury-dependent states, including epilepsy. The present study undertook a detailed analysis of GABA_AR signaling using whole-cell patch clamp recordings from mouse dentate granule cells (DGCs) in coronal slices containing dorsal hippocampus at 1–2 or 8–13 weeks after a focal, controlled cortical impact (CCI) or sham brain injury. Zolpidem, a benzodiazepine-like positive modulator of GABA_ARs, was used to test for changes in GABA_AR signaling of DGCs due to its selectivity for α₁ subunit-containing GABA_ARs. Electric charge transfer and statistical percent change were analyzed in order to directly compare tonic and phasic GABA_AR signaling and to account for zolpidem’s ability to modify multiple parameters of GABA_AR kinetics. We observed that baseline I_TonicGABA is preserved at both time-points tested in DGCs ipsilateral to injury (Ipsi-DGCs) compared to DGCs contralateral to injury (Contra-DGCs) or after sham injury (Sham-DGCs). Interestingly, application of zolpidem resulted in modulation of I_TonicGABA across groups, with Ipsi-DGCs exhibiting the greatest responsiveness to zolpidem. We also report that the combination of CCI and acute application of zolpidem profoundly augments the proportion of GABA_AR charge transfer mediated by tonic vs. synaptic currents at both time-points tested, whereas gene expression of GABA_AR α₁, α₂, α₃, and γ₂ subunits is unchanged at 8–13 weeks post-injury. Overall, this work highlights the shift toward elevated influence of tonic inhibition in Ipsi-DGCs, the impact of zolpidem on all components of inhibitory control of DGCs, and the sustained nature of these changes in inhibitory tone after CCI injury.

Hyperacute Excitotoxic Mechanisms and Synaptic Dysfunction Involved in Traumatic Brain Injury

The biological response of brain tissue to biomechanical strain are of fundamental importance in understanding sequela of a brain injury. The time after impact can be broken into four main phases: hyperacute, acute, subacute and chronic. It is crucial to understand the hyperacute neural outcomes from the biomechanical responses that produce traumatic brain injury (TBI) as these often result in the brain becoming sensitized and vulnerable to subsequent TBIs. While the precise physical mechanisms responsible for TBI are still a matter of debate, strain-induced shearing and stretching of neural elements are considered a primary factor in pathology; however, the injury-strain thresholds as well as the earliest onset of identifiable pathologies remain unclear. Dendritic spines are sites along the dendrite where the communication between neurons occurs. These spines are dynamic in their morphology, constantly changing between stubby, thin, filopodia and mushroom depending on the environment and signaling that takes place. Dendritic spines have been shown to react to the excitotoxic conditions that take place after an impact has occurred, with a shift to the excitatory, mushroom phenotype. Glutamate released into the synaptic cleft binds to NMDA and AMPA receptors leading to increased Ca2+ entry resulting in an excitotoxic cascade. If not properly cleared, elevated levels of glutamate within the synaptic cleft will have detrimental consequences on cellular signaling and survival of the pre- and post-synaptic elements. This review will focus on the synaptic changes during the hyperacute phase that occur after a TBI. With repetitive head trauma being linked to devastating medium – and long-term maladaptive neurobehavioral outcomes, including chronic traumatic encephalopathy (CTE), understanding the hyperacute cellular mechanisms can help understand the course of the pathology and the development of effective therapeutics.

Exosomal microRNA Differential Expression in Plasma of Young Adults with Chronic Mild Traumatic Brain Injury and Healthy Control

Chronic mild traumatic brain injury (mTBI) has long-term consequences, such as neurological disability, but its pathophysiological mechanism is unknown. Exosomal microRNAs (exomiRNAs) may be important mediators of molecular and cellular changes involved in persistent symptoms after mTBI. We profiled exosomal microRNAs (exomiRNAs) in plasma from young adults with or without a chronic mTBI to decipher the underlying mechanisms of its long-lasting symptoms after mTBI. We identified 25 significantly dysregulated exomiRNAs in the chronic mTBI group (n = 29, with 4.48 mean years since the last injury) compared to controls (n = 11). These miRNAs are associated with pathways of neurological disease, organismal injury and abnormalities, and psychological disease. Dysregulation of these plasma exomiRNAs in chronic mTBI may indicate that neuronal inflammation can last long after the injury and result in enduring and persistent post-injury symptoms. These findings are useful for diagnosing and treating chronic mTBIs.

The Novel Monoacylglycerol Lipase Inhibitor MJN110 Suppresses Neuroinflammation, Normalizes Synaptic Composition and Improves Behavioral Performance in the Repetitive Traumatic Brain Injury Mouse Model

Modulation of the endocannabinoid system has emerged as an effective approach for the treatment of many neurodegenerative and neuropsychological diseases. However, the underlying mechanisms are still uncertain. Using a repetitive mild traumatic brain injury (mTBI) mouse model, we found that there was an impairment in locomotor function and working memory within two weeks post-injury, and that treatment with MJN110, a novel inhibitor of the principal 2-arachidononyl glycerol (2-AG) hydrolytic enzyme monoacylglycerol lipase dose-dependently ameliorated those behavioral changes. Spatial learning and memory deficits examined by Morris water maze between three and four weeks post-TBI were also reversed in the drug treated animals. Administration of MJN110 selectively elevated the levels of 2-AG and reduced the production of arachidonic acid (AA) and prostaglandin E₂ (PGE₂) in the TBI mouse brain. The increased production of proinflammatory cytokines, accumulation of astrocytes and microglia in the TBI mouse ipsilateral cerebral cortex and hippocampus were significantly reduced by MJN110 treatment. Neuronal cell death was also attenuated in the drug treated animals. MJN110 treatment normalized the expression of the NMDA receptor subunits NR2A and NR2B, the AMPA receptor subunits GluR1 and GluR2, and the GABA_A receptor subunits α1, β2,3 and γ2, which were all reduced at 1, 2 and 4 weeks post-injury. The reduced inflammatory response and restored glutamate and GABA receptor expression likely contribute to the improved motor function, learning and memory in the MJN110 treated animals. The therapeutic effects of MJN110 were partially mediated by activation of CB1 and CB2 cannabinoid receptors and were eliminated when it was co-administered with DO34, a novel inhibitor of the 2-AG biosynthetic enzymes. Our results suggest that augmentation of the endogenous levels of 2-AG can be therapeutically useful in the treatment of TBI by suppressing neuroinflammation and maintaining the balance between excitatory and inhibitory neurotransmission.

Regulation of Parvalbumin Interactome in the Perilesional Cortex after Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) causes 10-20% of structural epilepsy, with seizures typically originating in the cortex. Alterations in the neuronal microcircuits in the cortical epileptogenic zone, however, are poorly understood. Here, we assessed TBI-induced changes in perisomatic gamma aminobutyric acid (GABA)-ergic innervation in the perilesional cortex. We hypothesized that TBI will damage parvalbumin (PV)-immunoreactive inhibitory neurons and induce regulation of the associated GABAergic molecular interactome. TBI was induced in adult male Sprague-Dawley rats by lateral fluid-percussion injury. At 1-month post-TBI, the number of PV-positive somata was plotted on unfolded cortical maps and the distribution and density of immunopositive terminals analyzed. Qualitative analysis revealed either patchy microlesions of several hundred micrometers in diameter or diffuse neuronal loss. Quantitative analysis demonstrated a reduction in the number of PV-positive interneurons in patches down to 0% of that in sham-operated controls in the perilesional cortex. In the majority of patches, the cell numbers ranged from 71% to 90% that of the controls. The loss of PV-positive somata was accompanied by decreased axonal labeling. In situ hybridization revealed downregulated PV mRNA expression in the perilesional cortex. Gene Set Enrichment Analysis indicated a robustly downregulated expression profile of PV-related genes, which was confirmed by quantitative reverse transcriptase polymerase chain reaction. Specifically, we found that genes encoding postsynaptic GABA-A receptor genes, Gabrg2 and Gabrd, were downregulated in TBI animals compared with controls. Our data suggests that patchy reduction in PV-positive perisomatic inhibitory innervation contributes to the development of focal cortical inhibitory deficit after TBI.

