Effects of (+)-bicuculline, a GABAa receptor antagonist, on auditory steady state response in free-moving rats

Bicuculline ameliorates metabolic dysfunction-associated steatotic liver disease by inhibiting the nuclear factor-kappa B pathway and reducing lipid accumulation

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) has emerged as a prominent and pervasive global health challenge. Bicuculline (BIC), which is a key active component of the anti-MASLD prescription "Eight Zhes Decoction", has been preliminarily shown by our research team to have significant potential in treating MASLD.

AIM

To determine BIC's efficacy in treating MASLD by regulating lipid metabolism and suppressing hepatic inflammation via nuclear factor-kappa B (NF-κB) pathway, identifying it as a therapeutic candidate.

METHODS

This study explored the potential of BIC in preventing and treating MASLD using zebrafish, cellular (HepG2 and AML12), and mouse models.

RESULTS

Our results indicate that BIC significantly reduces lipid accumulation and inflammation both in vivo and in vitro. Transcriptomic analysis suggested that the anti-MASLD effects of BIC are linked to the inhibition of the NF-κB pathway, which plays a critical role in mitigating inflammation and lipid deposition.

CONCLUSION

This study is the first to demonstrate that BIC specifically alleviates lipid accumulation and hepatic steatosis in MASLD models via the NF-κB signaling pathway. Overall, BIC has emerged as a promising candidate for treating MASLD.

Gamma-Aminobutyric Acid Action on Membrane and Electrical Properties of Synaptosomes and Model Lipid Bilayers

Dysfunction of the main inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is the underlying reason behind many neurological disorders including Alzheimer's and Huntington's diseases, autism spectrum disorders, anxiety, depression, hypertension, and cardiovascular diseases, among others. Here, we address neurotransmitter-induced alterations of synaptosomal and model membrane electrical properties for elucidating membrane-related biophysical mechanisms of neurological disorders. We focus on membrane surface characteristics of the pinched off nerve endings synaptosomes, which for decades have been a powerful tool in neurobiology. Microelectrophoretic measurements of GABA-treated negatively charged synaptosomes from rat cerebral cortex reveal lower negative zeta potential as a result of reduced electrical charge on the membrane surface at (1-4 h) after isolation. Conversely, enhancement of the surface parameters of synaptosomes (17-22 h) post isolation is obtained due to additional negatively exposed groups on the surface of the vesicles. The electrical properties of bilayer lipid membranes are probed by electrochemical impedance spectroscopy, reporting as light increase of the membrane electrical capacitance in the presence of GABA, likely related to membrane thinning and dielectric permittivity alterations. The neurotransmitter inhibits sodium-potassium as well as the total ATPase activity and slightly enhances magnesium-ATPase of native synaptic membranes. At low (pM) GABA concentrations the activity of acetylcholinesterase (AChE) in synaptic membranes increases. AChE inhibition is reported at higher GABA concentrations. The relation between the surface electrical properties of cells and the enzymatic activity of brain ATPases and AChE, as examined here, are expected to be helpful in the elucidation of membrane-mediated molecular mechanisms relevant to neurological disorders and conditions.

Neural mechanisms underlying reduced nocifensive sensitivity in autism-associated Shank3 mutant dogs

Autistic individuals carrying mutations in SHANK3 (encoding a synaptic scaffolding protein) have been consistently reported to exhibit reduced pain sensitivity. However, the neural mechanisms underlying impaired pain processing remain unclear. To investigate the role of SHANK3 in pain processing, we conducted behavioral, electrophysiological, and pharmacological tests upon nociceptive stimulation in a Shank3 mutant dog model. Behaviorally, Shank3 mutant dogs showed reduced nocifensive sensitivity compared to wild-type (WT) dogs. Electrophysiologically, Shank3 mutant dogs exhibited reduced neural responses elicited by the activations of both Aδ- and C-fiber nociceptors. Additionally, Shank3 mutants showed a lower level of aperiodic exponents, which serve as a marker for the excitatory-inhibitory balance of neural activity. The aperiodic exponents mediated the relationship between genotype and nocifensive sensitivity as well as between genotype and neural responses elicited by nociceptive stimuli. Pharmacologically, the reduced nocifensive sensitivity and atypical excitatory-inhibitory balance were rescued by a GABAAR antagonist pentylenetetrazole. These findings highlight the critical role of Shank3 in pain processing and suggest that an impaired excitatory-inhibitory balance may be responsible for the reduced nocifensive reactivity in autism.

