GABAergic Synaptic Transmission Research Articles

Integration of bioinformatics and machine learning approaches for the validation of pyrimidine metabolism-related genes and their implications in immunotherapy for osteoporosis

BackgroundOsteoporosis (OP), the “silent epidemic” of our century, poses a significant challenge to public health, predominantly affecting postmenopausal women and the elderly. It evolves from mild symptoms to pronounced severity, stabilizing eventually. Unique among OP’s characteristics is the altered metabolic profile of affected cells, particularly in pyrimidine metabolism (PyM), a crucial pathway for nucleotide turnover and pyrimidine decomposition. While metabolic adaptation is acknowledged as a therapeutic target in various diseases, the specific role of PyM genes (PyMGs) in OP’s molecular response remains to be clarified.MethodsIn pursuit of elucidating and authenticating PyMGs relevant to OP, we embarked on a comprehensive bioinformatics exploration. This entailed the integration of Weighted Gene Co-expression Network Analysis (WGCNA) with a curated list of 37 candidate PyMGs, followed by the examination of their biological functions and pathways via Gene Set Variation Analysis (GSVA). The Least Absolute Shrinkage and Selection Operator (LASSO) technique was harnessed to identify crucial hub genes. We evaluated the diagnostic prowess of five PyMGs in OP detection and explored their correlation with OP’s clinical traits, further validating their expression profiles through independent datasets (GSE2208, GSE7158, GSE56815, and GSE35956).ResultsOur analytical rigor unveiled five PyMGs—IGKC, TMEM187, RPS11, IGLL3P, and GOLGA8N—with significant ties to OP. A deeper dive into their biological functions highlighted their roles in estrogen response modulation, cytosolic calcium ion concentration regulation, and GABAergic synaptic transmission. Remarkably, these PyMGs emerged as potent diagnostic biomarkers for OP, distinguishing affected individuals with substantial accuracy.ConclusionsThis investigation brings to light five PyMGs intricately associated with OP, heralding new avenues for biomarker discovery and providing insights into its pathophysiological underpinnings. These findings not only deepen our comprehension of OP’s complexity but also herald the advent of more refined diagnostic and therapeutic modalities.

Cell-Type-Specific Effects of Somatostatin on Synaptic Transmission in the Anterior Cingulate Cortex.

Inhibitory modulation of glutamatergic information processing is a prerequisite for proper network function. Among the many groups of interneurons (INs), somatostatin-expressing interneurons (SOM-INs) play an important role in the maintenance of physiological brain activity. We have previously shown that somatostatin (SOM) causes a reduction in pyramidal cell (PC) excitability. However, the mechanisms of action of the peptide on cortical synaptic circuits are still unclear. To understand the effects of the neuropeptide SOM on cortical synaptic circuits, we performed a detailed side-by-side comparison of its postsynaptic effects on PCs, SOM-INs, and layer 1 interneurons (L1-INs) in the anterior cingulate cortex of male and female mice and found that SOM produced pronounced postsynaptic effects in PCs while having little to no effect on either IN type. This comparison allowed us to link the observed postsynaptic effects to SOM-induced modulations of glutamatergic and GABAergic synaptic transmission and to trace the impact of the neuropeptide on the neuronal circuitry between these three cell types. We show here that SOM depresses glutamatergic synaptic transmission via a presynaptic mechanism while exerting a differential impact on GABAA receptor- and GABAB receptor-mediated transmission at the pre- and postsynaptic level resulting in a shift of inhibition in L2/3 PCs from L1-INs to SOM-INs. In summary, this study unravels a novel aspect by which SOM modulates synaptic signaling between PCs, L1-INs, and SOM-INs.

GABAB receptor-mediated modulation in the developing dorsal nucleus of the lateral lemniscus.

