Inhibitory Neurotransmitter Research Articles

WITHDRAWN: Elevated GABAergic neurotransmission prevents chronic intermittent ethanol induced hyperexcitability of intrinsic and extrinsic inputs to the ventral subiculum of female rats

With the recent rise in the rate of alcohol use disorder (AUD) in women, the historical gap between men and women living with this condition is narrowing. While there are many commonalities in how men and women are impacted by AUD, an accumulating body of evidence is revealing sex-dependent adaptations that may require distinct therapeutic approaches. Preclinical rodent studies are beginning to shed light on sex differences in the effects of chronic alcohol exposure on synaptic activity in a number of brain regions. Prior studies from our laboratory revealed that, while withdrawal from chronic intermittent ethanol (CIE), a commonly used model of AUD, increased excitability in the ventral hippocampus (vHC) of male rats, this same treatment had the opposite effect in females. A follow-up study not only expanded on the synaptic mechanisms of these findings in male rats, but also established a CIE-dependent increase in the excitatory-inhibitory (E-I) balance of a glutamatergic projection from the basolateral amygdala to vHC (BLA-vHC). This pathway modulates anxiety-like behavior and could help explain the comorbid occurrence of anxiety disorders in individuals suffering from AUD. The present study sought to conduct a similar analysis of CIE effects on both synaptic mechanisms in the vHC and adaptations in the BLA-vHC pathway of female rats. Our findings indicate that CIE increases the strength of inhibitory neurotransmission in the vHC and that this sex-specific adaptation blocks, or at least delays, the increases in intrinsic vHC excitability and BLA-vHC synaptic transmission observed in males. Our findings establish the BLA-vHC pathway and the vHC as important circuitry to consider for future studies directed at identifying sex-dependent therapeutic approaches to AUD.

Insights into the Synaptic Properties of Dopamine Release Revealed by Single Walled Carbon Nanotube Biosensors

It is thought that there are two distinct modes of chemical neurotransmission, referred to as fast (synaptic) transmission and slow (volume) transmission. Fast transmission, mediated by ligand-gated ionotropic receptors, operate with millisecond temporal and nanometer spatial precision in excitatory and inhibitory synapses, primarily mediated by glutamate and GABA, respectively. In contrast, slow transmission relies on activation of G-protein coupled receptors (GPCRs) and is mediated by several classes of neuromodulators, including dopamine. Neuromodulators are thought to operate at temporal scales that range from hundreds of milliseconds to minutes, with a spatial specificity that is insufficiently understood but generally described as “diffuse”. In this work, we provide new evidence that shows the spatial precision of dopamine transmission is highly reminiscent of the spatial properties of signaling mediated by the fast acting neurotransmitters.To gain this insight, we used an optical assay named “DopaFilm” that is based on oligonucleotide functionalized single walled carbon nanotube dopamine sensors (nanosensors). Primary dopaminergic neurons were grown on top of glass coverslips functionalized with nanosensors, which enabled visualization of dopamine exocytosis events in single release sites under a continuous 785nm excitation laser. In axonal arbors, DopaFilm can report evoked and spontaneous dopamine release events with high signal to noise ratios of up to 50. Recording on DopaFilm revealed dopamine release is fast, calcium-dependent, and reliant on similar presynaptic protein machinery employed by fast neurotransmitters. These findings challenge the notion that dopamine is a slow transmitter; however it doesn’t preclude the possibility of imprecise spatial signaling, consistent with volume transmission theory. More recent data from our lab now challenges the spatial characteristics of volume transmission model as currently understood in the literature. In this talk, I will discuss new insights gained on dopamine signaling including clear examples of precise spatial arrangements of dopamine release sites, and ultrastructural, biochemical and spatial transcriptomic data that shows that neuromodulatory action can be highly spatially precise in nature.

A dendrite is a dendrite is a dendrite? Dendritic signal integration beyond the "antenna" model.

