Heterosynaptic GABAB Receptor Function within Feedforward Microcircuits Gates Glutamatergic Transmission in the Nucleus Accumbens Core

GABA system in the prefrontal cortex involved in psychostimulant addiction

Drug addiction is a chronic and relapse brain disorder. Psychostimulants such as cocaine and amphetamine are highly addictive drugs. Abuse drugs target various brain areas in the nervous system. Recent studies have shown that the prefrontal cortex (PFC) plays a key role in regulating addictive behaviors. The PFC is made up of excitatory glutamatergic cells and gamma-aminobutyric acid (GABAergic) interneurons. Recently, studies showed that GABA level was related with psychostimulant addiction. In this review, we will introduce the role and mechanism of GABA and γ-aminobutyric acid receptors (GABARs) of the PFC in regulating drug addiction, especially in psychostimulant addiction.

Oxytocin, GABA, and dopamine interplay in autism

Oxytocin plays an important role in brain development and is associated with various neurotransmitter systems in the brain. Abnormalities in the production, secretion, and distribution of oxytocin in the brain, at least during some stages of the development, are critical for the pathogenesis of neuropsychiatric diseases, particularly in the autism spectrum disorder. The etiology of autism includes changes in local sensory and dopaminergic areas of the brain, which are also supplied by the hypothalamic sources of oxytocin. It is very important to understand their mutual relationship. In this review, the relationship of oxytocin with several components of the dopaminergic system, gamma-aminobutyric acid (GABA) inhibitory neurotransmission and their alterations in the autism spectrum disorder is discussed. Special attention has been paid to the results describing a reduced expression of inhibitory GABAergic markers in the brain in the context of dopaminergic areas in various models of autism. It is presumed that the altered GABAergic neurotransmission, due to the absence or dysfunction of oxytocin at certain developmental stages, disinhibits the dopaminergic signaling and contributes to the autism symptoms.

Synaptic and cellular endocannabinoid signaling mechanisms regulate stress-induced plasticity of nucleus accumbens somatostatin neurons

Interneuron populations within the nucleus accumbens (NAc) orchestrate excitatory-inhibitory balance, undergo experience-dependent plasticity, and gate-motivated behavior, all biobehavioral processes heavily modulated by endogenous cannabinoid (eCB) signaling. While eCBs are well known to regulate synaptic plasticity onto NAc medium spiny neurons and modulate NAc function at the behavioral level, how eCBs regulate NAc interneuron function is less well understood. Here, we show that eCB signaling differentially regulates glutamatergic and feedforward GABAergic transmission onto NAc somatostatin-expressing interneurons (NAcSOM+) in an input-specific manner, while simultaneously increasing postsynaptic excitability of NAcSOM+ neurons, ultimately biasing toward vHPC (ventral hippocampal), and away from BLA (basolateral amygdalalar), activation of NAcSOM+ neurons. We further demonstrate that NAcSOM+ are activated by stress in vivo and undergo stress-dependent plasticity, evident as a global increase in intrinsic excitability and an increase in excitation-inhibition balance specifically at vHPC, but not BLA, inputs onto NAcSOM+ neurons. Importantly, both forms of stress-induced plasticity are dependent on eCB signaling at cannabinoid type 1 receptors. These findings reveal eCB-dependent mechanisms that sculpt afferent input and excitability of NAcSOM+ neurons and demonstrate a key role for eCB signaling in stress-induced plasticity of NAcSOM+-associated circuits.

Pallidal GABA B receptors: involvement in cortex beta dynamics and thalamic reticular nucleus activity

The external globus pallidus (GP) firing rate synchronizes the basal ganglia-thalamus-cortex network controlling GABAergic output to different nuclei. In this context, two findings are significant: the activity and GABAergic transmission of the GP modulated by GABA B receptors and the presence of the GP-thalamic reticular nucleus (RTn) pathway, the functionality of which is unknown. The functional participation of GABA B receptors through this network in cortical dynamics is feasible because the RTn controls transmission between the thalamus and cortex. To analyze this hypothesis, we used single-unit recordings of RTn neurons and electroencephalograms of the motor cortex (MCx) before and after GP injection of the GABA B agonist baclofen and the antagonist saclofen in anesthetized rats. We found that GABA B agonists increase the spiking rate of the RTn and that this response decreases the spectral density of beta frequency bands in the MCx. Additionally, injections of GABA B antagonists decreased the firing activity of the RTn and reversed the effects in the power spectra of beta frequency bands in the MCx. Our results proved that the GP modulates cortical oscillation dynamics through the GP-RTn network via tonic modulation of RTn activity.