The dorsal nucleus of the lateral lemniscus (DNLL) is a GABAergic, reciprocally connected auditory brainstem structure that continues to develop postnatally in rodents. One key feature of the DNLL is the generation of a strong, prolonged, ionotropic, GABAA receptor-mediated inhibition. Possible GABAB receptor-mediated signalling is unexplored in the DNLL. Here, we used Mongolian gerbils of either sex to describe GABAB receptor-mediated modulation of postsynaptic potassium currents and synaptic inputs in postnatal (P) animals of days 10/11 and 23-28. Throughout development, we observed the presence of a Baclofen-activated GABAB receptor-enhanced potassium outward conductance that is capable of suppressing action potential generation. In P10/11, old gerbils GABAB receptor activation enhances glutamatergic and suppresses ionotropic GABAergic synaptic transmission. During development, this differential modulation becomes less distinct, because in P22-28, old animals Baclofen-activated GABAB receptors rather enhance ionotropic GABAergic synaptic transmission, whereas glutamatergic transmission is both enhanced and suppressed. Blocking GABAB receptors causes an increase in ionotropic GABAergic transmission in P10/11 old gerbils that was independent on stimulation frequency but depended on the type of short-term plasticity. Together with the lack of Baclofen-induced changes in the synaptic paired-pulse ratio of either input type, we suggest that GABAB receptor-mediated modulation is predominantly postsynaptic and activates different signalling cascades. Thus, we argue that in DNLL neurons, the GABAB receptor is a post-synaptically located signalling hub that alters signalling cascades during development for distinct targets.

Aralia continentalis Root Enhances Non-Rapid Eye Movement Sleep by Activating GABAA Receptors.

Aralia continentalis exhibits various biological activities; however, their sleep-promoting effects have not been previously reported. In this study, we evaluated the hypnotic effects and sleep-wake profiles of A. continentalis root (KS-126) using a pentobarbital-induced sleep-acceleration test and polysomnographic recordings. Additionally, we investigated the molecular mechanism of KS-126 through patch-clamp electrophysiology. Our polysomnographic recordings revealed that KS-126 not only accelerated the onset of non-rapid eye movement sleep (NREMS) but also extends its duration. Considering the temporal dynamics of the sleep-wake stages, during the initial and subsequent periods KS-126 extended NREMS duration and decreased wakefulness, thereby enhancing sleep-promoting effects. Furthermore, the assessment of sleep quality via analysis of electroencephalogram power density indicated that KS-126 did not significantly alter sleep intensity. Finally, we found that KS-126 enhanced GABAA receptor-mediated synaptic responses in primary hippocampal neurons, leading to an increase in the percentage of the GABA current. This effect was not affected by the selective benzodiazepine receptor antagonist flumazenil, but was entirely inhibited by the GABAA receptor antagonist bicuculline. In conclusion, KS-126 extends the duration of NREMS without altering its intensity by prolonging GABAergic synaptic transmission, which modulates GABAA receptor function.

Disinhibition does not play a role in endomorphin-2-induced changes in inspiratory motoneuron output produced by in vitro neonatal rat preparations

Low level activation of mu-opioid receptors (MORs) in neonatal rat brainstem-spinal cord preparations increases inspiratory burst amplitude recorded on cervical spinal roots. We tested whether: (1) MOR activation with an endogenous ligand, such as endomorphin-2, increases inspiratory burst amplitude, (2) disinhibition of GABAergic or glycinergic inhibitory synaptic transmission is involved, and (3) inflammation alters endomorphin-2 effects. Using neonatal rat (P0-P3) brainstem-spinal cord preparations, bath-applied endomorphin-2 (10–200 nM) increased inspiratory burst amplitude and decreased burst frequency. Blockade of GABAA receptors (picrotoxin), glycine receptors (strychnine), or both (picrotoxin and strychnine) did not abolish endomorphin-2-induced effects. In preparations isolated from neonatal rats injected 3 h previously with lipopolysaccharide (LPS, 0.1 mg/kg), endomorphin-2 continued to decrease burst frequency but abolished the burst amplitude increase. Collectively, these data indicate that disinhibition of inhibitory synaptic transmission is unlikely to play a role in endomorphin-2-induced changes in inspiratory motor output, and that different mechanisms underlie the endomorphin-2-induced increases in inspiratory burst amplitude and decreases in burst frequency.

5-HT6 Receptors Control GABAergic Transmission and CA1 Pyramidal Cell Output of Dorsal Hippocampus.