Acute thalamic damage as a prognostic biomarker for post-traumatic epileptogenesis

OBJECTIVE

To identify magnetic resonance imaging (MRI) biomarkers for post-traumatic epilepsy.

METHODS

The EPITARGET (Targets and biomarkers for antiepileptogenesis, epitarget.eu) animal cohort completing T₂ relaxation and diffusion tensor MRI follow-up and 1-month-long video-electroencephalography monitoring included 98 male Sprague-Dawley rats with traumatic brain injury and 18 controls. T₂ imaging was performed on day (D) 2, D7, and D21 and diffusion tensor imaging (DTI) on D7 and D21 using a 7-Tesla Bruker PharmaScan MRI scanner. The mean and standard deviation (SD) of the T₂ relaxation rate, multiple diffusivity measures, and diffusion anisotropy at each time-point within the ventroposterolateral and ventroposteromedial thalamus were used as predictor variables in multi-variable logistic regression models to distinguish rats with and without epilepsy.

RESULTS

Twenty-nine percent (28/98) of the rats with traumatic brain injury (TBI) developed epilepsy. The best-performing logistic regression model utilized the D2 and D7 T₂ relaxation time as well as the D7 diffusion tensor data. The model distinguished rats with and without epilepsy (Bonferroni-corrected p-value < .001) with a cross-validated concordance statistic of 0.74 (95% confidence interval [CI] 0.60-0.84). In a cross-validated classification test, the model exhibited 54% sensitivity and 91% specificity, enriching the epilepsy rate within the study population from the expected 29% to 71%. A model using the D2 T₂ data only resulted in a 73% enriched epilepsy rate (regression p-value .007, cross-validated concordance 0.70, 95% CI 0.56-0.80, sensitivity 29%, specificity 96%).

SIGNIFICANCE

An MRI parameter set reporting on acute and subacute neuropathologic changes common to experimental and human TBI presents a diagnostic biomarker for post-traumatic epileptogenesis. Significant enrichment of the study population was achieved even when using a single time-point measurement, producing an expected epilepsy rate of 73%.

Traumatic Brain Injury Broadly Affects GABAergic Signaling in Dentate Gyrus Granule Cells

Traumatic brain injury (TBI) causes cellular and molecular alterations that contribute to neuropsychiatric disease and epilepsy. GABAergic dysfunction figures prominently in the pathophysiology of TBI, yet the effects of TBI on tonic inhibition in hippocampus remain uncertain. We used a mouse model of severe TBI [controlled cortical impact (CCI)] to investigate GABAergic signaling in dentate gyrus granule cells (DGGCs). Basal tonic GABA currents were not affected by CCI. However, tonic currents induced by the δ subunit-selective GABA_A receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP; 10 μm) were reduced by 44% in DGGCs ipsilateral to CCI (CCI-ipsi), but not in contralateral DGGCs. Reduced THIP currents were apparent one week after injury and persisted up to 15 weeks. The frequency of spontaneous IPSCs (sIPSCs) was reduced in CCI-ipsi cells, but the amplitude and kinetics of sIPSCs were unaffected. Immunohistochemical analysis showed reduced expression of GABA_A receptor δ subunits and GABA_B receptor B2 subunits after CCI, by 43% and 40%, respectively. Activation of postsynaptic GABA_B receptors caused a twofold increase in tonic currents, and this effect was markedly attenuated in CCI-ipsi cells (92% reduction). GABA_B receptor-activated K⁺ currents in DGGCs were also significantly reduced in CCI-ipsi cells, confirming a functional deficit of GABA_B receptors after CCI. Results indicate broad disruption of GABAergic signaling in DGGCs after CCI, with deficits in both phasic and tonic inhibition and GABA_B receptor function. These changes are predicted to disrupt operation of hippocampal networks and contribute to sequelae of severe TBI, including epilepsy.

Sleep-wake characteristics in a mouse model of severe traumatic brain injury: Relation to posttraumatic epilepsy

Study objectives

Traumatic brain injury (TBI) results in sequelae that include posttraumatic epilepsy (PTE) and sleep-wake disturbances. Here, we sought to determine whether sleep characteristics could predict development of PTE in a model of severe TBI.

Methods

Following controlled cortical impact (CCI) or sham injury (craniotomy only), CD-1 mice were implanted with epidural electroencephalography (EEG) and nuchal electromyography (EMG) electrodes. Acute (1st week) and chronic (months 1, 2, or 3) 1-week-long video-EEG recordings were performed after the injury to examine epileptiform activity. High-amplitude interictal events were extracted from EEG using an automated method. After scoring sleep-wake patterns, sleep spindles and EEG delta power were derived from nonrapid eye movement (NREM) sleep epochs. Brain CTs (computerized tomography) were performed in sham and CCI cohorts to quantify the brain lesions. We then employed a no craniotomy (NC) control to perform 1-week-long EEG recordings at week 1 and month 1 after surgery.

Results

Posttraumatic seizures were seen in the CCI group only, whereas interictal epileptiform activity was seen in CCI or sham. Sleep-wake disruptions consisted of shorter wake or NREM bout lengths and shorter duration or lower power for spindles in CCI and sham. NREM EEG delta power increased in CCI and sham groups compared with NC though the CCI group with posttraumatic seizures had lower power at a chronic time point compared with those without. Follow-up brain CTs showed a small lesion in the sham injury group suggesting a milder form of TBI that may account for their interictal activity and sleep changes.

Significance

In our TBI model, tracking changes in NREM delta power distinguishes between CCI acutely and animals that will eventually develop PTE, but further work is necessary to identify sleep biomarkers of PTE. Employing NC controls together with sham controls should be considered in future TBI studies.

Tonic GABAergic inhibition, via GABAA receptors containing αβƐ subunits, regulates excitability of ventral tegmental area dopamine neurons

The activity of midbrain dopamine neurons is strongly regulated by fast synaptic inhibitory γ‐Aminobutyric acid (GABA)ergic inputs. There is growing evidence in other brain regions that low concentrations of ambient GABA can persistently activate certain subtypes of GABA_A receptor to generate a tonic current. However, evidence for a tonic GABAergic current in midbrain dopamine neurons is limited. To address this, we conducted whole‐cell recordings from ventral tegmental area (VTA) dopamine neurons in brain slices from mice. We found that application of GABA_A receptor antagonists decreased the holding current, indicating the presence of a tonic GABAergic input. Global increases in GABA release, induced by either a nitric oxide donor or inhibition of GABA uptake, further increased this tonic current. Importantly, prolonged inhibition of the firing activity of local GABAergic neurons abolished the tonic current. A combination of pharmacology and immunohistochemistry experiments suggested that, unlike common examples of tonic inhibition, this current may be mediated by a relatively unusual combination of α4βƐ subunits. Lastly, we found that the tonic current reduced excitability in dopamine neurons suggesting a subtractive effect on firing activity.

Identification of MicroRNA-Potassium Channel Messenger RNA Interactions in the Brain of Rats With Post-traumatic Epilepsy

Background: Dysregulated expression of microRNAs and potassium channels have been reported for their contributions to seizure onset. However, the microRNA–potassium channel gene interactions in traumatic brain injury-induced post-traumatic epilepsy (PTE) remain unknown.

Methods: PTE was induced in male rats by intracranial injection with ferrous chloride (0.1 mol/L, 1 μl/min) at the right frontal cortex. Electroencephalography was recorded at 60 min, as well as day 1, 7, and 30, and the behavioral seizures were assessed before injection and at different time points after injection. Rats were killed on day 30 after injection. The right frontal cortex samples were collected and subjected to high throughput messenger RNA (mRNA) and microRNA sequencing. A network of differentially expressed potassium channel mRNAs and microRNAs was constructed using OryCun2.0 and subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses. The differential mRNA and microRNA expressions were verified using quantitative real-time-PCR. The microRNA–mRNA was subject to the Pearson correlation analysis.