Neurons in central nervous systems receive multiple synaptic inputs and transform them into a largely standardized output to their target cells-the action potential. A simplified model posits that synaptic signals are integrated by linear summation and passive propagation towards the axon initial segment, where the threshold for spike generation is either crossed or not. However, multiple lines of research during past decades have shown that signal integration in individual neurons is much more complex, with important functional consequences at the cellular, network, and behavioral-cognitive level. The interplay between concomitant excitatory and inhibitory postsynaptic potentials depends strongly on the relative timing and localization of the respective synapses. In addition, dendrites contain multiple voltage-dependent conductances, which allow scaling of postsynaptic potentials, non-linear input processing, and compartmentalization of signals. Together, these features enable a rich variety of single-neuron computations, including non-linear operations and synaptic plasticity. Hence, we have to revise over-simplified messages from textbooks and use simplified computational models like integrate-and-fire neurons with some caution. This concept article summarizes the most important mechanisms of dendritic integration and highlights some recent developments in the field.

Deletion of endocannabinoid synthesizing enzyme DAGLα from cerebellar Purkinje cells decreases social preference and elevates anxiety.

ABSTRACTThe endocannabinoid (eCB) signaling system is robustly expressed in the cerebellum starting from the embryonic developmental stages to adulthood. There it plays a key role in regulating cerebellar synaptic plasticity and excitability, suggesting that impaired eCB signaling will lead to deficits in cerebellar adjustments of ongoing behaviors and cerebellar learning. Indeed, human mutations inDAGLαare associated with neurodevelopmental disorders. In this study, we show that selective deletion of the eCB synthesizing enzyme diacylglycerol lipase alpha (Daglα) from mouse cerebellar Purkinje cells (PCs) alters motor and social behaviors, disrupts short-term synaptic plasticity in both excitatory and inhibitory synapses, and reduces Purkinje cell activity during social exploration. Our results provide the first evidence for cerebellar-specific eCB regulation of social behaviors and implicate eCB regulation of synaptic plasticity and PC activity as the neural substrates contributing to these deficits.Abstract FigureGraphical abstract.Cerebellar anatomy, morphology of Purkinje cells, localization, density, and spontaneous activity of excitatory and inhibitory synapses are normal in cerebellar-Purkinje-cell-specific Daglα KOs. However, endocannabinoid-dependent short-term synaptic plasticity (DSE and DSI) and activity of Purkinje cells in lobe VI during social exploration are dramatically reduced, and the KO mice exhibit alterations in sensorimotor coordination, deceased social preference, and increased anxiety.

Trolox, Ferulic, Sinapic, and Cinnamic Acid Derivatives of Proline and GABA with Antioxidant and/or Anti-Inflammatory Properties.

Degenerative conditions, such as neurodegenerative disorders (Alzheimer's disease (AD), Parkinson's disease (PD)) and cardiovascular diseases, are complex, multifactorial disorders whose pathophysiology has not been fully elucidated yet. As a result, the available treatment options cannot eliminate these diseases radically, but only alleviate the symptoms. Both inflammatory processes and oxidation are key factors in the development and evolution of neurodegeneration, while acetylcholinesterase inhibitors are the most used therapeutic options against AD. In this work, following the multi-targeting compound approach, we designed and synthesized a series of proline and gamma-aminobutyric acid (GABA) amides with various acidic moieties that possess an antioxidant and/or anti-inflammatory potency. Proline is the pharmacophore of nootropic drugs (e.g., piracetam) used for memory improvement, while GABA is the main inhibitory neurotransmitter in the central nervous system. The designed molecules were subjected to a preliminary screening of their bioactivity in antioxidant and anti-inflammatory assays, as well as against acetylcholinesterase. Most of the synthesized compounds could inhibit lipid peroxidation (IC50 as low as 8 μΜ) and oxidative protein glycation (inhibition of up to 48%) and reduce the 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH). In addition, all of the compounds were moderate inhibitors of lipoxygenase (LOX) (up to 46% at 100 μΜ) and could decrease carrageenan-induced paw edema in rats by up to 55%. Finally, some of the compounds were moderate acetylcholinesterase inhibitors (IC50 as low as 219 μΜ). The results confirmed the design rationale, indicating that the compounds could be further optimized as multi-targeting molecules directed against degenerative conditions.