The blockade of 5-HT6 receptors represents an experimental approach that might ameliorate the memory deficits associated with brain disorders, including Alzheimer's disease and schizophrenia. However, the synaptic mechanism by which 5-HT6 receptors control the GABAergic and glutamatergic synaptic transmission is barely understood. In this study, we demonstrate that pharmacological manipulation of 5-HT6 receptors with the specific agonist EMD 386088 (7.4nM) or the antagonist SB-399885 (300nM) modulates the field inhibitory postsynaptic potentials of the dorsal hippocampus and controls the strength of the population spike of pyramidal cells. Likewise, pharmacological modulation of 5-HT6 controls the magnitude of paired-pulse inhibition, a phenomenon mediated by GABAergic interneurons acting via GABAA receptors of pyramidal cells. The effects of pharmacological manipulation of the 5-HT6 receptor were limited to GABAergic transmission and did not affect the strength of field excitatory postsynaptic potentials mediated by the Schaffer collaterals axons. Lastly, in a modified version of the Pavlovian autoshaping task that requires the activation of the hippocampal formation, we demonstrated that the anti-amnesic effect induced by the blockade of the 5-HT6 receptor is prevented when the GAT1 transporter is blocked, suggesting that modulation of GABAergic transmission is required for the anti-amnesic properties of 5-HT6 receptor antagonists.

Impact and Role of Hypothalamic Corticotropin Releasing Hormone Neurons in Withdrawal from Chronic Alcohol Consumption in Female and Male Mice.

Worldwide, alcohol use and abuse are a leading risk of mortality, causing 5.3% of all deaths (World Health Organization, 2022). The endocrine stress system, initiated by the peripheral release of corticotropin releasing hormone (CRH) from primarily glutamatergic neurons in the paraventricular nucleus of the hypothalamus (PVN), is profoundly linked with alcohol use, abuse, and relapse (Blaine and Sinha, 2017). These PVN CRH-releasing (PVNCRH) neurons are essential for peripheral and central stress responses (Rasiah et al., 2023), but little is known about how alcohol affects these neurons. Here, we show that two-bottle choice alcohol consumption blunts the endocrine-mediated corticosterone response to stress during acute withdrawal in female mice. Conversely, using slice electrophysiology, we demonstrate that acute withdrawal engenders a hyperexcitable phenotype of PVNCRH neurons in females that is accompanied by increased glutamatergic transmission in both male and female mice. GABAergic synaptic transmission was unaffected by alcohol history. We then tested whether chemogenetic inhibition of PVNCRH neurons would restore stress response in female mice with a history of alcohol drinking in the looming disk test, which mimics an approaching predator threat. Accordingly, inhibition of PVNCRH neurons reduced active escape in hM4Di alcohol history mice only. This study indicates that stress-responsive PVNCRH neurons in females are particularly affected by a history of alcohol consumption. Interestingly, women have indicated an increase in heavy alcohol use to cope with stress (Rodriguez et al., 2020), perhaps pointing to a potential underlying mechanism in alcohol-mediated changes to PVNCRH neurons that alter stress response.SIGNIFICANCE STATEMENT Paraventricular nucleus of the hypothalamus neurons that release corticotropin releasing hormone (PVNCRH) are vital for stress response. These neurons have been understudied in relation to alcohol and withdrawal despite profound relations between stress, alcohol use disorders (AUD), and relapse. In this study, we use a variety of techniques to show that acute withdrawal from a history of alcohol impacts peripheral stress response, PVNCRH neurons, and behavior. Specifically, PVNCRH are in a hyperactive state during withdrawal, which drives an increase in active stress coping behaviors in female mice only. Understanding how alcohol use and withdrawal affects stress responding PVNCRH neurons may contribute to finding new potential targets for the treatment of alcohol use disorder.

Quantitative GABA magnetic resonance spectroscopy as a measure of motor learning function in the motor cortex after subarachnoid hemorrhage.

The neural mechanisms underlying gross and fine motor dysfunction after subarachnoid hemorrhage (SAH) remain unknown. The γ-aminobutyric acid (GABA) deficit hypothesis proposes that reduced neuronal GABA concentrations and the subsequent lack of GABA-mediated inhibition cause motor impairment after SAH. This study aimed to explore the correlation between GABA levels and a behavioral measure of motor performance in patients with SAH. Motor cortical GABA levels were assessed in 40 patients with SAH and 10 age-matched healthy controls using proton magnetic resonance spectroscopy. The GABA and N-acetylasparate (NAA) ratio was measured in the normal gray matter within the primary motor cortex. The relationship between GABA concentration and hand-motor performance was also evaluated. Results showed significantly lower GABA levels in patients with SAH's left motor cortex than in controls (GABA/NAA ratio: 0.282 ± 0.085 vs. 0.341 ± 0.031, respectively; p = 0.041). Reaction times (RTs), a behavioral measure of motor performance potentially dependent on GABAergic synaptic transmission, were significantly longer in patients than in controls (936.8 ± 303.8 vs. 440.2 ± 67.3 ms, respectively; p < 0.001). Moreover, motor cortical GABA levels and RTs exhibited a significant positive linear correlation among patients (r = 0.572, rs = 0.327, p = 0.0001). Therefore, a decrease in GABA levels in the primary motor cortex after SAH may lead to impaired cortical inhibition of neuronal function and indicates that GABA-mediated synaptic transmission in the motor cortex is critical for RT.