Results: A PTE rat model was successfully established, as evidenced by behavioral seizures and epileptiform discharges on electroencephalography in PTE rats compared with sham rats. Among the 91 mRNAs and 40 microRNAs that were significantly differentially expressed in the PTE rat brain, 4 mRNAs and 10 microRNAs were associated with potassium channels. Except for potassium calcium-activated channel subfamily N member 2, the other three potassium channel mRNAs were negatively correlated with seven microRNAs. These microRNA–mRNA pairs were enriched in annotations and pathways related to neuronal ion channels and neuroinflammation. Quantitative real-time-PCR and correlation analysis verified negative correlations in miR-449a-5p-KCNH2, miR-98-5p-KCNH2, miR-98-5p-KCNK15, miR-19b-3p-KCNK15, and miR-301a-3p-KCNK15 pairs.

Conclusion: We identified microRNA–potassium channel mRNA interactions associated with PTE, providing potential diagnostic markers and therapeutic targets for PTE.

The Emerging Roles of π Subunit-Containing GABAA Receptors in Different Cancers

Cancer is one of the leading causes of death in both developed and developing countries. Due to its heterogenous nature, it occurs in various regions of the body and often goes undetected until later stages of disease progression. Feasible treatment options are limited because of the invasive nature of cancer and often result in detrimental side-effects and poor survival rates. Therefore, recent studies have attempted to identify aberrant expression levels of previously undiscovered proteins in cancer, with the hope of developing better diagnostic tools and pharmaceutical options. One class of such targets is the π-subunit-containing γ-aminobutyric acid type A receptors. Although these receptors were discovered more than 20 years ago, there is limited information available. They possess atypical functional properties and are expressed in several non-neuronal tissues. Prior studies have highlighted the role of these receptors in the female reproductive system. New research focusing on the higher expression levels of these receptors in ovarian, breast, gastric, cervical, and pancreatic cancers, their physiological function in healthy individuals, and their pro-tumorigenic effects in these cancer types is reviewed here.

Possible interplay between the theories of pharmacoresistant epilepsy

Epilepsy is one of the oldest known neurological disorders and is characterized by recurrent seizure activity. It has a high incidence rate, affecting a broad demographic in both developed and developing countries. Comorbid conditions are frequent in patients with epilepsy and have detrimental effects on their quality of life. Current management options for epilepsy include the use of anti-epileptic drugs, surgery, or a ketogenic diet. However, more than 30% of patients diagnosed with epilepsy exhibit drug resistance to anti-epileptic drugs. Further, surgery and ketogenic diets do little to alleviate the symptoms of patients with pharmacoresistant epilepsy. Thus, there is an urgent need to understand the underlying mechanisms of pharmacoresistant epilepsy to design newer and more effective anti-epileptic drugs. Several theories of pharmacoresistant epilepsy have been suggested over the years, the most common being the gene variant hypothesis, network hypothesis, multidrug transporter hypothesis, and target hypothesis. In our review, we discuss the main theories of pharmacoresistant epilepsy and highlight a possible interconnection between their mechanisms that could lead to the development of novel therapies for pharmacoresistant epilepsy.

Enhancement of intrinsic neuronal excitability-mediated by a reduction in hyperpolarization-activated cation current (Ih ) in hippocampal CA1 neurons in a rat model of traumatic brain injury

Traumatic brain injury (TBI) is associated with epileptiform activity in the hippocampus; however, the underlying mechanisms have not been fully determined. The goal was to understand what changes take place in intrinsic neuronal physiology in the hippocampus after blunt force trauma to the cortex. In this context, hyperpolarization-activated cation current (I_h ) currents may have a critical role in modulating the neuronal intrinsic membrane excitability; therefore, its contribution to the TBI-induced hyperexcitability was assessed. In a model of TBI caused by controlled cortical impact (CCI), the intrinsic electrophysiological properties of pyramidal neurons were examined 1 week after TBI induction in rats. Whole-cell patch-clamp recordings were performed under current- and voltage-clamp conditions following ionotropic receptors blockade. Induction of TBI caused changes in the intrinsic excitability of pyramidal neurons, as shown by a significant increase and decrease in firing frequency and in the rheobase current, respectively (p < .05). The evoked firing rate and the action potential time to peak were also significantly increased and decreased, respectively (p < .05). In the TBI group, the amplitude of instantaneous and steady-state I_h currents was both significantly smaller than those in the control group (p < .05). The I_h current density was also significantly decreased (p < .001). Findings indicated that TBI led to an increase in the intrinsic excitability in CA1 pyramidal neurons and changes in I_h current could be, in part, one of the underlying mechanisms involved in this hyperexcitability.

Immunohistochemical distribution of 10 GABAA receptor subunits in the forebrain of the rhesus monkey Macaca mulatta

GABAA receptors are composed of five subunits arranged around a central chloride channel. Their subunits originate from different genes or gene families. The majority of GABAA receptors in the mammalian brain consist of two α-, two β- and one γ- or δ-subunit. This subunit organization crucially determines the physiological and pharmacological properties of the GABAA receptors. Using immunohistochemistry, we investigated the distribution of 10 GABAA receptor subunits (α1, α2, α3, α4, α5, β1, β2, β3, γ2, and δ) in the fore brain of three female rhesus monkeys (Macaca mulatta). Within the cerebral cortex, subunits α1, α5, β2, β3, and γ2 were found in all layers, α2, α3, and β1 were more concentrated in the inner and outer layers. The caudate/putamen was rich in α1, α2, α5, all three β-subunits, γ2, and δ. Subunits α3 and α5 were more concentrated in the caudate than in the putamen. In contrast, α1, α2, β1, β2, γ2, and δ were highest in the pallidum. Most dorsal thalamic nuclei contained subunits α1, α2, α4, β2, β3, and γ2, whereas α1, α3, β1, and γ2 were most abundant in the reticular nucleus. Within the amygdala, subunits α1, α2, α5, β1, β3, γ2, and δ were concentrated in the cortical nucleus, whereas in the lateral and basolateral amygdala α1, α2, α5, β1, β3, and δ, and in the central amygdala α1, α2, β3, and γ2 were most abundant. Interestingly, subunit α3-IR outlined the intercalated nuclei of the amygdala. In the hippocampus, subunits α1, α2, α5, β2, β3, γ2, and δ were highly expressed in the dentate molecular layer, whereas α1, α2, α3, α5, β1, β2, β3, and γ2 were concentrated in sector CA1 and the subiculum. The distribution of GABAA receptor subunits in the rhesus monkey was highly heterogeneous indicating a high number of differently assembled receptors. In most areas investigated, notably in the striatum/pallidum, amygdaloid nuclei and in the hippocampus it was more diverse than in the rat and mouse indicating a more heterogeneous and less defined receptor assembly in the monkey than in rodent brain.

Low brain endocannabinoids associated with persistent non-goal directed nighttime hyperactivity after traumatic brain injury in mice

Traumatic brain injury (TBI) is a frequent cause of chronic headache, fatigue, insomnia, hyperactivity, memory deficits, irritability and posttraumatic stress disorder. Recent evidence suggests beneficial effects of pro-cannabinoid treatments. We assessed in mice levels of endocannabinoids in association with the occurrence and persistence of comparable sequelae after controlled cortical impact in mice using a set of long-term behavioral observations in IntelliCages, motor and nociception tests in two sequential cohorts of TBI/sham mice. TBI mice maintained lower body weights, and they had persistent low levels of brain ethanolamide endocannabinoids (eCBs: AEA, OEA, PEA) in perilesional and subcortical ipsilateral brain tissue (6 months), but rapidly recovered motor functions (within days), and average nociceptive responses were within normal limits, albeit with high variability, ranging from loss of thermal sensation to hypersensitivity. TBI mice showed persistent non-goal directed nighttime hyperactivity, i.e. they visited rewarding and non-rewarding operant corners with high frequency and random success. On successful visits, they made more licks than sham mice resulting in net over-licking. The lower the eCBs the stronger was the hyperactivity. In reward-based learning and reversal learning tasks, TBI mice were not inferior to sham mice, but avoidance memory was less stable. Hence, the major late behavioral TBI phenotype was non-goal directed nighttime hyperactivity and "over-licking" in association with low ipsilateral brain eCBs. The behavioral phenotype would agree with a "post-TBI hyperactivity disorder". The association with persistently low eCBs in perilesional and subcortical regions suggests that eCB deficiency contribute to the post-TBI psychopathology.