Total Synthesis of (15R)- and (15S)-Prostaglandin A2.

From both pharmaceutical and structural perspectives, the large family of prostaglandins represent a truly remarkable class of natural products. Prostaglandin A2 is a tissue hormone naturally found in human seminal plasma and in the sea whip Plexaura homomalla with yet poorly understood biological or therapeutic effects. Herein, a novel strategy for the stereoselective construction of both naturally occurring prostaglandin A2 epimers and first insights into their functional effects on the major inhibitory neurotransmitter γ-aminobutyric acid (GABA) type A receptors (GABAAR) are provided. The synthesis of both epimers was achieved in only 11 steps starting from commercially available 2,5-dimethoxy-tetrahydrofuran employing an organocatalytic domino-aldol reaction, a Mizoroki-Heck reaction, a Wittig reaction as well as an oxidation-decarboxylation sequence. The (15R)-epimer significantly reduced GABA-induced currents through GABAA receptors while its (15S)-epimer did not show any significant effect. These data suggest that (15R)-PGA2 might serve as a novel scaffold for the development of selective GABAA receptor modulators.

Dorsomedial Striatum CB1R signaling is required for Pavlovian outcome devaluation in male Long Evans rats and reduces inhibitory synaptic transmission in both sexes.

Cannabinoid-1 receptor (CB1R) signaling in the dorsal striatum regulates the shift from flexible to habitual behavior in instrumental outcome devaluation. Based on prior work establishing individual, sex, and experience-dependent differences in Pavlovian behaviors, we predicted a role for dorsomedial striatum CB1R signaling in driving rigid responding in Pavlovian autoshaping and outcome devaluation. We trained male and female Long Evans rats in Pavlovian Lever Autoshaping (PLA). We gave intra-dorsomedial striatum (DMS) infusions of the CB1R inverse agonist, rimonabant, before satiety-induced outcome devaluation test sessions, where we sated rats on training pellets or home cage chow and tested them in brief nonreinforced Pavlovian Lever Autoshaping sessions. Overall, inhibition of DMS CB1R signaling prevented Pavlovian outcome devaluation but did not affect behavior in reinforced PLA sessions. Males were sensitive to devaluation while females were not and DMS CB1R inhibition impaired devaluation sensitivity in males. We then investigated how DMS CB1R signaling impacts local inhibitory synaptic transmission in male and female Long Evans rats. We recorded spontaneous inhibitory postsynaptic currents (sIPSC) from DMS neurons at baseline and before and after application of a CB1R agonist, WIN 55,212-2. We found that male rats showed decreased sIPSC frequency compared to females, and that CB1R activation reduced DMS inhibitory transmission independent of sex. Altogether our results demonstrate that DMS CB1Rs regulate Pavlovian devaluation sensitivity and inhibitory synaptic transmission and suggest that basal sex differences in inhibitory synaptic transmission may underly sex differences in DMS function and behavioral flexibility.

The relationship between visual acuity loss and GABAergic inhibition in amblyopia

Abstract Early childhood experience alters visual development, a process exemplified by amblyopia, a common neurodevelopmental condition resulting in cortically reduced vision in one eye. Visual deficits in amblyopia may be a consequence of abnormal suppressive interactions in the primary visual cortex by inhibitory neurotransmitter γ-aminobutyric acid (GABA). We examined the relationship between visual acuity loss and GABA+ in adult human participants with amblyopia. Single-voxel proton magnetic resonance spectroscopy (MRS) data were collected from the early visual cortex (EVC) and posterior cingulate cortex (control region) of 28 male and female adults with current or past amblyopia while they viewed flashing checkerboards monocularly, binocularly, or while they had their eyes closed. First, we compared GABA+ concentrations between conditions to evaluate suppressive binocular interactions. Then, we correlated the degree of visual acuity loss with GABA+ levels to test whether GABAergic inhibition could explain visual acuity deficits. Visual cortex GABA+ was not modulated by viewing condition, and we found weak evidence for a negative correlation between visual acuity deficits and GABA+. These findings suggest that reduced vision in one eye due to amblyopia is not strongly linked to GABAergic inhibition in the visual cortex. We advanced our understanding of early experience dependent plasticity in the human brain by testing the association between visual acuity deficits and visual cortex GABA in amblyopes of the most common subtypes. Our study shows that the relationship was not as clear as expected and provides avenues for future investigation.

