Inhibitory Synaptic Transmission Research Articles

Firing Patterns of Mitral Cells and Their Transformation in the Main Olfactory Bulb

Mitral cells (MCs) in the main olfactory bulb relay odor information to higher-order olfactory centers by encoding the information in the form of action potentials. The firing patterns of these cells are influenced by both their intrinsic properties and their synaptic connections within the neural network. However, reports on MC firing patterns have been inconsistent, and the mechanisms underlying these patterns remain unclear. Using whole-cell patch-clamp recordings in mouse brain slices, we discovered that MCs exhibit two types of integrative behavior: regular/rhythmic firing and bursts of action potentials. These firing patterns could be transformed both spontaneously and chemically. MCs with regular firing maintained their pattern even in the presence of blockers of fast synaptic transmission, indicating this was an intrinsic property. However, regular firing could be transformed into bursting by applying GABAA receptor antagonists to block inhibitory synaptic transmission. Burst firing could be reverted to regular firing by blocking ionotropic glutamate receptors, rather than applying a GABAA receptor agonist, indicating that ionotropic glutamatergic transmission mediated this transformation. Further experiments on long-lasting currents (LLCs), which generated burst firing, also supported this mechanism. In addition, cytoplasmic Ca2+ in MCs was involved in the transformation of firing patterns mediated by glutamatergic transmission. Metabotropic glutamate receptors also played a role in LLCs in MCs. These pieces of evidence indicate that odor information can be encoded on a mitral cell (MC) platform, where it can be relayed to higher-order olfactory centers through intrinsic and dendrodendritic mechanisms in MCs.

Suppression of excitatory synaptic transmission in the centrolateral amygdala via presynaptic histamine H3 heteroreceptors.

The central histaminergic system has a pivotal role in emotional regulation and psychiatric disorders, including anxiety, depression and schizophrenia. However, the effect of histamine on neuronal activity of the centrolateral amygdala (CeL), an essential node for fear and anxiety processing, remains unknown. Here, using immunostaining and whole-cell patch clamp recording combined with optogenetic manipulation of histaminergic terminals in CeL slices prepared from histidine decarboxylase (HDC)-Cre rats, we show that histamine selectively suppresses excitatory synaptic transmissions, including glutamatergic transmission from the basolateral amygdala, on both PKC-δ- and SOM-positive CeL neurons. The histamine-induced effect is mediated by H3 receptors expressed on VGLUT1-/VGLUT2-positive presynaptic terminals in CeL. Furthermore, optoactivation of histaminergic afferent terminals from the hypothalamic tuberomammillary nucleus (TMN) also significantly suppresses glutamatergic transmissions in CeL via H3 receptors. Histamine neither modulates inhibitory synaptic transmission by presynaptic H3 receptors nor directly excites CeL neurons by postsynaptic H1, H2 or H4 receptors. These results suggest that histaminergic afferent inputs and presynaptic H3 heteroreceptors may hold a critical position in balancing excitatory and inhibitory synaptic transmissions in CeL by selective modulation of glutamatergic drive, which may not only account for the pathophysiology of psychiatric disorders but also provide potential psychotherapeutic targets. KEY POINTS: Histamine selectively suppresses the excitatory, rather than inhibitory, synaptic transmissions on both PKC-δ- and SOM-positive neurons in the centrolateral amygdala (CeL). H3 receptors expressed on VGLUT1- or VGLUT2-positive afferent terminals mediate the suppression of histamine on glutamatergic synaptic transmission in CeL. Optogenetic activation of hypothalamic tuberomammillary nucleus (TMN)-CeL histaminergic projections inhibits glutamatergic transmission in CeL via H3 receptors.

Epigenetic underpinnings of the autistic mind: Histone modifications and prefrontal excitation/inhibition imbalance.