Exploring the antinociceptive effect of taraxasterol in mice: Possible mechanisms

OBJECTIVES

Taraxasterol is the active ingredient of Taraxacum officinale which has been used in traditional medicine for its several therapeutic effects. This study aims first to evaluate the potential spinal/supraspinal and peripheral/visceral antinociceptive effect of taraxasterol and then to investigate the contribution of GABAergic, opioidergic systems, and KATP channels to its antinociceptive effect.

METHODS

The antinociceptive activity of taraxasterol (2.5, 5, and 10 mg/kg i.p.) was investigated with hot-plate, tail-immersion, and acetic acid-induced abdominal writhing tests (for supraspinal, spinal, peripheral/visceral pain evaluation, respectively) in BALB/c male mice, and percentage of possible maximum effect (MPE%) values were calculated. Mechanism of action studies were performed by pre-administering bicuculline, naloxone, and glibenclamide.

RESULTS

Taraxasterol increased the MPE% values in hot-plate and tail-immersion tests at 2.5, 5, and 10 mg/kg doses (P < 0.001) and decreased the mean number of writhes at 10 mg/kg in the abdominal writhing test (P < 0.05). Naloxone and bicuculline pre-administration reversed the antinociceptive effect of taraxasterol in hot-plate and tail-immersion tests and it had no effect in the abdominal writhing test. Pre-administration of glibenclamide reversed the antinociceptive effect of taraxasterol in all tests.

CONCLUSION

Our study is the first to show the involvement of GABAergic and opioidergic systems in the antinociceptive effect of taraxasterol in supraspinal and spinal pain tests, and KATP channels in tests evaluating supraspinal, spinal, and peripheral pain pathways. Taraxasterol is a potential new herbal medicine that can be used for pain control.

The neurotensin receptor 1 agonist PD149163 alleviates visceral hypersensitivity and colonic hyperpermeability in rat irritable bowel syndrome model

BACKGROUND

An impaired intestinal barrier with the activation of corticotropin-releasing factor (CRF), Toll-like receptor 4 (TLR4), and proinflammatory cytokine signaling, resulting in visceral hypersensitivity, is a crucial aspect of irritable bowel syndrome (IBS). The gut exhibits abundant expression of neurotensin; however, its role in the pathophysiology of IBS remains uncertain. This study aimed to clarify the effects of PD149163, a specific agonist for neurotensin receptor 1 (NTR1), on visceral sensation and gut barrier in rat IBS models.

METHODS

The visceral pain threshold in response to colonic balloon distention was electrophysiologically determined by monitoring abdominal muscle contractions, while colonic permeability was measured by quantifying absorbed Evans blue in colonic tissue in vivo in adult male Sprague-Dawley rats. We employed the rat IBS models, i.e., lipopolysaccharide (LPS)- and CRF-induced visceral hypersensitivity and colonic hyperpermeability, and explored the effects of PD149163.

KEY RESULTS

Intraperitoneal PD149163 (160, 240, 320 μg kg-1) prevented LPS (1 mg kg-1, subcutaneously)-induced visceral hypersensitivity and colonic hyperpermeability dose-dependently. It also prevented the gastrointestinal changes induced by CRF (50 μg kg-1, intraperitoneally). Peripheral atropine, bicuculline (a GABAA receptor antagonist), sulpiride (a dopamine D2 receptor antagonist), astressin2-B (a CRF receptor subtype 2 [CRF2] antagonist), and intracisternal SB-334867 (an orexin 1 receptor antagonist) reversed these effects of PD149163 in the LPS model.

CONCLUSIONS AND INFERENCES

PD149163 demonstrated an improvement in visceral hypersensitivity and colonic hyperpermeability in rat IBS models through the dopamine D2, GABAA, orexin, CRF2, and cholinergic pathways. Activation of NTR1 may modulate these gastrointestinal changes, helping to alleviate IBS symptoms.