Exploring Neuronal Vulnerability to Head Trauma Using a Whole Exome Approach

Brain injuries are associated with oxidative stress and a need to restore neuronal homeostasis. Mutations in ion channel genes, in particular CACNA1A, have been implicated in familial hemiplegic migraine (FHM) and in the development of concussion-related symptoms in response to trivial head trauma. The aim of this study was to explore the potential role of variants in other ion channel genes in the development of such responses. We conducted whole exome sequencing (WES) on16 individuals who developed a range of neurological and concussion-related symptoms following minor or trivial head injuries. All individuals were initially tested and shown to be negative for mutations in known FHM genes. Variants identified from the WES results were filtered to identify rare variants (minor allele frequency [MAF] <0.01) in genes related to neural processes as well as genes highly expressed in the brain using a combination of in silico prediction tools (SIFT, PolyPhen, PredictSNP, Mutation Taster, and Mutation Assessor). Rare (MAF <0.001) or novel heterozygous variants in 7 ion channel genes were identified in 37.5% (6/16) of the cases (CACNA1I, CACNA1C, ATP10A, ATP7B, KCNAB1, KCNJ10, and SLC26A4), rare variants in neurotransmitter genes were found in 2 cases (GABRG1 and GRIK1), and rare variants in 3 ubiquitin-related genes identified in 4 cases (SQSTM1, TRIM2, and HECTD1). In this study, the largest proportion of potentially pathogenic variants in individuals with severe responses to minor head trauma were identified in genes previously implicated in migraine and seizure-related autosomal recessive neurological disorders. Together with results implicating variants in the hemiplegic migraine genes, CACNA1A and ATP1A2, in severe head trauma response, our results support a role for heterozygous deleterious mutations in genes implicated in neurological dysfunction and potentially increasing the risk of poor response to trivial head trauma.

Ameliorative effect of curcumin on altered expression of CACNA1A and GABRD in the pathogenesis of FeCl3-induced epilepsy

The pivotal role played by ion-channel dysregulations in the pathogenesis of epilepsy has always garnered much attention. Since mutation of ion-channel proteins CACNA1A and GABRD have been associated with epilepsy, it is important to determine the post-traumatic epilepsy-associated changes in expression levels of these ion channel proteins. Additionally, curcumin is already known for its antiepileptic and neuroprotective potential in FeCl₃-induced model of post-traumatic epilepsy. Thus, we investigated FeCl₃-induced epilepsy mediated differential expression of CACNA1A and GABRD in the cortical region of the rat brain. Furthermore, we investigated the effect of curcumin on the expression of both proteins. For this, epilepsy was induced by intracortical FeCl₃ injection (5 μl of 100 mM). Additionally, curcumin (conc. 1000 ppm; 75 mg/kg of b.wt.; for 14 and 28 days) was administered, mixed with normal food pellets. Results obtained from EEG-MUA and Morris water maze assay demonstrate the progression of epilepsy after FeCl₃ injection. Additionally, western blotting and histological studies show the downregulation of CACNA1A and GABRD during epileptogenesis. It was observed that epilepsy-associated decline in learning and memory of animals might be linked with the dysregulation of both proteins. Results also demonstrated that curcumin administration ameliorated epilepsy-associated change in expression of both CACNA1A and GABRD proteins. In conclusion, the neuroprotective effect of curcumin against iron-induced epilepsy might be accompanied by the alleviated upregulation of these channel proteins.

Presynaptic GABAA Receptors Modulate Thalamocortical Inputs in Layer 4 of Rat V1

Fast inhibitory GABAergic transmission plays a fundamental role in neural circuits. Current theories of cortical function assume that fast GABAergic inhibition acts via GABAA receptors on postsynaptic neurons, while presynaptic effects of GABA depend on GABAB receptor activation. Manipulations of GABAA receptor activity in vivo produced different effects on cortical function, which were generally ascribed to the mode of action of a drug, more than its site of action. Here we show that in rodent primary visual cortex, α4-containing GABAA receptors can be located on subsets of glutamatergic and GABAergic presynaptic terminals and decrease synaptic transmission. Our data provide a novel mechanistic insight into the effects of changes in cortical inhibition; the ability to modulate inputs onto cortical circuits locally, via presynaptic regulation of release by GABAA receptors.

No prevention or cure of epilepsy as yet

Approximately 20% of all epilepsy is caused by acute acquired injury such as traumatic brain injury, stroke and CNS infection. The known onset of the injury which triggers the epileptogenic process, early presentation to medical care, and a latency between the injury and the development of clinical epilepsy present an opportunity to intervene with treatment to prevent epilepsy. No such treatment exists and yet there has been remarkably little clinical research during the last 20 years to try to develop such treatment. We review possible reasons for this, possible ways to rectify the situations and note some of the ways currently under way to do so. Resective surgical treatment can achieve "cure" in some patients but is sparsely utilized. In certain "self-limiting" syndromes of childhood and adolescence epilepsy remits spontaneously. In a proportion of patients who become seizure free on medications or with dietary treatment, seizure freedom persists when treatment is discontinued. We discuss these situations which can be considered "cures"; and note that at present we have little understanding of mechanism of such cures, and cannot therefore translate them into a treatment paradigm targeting a "cure" of epilepsy. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Delayed creatine supplementation counteracts reduction of GABAergic function and protects against seizures susceptibility after traumatic brain injury in rats

Traumatic brain injury (TBI) is a devastating disease frequently followed by behavioral disabilities including post-traumatic epilepsy (PTE). Although reasonable progress in understanding its pathophysiology has been made, treatment of PTE is still limited. Several studies have shown the neuroprotective effect of creatine in different models of brain pathology, but its effects on PTE is not elucidated. Thus, we decided to investigate the impact of delayed and chronic creatine supplementation on susceptibility to epileptic seizures evoked by pentylenetetrazol (PTZ) after TBI. Our experimental data revealed that 4 weeks of creatine supplementation (300 mg/kg, p.o.) initiated 1 week after fluid percussion injury (FPI) notably increased the latency to first myoclonic and tonic-clonic seizures, decreased the time spent in tonic-clonic seizure, seizure intensity, epileptiform discharges and spindle oscillations induced by a sub-convulsant dose of PTZ (35 mg/kg, i.p.). Interestingly, this protective effect persists for 1 week even when creatine supplementation is discontinued. The anticonvulsant effect of creatine was associated with its ability to reduce cell loss including the number of parvalbumin positive (PARV+) cells in CA3 region of the hippocampus. Furthermore, creatine supplementation also protected against the reduction of GAD67 levels, GAD activity and specific [³H]flunitrazepam binding in the hippocampus. These findings showed that chronic creatine supplementation may play a neuroprotective role on brain excitability by controlling the GABAergic function after TBI, providing a possible new strategy for the treatment of PTE.

Glycolytic inhibitor 2-deoxyglucose prevents cortical hyperexcitability after traumatic brain injury

Traumatic brain injury (TBI) causes cortical dysfunction and can lead to post-traumatic epilepsy. Multiple studies demonstrate that GABAergic inhibitory network function is compromised following TBI, which may contribute to hyperexcitability and motor, behavioral, and cognitive deficits. Preserving the function of GABAergic interneurons, therefore, is a rational therapeutic strategy to preserve cortical function after TBI and prevent long-term clinical complications. Here, we explored an approach based on the ketogenic diet, a neuroprotective and anticonvulsant dietary therapy which results in reduced glycolysis and increased ketosis. Utilizing a pharmacologic inhibitor of glycolysis (2-deoxyglucose, or 2-DG), we found that acute in vitro application of 2-DG decreased the excitability of excitatory neurons, but not inhibitory interneurons, in cortical slices from naïve mice. Employing the controlled cortical impact (CCI) model of TBI in mice, we found that in vitro 2-DG treatment rapidly attenuated epileptiform activity seen in acute cortical slices 3 to 5 weeks after TBI. One week of in vivo 2-DG treatment immediately after TBI prevented the development of epileptiform activity, restored excitatory and inhibitory synaptic activity, and attenuated the loss of parvalbumin-expressing inhibitory interneurons. In summary, 2-DG may have therapeutic potential to restore network function following TBI.