Autism spectrum disorder (ASD) is complex neurobehavioral condition influenced by several cellular and molecular mechanisms that are often concerned with synaptogenesis and synaptic activity. Based on the excitation/inhibition (E/I) imbalance theory, ASD could be the result of disruption in excitatory and inhibitory synaptic transmission across the brain. The prefrontal cortex (PFC) is the chief regulator of executive function and can be affected by altered neuronal excitation and inhibition in the course of ASD. The molecular mechanisms involved in E/I imbalance are subject to epigenetic regulation. In ASD, altered enrichment and spreading of histone H3 and H4 modifications such as the activation-linked H3K4me2/3, H3K9ac, and H3K27ac, and repression-linked H3K9me2, H3K27me3, and H4K20me2 in the PFC result in dysregulation of molecules mediating synaptic excitation (ARC, EGR1, mGluR2, mGluR3, GluN2A, and GluN2B) and synaptic inhibition (BSN, EphA7, SLC6A1). Histone modifications are a dynamic component of the epigenetic regulatory elements with a pronounced effect on patterns of gene expression with regards to any biological process. The excitation/inhibition imbalance associated with ASD is based on the excitatory and inhibitory synaptic activity in different regions of the brain, including the PFC, the ultimate outcome of which is highly influenced by transcriptional activity of relevant genes.

Reduced inhibitory synaptic transmission onto striatopallidal neurons may underlie aging-related motor skill deficits

Human beings are living longer than ever before and aging is accompanied by an increased incidence of motor deficits, including those associated with the neurodegenerative conditions, Parkinson's disease (PD) and Huntington's disease (HD). However, the biological correlates underlying this epidemiological finding, especially the functional basis at the synapse level, have been elusive. This study reveals that motor skill performance examined via rotarod, beam walking and pole tests is impaired in aged mice. This study, via electrophysiology recordings, further identifies an aging-related reduction in the efficacy of inhibitory synaptic transmission onto dorsolateral striatum (DLS) indirect-pathway medium spiny neurons (iMSNs), i.e., a disinhibition effect on DLS iMSNs. In addition, pharmacologically enhancing the activity of DLS iMSNs by infusing an adenosine A2A receptor (A2AR) agonist, which presumably mimics the disinhibition effect, impairs motor skill performance in young mice, simulating the behavior in aged naïve mice. Conversely, pharmacologically suppressing the activity of DLS iMSNs by infusing an A2AR antagonist, in order to offset the disinhibition effect, restores motor skill performance in aged mice, mimicking the behavior in young naïve mice. In conclusion, this study identifies a functional inhibitory synaptic plasticity in DLS iMSNs that likely contributes to the aging-related motor skill deficits, which would potentially serve as a striatal synaptic basis underlying age being a prominent risk factor for neurodegenerative motor deficits.

Mu-opioid receptor activation in the habenula modulates synaptic transmission and depression-like behaviors

Opioid system dysregulation in response to stress is known to lead to psychiatric disorders including major depression. Among three different types of opioid receptors, the mu-type receptors (mORs) are highly expressed in the habenula complex, however, the action of mORs in this area and its interaction with stress exposure is largely unknown. Therefore, we investigated the roles of mORs in the habenula using male rats of an acute learned helplessness (aLH) model. First, we found that mOR activation decreased both excitatory and inhibitory synaptic transmission onto the lateral habenula (LHb). Intriguingly, this mOR-induced synaptic depression was reduced in an animal model of depression compared to that of controls. In naïve animals, we found an unexpected interaction between mORs and the endocannabinoid (eCB) signaling occurring in the LHb, which mediates presynaptic alteration occurring with mOR activation. However, we did not observe presynaptic alteration by mOR activation after stress exposure. Moreover, selective mOR activation in the habenula before, but not after, stress exposure effectively reduced helpless behaviors compared to aLH animals. Our observations are consistent with clinical reports suggesting the involvement of mOR signaling in depression, and additionally reveal a critical time window of mOR action in the habenula for ameliorating helplessness symptoms.

Stimulus-related modulation in the 1/f spectral slope suggests an impaired inhibition during a working memory task in people with multiple sclerosis.

