Targeting GABAC Receptors Improves Post-Stroke Motor Recovery

Post-Stroke Recovery in Relation to Parvalbumin-Positive Interneurons and Perineuronal Nets

BACKGROUND

There is a critical time window of post-stroke neuroplasticity when spontaneous behavioral recovery occurs. Potential factors responsible for this heightened plasticity are the reduction of parvalbumin-immunoreactive (PV+) interneuron inhibitory signaling and the disappearance of extracellular matrix synaptic stabilizers called perineuronal net(s; PNN/PNNs).

OBJECTIVE

This study investigated whether behavioral recovery during this critical period following stroke is associated with changes in densities of PV+ interneurons and PNNs.

METHODS

Male, Sprague-Dawley rats received forelimb motor cortex stroke (n = 43) using endothelin-1, or vehicle injections (n = 44). Cohorts of rats underwent a battery of motor tests and were sacrificed within the post-stroke critical window on day 1, and 1, 2, 4, and 6 weeks. Using immunofluorescent labeling, PNNs (wisteria floribunda agglutinin; WFA+ cells), PV+ interneurons, and cells expressing both PV and PNNs were quantified in contra- and ipsilesional cortices to elucidate their spatial-temporal profiles following stroke.

RESULTS

PV+ interneuron density decreased significantly at 1-day post-stroke in the lateral ipsilesional cortex, while the density of PNNs was significantly lower up to 4 weeks post-stroke in the lateral ipsilesional cortex and at 1 and 2 weeks post-stroke in the medial ipsilesional cortex. Reduction of combined PV+/PNN signaling coincided with spontaneous behavioral recovery.

CONCLUSIONS

These results suggest that post-stroke behavioral recovery corresponds to an early reduction in PV+/PNN co-labeled cells in conjunction with an early temporally-dependent reduction in PV+ interneuron signaling and chronic disappearance of PNNs. Interventions targeting PNNs or PV+ interneuron signaling have significant potential for extending the critical window of recovery following stroke.

Insights and progress on the biosynthesis, metabolism, and physiological functions of gamma-aminobutyric acid (GABA): a review

GABA (γ-aminobutyric acid) is a non-protein amino acid that occurs naturally in the human brain, animals, plants and microorganisms. It is primarily produced by the irreversible action of glutamic acid decarboxylase (GAD) on the α-decarboxylation of L-glutamic acid. As a major neurotransmitter in the brain, GABA plays a crucial role in behavior, cognition, and the body's stress response. GABA is mainly synthesized through the GABA shunt and the polyamine degradation pathways. It works through three receptors (GABAA, GABAB, and GABAC), each exhibiting different pharmacological and physiological characteristics. GABA has a variety of physiological roles and applications. In plants, it regulates growth, development and stress responses. In mammals, it influences physiological functions such as nervous system regulation, blood pressure equilibrium, liver and kidneys enhancement, hormone secretion regulation, immunity enhancement, cancer prevention, as well as anti-aging effects. As a biologically active ingredient, GABA possesses unique physiological effects and medicinal value, leading to its widespread application and substantially increased market demand in the food and pharmaceutical industries. GABA is primarily produced through chemical synthesis, plant enrichment and microbial fermentation. In this review, we first make an overview of GABA, focusing on its synthesis, metabolism, GABA receptors and physiological functions. Next, we describe the industrial production methods of GABA. Finally, we discuss the development of ligands for the GABA receptor binding site, the prospects of GABA production and application, as well as its clinical trials in potential drugs or compounds targeting GABA for the treatment of epilepsy. The purpose of this review is to attract researchers from various fields to focus on GABA research, promote multidisciplinary communications and collaborations, break down disciplinary barriers, stimulate innovative research ideas and methods, and advance the development and application of GABA in medicine, agriculture, food and other fields.

The Excessive Tonic Inhibition of the Peri-infarct Cortex Depresses Low Gamma Rhythm Power During Poststroke Recovery

The cortex immediately surrounding a brain ischemic lesion, the peri-infarct cortex (PIC), harbors a large part of the potential to recover lost functions. However, our understanding of the neurophysiological conditions in which synaptic plasticity operates remains limited. Here we hypothesized that the chronic imbalance between excitation and inhibition of the PIC prevents the normalization of the gamma rhythm, a waveband of neural oscillations thought to orchestrate action potential trafficking. Probing the local field potential activity of the forelimb primary sensory cortex (S1FL) located in the PIC of male adult mice, we found a constant, deep reduction of low-gamma oscillation power (L-gamma; 30-50 Hz) precisely during the critical time window for recovery (1-3 weeks after stroke). The collapse of L-gamma power negatively correlated with behavioral progress in affected forelimb use. Mapping astrocyte reactivity and GABA-like immunoreactivity in the PIC revealed a parallel high signal, which gradually increased when approaching the lesion. Increasing tonic inhibition with local infusion of GABA or by blocking its recapture reduced L-gamma oscillation power in a magnitude similar to stroke. Conversely, the negative allosteric modulation of tonic GABA conductance using L655,708 or the gliopeptide ODN rescued the L-gamma power of the PIC. Altogether the present data point out that the chronic excess of ambient GABA in the PIC limits the generation of L-gamma oscillations in the repairing cortex and suggests that rehabilitative interventions aimed at normalizing low-gamma power within the critical period of stroke recovery could optimize the restitution of lost functions.