Chronic treatment with D2-antagonist haloperidol leads to inhibitory/excitatory imbalance in striatal D1-neurons

Striatal dysfunction has been implicated in the pathophysiology of schizophrenia, a disorder characterized by positive symptoms such as hallucinations and delusions. Haloperidol is a typical antipsychotic medication used in the treatment of schizophrenia that is known to antagonize dopamine D2 receptors, which are abundantly expressed in the striatum. However, haloperidol’s delayed therapeutic effect also suggests a mechanism of action that may go beyond the acute blocking of D2 receptors. Here, we performed proteomic analysis of striatum brain tissue and found more than 400 proteins significantly altered after 30 days of chronic haloperidol treatment in mice, namely proteins involved in glutamatergic and GABAergic synaptic transmission. Cell-type specific electrophysiological recordings further revealed that haloperidol not only reduces the excitability of striatal medium spiny neurons expressing dopamine D2 receptors (D2-MSNs) but also affects D1-MSNs by increasing the ratio of inhibitory/excitatory synaptic transmission (I/E ratio) specifically onto D1-MSNs but not D2-MSNs. Therefore, we propose the slow remodeling of D1-MSNs as a mechanism mediating the delayed therapeutic effect of haloperidol over striatum circuits. Understanding how haloperidol exactly contributes to treating schizophrenia symptoms may help to improve therapeutic outcomes and elucidate the molecular underpinnings of this disorder.

Fasting Modulates GABAergic Synaptic Transmission to Arcuate Kisspeptin Neurons in Female Mice.

It is well-established that the hypothalamic-pituitary-gonadal (HPG) axis is suppressed due to negative energy balance. However, less information is available on whether kisspeptin neuronal activity contributes to fasting-induced responses. In the present study, female and male mice were fasted for 24 hours or provided food ad libitum (fed group) to determine whether acute fasting is sufficient to modulate kisspeptin neuronal activity. In female mice, fasting attenuated luteinizing hormone (LH) and prolactin (PRL) serum levels and increased follicle-stimulating hormone levels compared with the fed group. In contrast, fasting did not affect gonadotropin or PRL secretion in male mice. By measuring genes related to LH pulse generation in micropunches obtained from the arcuate nucleus of the hypothalamus (ARH), we observed that fasting reduced Kiss1 mRNA levels in female and male mice. In contrast, Pdyn expression was upregulated only in fasted female mice, whereas no changes in the Tac2 mRNA levels were observed in both sexes. Interestingly, the frequency and amplitude of the GABAergic postsynaptic currents recorded from ARH kisspeptin neurons (ARHKisspeptin) were reduced in 24-hour fasted female mice but not in males. Additionally, neuropeptide Y induced a hyperpolarization in the resting membrane potential of ARHKisspeptin neurons of fed female mice but not in males. Thus, the response of ARHKisspeptin neurons to fasting is sexually dependent with a female bias, associated with changes in gonadotropins and PRL secretion. Our findings suggest that GABAergic transmission to ARHKisspeptin neurons modulates the activity of the HPG axis during situations of negative energy balance.