An imbalance of excitatory and inhibitory synaptic transmission in multiple sclerosis (MS) may lead to cognitive impairment, such as impaired working memory. The 1/f slope of electroencephalography/magnetoencephalography (EEG/MEG) power spectra is shown to be a non-invasive proxy of excitation/inhibition balance. A flatter slope is associated with higher excitation/lower inhibition. To assess the 1/f slope modulation induced by stimulus and its association with behavioral and cognitive measures. We analyzed MEG recordings of 38 healthy controls (HCs) and 79 people with multiple sclerosis (pwMS) while performing an n-back task including target and distractor stimuli. Target trials require an answer, while distractor trials do not. We computed the 1/f spectral slope through the fitting oscillations and one over f (FOOOF) algorithm within the time windows 1 second before and after each stimulus presentation. We observed a flatter 1/f slope after distractor stimuli in pwMS compared to HCs. The 1/f slope was significantly steeper after stimulus for both HCs and pwMS and was significantly correlated with reaction times. This modulation in 1/f slope was significantly correlated with visuospatial memory assessed by the BVMT-R test. Our results suggest possible inhibitory mechanism deficits in pwMS during a working memory task.

Prenatal 1-Nitropyrene Exposure Causes Autism-Like Behavior Partially by Altering DNA Hydroxymethylation in Developing Brain.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder, characterized by social communication disability and stereotypic behavior. This study aims to investigate the impact of prenatal exposure to 1-nitropyrene (1-NP), a key component of motor vehicle exhaust, on autism-like behaviors in a mouse model. Three-chamber test finds that prenatal 1-NP exposure causes autism-like behaviors during the weaning period. Patch clamp shows that inhibitory synaptic transmission is reduced in medial prefrontal cortex of 1-NP-exposed weaning pups. Immunofluorescence finds that prenatal 1-NP exposure reduces the number of prefrontal glutamate decarboxylase 67 (GAD67) positive interneurons in fetuses and weaning pups. Moreover, prenatal 1-NP exposure retards tangential migration of GAD67-positive interneurons and downregulates interneuron migration-related genes, such as Nrg1, Erbb4, and Sema3F, in fetal forebrain. Mechanistically, prenatal 1-NP exposure reduces hydroxymethylation of interneuron migration-related genes through inhibiting ten-eleven translocation (TET) activity in fetal forebrain. Supplement with alpha-ketoglutarate (α-KG), a cofactor of TET enzyme, reverses 1-NP-induced hypohydroxymethylation at specific sites of interneuron migration-related genes. Moreover, α-KG supplement alleviates 1-NP-induced migration retardation of interneurons in fetal forebrain. Finally, maternal α-KG supplement improves 1-NP-induced autism-like behaviors in weaning offspring. In conclusion, prenatal 1-NP exposure causes autism-like behavior partially by altering DNA hydroxymethylation of interneuron migration-related genes in developing brain.

Loss of Postnatal Arx Transcriptional Activity in Parvalbumin Interneurons Reveals Non-cell Autonomous Disturbances in CA1 Pyramidal Cells

Maintenance of proper electrophysiological and connectivity profiles in the adult brain may be a perturbation point in neurodevelopmental disorders (NDDs). How these profiles are maintained within mature circuits is unclear. We recently demonstrated that postnatal ablation of the Aristaless (Arx) homeobox gene in parvalbumin interneurons (PVIs) alone led to dysregulation of their transcriptome and alterations in their functional as well as network properties in the hippocampal cornu Ammoni first region (CA1). Here, we characterized CA1 pyramidal cells (PCs) responses in this conditional knockout (CKO) mouse to further understand the circuit mechanisms by which postnatal Arx expression regulates mature CA1 circuits. Field recordings of network excitability showed that CA1 PC ensembles were less excitable in response to unpaired stimulations but exhibited enhanced excitability in response to paired-pulse stimulations. Whole-cell voltage clamp recordings revealed a significant increase in the frequency of spontaneous inhibitory postsynaptic currents onto PCs. In contrast, excitatory drive from evoked synaptic transmission was reduced while that of inhibitory synaptic transmission was increased. Current clamp recordings showed increase excitability in several sub- and threshold membrane properties that correlated with an increase in voltage-gated Na+ current. Our data suggest that, in addition to cell-autonomous disruption in PVIs, loss of Arx postnatal transcriptional activity in PVIs led to complex dysfunctions in PCs in CA1 microcircuits. These non-cell autonomous effects are likely the product of breakdown in feedback and/or feedforward processes and should be considered as fundamental contributors to the circuit mechanisms of NDDs such as Arx-linked early-onset epileptic encephalopathies.