Divergent mechanisms of steroid inhibition in the human ρ1 GABAA receptor

ρ-type γ-aminobutyric acid-A (GABAA) receptors are widely distributed in the retina and brain, and are potential drug targets for the treatment of visual, sleep and cognitive disorders. Endogenous neuroactive steroids including β-estradiol and pregnenolone sulfate negatively modulate the function of ρ1 GABAA receptors, but their inhibitory mechanisms are not clear. By combining five cryo-EM structures with electrophysiology and molecular dynamics simulations, we characterize binding sites and negative modulation mechanisms of β-estradiol and pregnenolone sulfate at the human ρ1 GABAA receptor. β-estradiol binds in a pocket at the interface between extracellular and transmembrane domains, apparently specific to the ρ subfamily, and disturbs allosteric conformational transitions linking GABA binding to pore opening. In contrast, pregnenolone sulfate binds inside the pore to block ion permeation, with a preference for activated structures. These results illuminate contrasting mechanisms of ρ1 inhibition by two different neuroactive steroids, with potential implications for subtype-specific gating and pharmacological design.

Milestone review: GABA, from chemistry, conformations, ionotropic receptors, modulators, epilepsy, flavonoids, and stress to neuro-nutraceuticals

Arising out of a PhD project more than 50 years ago to synthesise analogues of the neurotransmitter GABA, a series of new chemical entities were found to have selective actions on ionotropic GABA receptors. Several of these neurochemicals are now commercially available. A new subtype of these receptors was discovered that could be a target for the treatment of myopia, the facilitation of learning and memory, and the improvement of post-stroke motor recovery. The development of these new chemical entities over many years demonstrates the importance of neurochemicals with which to investigate selective aspects of GABA receptors and illustrates the significance of collaboration between chemists and biologists in neurochemistry. Vital were the improvements in synthetic organic chemistry and the use of functional human receptors expressed in oocytes. Current interest in ionotropic GABA receptors includes the clinical development of subtype-specific agents and the role of gain-of-function receptor variants in epilepsy. Dietary flavonoids were found to cross the blood-brain barrier to influence brain function. Natural and synthetic flavonoids had a range of effects on GABA receptors, ranging from positive, silent, and negative allosteric modulators, to even second-order modulation of first-order modulators. Flavonoids have been called "a new family of benzodiazepines." Like benzodiazepines, flavonoids reduce stress. Stress produces changes in GABA receptors in the brain that may be because of changes in endogenous modulators, such as neurosteroids and corticosteroids. GABA also occurs naturally in the diet leading to studies of the effects of oral GABA on brain function. This finding has resulted in studies of GABA and related neurochemicals as neuro-nutraceuticals. GABA systems in the gut microbiome are essential to such studies. The actions of oral GABA and of GABA-enriched beverages and foodstuffs are now an area of considerable scientific and commercial interest. GABA is a deceptively simple chemical that can take up many shapes, which may underlie its complex functions. The need for new chemical entities with selective actions for further studies highlights the need for continuing collaboration between chemists and biologists.

Allicin promotes functional recovery in ischemic stroke via glutathione peroxidase-1 activation of Src-Akt-Erk

Allicin exhibits various pharmacological activities and has been suggested to be beneficial in the treatment of stroke. However, the underlying mechanisms are largely unknown. Here, we confirmed that allicin protected the brain from cerebral injury, which could be ascribed to its anti‑apoptotic and anti‑inflammatory effects, as well as the regulation of lipid metabolism, using proteomics and metabolomics analysis. Our results suggested that allicin could significantly ameliorate behavioral characteristics, cerebral infarct area, cell apoptosis, inflammatory factors, and lipid metabolic-related factors (arachidonic acid, 15-hydroperoxy-eicosatetraenoic acid (15S-HPETE), palmitoylcarnitine, and acylcarnitine) by recalibrating astrocyte homeostasis in mice with photothrombotic stroke (PT). In astrocytes, allicin significantly increased glutathione peroxidase 1 (GPX1) levels and inhibited the arachidonic acid-related pathway, which was also observed in the brains of mice with PT. Allicin was proven to inhibit hypoxia-induced astrocyte apoptosis by increasing GPX1 expression, activating proto-oncogene tyrosine-protein kinase Src (Src)- protein kinase B (AKT)-extracellular signal-regulated kinase (ERK) phosphorylation, and decreasing lipid peroxidation. Thus, we concluded that allicin significantly prevented and ameliorated ischemic stroke by increasing GPX1 levels to complete the complex physiological process.