Retina‐Like Chlorophyll Heterojunction‐Based Optoelectronic Memristor with All‐Optically Modulated Synaptic Plasticity Enabling Neuromorphic Edge Detection

AbstractOptoelectronic memristors, which possess the potential capacities of in‐sensor computing, promote the development of highly efficient neuromorphic vision. In this work, a novel optoelectronic memristor based on chlorophyll (Chl) heterojunction is proposed, which consists of two types of Chl derivatives (zinc methyl 3‐devinyl‐3‐hydroxymethyl‐pyropheophorbide‐a and methyl 131‐deoxo‐131‐dicyanomethylene‐pyropheophorbide‐a). Chl heterojunction improves the optoelectronic performance of the device due to its ability to efficiently separate photogenerated electron‐hole pairs. The device exhibits the synaptic potentiation and inhibition behaviors under light stimulations of 430 and 730 nm, respectively, thus demonstrating the all‐optically modulated synaptic plasticity. The switching mechanism can be attributed to the photo‐ionization/deionization of oxygen vacancies at the zinc oxide (ZnO)/Chl interface. In addition, the image pre‐processing functions of contrast enhancement and noise reduction are implemented in a memristive array. In particular, the edge detection function has been implemented by utilizing reversible optical modulation, which highlights the object outline. The optoelectronic memristor based on the Chl heterojunction proposed here provides a promising foundation for advancing neuromorphic vision.

Reduced Thalamic γ-Aminobutyric Acid (GABA) in Painless but Not Painful Diabetic Peripheral Neuropathy.

Alterations in the structure, function, and microcirculation of the thalamus, a key brain region involved in pain pathways, have previously been demonstrated in patients with Painless- and Painful-diabetic peripheral neuropathy (DPN). However, thalamic neurotransmitter levels including GABA (inhibitory neurotransmitter) and glutamate (excitatory neurotransmitter) in different DPN phenotypes are not known. We performed a Magnetic Resonance Spectroscopy study and quantified GABA and glutamate levels within the thalamus, in a carefully characterised cohort of participants with Painless- and Painful-DPN. Participants with DPN (Painful- and Painless combined) had a significantly lower GABA:H2O ratio compared to those without DPN (Healthy volunteers [HV] and diabetes without DPN [No-DPN]). Participants with Painless-DPN had the lowest GABA:H2O ratio, which reached significance compared with HV and No-DPN, but not Painful-DPN. There was no difference in GABA:H2O in Painful-DPN compared with all other groups. A significant correlation with GABA:H2O and neuropathy severity was also seen. This study demonstrates that lower levels of thalamic GABA in participants with Painless-DPN may reflect neuroplasticity due to reduced afferent pain impulses. Whereas partially preserved levels of GABA in Painful-DPN may indicate that central GABAergic pathways are involved in the mechanisms of neuropathic pain in diabetes.

Volume electron microscopy analysis of synapses in primary regions of the human cerebral cortex.

Functional and structural studies investigating macroscopic connectivity in the human cerebral cortex suggest that high-order associative regions exhibit greater connectivity compared to primary ones. However, the synaptic organization of these brain regions remains unexplored. In the present work, we conducted volume electron microscopy to investigate the synaptic organization of the human brain obtained at autopsy. Specifically, we examined layer III of Brodmann areas 17, 3b, and 4, as representative areas of primary visual, somatosensorial, and motor cortex. Additionally, we conducted comparative analyses with our previous datasets of layer III from temporopolar and anterior cingulate associative cortical regions (Brodmann areas 24, 38, and 21). 9,690 synaptic junctions were 3D reconstructed, showing that certain synaptic characteristics are specific to particular regions. The number of synapses per volume, the proportion of the postsynaptic targets, and the synaptic size may distinguish one region from another, regardless of whether they are associative or primary cortex. By contrast, other synaptic characteristics were common to all analyzed regions, such as the proportion of excitatory and inhibitory synapses, their shapes, their spatial distribution, and a higher proportion of synapses located on dendritic spines. The present results provide further insights into the synaptic organization of the human cerebral cortex.