Essential Role of Latrophilin-1 Adhesion GPCR Nanoclusters in Inhibitory Synapses.

Latrophilin-1 (Lphn1, aka CIRL1 and CL1; gene symbol Adgrl1) is an adhesion GPCR that has been implicated in excitatory synaptic transmission as a candidate receptor for α-latrotoxin. Here we analyzed conditional knock-in/knock-out mice for Lphn1 that contain an extracellular myc epitope tag. Mice of both sexes were used in all experiments. Surprisingly, we found that Lphn1 is localized in cultured neurons to synaptic nanoclusters that are present in both excitatory and inhibitory synapses. Conditional deletion of Lphn1 in cultured neurons failed to elicit a detectable impairment in excitatory synapses but produced a decrease in inhibitory synapse numbers and synaptic transmission that was most pronounced for synapses close to the neuronal soma. No changes in axonal or dendritic outgrowth or branching were observed. Our data indicate that Lphn1 is among the few postsynaptic adhesion molecules that are present in both excitatory and inhibitory synapses and that Lphn1 by itself is not essential for excitatory synaptic transmission but is required for some inhibitory synaptic connections.

The homeostatic effects of the RE-1 silencing transcription factor on cortical networks are altered under ictogenic conditions in the mouse.

The Repressor Element-1 Silencing Transcription Factor (REST) is an epigenetic master regulator playing a crucial role in the nervous system. In early developmental stages, REST downregulation promotes neuronal differentiation and the acquisition of the neuronal phenotype. In addition, postnatal fluctuations in REST expression contribute to shaping neuronal networks and maintaining network homeostasis. Here we investigate the role of the early postnatal deletion of neuronal REST in the assembly and strength of excitatory and inhibitory synaptic connections. We investigated excitatory and inhibitory synaptic transmission by patch-clamp recordings in acute neocortical slices in a conditional knockout mouse model (RestGTi) in which Rest was deleted by delivering PHP.eB adeno-associated viruses encoding CRE recombinase under the control of the human synapsin I promoter in the lateral ventricles of P0-P1 pups. We show that, under physiological conditions, Rest deletion increased the intrinsic excitability of principal cortical neurons in the primary visual cortex and the density and strength of excitatory synaptic connections impinging on them, without affecting inhibitory transmission. Conversely, in the presence of a pathological excitation/inhibition imbalance induced by pentylenetetrazol, Rest deletion prevented the increase in synaptic excitation and decreased seizure severity. The data indicate that REST exerts distinct effects on the excitability of cortical circuits depending on whether it acts under physiological conditions or in the presence of pathologic network hyperexcitability. In the former case, REST preserves a correct excitatory/inhibitory balance in cortical circuits, while in the latter REST loses its homeostatic activity and may become pro-epileptogenic.

Cerebral venous congestion alters CNS homeostatic plasticity, evoking tinnitus-like behavior