40 Hz Steady-State Response in Human Auditory Cortex Is Shaped by Gabaergic Neuronal Inhibition

The 40 Hz auditory steady-state response (ASSR), an oscillatory brain response to periodically modulated auditory stimuli, is a promising, noninvasive physiological biomarker for schizophrenia and related neuropsychiatric disorders. The 40 Hz ASSR might be amplified by synaptic interactions in cortical circuits, which are, in turn, disturbed in neuropsychiatric disorders. Here, we tested whether the 40 Hz ASSR in the human auditory cortex depends on two key synaptic components of neuronal interactions within cortical circuits: excitation via N-methyl-aspartate glutamate (NMDA) receptors and inhibition via gamma-amino-butyric acid (GABA) receptors. We combined magnetoencephalography (MEG) recordings with placebo-controlled, low-dose pharmacological interventions in the same healthy human participants (13 males, 7 females). All participants exhibited a robust 40 Hz ASSR in auditory cortices, especially in the right hemisphere, under a placebo. The GABAA receptor-agonist lorazepam increased the amplitude of the 40 Hz ASSR, while no effect was detectable under the NMDA blocker memantine. Our findings indicate that the 40 Hz ASSR in the auditory cortex involves synaptic (and likely intracortical) inhibition via the GABAA receptor, thus highlighting its utility as a mechanistic signature of cortical circuit dysfunctions involving GABAergic inhibition.

Abnormal phase entrainment of low- and high-gamma-band auditory steady-state responses in schizophrenia

Introduction

Gamma-band oscillatory deficits have attracted considerable attention as promising biomarkers of schizophrenia (SZ). Notably, a reduced auditory steady-state response (ASSR) in the low gamma band (40 Hz) is widely recognized as a robust finding among SZ patients. However, a comprehensive investigation into the potential utility of the high-gamma-band ASSR in detecting altered neural oscillations in SZ has not yet been conducted.

Methods

The present study aimed to assess the ASSR using magnetoencephalography (MEG) data obtained during steady-state stimuli at frequencies of 20, 30, 40, and 80 Hz from 23 SZ patients and 21 healthy controls (HCs). To evaluate the ASSR, we examined the evoked power and phase-locking factor (PLF) in the time-frequency domain for both the primary and secondary auditory cortices. Furthermore, we calculated the phase-locking angle (PLA) to examine oscillatory phase lead or delay in SZ patients. Taking advantage of the high spatial resolution of MEG, we also focused on the hemispheric laterality of low- and high-gamma-band ASSR deficits in SZ.

Results

We found abnormal phase delay in the 40 Hz ASSR within the bilateral auditory cortex of SZ patients. Regarding the 80 Hz ASSR, our investigation identified an aberrant phase lead in the left secondary auditory cortex in SZ, accompanied by reduced evoked power in both auditory cortices.

Discussion

Given that abnormal phase lead on 80 Hz ASSR exhibited the highest discriminative power between HC and SZ, we propose that the examination of PLA in the 80 Hz ASSR holds significant promise as a robust candidate for identifying neurophysiological endophenotypes associated with SZ. Furthermore, the left-hemisphere phase lead observed in the deficits of 80 Hz PLA aligns with numerous prior studies, which have consistently proposed that SZ is characterized by left-lateralized brain dysfunctions.

Auditory steady-state responses in the auditory cortex of mice during estrus cycle

Auditory-steady state responses (ASSRs) disclose brain's potency to oscillate and have been suggested to serve as biomarkers in various psychiatric disorders. GABAergic neurotransmission, a critical component for brain oscillations, is heavily influenced by sex hormones. In line, the severity of symptoms in psychiatric disorders is linked to changes in sex hormones during menstrual cycle. However, how these sex hormones affect ASSRs remain largely unknown. This was addressed by performing chronic recordings of ASSRs in mice while monitoring its estrus cycle. Here, the stability of ASSRs during long term recordings were validated and showed good reliability. 40 Hz ASSRs showed changes throughout estrus cycle where it decreased in metestrus phase compared to diestrus phase. In contrast, other frequency ASSRs did not show significant changes throughout estrus cycle. Taken together, our findings illustrate that the estrus cycle can influence the generation of ASSRs and the phase of the estrus cycle should be taken into consideration when ASSRs are recorded in females.

hUC-MSC-mediated recovery of subacute spinal cord injury through enhancing the pivotal subunits β3 and γ2 of the GABAA receptor