Somatostatin Interneurons Recruit Pre- and Postsynaptic GABAB Receptors in the Adult Mouse Dentate Gyrus.

The integration of spatial information in the mammalian dentate gyrus (DG) is critical to navigation. Indeed, DG granule cells (DGCs) rely upon finely balanced inhibitory neurotransmission in order to respond appropriately to specific spatial inputs. This inhibition arises from a heterogeneous population of local GABAergic interneurons (INs) that activate both fast, ionotropic GABAA receptors (GABAAR) and slow, metabotropic GABAB receptors (GABABR), respectively. GABABRs in turn inhibit pre- and postsynaptic neuronal compartments via temporally long-lasting G-protein-dependent mechanisms. The relative contribution of each IN subtype to network level GABABR signal setting remains unknown. However, within the DG, the somatostatin (SSt) expressing IN subtype is considered crucial in coordinating appropriate feedback inhibition on to DGCs. Therefore, we virally delivered channelrhodopsin 2 to the DG in order to obtain control of this specific SSt IN subpopulation in male and female adult mice. Using a combination of optogenetic activation and pharmacology, we show that SSt INs strongly recruit postsynaptic GABABRs to drive greater inhibition in DGCs than GABAARs at physiological membrane potentials. Furthermore, we show that in the adult mouse DG, postsynaptic GABABR signaling is predominantly regulated by neuronal GABA uptake and less so by astrocytic mechanisms. Finally, we confirm that activation of SSt INs can also recruit presynaptic GABABRs, as has been shown in neocortical circuits. Together, these data reveal that GABABR signaling allows SSt INs to control DG activity and may constitute a key mechanism for gating spatial information flow within hippocampal circuits.

Optimization of Fermentative Parameters to Improve Gamma-Aminobutyric Acid (GABA) Production by Lactiplantibacillus plantarum B13

Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the mammalian brain, and it possesses several physiological properties, such as depression reduction and anxiety release. GABA production by microbial synthesis is favoured over other methods like enzymatic and chemical synthesis due to the ease of operation and less formation of harmful pollutants. Lactic acid bacteria are widely applied for GABA production because of high GABA yield and their Generally Recognized as Safe (GRAS) status , which is critical in food and ingredient safety. In this study, various fermentation conditions, including incubation time, pH, temperature, monosodium glutamate (MSG) concentration, pyridoxal-5’-phosphate (PLP) concentration and glucose concentration were screened by one-factor-at-a-time strategy to achieve the optimal GABA production by a potential probiotic strain, Lactiplantibacillus plantarum B13. The result revealed the strain exhibited the optimal GABA production of 19.073 ± 0.5214 g/L with the highest GABA productivity of 0.424 g/L/h under fixed conditions: incubation time of 66 hours, pH 5.5, temperature of 35°C, MSG concentration of 5% (w/v), PLP concentration of 0.7 mM PLP and glucose concentration of 60 g/L. The findings of this study show that fermentation parameters are dependent on species and strains due to the different properties of glutamic acid decarboxylase enzymes and optimization of single parameters is important as a preliminary step to identify the range of fermentation factors that affect GABA yield prior further research endeavours. This study also has great implications for GABA production by L. plantarum B13 and provides a prerequisite for developing new healthy products enriched with GABA as daily supplements to support relaxation and regulate mood, reduce stress and promote better sleep.