BackgroundBrain function and neuronal activity depend on a constant supply of blood from the cerebral circulation. The cerebral venous system (CVS) contains approximately 70% of the total cerebral blood volume; similar to the cerebral arterial system, the CVS plays a prominent role in the maintenance of central nervous system (CNS) homeostasis. Impaired venous autoregulation, which can appear in forms such as cerebral venous congestion, may lead to metabolic abnormalities in the brain, causing severe cerebral functional defects and even chronic tinnitus. However, the role of cerebral venous congestion in the progression of tinnitus is underrecognized, and its pathophysiology is still incompletely understood. This study elucidated the specific pathogenetic role of cerebral venous congestion in the onset and persistence of tinnitus and the possible neurophysiological mechanisms.ResultsWe found that a rat model of cerebral venous congestion exhibited tinnitus-like behavioral manifestations at 14 days postoperatively; from that point onward, they showed signs of persistent tinnitus without significant hearing impairment. Subsequent neuroimaging and neurochemical findings showed CNS homeostatic plasticity disturbance in rats with cerebral venous congestion, reflected in increased neural metabolic activity, ultrastructural synaptic changes, upregulated synaptic efficacy, reduced inhibitory synaptic transmission (due to GABA deficiency), and elevated expression of neuroplasticity-related proteins in central auditory and extra-auditory pathways.ConclusionCollectively, our data suggest that alternations in CNS homeostatic plasticity may play a vital role in tinnitus pathology caused by cerebral venous congestion. These findings provide a new perspective on tinnitus related to cerebral venous congestion and may facilitate the development of precise interventions to interrupt its pathogenesis.

The gut metabolite indole-3-propionic acid activates ERK1 to restore social function and hippocampal inhibitory synaptic transmission in a 16p11.2 microdeletion mouse model

BackgroundMicrodeletion of the human chromosomal region 16p11.2 (16p11.2+/-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{+/-}$$\\end{document}) is a prevalent genetic factor associated with autism spectrum disorder (ASD) and other neurodevelopmental disorders. However its pathogenic mechanism remains unclear, and effective treatments for 16p11.2+/-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{+/-}$$\\end{document} syndrome are lacking. Emerging evidence suggests that the gut microbiota and its metabolites are inextricably linked to host behavior through the gut-brain axis and are therefore implicated in ASD development. Despite this, the functional roles of microbial metabolites in the context of 16p11.2+/-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{+/-}$$\\end{document} are yet to be elucidated. This study aims to investigate the therapeutic potential of indole-3-propionic acid (IPA), a gut microbiota metabolite, in addressing behavioral and neural deficits associated with 16p11.2+/-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{+/-}$$\\end{document}, as well as the underlying molecular mechanisms.ResultsMice with the 16p11.2+/-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{+/-}$$\\end{document} showed dysbiosis of the gut microbiota and a significant decrease in IPA levels in feces and blood circulation. Further, these mice exhibited significant social and cognitive memory impairments, along with hyperactivation of hippocampal dentate gyrus neurons and reduced inhibitory synaptic transmission in this region. However, oral administration of IPA effectively mitigated the histological and electrophysiological alterations, thereby ameliorating the social and cognitive deficits of the mice. Remarkably, IPA treatment significantly increased the phosphorylation level of ERK1, a protein encoded by the Mapk3 gene in the 16p11.2 region, without affecting the transcription and translation of the Mapk3 gene.ConclusionsOur study reveals that 16p11.2+/-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{+/-}$$\\end{document} leads to a decline in gut metabolite IPA levels; however, IPA supplementation notably reverses the behavioral and neural phenotypes of 16p11.2+/-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{+/-}$$\\end{document} mice. These findings provide new insights into the critical role of gut microbial metabolites in ASD pathogenesis and present a promising treatment strategy for social and cognitive memory deficit disorders, such as 16p11.2 microdeletion syndrome.92Bbfs5rK2Gd_SbL4an2CwVideo

Genetic background determines synaptic phenotypes in Arid1b-mutant mice.