Developmental hearing loss-induced perceptual deficits are rescued by cortical expression of GABAB receptors

Even transient periods of developmental hearing loss during the developmental critical period have been linked to long-lasting deficits in auditory perception, including temporal and spectral processing, which correlate with speech perception and educational attainment. In gerbils, hearing loss-induced perceptual deficits are correlated with a reduction of both ionotropic GABAA and metabotropic GABAB receptor-mediated synaptic inhibition in auditory cortex, but most research on critical period plasticity has focused on GABAA receptors. We developed viral vectors to express both endogenous GABAA or GABAB receptor subunits in auditory cortex and tested their capacity to restore perception of temporal and spectral auditory cues following critical period hearing loss in the Mongolian gerbil. HL significantly impaired perception of both temporal and spectral auditory cues. While both vectors similarly increased IPSCs in auditory cortex, only overexpression of GABAB receptors improved perceptual thresholds after HL to be similar to those of animals without developmental hearing loss. These findings identify the GABAB receptor as an important regulator of sensory perception in cortex and point to potential therapeutic targets for developmental sensory disorders.

SNAP25 differentially contributes to Gi/o-coupled receptor function at glutamatergic synapses in the nucleus accumbens

The nucleus accumbens (NAc) guides reward-related motivated behavior implicated in pathological behavioral states, including addiction and depression. These behaviors depend on the precise neuromodulatory actions of G_i/o-coupled G-protein-coupled receptors (GPCRs) at glutamatergic synapses onto medium spiny projection neurons (MSNs). Previous work has shown that discrete classes of G_i/o-coupled GPCR mobilize Gβγ to inhibit vesicular neurotransmitter release via t-SNARE protein, SNAP25. However, it remains unknown which Gαi/o systems in the NAc utilize Gβγ-SNARE signaling to dampen glutamatergic transmission. Utilizing patch-clamp electrophysiology and pharmacology in a transgenic mouse line with a C-terminal three-residue deletion of SNAP25 (SNAP25Δ3) weaking the Gβγ-SNARE interaction, we surveyed a broad cohort of G_i/o-coupled GPCRs with robust inhibitory actions at glutamatergic synapses in the NAc. We find that basal presynaptic glutamate release probability is reduced in SNAP25Δ3 mice. While κ opioid, CB1, adenosine A1, group II metabotropic glutamate receptors, and histamine H3 receptors inhibit glutamatergic transmission onto MSNs independent of SNAP25, we report that SNAP25 contributes significantly to the actions of GABA_B, 5-HT1_B/D, and μ opioid receptors. These findings demonstrate that presynaptic G_i/o-coupled GPCRs recruit heterogenous effector mechanisms at glutamatergic synapses in the NAc, with a subset requiring SNA25-dependent Gβγ signaling.

Distinct mechanisms of CB1 and GABAB receptor presynaptic modulation of striatal indirect pathway projections to mouse globus pallidus

Presynaptic modulation is a fundamental process regulating synaptic transmission. Striatal indirect pathway projections originate from A2A-expressing spiny projection neurons (iSPNs), targeting the globus pallidus external segment (GPe) and control the firing of the tonically active GPe neurons via GABA release. It is unclear if and how the presynaptic G-protein-coupled receptors (GPCRs), GABAB and CB1 receptors modulate iSPN-GPe projections. Here we used an optogenetic platform to study presynaptic Ca2+ and GABAergic transmission at iSPN projections, using a genetic strategy to express the calcium sensor GCaMP6f or the excitatory channelrhodopsin (hChR2) on iSPNs. We found that P/Q-type calcium channels are the primary voltage-gated Ca2+ channel (VGCC) subtype controlling presynaptic calcium and GABA release at iSPN-GPe projections. N-type and L-type VGCCs also contribute to GABA release at iSPN-GPe synapses. GABAB receptor activation resulted in a reversible inhibition of presynaptic Ca2+ transients (PreCaTs) and an inhibition of GABAergic transmission at iSPN-GPe synapses. CB1 receptor activation did not inhibit PreCaTs but inhibited GABAergic transmission at iSPN-GPe projections. CB1 effects on GABAergic transmission persisted in experiments where NaV and KV 1 were blocked, indicating a VGCC- and KV 1-independent presynaptic mechanism of action of CB1 receptors. Taken together, presynaptic modulation of iSPN-GPe projections by CB1 and GABAB receptors is mediated by distinct mechanisms. KEY POINTS: P/Q-type are the predominant voltage-gated Ca2+ channels controlling presynaptic Ca2+ and GABA release on the striatal indirect pathway projections. GABAB receptors modulate iSPN-GPe projections via a VGCC-dependent mechanism. CB1 receptors modulate iSPN-GPe projections via a VGCC-independent mechanism.