Forskolin reverses the O-GlcNAcylation dependent decrease in GABAAR current amplitude at hippocampal synapses possibly at a neurosteroid site on GABAARs

GABAergic transmission is influenced by post-translational modifications, like phosphorylation, impacting channel conductance, allosteric modulator sensitivity, and membrane trafficking. O-GlcNAcylation is a post-translational modification involving the O-linked attachment of β-N-acetylglucosamine on serine/threonine residues. Previously we reported an acute increase in O-GlcNAcylation elicits a long-term depression of evoked GABAAR inhibitory postsynaptic currents (eIPSCs) onto hippocampal principal cells. Importantly, O-GlcNAcylation and phosphorylation can co-occur or compete for the same residue; whether they interact in modulating GABAergic IPSCs is unknown. We tested this by recording IPSCs from hippocampal principal cells and pharmacologically increased O-GlcNAcylation, before or after increasing serine phosphorylation using the adenylate cyclase activator, forskolin. Although forskolin had no significant effect on baseline eIPSC amplitude, we found that a prior increase in O-GlcNAcylation unmasks a forskolin-dependent increase in eIPSC amplitude, reversing the O-GlcNAc-induced eIPSC depression. Inhibition of adenylate cyclase or protein kinase A did not prevent the potentiating effect of forskolin, indicating serine phosphorylation is not the mechanism. Surprisingly, increasing O-GlcNAcylation also unmasked a potentiating effect of the neurosteroids 5α-pregnane-3α,21-diol-20-one (THDOC) and progesterone on eIPSC amplitude in about half of the recorded cells, mimicking forskolin. Our findings show that under conditions of heightened O-GlcNAcylation, the neurosteroid site on synaptic GABAARs is possibly accessible to agonists, permitting strengthening of synaptic inhibition.

Crystal structure of the GluK1 ligand-binding domain with kainate and the full-spanning positive allosteric modulator BPAM538

Kainate receptors play an important role in the central nervous system by mediating postsynaptic excitatory neurotransmission and modulating the release of the inhibitory neurotransmitter GABA through a presynaptic mechanism. To date, only three structures of the ligand-binding domain (LBD) of the kainate receptor subunit GluK1 in complex with positive allosteric modulators have been determined by X-ray crystallography, all belonging to class II modulators. Here, we report a high-resolution structure of GluK1-LBD in complex with kainate and BPAM538, which belongs to the full-spanning class III. One BPAM538 molecule binds at the GluK1 dimer interface, thereby occupying two allosteric binding sites simultaneously. BPAM538 stabilizes the active receptor conformation with only minor conformational changes being introduced to the receptor. Using a calcium-sensitive fluorescence-based assay, a 5-fold potentiation of the kainate response (100 μM) was observed in presence of 100 μM BPAM538 at GluK1(Q)b, whereas no potentiation was observed at GluK2(VCQ)a. Using electrophysiology recordings of outside-out patches excised from HEK293 cells, BPAM538 increased the peak response of GluK1(Q)b co-expressed with NETO2 to rapid application of 10 mM L-glutamate with 130 ± 20 %, and decreased desensitization determined as the steady-state/peak response ratio from 23 ± 2 % to 90 ± 4 %. Based on dose–response relationship experiments on GluK1(Q)b the EC50 of BPAM538 was estimated to be 58 ± 29 μM.

Dysregulation of kappa opioid receptor neuromodulation of lateral habenula synaptic function following a repetitive mild traumatic brain injury