ARID1B, a chromatin remodeler, is strongly implicated in autism spectrum disorders (ASD). Two previous studies on Arid1b-mutant mice with the same exon 5 deletion in different genetic backgrounds revealed distinct synaptic phenotypes underlying the behavioral abnormalities: The first paper reported decreased inhibitory synaptic transmission in layer 5 pyramidal neurons in the medial prefrontal cortex (mPFC) region of the heterozygous Arid1b-mutant (Arid1b+/-) brain without changes in excitatory synaptic transmission. In the second paper, in contrast, we did not observe any inhibitory synaptic change in layer 5 mPFC pyramidal neurons, but instead saw decreased excitatory synaptic transmission in layer 2/3 mPFC pyramidal neurons without any inhibitory synaptic change. In the present report, we show that when we changed the genetic background of Arid1b+/- mice from C57BL/6 N to C57BL/6 J, to mimic the mutant mice of the first paper, we observed both the decreased inhibitory synaptic transmission in layer 5 mPFC pyramidal neurons reported in the first paper, and the decreased excitatory synaptic transmission in mPFC layer 2/3 pyramidal neurons reported in the second paper. These results suggest that genetic background can be a key determinant of the inhibitory synaptic phenotype in Arid1b-mutant mice while having minimal effects on the excitatory synaptic phenotype.

Activation of the CXCR4 Receptor by Chemokine CXCL12 Increases the Excitability of Neurons in the Rat Central Amygdala.

Primarily regarded as immune proteins, chemokines are emerging as a family of molecules serving neuromodulatory functions in the developing and adult brain. Among them, CXCL12 is constitutively and widely expressed in the CNS, where it was shown to act on cellular, synaptic, network, and behavioral levels. Its receptor, CXCR4, is abundant in the amygdala, a brain structure involved in pathophysiology of anxiety disorders. Dysregulation of CXCL12/CXCR4 signaling has been implicated in anxiety-related behaviors. Here we demonstrate that exogenous CXCL12 at 2 nM but not at 5 nM increased neuronal excitability in the lateral division of the rat central amygdala (CeL) which was evident in the Late-Firing but not Regular-Spiking neurons.These effects were blocked by AMD3100, a CXCR4 antagonist. Moreover, CXCL12 increased the excitability of the neurons of the basolateral amygdala (BLA) that is known to project to the CeL. However, CXCL12 increased neither the spontaneous excitatory nor spontaneous inhibitory synaptic transmission in the CeL. In summary, the data reveal specific activation of Late-Firing CeL cells along with BLA neurons by CXCL12 and suggest that this chemokine may alter information processing by the amygdala that likely contributes to anxiety and fear conditioning.

Elucidation of the pathology of mental disorders focusing on polyunsaturated fatty acids and FABPs

Polyunsaturated fatty acids (PUFAs) are essential for brain development and function, and an imbalance of brain PUFAs is linked to mental disorders like autism and schizophrenia. However, the cellular and molecular mechanisms underlying the effects of PUFAs on the brain remain largely unknown. Since they are insoluble in water, specific transporters like fatty acid binding proteins (FABPs), are required for transport and function of PUFAs within cells. We focused on the relationship between FABP-mediated homeostasis of brain PUFAs and neural plasticity. We found that FABP3, with a high affinity for n-6 PUFAs, is predominantly expressed in the GABAergic inhibitory interneurons of the anterior cingulate cortex (ACC) in the adult mouse brain. FABP3 knockout (KO) mice show increased GABA synthesis and inhibitory synaptic transmission in the ACC. We also found that FABP7 controls lipid raft function in astrocytes, and astrocytes lacking FABP7 exhibit changes in response to external stimuli. Furthermore, in FABP7 KO mice, dendritic protrusion formation in pyramidal neurons becomes abnormal, and we have reported a decrease in spine density and excitatory synaptic transmission. Here, we introduced recent advances in the understanding of the functions of PUFAs and FABPs in the brain, focusing especially on FABP3 and FABP7, in relation to human mental disorders.

Divergent changes in PBN excitability in a mouse model of neuropathic pain.