Isoliquiritigenin modulates the activity of LTS and non-LTS cells in the ventrolateral preoptic area via GABAA receptors

ObjectiveIsoliquiritigenin (ILTG) is a chalcone compound that exhibits hypnotic effects via gamma-aminobutyric acid type A (GABAA) receptors. The ventrolateral preoptic area (VLPO) is a sleep-promoting center that contains a large number of GABA-releasing cells. There are two cell types in the VLPO: one generates a low-threshold spike (LTS), whereas the other lacks an LTS (non-LTS). MethodWhole-cell patch-clamp technology was used to detect the firing and currents of LTS and non-LTS cells in the VLPO. ResultsBath administration of ILTG (10 μM) increased the firing rate of VLPO LTS cells, reversed by flumazenil (5 μM), a GABAA benzodiazepine site antagonist. However, the firing rate of VLPO non-LTS cells was inhibited by ILTG (10 μM), also reversed by flumazenil (5 μM). No differences were detected regarding resting membrane potential (RMP) amplitude, spike threshold, afterhyperpolarization (AHP) amplitude, or action potential duration (APD50) after ILTG (10 μM) perfusion in VLPO LTS cells. RMP amplitude was more hyperpolarized and spike threshold was higher after ILTG (10 μM) application in VLPO non-LTS cells. In addition, ILTG significantly reduced the frequency of miniature inhibitory postsynaptic currents (mIPSCs) in VLPO LTS cells. ILTG significantly increased the amplitude of mIPSCs in VLPO non-LTS cells. ConclusionsThis study revealed that ILTG suppresses presynaptic GABA release on VLPO LTS cells, thereby increasing their excitability. ILTG enhances postsynaptic GABAA receptor function on VLPO non-LTS cells, thereby decreasing their excitability. These results suggest that ILTG may produce hypnotic effects by modulating the GABAergic synaptic transmission properties of these two cell types.

Noradrenaline depresses facial stimulation-evoked cerebellar MLI-PC synaptic transmission via α2-AR/PKA signaling cascade in vivo in mice

The noradrenergic fibers of the locus coeruleus, together with mossy fibers and climbing fibers, comprise the three types of cerebellar afferents that modulate the cerebellar neuronal circuit. We previously demonstrated that noradrenaline (NA) modulated synaptic transmission in the mouse cerebellar cortex via adrenergic receptors (ARs). In the present study, we investigated the effect of NA on facial stimulation-evoked cerebellar molecular layer interneuron (MLI)-Purkinje cell (PC) synaptic transmission in urethane-anesthetized mice using an in vivo cell-attached recording technique and a pharmacological method. MLI-PC synaptic transmission was induced by air-puff stimulation (duration: 60 ms) of the ipsilateral whisker pad, which exhibited positive components (P1 and P2) accompanied by a pause in simple spike activity. Cerebellar molecular layer application of NA (15 µM) decreased the amplitude and area under the curve of P1, and the pause in simple spike activity, but increased the P2/P1 ratio. The NA-induced decrease in P1 amplitude was concentration-dependent, and the half-inhibitory concentration was 10.94 µM. The NA-induced depression of facial stimulation-evoked MLI-PC GABAergic synaptic transmission was completely abolished by blockade of α-ARs or α2-ARs, but not by antagonism of α1-ARs or β-ARs. Bath application of an α2-AR agonist inhibited MLI-PC synaptic transmission and attenuated the effect of NA on the synaptic response. NA-induced depression of MLI-PC synaptic transmission was completely blocked by a mixture of α2A- and 2B-AR antagonists, and was abolished by inhibition of protein kinase A. In addition, electrical stimulation of the molecular layer evoked MLI-PC GABAergic synaptic transmission in the presence of an AMPA receptor antagonist, which was inhibited by NA through α2-ARs. Our results indicate that NA inhibits MLI-PC GABAergic synaptic transmission by reducing GABA release via an α2-AR/PKA signaling pathway.

Dexmedetomidine relieves inflammatory pain by enhancing GABAergic synaptic activity in pyramidal neurons of the anterior cingulate cortex

Pyramidal neuron (Pyn) hyperactivity in the anterior cingulate cortex (ACC) is involved in the modulation of pain. Previous studies indicate that the activation of α2 adrenoceptors (α2-ARs) by dexmedetomidine (DEX) is a safe and effective means of alleviating multiple types of pain. Here, we showed that systemically administered DEX can ameliorate the inflammatory pain induced by hindpaw injection of formalin (FA) and further examined the molecular and synaptic mechanisms of this DEX-elicited antinociceptive effect. We found that FA caused an increase in c-Fos expression in contralateral layer 2/3 (L2/3) ACC, and that intra-ACC infusion of DEX could also relieve phase 2 inflammatory pain behavior. DEX elicited an increase in the amplitude and frequency of miniature inhibitory post-synaptic currents (mIPSCs) and evoked IPSC amplitude, as well as a reduction in the hyperexcitability and both paired-pulse and excitation/inhibition ratios in contralateral L2/3 ACC Pyns of FA mice. These electrophysiological effects were associated with the upregulation of GABA A receptor (GABAAR) subunits. The interaction of phosphorylated Akt (p-Akt) with GABAAR subunits increased in the ACC following administration of DEX. These results suggest that DEX treatment reduces hyperactivity and enhances GABAergic inhibitory synaptic transmission in ACC Pyns, which produces analgesic effects by increasing GABAAR levels and activating the Akt signaling pathway.