Mild traumatic brain injury (mTBI) increases the risk of affective disorders, anxiety and substance use disorder. The lateral habenula (LHb) plays an important role in pathophysiology of psychiatric disorders. Recently, we demonstrated a causal link between mTBI-induced LHb hyperactivity due to excitation/inhibition (E/I) imbalance and motivational deficits in male mice using a repetitive closed head injury mTBI model. A major neuromodulatory system that is responsive to traumatic brain injuries, influences affective states and also modulates LHb activity is the dynorphin/kappa opioid receptor (Dyn/KOR) system. However, the effects of mTBI on KOR neuromodulation of LHb function are unknown. Here, we first used retrograde tracing in male and female Cre mouse lines and identified several major KOR-expressing and two prominent Dyn-expressing inputs projecting to the mouse LHb, highlighting the medial prefrontal cortex (mPFC) and the ventromedial nucleus of the hypothalamus (VMH) as the main LHb-projecting Dyn inputs that regulate KOR signaling to the LHb. We then functionally evaluated the effects of in vitro KOR modulation of spontaneous synaptic activity within the LHb of male and female sham and mTBI mice at 4 week post-injury. We observed sex-specific differences in spontaneous release of glutamate and GABA from presynaptic terminals onto LHb neurons with higher levels of presynaptic glutamate and GABA release in females compared to male mice. However, KOR effects on the spontaneous E/I ratios and synaptic drive ratio within the LHb did not differ between male and female sham and mTBI mice. KOR activation generally suppressed spontaneous glutamatergic transmission without altering GABAergic transmission, resulting in a significant but sex-similar reduction in net spontaneous E/I and synaptic drive ratios in LHb neurons of sham mice. Following mTBI, while responses to KOR activation at LHb glutamatergic synapses remained intact, LHb GABAergic synapses acquired an additional sensitivity to KOR-mediated inhibition where we observed a reduction in GABA release probability in response to KOR stimulation in LHb neurons of mTBI mice. Further analysis of percent change in spontaneous synaptic ratios induced by KOR activation revealed that independent of sex mTBI switches KOR-driven synaptic inhibition of LHb neurons (normally observed in sham mice) in a subset of mTBI mice toward synaptic excitation resulting in mTBI-induced divergence of KOR actions within the LHb. Overall, we uncovered the sources of major Dyn/KOR-expressing synaptic inputs projecting to the mouse LHb. We demonstrate that an engagement of intra-LHb Dyn/KOR signaling provides a global KOR-driven synaptic inhibition within the mouse LHb independent of sex. The additional engagement of KOR-mediated action on LHb GABAergic transmission by mTBI could contribute to the E/I imbalance after mTBI, with Dyn/KOR signaling serving as a disinhibitory mechanism for LHb neurons of a subset of mTBI mice.

Lack of evidence for direct ligand-gated ion channel activity of GluD receptors

Delta receptors (GluD1 and GluD2), members of the large ionotropic glutamate receptor (iGluR) family, play a central role in numerous neurodevelopmental and psychiatric disorders. The amino-terminal domain (ATD) of GluD orchestrates synapse formation and maturation processes through its interaction with the Cbln family of synaptic organizers and neurexin (Nrxn). The transsynaptic triad of Nrxn-Cbln-GluD also serves as a potent regulator of synaptic plasticity, at both excitatory and inhibitory synapses. Despite these recognized functions, there is still debate as to whether GluD functions as a "canonical" ion channel, similar to other iGluRs. A recent report proposes that the ATD of GluD2 imposes conformational constraints on channel activity; removal of this constraint by binding to Cbln1 and Nrxn, or removal of the ATD, reveals channel activity in GluD2 upon administration of glycine (Gly) and d-serine (d-Ser), two GluD ligands. We were able to reproduce currents when Gly or d-Ser was administered to clusters of heterologous human embryonic kidney 293 (HEK293) cells expressing Cbln1, GluD2 (or GluD1), and Nrxn. However, Gly or d-Ser, but also l-glutamate (l-Glu), evoked similar currents in naive (i.e., untransfected) HEK293 cells and in GluD2-null Purkinje neurons. Furthermore, no current was detected in isolated HEK293 cells expressing GluD2 lacking the ATD upon administration of Gly. Taken together, these results cast doubt on the previously proposed hypothesis that extracellular ligands directly gate wild-type GluD channels.