Bumetanide Prevents Brain Trauma-Induced Depressive-Like Behavior

Brain trauma triggers a cascade of deleterious events leading to enhanced incidence of drug resistant epilepsies, depression, and cognitive dysfunctions. The underlying mechanisms leading to these alterations are poorly understood and treatment that attenuates those sequels are not available. Using controlled-cortical impact as an experimental model of brain trauma in adult mice, we found a strong suppressive effect of the sodium-potassium-chloride importer (NKCC1) specific antagonist bumetanide on the appearance of depressive-like behavior. We demonstrate that this alteration in behavior is associated with an impairment of post-traumatic secondary neurogenesis within the dentate gyrus of the hippocampus. The mechanism mediating the effect of bumetanide involves early transient changes in the expression of chloride regulatory proteins and qualitative changes in GABA(A) mediated transmission from hyperpolarizing to depolarizing after brain trauma. This work opens new perspectives in the early treatment of human post-traumatic induced depression. Our results strongly suggest that bumetanide might constitute an efficient prophylactic treatment to reduce neurological and psychiatric consequences of brain trauma.

Effort and Fatigue-Related Functional Connectivity in Mild Traumatic Brain Injury

Mental fatigue in healthy individuals is typically observed under conditions of high cognitive demand, particularly when effort is required to perform a task for a long period of time-thus the concepts of fatigue and effort are closely related. In brain injured individuals, mental fatigue can be a persistent and debilitating symptom. Presence of fatigue after brain injury is prognostic for return to work/school and engagement in activities of daily life. As such, it should be a high priority for treatment in this population, but because there is little understanding of its behavioral and neural underpinnings, the target for such treatment is unknown. Here, the neural underpinnings of fatigue and effort are investigated in active duty military service members with mild traumatic brain injury (mTBI) and demographically-matched orthopedic controls. Participants performed a Constant Effort task for which they were to hold a pre-defined effort level constant for long durations during fMRI scanning. The task allowed for investigation of the neural systems underlying fatigue and their relationship with sense of effort. While brain activation associated with effort and fatigue did not differentiate the mTBI and controls, functional connectivity amongst active brain regions did. The mTBI group demonstrated immediate hyper-connectivity that increased with effort level but diminished quickly when there was a need to maintain effort. Controls, in contrast, demonstrated a similar pattern of hyper-connectivity, but only when maintaining effort over time. Connectivity, particularly between the left anterior insula, rostral anterior cingulate cortex, and right-sided inferior frontal regions, correlated with effort-level and state fatigue in mTBI participants. These connections also correlated with effort level in the Control group, but only the connection between the left insula and superior medial frontal gyrus correlated with fatigue, suggesting a differing pattern of connectivity. These findings align, in part, with the dopamine imbalance, and neural efficiency hypotheses that pose key roles for medial frontal connections with insular or striatal regions in motivating or optimizing performance. Sense of effort and fatigue are closely related. As people fatigue, sense of effort increases systematically. The data propose a complex link between sense of effort, fatigue, and mTBI that is centered in what may be an inefficient neural system due to brain trauma that warrants further investigation.

Cortical Neuromodulation of Remote Regions after Experimental Traumatic Brain Injury Normalizes Forelimb Function but is Temporally Dependent

Traumatic brain injury (TBI) results in well-known, significant alterations in structural and functional connectivity. Although this is especially likely to occur in areas of pathology, deficits in function to and from remotely connected brain areas, or diaschisis, also occur as a consequence to local deficits. As a result, consideration of the network wiring of the brain may be required to design the most efficacious rehabilitation therapy to target specific functional networks to improve outcome. In this work, we model remote connections after controlled cortical impact injury (CCI) in the rat through the effect of callosal deafferentation to the opposite, contralesional cortex. We show rescue of significantly reaching deficits in injury-affected forelimb function if temporary, neuromodulatory silencing of contralesional cortex function is conducted at 1 week post-injury using the γ-aminobutyric acid (GABA) agonist muscimol, compared with vehicle. This indicates that subacute, injury-induced remote circuit modifications are likely to prevent normal ipsilesional control over limb function. However, by conducting temporary contralesional cortex silencing in the same injured rats at 4 weeks post-injury, injury-affected limb function either remains unaffected and deficient or is worsened, indicating that circuit modifications are more permanently controlled or at least influenced by the contralesional cortex at extended post-injury times. We provide functional magnetic resonance imaging (MRI) evidence of the neuromodulatory effect of muscimol on forelimb-evoked function in the cortex. We discuss these findings in light of known changes in cortical connectivity and excitability that occur in this injury model, and postulate a mechanism to explain these findings.

GABA promotes survival and axonal regeneration in identifiable descending neurons after spinal cord injury in larval lampreys

The poor regenerative capacity of descending neurons is one of the main causes of the lack of recovery after spinal cord injury (SCI). Thus, it is of crucial importance to find ways to promote axonal regeneration. In addition, the prevention of retrograde degeneration leading to the atrophy/death of descending neurons is an obvious prerequisite to activate axonal regeneration. Lampreys show an amazing regenerative capacity after SCI. Recent histological work in lampreys suggested that GABA, which is massively released after a SCI, could promote the survival of descending neurons. Here, we aimed to study if GABA, acting through GABAB receptors, promotes the survival and axonal regeneration of descending neurons of larval sea lampreys after a complete SCI. First, we used in situ hybridization to confirm that identifiable descending neurons of late-stage larvae express the gabab1 subunit of the GABAB receptor. We also observed an acute increase in the expression of this subunit in descending neurons after SCI, which further supported the possible role of GABA and GABAB receptors in promoting the survival and regeneration of these neurons. So, we performed gain and loss of function experiments to confirm this hypothesis. Treatments with GABA and baclofen (GABAB agonist) significantly reduced caspase activation in descending neurons 2 weeks after a complete SCI. Long-term treatments with GABOB (a GABA analogue) and baclofen significantly promoted axonal regeneration of descending neurons after SCI. These data indicate that GABAergic signalling through GABAB receptors promotes the survival and regeneration of descending neurons after SCI. Finally, we used morpholinos against the gabab1 subunit to knockdown the expression of the GABAB receptor in descending neurons. Long-term morpholino treatments caused a significant inhibition of axonal regeneration. This shows that endogenous GABA promotes axonal regeneration after a complete SCI in lampreys by activating GABAB receptors.

Progesterone Sharpens Temporal Response Profiles of Sensory Cortical Neurons in Animals Exposed to Traumatic Brain Injury

Traumatic brain injury (TBI) initiates a cascade of pathophysiological changes that are both complex and difficult to treat. Progesterone (P4) is a neuroprotective treatment option that has shown excellent preclinical benefits in the treatment of TBI, but these benefits have not translated well in the clinic. We have previously shown that P4 exacerbates the already hypoactive upper cortical responses in the short-term post-TBI and does not reduce upper cortical hyperactivity in the long term, and we concluded that there is no tangible benefit to sensory cortex firing strength. Here we examined the effects of P4 treatment on temporal coding resolution in the rodent sensory cortex in both the short term (4 d) and long term (8 wk) following impact-acceleration–induced TBI. We show that in the short-term postinjury, TBI has no effect on sensory cortex temporal resolution and that P4 also sharpens the response profile in all cortical layers in the uninjured brain and all layers other than layer 2 (L2) in the injured brain. In the long term, TBI broadens the response profile in all cortical layers despite firing rate hyperactivity being localized to upper cortical layers and P4 sharpens the response profile in TBI animals in all layers other than L2 and has no long-term effect in the sham brain. These results indicate that P4 has long-term effects on sensory coding that may translate to beneficial perceptual outcomes. The effects seen here, combined with previous beneficial preclinical data, emphasize that P4 is still a potential treatment option in ameliorating TBI-induced disorders.