(R,S)-trihexyphenidyl, acting via a muscarinic receptor-independent mechanism, inhibits hippocampal glutamatergic and GABAergic synaptic transmissions: Potential relevance for treatment of organophosphorus intoxication

Preclinical studies have reported that, compared to the muscarinic receptor (mAChR) antagonist atropine, (R,S)-trihexyphenidyl (THP) more effectively counters the cholinergic crisis, seizures, and neuropathology triggered by organophosphorus (OP)-induced acetylcholinesterase (AChE) inhibition. The greater effectiveness of THP was attributed to its ability to block mAChRs and N-methyl-d-aspartate-type glutamatergic receptors (NMDARs) in the brain. However, THP also inhibits α7 nicotinic receptors (nAChRs). The present study examined whether THP-induced inhibition of mAChRs, α7 nAChRs, and NMDARs is required to suppress glutamatergic synaptic transmission, whose overstimulation sustains OP-induced seizures. In primary hippocampal cultures, THP (1–30 μM) suppressed the frequency of excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs, respectively) recorded from neurons in nominally Mg2+-free solution. A single sigmoidal function adequately fit the overlapping concentration-response relationships for THP-induced suppression of IPSC and EPSC frequencies yielding an IC50 of 6.3 ± 1.3 μM. Atropine (1 μM), the NMDAR antagonist d,l-2-amino-5-phosphonopentanoic acid (D,L-AP5, 50 μM), and the α7 nAChR antagonist methyllycaconitine (MLA, 10 nM) did not prevent THP-induced inhibition of synaptic transmission. THP (10 μM) did not affect the probability of transmitter release because it had no effect on the frequency of miniature IPSCs and EPSCs recorded in the presence of tetrodotoxin. Additionally, THP had no effect on the amplitudes and decay-time constants of miniature IPSCs and EPSCs; therefore, it did not affect the activity of postsynaptic GABAA and glutamate receptors. This study provides the first demonstration that THP can suppress action potential-dependent synaptic transmission via a mechanism independent of NMDAR, mAChR, and α7 nAChR inhibition.

Altered DNA methylome profiles of blood leukocytes in Chinese patients with mild cognitive impairment and Alzheimer's disease.

Objective: DNA methylation plays a potential role in the pathogenesis of Alzheimer's disease (AD). However, little is known about the global changes of blood leukocyte DNA methylome profiles from Chinese patients with mild cognitive impairment (MCI) and with AD, or the specific DNA methylation-based signatures associated with MCI and AD. In this study, we sought to dissect the characteristics of blood DNA methylome profiles in MCI- and AD-affected Chinese patients with the aim of identifying novel DNA methylation biomarkers for AD. Methods: In this study, we profiled the DNA methylome of peripheral blood leukocytes from 20 MCI- and 20 AD-affected Chinese patients and 20 cognitively healthy controls (CHCs) with the Infinium Methylation EPIC BeadChip array. Results: We identified significant alterations of the methylome profiles in MCI and AD blood leukocytes. A total of 2,582 and 20,829 CpG sites were significantly and differentially methylated in AD and MCI compared with CHCs (adjusted p < 0.05), respectively. Furthermore, 441 differentially methylated positions (DMPs), aligning to 213 unique genes, were overlapped by the three comparative groups of AD versus CHCs, MCI versus CHCs, and AD versus MCI, of which 6 and 5 DMPs were continuously hypermethylated and hypomethylated in MCI and AD relative to CHCs (adjusted p < 0.05), respectively, such as FLNC cg20186636 and AFAP1 cg06758191. The DMPs with an area under the curve >0.900, such as cg18771300, showed high potency for predicting MCI and AD. In addition, gene ontology and pathway enrichment results showed that these overlapping genes were mainly involved in neurotransmitter transport, GABAergic synaptic transmission, signal release from synapse, neurotransmitter secretion, and the regulation of neurotransmitter levels. Furthermore, tissue expression enrichment analysis revealed a subset of potentially cerebral cortex-enriched genes associated with MCI and AD, including SYT7, SYN3, and KCNT1. Conclusion: This study revealed a number of potential biomarkers for MCI and AD, also highlighted the presence of epigenetically dysregulated gene networks that may engage in the underlying pathological events resulting in the onset of cognitive impairment and AD progression. Collectively, this study provides prospective cues for developing therapeutic strategies to improve cognitive impairment and AD course.