Caspase-1 inhibitor CZL80 protects against acute seizures via amplifying the inhibitory neural transmission

Current anti-seizure medications (ASDs) primarily target ion channels or neurotransmissions; however, their practicability is limited by unwanted side-effects and pharmacoresistance. Cumulative evidence has proposed pro-inflammatory caspase-1 as a potential target for developing ASDs. In this study, we showed that the small-molecular caspase-1 inhibitor CZL80 can prevent seizures in various models including the maximal electroshock (MES), the pentylenetetrazol (PTZ), and the amygdaloid kindled models. Specifically, we discovered that CZL80 prevented death, reduced the duration of generalized seizures, and increased the threshold of generalized seizures in a dose-dependent manner in the MES model. In the PTZ model, CZL80 decreased the seizure stages, prolonged the latency to stage 4 seizures, and decreased the death rate. And in amygdaloid kindled rats, CZL80 inhibited the seizure stages, shortened the durations of both generalized seizures and after-discharges. And the anti-seizure efficacy of CZL80 was diminished in caspase-1 knockout mice. In vitro electrophysiology recordings revealed that CZL80 was able to decreased the excitability of glutamatergic pyramidal neurons, as denoted by reducing the spontaneous neuronal firings and increasing the rheobase injected currents to elicit action potentials. Furthermore, CZL80 was able to increase the amplitudes of inhibitory post-synaptic currents (IPSC), while the excitatory post-synaptic currents (EPSC) were not influenced. Lastly, daily administration of CZL80 for 3 weeks did not influence the normal locomotor functions in mice. In sum, our results highlighted CZL80 as a potential anti-seizure therapy with therapeutic significance.

Electrosorption Mechanism of Zwitterionic Amino Acid Neurotransmitters in Iontronic Devices

AbstractNeurotransmitters carrying specific chemical information play a key role in the nervous system, which inspires ion‐based devices to mimic biological functions of nervous system, including sensing, transduction, and computing. In this work, the interaction mechanism of zwitterionic amino acids, glycine (Gly), and gamma‐aminobutyric acid (GABA) (two common inhibitory neurotransmitters) are analyzed with porous carbon electrodes. The charge balance of these zwitterionic neurotransmitters relies on zwitterion protonation in the vicinity of the negative electrodes (produced cations adsorbed by the negative electrode) and deprotonation near the positive electrode (produced anions to balance the positive charges) as demonstrated based on the theoretical dissociation analyses and local pH measurements. Additionally, electrosorption‐induced concentration changes of Gly and GABA in aqueous solutions and phosphate‐buffered saline (PBS) solutions are realized by electrosorption via nanoporous carbon electrodes. Based on this mechanistic understanding, the ionologic functions in printed ionic electrolyte double‐layer transistors are demonstrated. These neurotransmitter‐based iontronic devices hold potential for further organism‐machine interfacing and neuromorphic computing applications.

Presynaptic hyperexcitability reversed by positive allosteric modulation of a GABABR epilepsy variant.

GABABRs are key membrane proteins that continually adapt the excitability of the nervous system. These G-protein coupled receptors are activated by the brain's premier inhibitory neurotransmitter GABA. They are obligate heterodimers composed of GABA-binding GABABR1 and G-protein-coupling GABABR2 subunits. Recently, three variants (G693W, S695I, I705N) have been identified in the gene (GABBR2) encoding for GABABR2. Individuals that harbour any of these variants exhibit severe developmental epileptic encephalopathy and intellectual disability, but the underlying pathogenesis that is triggered in neurons, remains unresolved. Using a range of confocal imaging, flow cytometry, structural modelling, biochemistry, live cell Ca2+ imaging of presynaptic terminals, whole-cell electrophysiology of HEK-293T cells and neurons, and two-electrode voltage clamping of Xenopus oocytes we have probed the biophysical and molecular trafficking and functional profiles of G693W, S695I and I705N variants. We report that all three point mutations impair neuronal cell surface expression of GABABRs, reducing signalling efficacy. However, a negative effect evident for one variant perturbed neurotransmission by elevating presynaptic Ca2+ signalling. This is reversed by enhancing GABABR signalling via positive allosteric modulation. Our results highlight the importance of studying neuronal receptors expressed in nervous system tissue and provide new mechanistic insights into how GABABR variants can initiate neurodevelopmental disease whilst highlighting the translational suitability and therapeutic potential of allosteric modulation for correcting these deficits.