A novel action of lacosamide on GABAA currents sets the ground for a synergic interaction with levetiracetam in treatment of epilepsy

Epilepsy is one of the most common chronic neurological diseases, and its pharmacological treatment holds great importance for both physicians and national authorities, especially considering the high proportion of drug-resistant patients (about 30%). Lacosamide (LCM) is an effective and well-tolerated new-generation antiepileptic drug (AED), currently licensed as add-on therapy for partial-onset seizures. However, LCM mechanism of action is still a matter of debate, although its effect on the voltage sensitive sodium channels is by far the most recognized. This study aimed to retrospectively analyze a cohort of 157 drug-resistant patients treated with LCM to describe the most common and effective therapeutic combinations and to investigate if the LCM can affect also GABA_A-mediated neurotransmission as previously shown for levetiracetam (LEV). In our cohort, LEV resulted the compound most frequently associated with LCM in the responder subgroup. We therefore translated this clinical observation into the laboratory bench by taking advantage of the technique of "membrane micro-transplantation" in Xenopus oocytes and electrophysiological approaches to study human GABA_A-evoked currents. In cortical brain tissues from refractory epileptic patients, we found that LCM reduces the use-dependent GABA impairment (i.e., "rundown") that it is considered one of the specific hallmarks of drug-resistant epilepsies. Notably, in line with our clinical observations, we found that the co-treatment with subthreshold concentrations of LCM and LEV, which had no effect on GABA_A currents on their own, reduced GABA impairment in drug-resistant epileptic patients, and this effect was blocked by PKC inhibitors. Our findings demonstrate, for the first time, that LCM targets GABA_A receptors and that it can act synergistically with LEV, improving the GABAergic function. This novel mechanism might contribute to explain the clinical efficacy of LCM-LEV combination in several refractory epileptic patients.

New insights in the systemic and molecular underpinnings of general anesthetic actions mediated by γ-aminobutyric acid A receptors

PURPOSE OF REVIEW

The review highlights novel insights into the role of γ-aminobutyric acid A (GABAA) receptors in mediating clinically relevant actions of anesthetic agents.

RECENT FINDINGS

GABAA receptors in the hippocampus are located on glutamatergic pyramidal cells and GABAergic interneurons. Etomidate-induced inhibition of a synaptic correlate of learning and memory is caused by receptors on nonpyramidal neurons, likely on interneurons that incorporate α5 subunits. Selective enhancement of α2 subunit containing GABAA receptors in the spinal cord provides antihyperalgesia against inflammatory and neuropathic pain without causing sedation, motor impairment, and tolerance development. Inflammation, traumatic brain injury, and exposure to anesthetic agents modify the expression patterns of GABAA receptors in a subtype-specific manner. These modifications may persist for weeks. The neuroactive steroid alphaxalone causes fast-onset and short-duration anesthesia in humans. Cardiovascular and respiratory side-effects are less severe than with propofol.

SUMMARY

Identification of the molecular and cellular substrates involved in anesthesia and insights into disease and drug-induced alterations in the expression patterns of GABAA receptors in the central nervous system are emphasizing the need for individualized anesthesia care. Introducing neuroactive steroids into clinical anesthesia is expected to reduce cardiovascular and respiratory side-effects.

Icariin Improves Cognitive Impairment after Traumatic Brain Injury by Enhancing Hippocampal Acetylation

OBJECTIVE

To examine the effect of icariin (ICA) on the cognitive impairment induced by traumatic brain injury (TBI) in mice and the underlying mechanisms related to changes in hippocampal acetylation level.

METHODS

The modifified free-fall method was used to establish the TBI mouse model. Mice with post-TBI cognitive impairment were randomly divided into 3 groups using the randomised block method (n=7): TBI (vehicle-treated), low-dose (75 mg/kg) and high-dose (150 mg/kg) of ICA groups. An additional sham-operated group (vehicle-treated) was employed. The vehicle or ICA was administrated by gavage for 28 consecutive days. The Morris water maze (MWM) test was conducted. Acetylcholine (ACh) content, mRNA and protein levels of choline acetyltransferase (ChAT), and protein levels of acetylated H3 (Ac-H3) and Ac-H4 were detected in the hippocampus.

RESULTS

Compared with the sham-operated group, the MWM performance, hippocampal ACh content, mRNA and protein levels of ChAT, and protein levels of Ac-H3 and Ac-H4 were signifificantly decreased in the TBI group (P<0.05). High-dose of ICA signifificantly ameliorated the TBI-induced weak MWM performance, increased hippocampal ACh content, and mRNA and protein levels of ChAT, as well as Ac-H3 protein level compared with the TBI group (P<0.05).

CONCLUSION

ICA improved post-TBI cognitive impairment in mice by enhancing hippocampal acetylation, which improved hippocampal cholinergic function and ultimately improved cognition.

Anatomical recovery of the GABAergic system after a complete spinal cord injury in lampreys

Lampreys recover locomotion spontaneously several weeks after a complete spinal cord injury. Dysfunction of the GABAergic system following SCI has been reported in mammalian models. So, it is of great interest to understand how the GABAergic system of lampreys adapts to the post-injury situation and how this relates to spontaneous recovery. The spinal cord of lampreys contains 3 populations of GABAergic neurons and most of the GABAergic innervation of the spinal cord comes from these local cells. GABAB receptors are expressed in the spinal cord of lampreys and they play important roles in the control of locomotion. The aims of the present study were to quantify: 1) the changes in the number of GABAergic neurons and innervation of the spinal cord and 2) the changes in the expression of the gabab receptor subunits b1 and b2 in the spinal cord of the sea lamprey after SCI. We performed complete spinal cord transections at the level of the fifth gill of mature larval lampreys and GABA immunohistochemistry or gabab in situ hybridization experiments. Animals were analysed up to 10 weeks post-lesion (wpl), when behavioural analyses showed that they recovered normal appearing locomotion (stage 6 in the Ayer's scale of locomotor recovery). We observed a significant decrease in the number of GABA-ir cells and fibres 1 h after lesion both rostral and caudal to the lesion site. GABA-ir cell numbers and innervation were recovered to control levels 1 to 2 wpl. At 1, 4 and 10 wpl the expression of gabab1 and gabab2 transcripts was significantly decreased in the spinal cord compared to control un-lesioned animals. This is the first study reporting the quantitative long-term changes in the number of GABAergic cells and fibres and in the expression of gabab receptors in the spinal cord of any vertebrate following a traumatic SCI. Our results show that in lampreys there is a full recovery of the GABAergic neurons and a decrease in the expression of gabab receptors when functional recovery is achieved.

Commonalities in epileptogenic processes from different acute brain insults: Do they translate?

The most common forms of acquired epilepsies arise following acute brain insults such as traumatic brain injury, stroke, or central nervous system infections. Treatment is effective for only 60%-70% of patients and remains symptomatic despite decades of effort to develop epilepsy prevention therapies. Recent preclinical efforts are focused on likely primary drivers of epileptogenesis, namely inflammation, neuron loss, plasticity, and circuit reorganization. This review suggests a path to identify neuronal and molecular targets for clinical testing of specific hypotheses about epileptogenesis and its prevention or modification. Acquired human epilepsies with different etiologies share some features with animal models. We identify these commonalities and discuss their relevance to the development of successful epilepsy prevention or disease modification strategies. Risk factors for developing epilepsy that appear common to multiple acute injury etiologies include intracranial bleeding, disruption of the blood-brain barrier, more severe injury, and early seizures within 1 week of injury. In diverse human epilepsies and animal models, seizures appear to propagate within a limbic or thalamocortical/corticocortical network. Common histopathologic features of epilepsy of diverse and mostly focal origin are microglial activation and astrogliosis, heterotopic neurons in the white matter, loss of neurons, and the presence of inflammatory cellular infiltrates. Astrocytes exhibit smaller K+ conductances and lose gap junction coupling in many animal models as well as in sclerotic hippocampi from temporal lobe epilepsy patients. There is increasing evidence that epilepsy can be prevented or aborted in preclinical animal models of acquired epilepsy by interfering with processes that appear common to multiple acute injury etiologies, for example, in post-status epilepticus models of focal epilepsy by transient treatment with a trkB/PLCγ1 inhibitor, isoflurane, or HMGB1 antibodies and by topical administration of adenosine, in the cortical fluid percussion injury model by focal cooling, and in the albumin posttraumatic epilepsy model by losartan. Preclinical studies further highlight the roles of mTOR1 pathways, JAK-STAT3, IL-1R/TLR4 signaling, and other inflammatory pathways in the genesis or modulation of epilepsy after brain injury. The wealth of commonalities, diversity of molecular targets identified preclinically, and likely multidimensional nature of epileptogenesis argue for a combinatorial strategy in prevention therapy. Going forward, the identification of impending epilepsy biomarkers to allow better patient selection, together with better alignment with multisite preclinical trials in animal models, should guide the clinical testing of new hypotheses for epileptogenesis and its prevention.