Tonic activation of GABAB receptors via GAT-3 mediated GABA release reduces network activity in the developing somatosensory cortex in GAD67-GFP mice.

The efficiency of neocortical information processing critically depends on the balance between the glutamatergic (excitatory, E) and GABAergic (inhibitory, I) synaptic transmission. A transient imbalance of the E/I-ratio during early development might lead to neuropsychiatric disorders later in life. The transgenic glutamic acid decarboxylase 67-green fluorescent protein (GAD67-GFP) mouse line (KI) was developed to selectively visualize GABAergic interneurons in the CNS. However, haplodeficiency of the GAD67 enzyme, the main GABA synthetizing enzyme in the brain, temporarily leads to a low GABA level in the developing brain of these animals. However, KI mice did not demonstrate any epileptic activity and only few and mild behavioral deficits. In the present study we investigated how the developing somatosensory cortex of KI-mice compensates the reduced GABA level to prevent brain hyperexcitability. Whole-cell patch clamp recordings from layer 2/3 pyramidal neurons at P14 and at P21 revealed a reduced frequency of miniature inhibitory postsynaptic currents (mIPSCs) in KI mice without any change in amplitude or kinetics. Interestingly, mEPSC frequencies were also decreased, while the E/I-ratio was nevertheless shifted toward excitation. Surprisingly, multi-electrode-recordings (MEA) from acute slices revealed a decreased spontaneous neuronal network activity in KI mice compared to wild-type (WT) littermates, pointing to a compensatory mechanism that prevents hyperexcitability. Blockade of GABAB receptors (GABABRs) with CGP55845 strongly increased the frequency of mEPSCs in KI, but failed to affect mIPSCs in any genotype or age. It also induced a membrane depolarization in P14 KI, but not in P21 KI or WT mice. MEA recordings in presence of CGP55845 revealed comparable levels of network activity in both genotypes, indicating that tonically activated GABABRs balance neuronal activity in P14 KI cortex despite the reduced GABA levels. Blockade of GABA transporter 3 (GAT-3) reproduced the CGP55845 effects suggesting that tonic activation of GABABRs is mediated by ambient GABA released via GAT-3 operating in reverse mode. We conclude that GAT-3-mediated GABA release leads to tonic activation of both pre- and postsynaptic GABABRs and restricts neuronal excitability in the developing cortex to compensate for reduced neuronal GABA synthesis. Since GAT-3 is predominantly located in astrocytes, GAD67 haplodeficiency may potentially stimulate astrocytic GABA synthesis through GAD67-independent pathways.

The potential role of astroglial GABAA receptors in autoimmune encephalitis associated with GABAA receptor antibodies and seizures.