The transition from acute to chronic pain involves maladaptive plasticity in central nociceptive pathways. Growing evidence suggests that changes within the parabrachial nucleus (PBN), an important component of the spino-parabrachio-amygdaloid pain pathway, are key contributors to the development and maintenance of chronic pain. In animal models of chronic pain, PBN neurons become sensitive to normally innocuous stimuli and responses to noxious stimuli become amplified and more often produce after-discharges that outlast the stimulus. Using ex vivo slice electrophysiology and two mouse models of neuropathic pain, sciatic cuff and chronic constriction of the infraorbital nerve (CCI-ION), we find that changes in the firing properties of PBN neurons and a shift in inhibitory synaptic transmission may underlie this phenomenon. Compared to PBN neurons from shams, a larger proportion of PBN neurons from mice with a sciatic cuff were spontaneously active at rest, and these same neurons showed increased excitability relative to shams. In contrast, quiescent PBN neurons from cuff mice were less excitable than those from shams. Despite an increase in excitability in a subset of PBN neurons, the presence of after-discharges frequently observed in vivo were largely absent ex vivo in both injury models. However, GABAB-mediated presynaptic inhibition of GABAergic terminals is enhanced in PBN neurons after CCI-ION. These data suggest that the amplified activity of PBN neurons observed in rodent models of chronic pain arise through a combination of changes in firing properties and network excitability.Significance Statement Hyperactivity of neurons in the parabrachial nucleus (PBN) is causally linked to exaggerated pain behaviors in rodent models of chronic pain but the underlying mechanisms remain unknown. Using two mouse models of neuropathic pain, we show the intrinsic properties of PBN neurons are largely unaltered following injury. However, subsets of PBN neurons become more excitable and GABAB receptor mediated suppression of inhibitory terminals is enhanced after injury. Thus, shifts in network excitability may be a contributing factor in injury induced potentiation of PBN activity.

GABAA receptor subunit M2-M3 linkers have asymmetric roles in pore gating and diazepam modulation

GABAA receptors (GABAARs) are neurotransmitter-gated ion channels critical for inhibitory synaptic transmission as well as the molecular target for benzodiazepines (BZDs), one of the most widely prescribed class of psychotropic drugs today. Despite structural insight into the conformations underlying functional channel states, the detailed molecular interactions involved in conformational transitions and the physical basis for their modulation by BZDs are not fully understood. We previously identified that alanine substitution at the central residue in the α1 subunit M2-M3 linker (V279A) enhances the efficiency of linkage between the BZD site and the pore gate. Here, we expand on this work by investigating the effect of alanine substitutions at the analogous positions in the M2-M3 linkers of β2 (I275A) and γ2 (V290A) subunits, which together with α1 comprise typical heteromeric α1β2γ2 synaptic GABAARs. We find that these mutations confer subunit-specific effects on the intrinsic pore closed-open equilibrium and its modulation by the BZD diazepam (DZ). The mutations α1(V279A) or γ2(V290A) bias the channel toward a closed conformation, whereas β2(I275A) biases the channel toward an open conformation to the extent that the channel becomes leaky and opens spontaneously in the absence of agonist. In contrast, only α1(V279A) enhances the efficiency of DZ-to-pore linkage, whereas mutations in the other two subunits have no effect. These observations show that the central residue in the M2-M3 linkers of distinct subunits in synaptic α1β2γ2 GABAARs contribute asymmetrically to the intrinsic closed-open equilibrium and its modulation by DZ.

Ethanol Differentially Affects Excitatory and Inhibitory Synaptic Transmission in Visual Cortex of Wild-type and Adenosine A1R Knock-out Mice

Ethanol is one of the most commonly used and abused substances in the world. While the behavioral effects of ethanol are well characterized, mechanisms of its action on neurons and synapses remain elusive. Prior research suggested that ethanol could affect neurons by interfering with metabolism of biologically active molecules, such as adenosine. Here, we explored the involvement of adenosine A1 receptors (A1R) in mediating ethanol’s effects on synaptic transmission to layer 2/3 pyramidal neurons of visual cortex using wild type (WT) and A1R knock-out (KO) mice. Ethanol differentially affected excitatory and inhibitory transmission in WT and KO mice. In slices from WT mice ethanol had heterogeneous effects on excitatory transmission (facilitation, suppression or no change), with no net change. Ethanol’s effects remained heterogeneous during acute blockade of A1Rs with a selective antagonist DPCPX. However, in A1RKO mice ethanol consistently suppressed excitatory transmission, with no cases of enhancement observed. Inhibitory transmission was suppressed by ethanol in both WT and A1RKO mice. At both excitatory and inhibitory synapses, changes of response amplitude correlated with changes of paired-pulse ratio, suggesting involvement of presynaptic mechanisms. We conclude that A1Rs are not involved in mediating effects of ethanol on synaptic transmission in mouse visual cortex. However, A1Rs are necessary for development of mechanisms mediating facilitation at some excitatory synapses. Our results add evidence for the diversity of ethanol’s effects and mechanisms of action on synaptic transmission in different brain structures, and even in the same brain area (visual cortex) in different species, rats vs mice.