Alterations in the Timing of Huperzine A Cerebral Pharmacodynamics in the Acute Traumatic Brain Injury Setting

Traumatic brain injury (TBI) may affect the pharmacodynamics of centrally acting drugs. Paired-pulse transcranial magnetic stimulation (ppTMS) is a safe and noninvasive measure of cortical gamma-aminobutyric acid (GABA)-mediated cortical inhibition. Huperzine A (HupA) is a naturally occurring acetylcholinesterase inhibitor with newly discovered potent GABA-mediated antiepileptic capacity, which is reliably detected by ppTMS. To test whether TBI alters cerebral HupA pharmacodynamics, we exposed rats to fluid percussion injury (FPI) and tested whether ppTMS metrics of cortical inhibition differ in magnitude and temporal pattern in injured rats. Anesthetized adult rats were exposed to FPI or sham injury. Ninety minutes post-TBI, rats were injected with HupA or saline (0.6 mg/kg, intraperitoneally). TBI resulted in reduced cortical inhibition 90 min after the injury (N = 18) compared to sham (N = 13) controls (p = 0.03). HupA enhanced cortical inhibition after both sham injury (N = 6; p = 0.002) and TBI (N = 6; p = 0.02). The median time to maximum HupA inhibition in sham and TBI groups were 46.4 and 76.5 min, respectively (p = 0.03). This was consistent with a quadratic trend comparison that projects HupA-mediated cortical inhibition to last longer in injured rats (p = 0.007). We show that 1) cortical GABA-mediated inhibition, as measured by ppTMS, decreases acutely post-TBI, 2) HupA restores lost post-TBI GABA-mediated inhibition, and 3) HupA-mediated enhancement of cortical inhibition is delayed post-TBI. The plausible reasons of the latter include 1) low HupA volume of distribution rendering HupA confined in the intravascular compartment, therefore vulnerable to reduced post-TBI cerebral perfusion, and 2) GABAR dysfunction and increased AChE activity post-TBI.

Stereotactic Atlas-Guided Laser Capture Microdissection of Brain Regions Affected by Traumatic Injury

The ability to isolate specific brain regions of interest can be impeded in tissue disassociation techniques that do not preserve their spatial distribution. Such techniques also potentially skew gene expression analysis because the process itself can alter expression patterns in individual cells. Here we describe a laser capture microdissection (LCM) method to selectively collect specific brain regions affected by traumatic brain injury (TBI) by using a modified Nissl (cresyl violet) staining protocol and the guidance of a rat brain atlas. LCM provides access to brain regions in their native positions and the ability to use anatomical landmarks for identification of each specific region. To this end, LCM has been used previously to examine brain region specific gene expression in TBI. This protocol allows examination of TBI-induced alterations in gene and microRNA expression in distinct brain areas within the same animal. The principles of this protocol can be amended and applied to a wide range of studies examining genomic expression in other disease and/or animal models.

INTERNEURONOPATHIES AND THEIR ROLE IN EARLY LIFE EPILEPSIES AND NEURODEVELOPMENTAL DISORDERS

GABAergic interneurons control the neural circuitry and network activity in the brain. The advances in genetics have identified genes that control the development, maturation and integration of GABAergic interneurons and implicated them in the pathogenesis of epileptic encephalopathies or neurodevelopmental disorders. For example, mutations of the Aristaless-Related homeobox X-linked gene (ARX) may result in defective GABAergic interneuronal migration in infants with epileptic encephalopathies like West syndrome (WS), Ohtahara syndrome or X-linked lissencephaly with abnormal genitalia (XLAG). The concept of "interneuronopathy", i.e. impaired development, migration or function of interneurons, has emerged as a possible etiopathogenic mechanism for epileptic encephalopathies. Treatments that enhance GABA levels, may help seizure control but do not necessarily show disease modifying effect. On the other hand, interneuronopathies can be seen in other conditions in which epilepsy may not be the primary manifestation, such as autism. In this review, we plan to outline briefly the current state of knowledge on the origin, development, and migration and integration of GABAergic interneurons, present neurodevelopmental conditions, with or without epilepsy, that have been associated with interneuronopathies and discuss the evidence linking certain types of interneuronal dysfunction with epilepsy and/or cognitive or behavioral deficits.

Prevention of epilepsy: Should we be avoiding clinical trials?

Epilepsy prevention is one of the great unmet needs in epilepsy. Approximately 15% of all epilepsy is caused by an acute acquired CNS insult such as traumatic brain injury (TBI), stroke or encephalitis. There is a latent period between the insult and epilepsy onset that presents an opportunity to intervene with preventive treatment that is unique in neurology. Yet no phase 3 epilepsy prevention studies, and only 2 phase 2 studies have been initiated in the last 16years. Current prevailing opinion is that the research community is not ready for clinical preventive epilepsy studies, and that animal models should first be refined and biomarkers of epileptogenesis and of epilepsy discovered before clinical studies are embarked upon. We review data to suggest that there is basis to do epilepsy prevention studies now with the current knowledge and available drugs, and that those studies are feasible with currently available tools. We suggest that a different approach is needed from the past in order to maximize chances of success, minimize the cost, and set up platform for future preventive treatment development. That approach should include close coordination of preclinical and clinical development programs in a combined PTE prevention strategy, consideration of polytherapy, and simultaneous, combined clinical development of preventive treatment and of biomarker discovery. We argue that the currently favored approach of eschewing clinical studies until biomarkers are available will delay the discovery of epilepsy prevention treatment by at least 10 years and significantly increase the cost of such discovery.

Analgesic Effect of 17β-Estradiol on Nucleus Paragigantocellularis Lateralis of Male Rats Mediated Via GABAA Receptors

Introduction:

Beside its autonomic functions, the nucleus paragigantocellularis lateralis (LPGi) is involved in the descending pain modulation. 17β-Estradiol is a neuroactive steroid found in several brain areas such as LPGi. Intra-LPGi microinjection of 17β-estradiol can elicit the analgesic responses. 17β-Estradiol modulates nociception by binding to estrogenic receptors as well as allosteric interaction with other membrane-bound receptors like GABA_A receptors. This study aimed to examine the role of GABA_A receptors in the pain modulating effect of intra-LPGi injection of 17β-estradiol.

Methods:

To study the antinociceptive effects of 17β-estradiol, cannulation into the LPGi nucleus of male Wistar rats was performed. About 500 nL of drug was administered 15 minutes prior to formalin injection (50 μL of 4%). Then, formalin-induced flexing and licking behaviors were recorded for 60 minutes. For evaluating the role of GABA_A receptors in the estradiol-induced pain modulation, 17β-estradiol was administered into the LPGi nucleus 15 minutes after the injection of 25 ng/μL bicuculline (the GABA_A receptor antagonist). Then, the formalin-induced responses were recorded.

Results:

The results of the current study showed that intra-LPGi injection of 17β-estradiol decreased the flexing duration in both phases of formalin test (P<0.001); but it only attenuated the second phase of licking behavior (P<0.001). 17β-estradiol attenuated the second phase of formalin test of both behaviors (P<0.001). Bicuculline prevented the antinociceptive effect of intra-LPGi 17β-estradiol in both first and second phases of formalin-induced responses (P<0.001).

Conclusion:

According to the results of this study, the analgesic effect of intra-LPGi 17β-estradiol on the formalin-induced inflammatory pain might be mediated via GABA_A receptors.