The γ-aminobutyric acid (GABA) is the main inhibitory transmitter in the central nervous system and GABA receptors mediate the inhibitory synaptic transmission. GABA binding to neuronal GABAA R leads to a rapid hyperpolarization and a higher excitation threshold due to an increase in membrane Cl- permeability. The synaptic GABAA R is mostly composed of two α(1-3), two β, and one γ subunit with the most abundant configuration α1β2γ2. Recently, antibodies (Abs) against α1, β3, and γ2 subunits of GABAA R were detected in a severe form of autoimmune encephalitis with refractory seizures, status epilepticus, and multifocal brain lesions, affecting gray and white matter. Experimental studies confirmed multiple mechanisms and direct functional effects of GABAA R Abs on neurons with decreased GABAergic synaptic transmission and increased neuronal excitability. The expression of GABAA R on astrocytes is well established. However, extensive studies about the effects of autoimmune GABAA R Abs on astrocytic GABAA R are missing. We hypothesize that GABAA R Abs may lead additionally to blocking astrocytic GABAA Rs with impaired Ca2+ homeostasis/spreading, astrocytic Cl- imbalance, dysfunction of astrocyte-mediated gliotransmission (e.g., decreased adenosine levels) and accumulation of excitatory neurotransmission, all this contributing to seizures, variable clinical/MRI presentations, and severity. The most abundant expressed GABAA R subunits in rodent astrocytes are α1, α2, β1, β3, and γ1 localized in both white and gray matter. Data about GABAA R subunits in human astrocytes are even more limited, comprising α2, β1, and γ1. Overlapping binding of GABAA R Abs to neuronal and astroglial receptors is still possible. In vitro and in vivo animal models can be helpful to test the effects of GABAA R Abs on glia. This is from an epileptological point of view relevant because of the increasing evidence, confirming the glial involvement in the pathogenesis of epilepsy. Taken together, autoimmune disorders are complex and multiple mechanisms including glia could contribute to the pathogenesis of GABAA R encephalitis with seizures.

DSCAM gene triplication causes excessive GABAergic synapses in the neocortex in Down syndrome mouse models.

Down syndrome (DS) is caused by the trisomy of human chromosome 21 (HSA21). A major challenge in DS research is to identify the HSA21 genes that cause specific symptoms. Down syndrome cell adhesion molecule (DSCAM) is encoded by a HSA21 gene. Previous studies have shown that the protein level of the Drosophila homolog of DSCAM determines the size of presynaptic terminals. However, whether the triplication of DSCAM contributes to presynaptic development in DS remains unknown. Here, we show that DSCAM levels regulate GABAergic synapses formed on neocortical pyramidal neurons (PyNs). In the Ts65Dn mouse model for DS, where DSCAM is overexpressed due to DSCAM triplication, GABAergic innervation of PyNs by basket and chandelier interneurons is increased. Genetic normalization of DSCAM expression rescues the excessive GABAergic innervations and the increased inhibition of PyNs. Conversely, loss of DSCAM impairs GABAergic synapse development and function. These findings demonstrate excessive GABAergic innervation and synaptic transmission in the neocortex of DS mouse models and identify DSCAM overexpression as the cause. They also implicate dysregulated DSCAM levels as a potential pathogenic driver in related neurological disorders.

GABAergic synaptic transmission and plasticity oscillate across sleep and wake.

GABAergic synaptic transmission and plasticity oscillate across sleep and wake.

GLP-1 enhances hyperpolarization-activated currents of mouse cerebellar Purkinje cell in vitro.

Glucagon-like peptide-1 (GLP-1) is mainly secreted by preglucagonergic neurons in the nucleus tractus solitarius, which plays critical roles in regulation of neuronal activity in the central nervous system through its receptor. In the cerebellar cortex, GLP-1 receptor is abundantly expressed in the molecular layer, Purkinje cell (PC) layer and granular layer, indicating that GLP-1 may modulate the cerebellar neuronal activity. In this study, we investigated the mechanism by which GLP1 modulates mouse cerebellar PC activity in vitro. After blockade of glutamatergic and GABAergic synaptic transmission in PCs, GLP1 increased the spike firing rate accompanied by depolarization of membrane potential and significantly depressed the after-hyperpolarizing potential and outward rectifying current of spike firing discharges via GLP1 receptors. In the presence of TTX and Ba2+, GLP1 significantly enhanced the hyperpolarized membrane potential-evoked instant current, steady current, tail current (I-tail) and hyperpolarization-activated (IH) current. Application of a selective IH channel antagonist, ZD7288, blocked IH and abolished the effect of GLP1 on PC membrane currents. The GLP1 induced enhancement of membrane currents was also abolished by a selective GLP1 receptor antagonist, exendin-9-39, as well as by protein kinase A (PKA) inhibitors, KT5720 and H89. In addition, immunofluorescence detected GLP1 receptor in the mouse cerebellar cortex, mostly in PCs. These results indicated that GLP1 receptor activation enhanced IH channel activity via PKA signaling, resulting in increased excitability of mouse cerebellar PCs in vitro. The present findings indicate that GLP1 plays a critical role in modulating cerebellar function by regulating the spike firing activity of mouse cerebellar PCs.