Rationale: Spinal cord injury (SCI) remains an incurable neurological disorder leading to permanent and profound neurologic deficits and disabilities. Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) are particularly appealing in SCI treatment to curtail damage, restore homeostasis and possible neural relay. However, the detailed mechanisms underlying hUC-MSC-mediated functional recovery of SCI have not been fully elucidated. The purpose of our current study is to identify novel therapeutic targets and depict the molecular mechanisms underlying the hUC-MSC-mediated recovery of subacute SCI. Methods: Adult female rats suffering from subacute incomplete thoracic SCI were treated with intrathecal transplantation of hUC-MSCs. The beneficial effects of hUC-MSCs on SCI repair were evaluated by a series of behavioral analyses, motor evoked potentials (MEPs) recording of hindlimb and immunohistochemistry. We carried out extensive transcriptome comparative analyses of spinal cord tissues at the lesion site from the subacute phase of SCI (sub-SCI) either treated without (+PBS) or with hUC-MSCs (+MSC) at 0 (sub-SCI), 1, 2, and 4 weeks post-transplantation (wpt), as well as normal spinal cord segments of intact/sham rats (Intact). Adeno-associated virus (AAV)-mediated neuron-specific expression system was employed to functionally screen specific γ-aminobutyric acid type A receptor (GABAAR) subunits promoting the functional recovery of SCI in vivo. The mature cortical axon scrape assay and transplantation of genetically modified MSCs with either overexpression or knockdown of brain-derived neurotrophic factor (BDNF) were employed to demonstrate that hUC-MSCs ameliorated the reduction of GABAAR subunits in the injured spinal cord via BDNF secretion in vitro and in vivo, respectively. Results: Comparative transcriptome analysis revealed the GABAergic synapse pathway is significantly enriched as a main target of hUC-MSC-activated genes in the injured spinal cord. Functional screening of the primary GABAAR subunits uncovered that Gabrb3 and Garbg2 harbored the motor and electrophysiological recovery-promoting competence. Moreover, targeting either of the two pivotal subunits β3 or γ2 in combination with/without the K+/Cl- cotransporter 2 (KCC2) reinforced the therapeutic effects. Mechanistically, BDNF secreted by hUC-MSCs contributed to the upregulation of GABAAR subunits (β3 & γ2) and KCC2 in the injured neurons. Conclusions: Our study identifies a novel mode for hUC-MSC-mediated locomotor recovery of SCI through synergistic upregulation of GABAAR β3 and γ2 along with KCC2 by BDNF secretion, indicating the significance of restoring the excitation/inhibition balance in the injured neurons for the reestablishment of neuronal circuits. This study also provides a potential combinatorial approach by targeting the pivotal subunit β3 or γ2 and KCC2, opening up possibilities for efficacious drug design.

Gamma power abnormalities in a Fmr1-targeted transgenic rat model of fragile X syndrome

Fragile X syndrome (FXS) is characteristically displayed intellectual disability, hyperactivity, anxiety, and abnormal sensory processing. Electroencephalography (EEG) abnormalities are also observed in subjects with FXS, with many researchers paying attention to these as biomarkers. Despite intensive preclinical research using Fmr1 knock out (KO) mice, an effective treatment for FXS has yet to be developed. Here, we examined Fmr1-targeted transgenic rats (Fmr1-KO rats) as an alternative preclinical model of FXS. We characterized the EEG phenotypes of Fmr1-KO rats by measuring basal EEG power and auditory steady state response (ASSR) to click trains of stimuli at a frequency of 10–80 Hz. Fmr1-KO rats exhibited reduced basal alpha power and enhanced gamma power, and these rats showed enhanced locomotor activity in novel environment. While ASSR clearly peaked at around 40 Hz, both inter-trial coherence (ITC) and event-related spectral perturbation (ERSP) were significantly reduced at the gamma frequency band in Fmr1-KO rats. Fmr1-KO rats showed gamma power abnormalities and behavioral hyperactivity that were consistent with observations reported in mouse models and subjects with FXS. These results suggest that gamma power abnormalities are a translatable biomarker among species and demonstrate the utility of Fmr1-KO rats for investigating drugs for the treatment of FXS.