Converging synaptic and network dysfunctions in distinct autoimmune encephalitis

Psychiatric and neurological symptoms, as well as cognitive deficits, represent a prominent phenotype associated with variable forms of autoimmune encephalitis, regardless of the neurotransmitter receptor targeted by autoantibodies. The mechanistic underpinnings of these shared major neuropsychiatric symptoms remain however unclear. Here, we investigate the impacts of patient-derived monoclonal autoantibodies against the glutamatergic NMDAR (NMDAR mAb) and inhibitory GABAaR (GABAaR mAb) signalling in the hippocampal network. Unexpectedly, both excitatory and inhibitory synaptic receptor membrane dynamics, content and transmissions are altered by NMDAR or GABAaR mAb, irrespective of the affinity or antagonistic effect of the autoantibodies. The effect of NMDAR mAb on inhibitory synapses and GABAaR mAb on excitatory synapses requires neuronal activity and involves protein kinase signalling. At the cell level, both autoantibodies increase the excitation/inhibition balance of principal cell inputs. Furthermore, NMDAR or GABAaR mAb leads to hyperactivation of hippocampal networks through distinct alterations of principal cell and interneuron properties. Thus, autoantibodies targeting excitatory NMDAR or inhibitory GABAaR trigger convergent network dysfunctions through a combination of shared and distinct mechanisms.

MEF2C Hypofunction in GABAergic Cells Alters Sociability and Prefrontal Cortex Inhibitory Synaptic Transmission in a Sex-Dependent Manner

BackgroundHeterozygous mutations or deletions of MEF2C cause a neurodevelopmental disorder termed MEF2C haploinsufficiency syndrome (MCHS), characterized by autism spectrum disorder and neurological symptoms. In mice, global Mef2c heterozygosity has produced multiple MCHS-like phenotypes. MEF2C is highly expressed in multiple cell types of the developing brain, including GABAergic (gamma-aminobutyric acidergic) inhibitory neurons, but the influence of MEF2C hypofunction in GABAergic neurons on MCHS-like phenotypes remains unclear. MethodsWe employed GABAergic cell type–specific manipulations to study mouse Mef2c heterozygosity in a battery of MCHS-like behaviors. We also performed electroencephalography, single-cell transcriptomics, and patch-clamp electrophysiology and optogenetics to assess the impact of Mef2c haploinsufficiency on gene expression and prefrontal cortex microcircuits. ResultsMef2c heterozygosity in developing GABAergic cells produced female-specific deficits in social preference and altered approach-avoidance behavior. In female, but not male, mice, we observed that Mef2c heterozygosity in developing GABAergic cells produced 1) differentially expressed genes in multiple cell types, including parvalbumin-expressing GABAergic neurons, 2) baseline and social-related frontocortical network activity alterations, and 3) reductions in parvalbumin cell intrinsic excitability and inhibitory synaptic transmission onto deep-layer pyramidal neurons. ConclusionsMEF2C hypofunction in female, but not male, developing GABAergic cells is important for typical sociability and approach-avoidance behaviors and normal parvalbumin inhibitory neuron function in the prefrontal cortex of mice. While there is no apparent sex bias in autism spectrum disorder symptoms of MCHS, our findings suggest that GABAergic cell-specific dysfunction in females with MCHS may contribute disproportionately to sociability symptoms.