A Preclinical Systematic Review and Meta-Analysis of Behavior Testing in Mice Models of Ischemic Stroke

Stroke remains one of the most important causes of death and disability. Preclinical research is a powerful tool for understanding the molecular and cellular response to stroke. However, a lack of standardization in animal evaluation does not always ensure reproducible results. In the present study, we wanted to identify the best strategy for evaluating animal behavior post-experimental stroke. As such, a meta-analysis was made, evaluating behavioral tests done on male C57BL/6 mice subjected to stroke or sham surgery. Overall, fifty-six studies were included. Our results suggest that different types of tests should be used depending on the post-stroke period one needs to analyze. In the hyper-acute, post-stroke period, the best quantifier will be animal examination scoring, as it is a fast and inexpensive way to identify differences between groups. When evaluating stoke mice in the acute phase, a mix of animal examination and motor tests that focus on movement asymmetry (foot-fault and cylinder testing) seem to have the best chance of picking up differences between groups. Complex tasks (the rotarod test and Morris water maze) should be used within the chronic phase to evaluate differences between the late-subacute and chronic phases.

Acupuncture alleviates spinal hyperreflexia and motor dysfunction in post-ischemic stroke rats with spastic hypertonia via KCC2-mediated spinal GABAA activation

The majority of patients simultaneously develop motor dysfunction and spastic hypertonia after ischemic strokes, which can be associated with an increasing trend in motor impairments, seriously impeding the rehabilitation process. Evidence suggests that some deficits in the KCC2 expression in the spinal cord along with maladaptive endogenous plasticity via GABA_A receptors are often involved in the pathology of spastic hypertonia after a stroke. In this respect, acupuncture has been commonly used in clinical settings for post-stroke patients' rehabilitation. Nevertheless, the mechanism of the modulating activity of this alternative medicine in the spinal pathways to relieve spasticity and improve functional recovery after a stroke has still remained unclear. Utilizing laser speckle imaging, functional assessments (viz. neurologic function scale, muscular tension scale, foot balance test, and gait analysis), H-reflex recording, TTC, Western blotting, RT-qPCR, ELISA, and immunofluorescence molecular assay, the study results illustrated that acupuncture could significantly alleviate the spinal hyperreflexia, decrease muscle tone, and enhance locomotor function by elevating the GABA, KCC2, and GABA_Aγ2 expressions in the lumbar spine of a rat model of post-ischemic stroke with spastic hypertonia. Furthermore, the KCC2 antagonist DIOA abolished the benefits induced by this practice. Overall, the data revealed that acupuncture is a promising therapeutic approach for spastic hypertonia after a stroke, and the positive outcomes in this sense could be achieved via activating the KCC2-mediated spinal GABA_A signaling pathway.

Pharmacological Effect of GABA Analogues on GABA-ϱ2 Receptors and Their Subtype Selectivity

GABAρ receptors are distinctive GABAergic receptors from other ionotropic GABA_A and metabotropic GABA_B receptors in their pharmacological, biochemical, and electrophysiological properties. Although GABA-ρ1 receptors are the most studied in this subfamily, GABA-ρ2 receptors are widely distributed in the brain and are considered a potential target for treating neurological disorders such as stroke. The structure of GABA-ρ2 receptors and their pharmacological features are poorly studied. We generated the first homology model of GABA-ρ2 channel, which predicts similar major interactions of GABA with the binding-site residues in GABA-ρ1 and GABA-ρ2 channels. We also investigated the pharmacological properties of several GABA analogues on the activity of GABA-ρ2 receptors. In comparison to their pharmacological effect on GABA-ρ1 receptors, the activation effect of these ligands and their potentiation/inhibition impact on GABA response have interestingly shown inter-selectivity between the two GABA-ρ receptors. Our results suggest that several GABA analogues can be used as research tools to study the distinctive physiology of GABA-ρ1 and GABA-ρ2 receptors. Furthermore, their partial agonist effect may hold promise for the future discovery of selective modulatory agents on GABA_A receptors.

Symmetric and Asymmetric Synapses Driving Neurodegenerative Disorders

In 1959, E. G. Gray described two different types of synapses in the brain for the first time: symmetric and asymmetric. Later on, symmetric synapses were associated with inhibitory terminals, and asymmetric synapses to excitatory signaling. The balance between these two systems is critical to maintain a correct brain function. Likewise, the modulation of both types of synapses is also important to maintain a healthy equilibrium. Cerebral circuitry responds differently depending on the type of damage and the timeline of the injury. For example, promoting symmetric signaling following ischemic damage is beneficial only during the acute phase; afterwards, it further increases the initial damage. Synapses can be also altered by players not directly related to them; the chronic and long-term neurodegeneration mediated by tau proteins primarily targets asymmetric synapses by decreasing neuronal plasticity and functionality. Dopamine represents the main modulating system within the central nervous system. Indeed, the death of midbrain dopaminergic neurons impairs locomotion, underlying the devastating Parkinson’s disease. Herein, we will review studies on symmetric and asymmetric synapses plasticity after three different stressors: symmetric signaling under acute damage—ischemic stroke; asymmetric signaling under chronic and long-term neurodegeneration—Alzheimer’s disease; symmetric and asymmetric synapses without modulation—Parkinson’s disease.