Chronically dysregulated NOTCH1 interactome in the dentate gyrus after traumatic brain injury

Traumatic brain injury (TBI) can result in several dentate gyrus-regulated disabilities. Almost nothing is known about the chronic molecular changes after TBI, and their potential as treatment targets. We hypothesized that chronic transcriptional alterations after TBI are under microRNA (miRNA) control. Expression of miRNAs and their targets in the dentate gyrus was analyzed using microarrays at 3 months after experimental TBI. Of 305 miRNAs present on the miRNA-array, 12 were downregulated (p<0.05). In parallel, 75 of their target genes were upregulated (p<0.05). A bioinformatics analysis of miRNA targets highlighted the dysregulation of the transcription factor NOTCH1 and 39 of its target genes (NOTCH1 interactome). Validation assays confirmed downregulation of miR-139-5p, upregulation of Notch1 and its activated protein, and positive enrichment of NOTCH1 target gene expression. These findings demonstrate that miRNA-based transcriptional regulation can be present at chronic time points after TBI, and highlight the NOTCH1 interactome as one of the mechanisms behind the dentate gyrus pathology-related morbidities.

Hyper-connectivity of the thalamus during early stages following mild traumatic brain injury

The thalamo-cortical resting state functional connectivity of seven sub-thalamic regions were examined in a prospectively recruited population of 77 acute mild TBI (mTBI) patients within the first 10 days (mean 6 ± 3 days) of injury and 35 neurologically intact control subjects using the Oxford thalamic connectivity atlas. Neuropsychological assessments were conducted using the Automated Neuropsychological Assessment Metrics (ANAM). A subset of participants received a magentic resonance spectroscopy (MRS) exam to determine metabolite concentrations in the thalamus and the posterior cingulate cortex. Results show that patients performed worse than the control group on various subtests of ANAM and the weighted throughput score, suggesting reduced cognitive performance at this early stage of injury. Both voxel and region of interest based analysis of the resting state fMRI data demonstrated that acute mTBI patients have increased functional connectivity between the various sub-thalamic regions and cortical regions associated with sensory processing and the default mode network (DMN). In addition, a significant reduction in NAA/Cr was observed in the thalamus in the mTBI patients. Furthermore, an increase in Cho/Cr ratio specific to mTBI patients with self-reported sensory symptoms was observed compared to those without self-reported sensory symptoms. These results provide novel insights into the neural mechanisms of the brain state related to internal rumination and arousal, which have implications for new interventions for mTBI patients with persistent symptoms. Furthermore, an understanding of heightened sensitivity to sensory related inputs during early stages of injury may facilitate enhanced prediction of safe return to work.

Traumatic Brain Injury and Neuronal Functionality Changes in Sensory Cortex

Traumatic brain injury (TBI), caused by direct blows to the head or inertial forces during relative head-brain movement, can result in long-lasting cognitive and motor deficits which can be particularly consequential when they occur in young people with a long life ahead. Much is known of the molecular and anatomical changes produced in TBI but much less is known of the consequences of these changes to neuronal functionality, especially in the cortex. Given that much of our interior and exterior lives are dependent on responsiveness to information from and about the world around us, we have hypothesized that a significant contributor to the cognitive and motor deficits seen after TBI could be changes in sensory processing. To explore this hypothesis, and to develop a model test system of the changes in neuronal functionality caused by TBI, we have examined neuronal encoding of simple and complex sensory input in the rat’s exploratory and discriminative tactile system, the large face macrovibrissae, which feeds to the so-called “barrel cortex” of somatosensory cortex. In this review we describe the short-term and long-term changes in the barrel cortex encoding of whisker motion modeling naturalistic whisker movement undertaken by rats engaged in a variety of tasks. We demonstrate that the most common form of TBI results in persistent neuronal hyperexcitation specifically in the upper cortical layers, likely due to changes in inhibition. We describe the types of cortical inhibitory neurons and their roles and how selective effects on some of these could produce the particular forms of neuronal encoding changes described in TBI, and then generalize to compare the effects on inhibition seen in other forms of brain injury. From these findings we make specific predictions as to how non-invasive extra-cranial electrophysiology can be used to provide the high-precision information needed to monitor and understand the temporal evolution of changes in neuronal functionality in humans suffering TBI. Such detailed understanding of the specific changes in an individual patient’s cortex can allow for treatment to be tailored to the neuronal changes in that particular patient’s brain in TBI, a precision that is currently unavailable with any technique.

From Molecular Circuit Dysfunction to Disease: Case Studies in Epilepsy, Traumatic Brain Injury, and Alzheimer's Disease

Complex circuitry with feed-forward and feed-back systems regulate neuronal activity throughout the brain. Cell biological, electrical, and neurotransmitter systems enable neural networks to process and drive the entire spectrum of cognitive, behavioral, and motor functions. Simultaneous orchestration of distinct cells and interconnected neural circuits relies on hundreds, if not thousands, of unique molecular interactions. Even single molecule dysfunctions can be disrupting to neural circuit activity, leading to neurological pathology. Here, we sample our current understanding of how molecular aberrations lead to disruptions in networks using three neurological pathologies as exemplars: epilepsy, traumatic brain injury (TBI), and Alzheimer's disease (AD). Epilepsy provides a window into how total destabilization of network balance can occur. TBI is an abrupt physical disruption that manifests in both acute and chronic neurological deficits. Last, in AD progressive cell loss leads to devastating cognitive consequences. Interestingly, all three of these neurological diseases are interrelated. The goal of this review, therefore, is to identify molecular changes that may lead to network dysfunction, elaborate on how altered network activity and circuit structure can contribute to neurological disease, and suggest common threads that may lie at the heart of molecular circuit dysfunction.

Differential susceptibility of cortical and subcortical inhibitory neurons and astrocytes in the long term following diffuse traumatic brain injury

Long-term diffuse traumatic brain injury (dTBI) causes neuronal hyperexcitation in supragranular layers in sensory cortex, likely through reduced inhibition. Other forms of TBI affect inhibitory interneurons in subcortical areas but it is unknown if this occurs in cortex, or in any brain area in dTBI. We investigated dTBI effects on inhibitory neurons and astrocytes in somatosensory and motor cortex, and hippocampus, 8 weeks post-TBI. Brains were labeled with antibodies against calbindin (CB), parvalbumin (PV), calretinin (CR) and neuropeptide Y (NPY), and somatostatin (SOM) and glial fibrillary acidic protein (GFAP), a marker for astrogliosis during neurodegeneration. Despite persistent behavioral deficits in rotarod performance up to the time of brain extraction (TBI = 73.13 ± 5.23% mean ± SEM, Sham = 92.29 ± 5.56%, P < 0.01), motor cortex showed only a significant increase, in NPY neurons in supragranular layers (mean cells/mm² ± SEM, Sham = 16 ± 0.971, TBI = 25 ± 1.51, P = 0.001). In somatosensory cortex, only CR⁺ neurons showed changes, being decreased in supragranular (TBI = 19 ± 1.18, Sham = 25 ± 1.10, P < 0.01) and increased in infragranular (TBI = 28 ± 1.35, Sham = 24 ± 1.07, P < 0.05) layers. Heterogeneous changes were seen in hippocampal staining: CB⁺ decreased in dentate gyrus (TBI = 2 ± 0.382, Sham = 4 ± 0.383, P < 0.01), PV⁺ increased in CA1 (TBI = 39 ± 1.26, Sham = 33 ± 1.69, P < 0.05) and CA2/3 (TBI = 26 ± 2.10, Sham = 20 ± 1.49, P < 0.05), and CR⁺ decreased in CA1 (TBI = 10 ± 1.02, Sham = 14 ± 1.14, P < 0.05). Astrogliosis significantly increased in corpus callosum (TBI = 6.7 ± 0.69, Sham = 2.5 ± 0.38; P = 0.007). While dTBI effects on inhibitory neurons appear region- and type-specific, a common feature in all cases of decrease was that changes occurred in dendrite targeting interneurons involved in neuronal integration. J. Comp. Neurol. 524:3530-3560, 2016. © 2016 Wiley Periodicals, Inc.