The benefits of propofol on cancer treatment: Decipher its modulation code to immunocytes

Anesthetics are essential for cancer surgery, but accumulated research have proven that some anesthetics promote the occurrence of certain cancers, leading to adverse effects in the lives of patients. Although anesthetic technology is mature, there is no golden drug selection standard for surgical cancer treatment. To afford the responsibility of human health, a more specific regimen for cancer resection is indeed necessary. Immunosuppression in oncologic surgery has an adverse influence on the outcomes of patients. The choice of anesthetic strategies influences perioperative immunity. Among anesthetics, propofol has shown positive effects on immunity. Apart from that, propofol's anticancer effect has been generally reported, which makes it more significant in oncologic surgery. However, the immunoregulative function of propofol is not reorganized well. Herein, we have summarized the impact of propofol on different immunocytes, proposed its potential mechanism for the positive effect on cancer immunity, and offered a conceivable hypothesis on its regulation to postoperative inflammation. We conclude that the priority of propofol is high in oncologic surgery and propofol may be a promising immunomodulatory drug for tumor therapy.

Unravelling biological roles and mechanisms of GABABR on addiction and depression through mood and memory disorders

The metabotropic γ-aminobutyric acid type B receptor (GABA_BR) remains a hotspot in the recent research area. Being an idiosyncratic G-protein coupled receptor family member, the GABA_BR manifests adaptively tailored functionality under multifarious modulations by a constellation of agents, pointing to cross-talk between receptors and effectors that converge on the domains of mood and memory. This review systematically summarizes the latest achievements in signal transduction mechanisms of the GABA_BR-effector-regulator complex and probes how the up-and down-regulation of membrane-delimited GABA_BRs are associated with manifold intrinsic and extrinsic agents in synaptic strength and plasticity. Neuropsychiatric conditions depression and addiction share the similar pathophysiology of synapse inadaptability underlying negative mood-related processes, memory formations, and impairments. In the attempt to emphasize all convergent discoveries, we hope the insights gained on the GABA_BR system mechanisms of action are conducive to designing more therapeutic candidates so as to refine the prognosis rate of diseases and minimize side effects.

Presynaptic cGMP sets synaptic strength in the striatum and is important for motor learning

The striatum is a subcortical brain region responsible for the initiation and termination of voluntary movements. Striatal spiny projection neurons receive major excitatory synaptic input from neocortex and thalamus, and cyclic nucleotides have long been known to play important roles in striatal function. Yet, the precise mechanism of action is unclear. Here, we combine optogenetic stimulation, 2‐photon imaging, and genetically encoded scavengers to dissect the regulation of striatal synapses in mice. Our data show that excitatory striatal inputs are tonically depressed by phosphodiesterases (PDEs), in particular PDE1. Blocking PDE activity boosts presynaptic calcium entry and glutamate release, leading to strongly increased synaptic transmission. Although PDE1 degrades both cAMP and cGMP, we uncover that the concentration of cGMP, not cAMP, controls the gain of striatal inputs. Disturbing this gain control mechanism in vivo impairs motor skill learning in mice. The tight dependence of striatal excitatory synapses on PDE1 and cGMP offers a new perspective on the molecular mechanisms regulating striatal activity.

Role of the striatal dopamine, GABA and opioid systems in mediating feeding and fat intake

Food intake, which is a highly reinforcing behavior, provides nutrients required for survival in all animals. However, when fat and sugar consumption goes beyond the daily needs, it can favor obesity. The prevalence and severity of this health problem has been increasing with time. Besides covering nutrient and energy needs, food and in particular its highly palatable components, such as fats, also induce feelings of joy and pleasure. Experimental evidence supports a role of the striatal complex and of the mesolimbic dopamine system in both feeding and food-related reward processing, with the nucleus accumbens as a key target for reward or reinforcing-associated signaling during food intake behavior. In this review, we provide insights concerning the impact of feeding, including fat intake, on different types of receptors and neurotransmitters present in the striatal complex. Reciprocally, we also cover the evidence for a modulation of palatable food intake by different neurochemical systems in the striatal complex and in particular the nucleus accumbens, with a focus on dopamine, GABA and the opioid system.

Keeping the Balance: GABAB Receptors in the Developing Brain and Beyond

The main neurotransmitter in the brain responsible for the inhibition of neuronal activity is γ-aminobutyric acid (GABA). It plays a crucial role in circuit formation during development, both via its primary effects as a neurotransmitter and also as a trophic factor. The GABA_B receptors (GABA_BRs) are G protein-coupled metabotropic receptors; on one hand, they can influence proliferation and migration; and, on the other, they can inhibit cells by modulating the function of K⁺ and Ca²⁺ channels, doing so on a slower time scale and with a longer-lasting effect compared to ionotropic GABA_A receptors. GABA_BRs are expressed pre- and post-synaptically, at both glutamatergic and GABAergic terminals, thus being able to shape neuronal activity, plasticity, and the balance between excitatory and inhibitory synaptic transmission in response to varying levels of extracellular GABA concentration. Furthermore, given their subunit composition and their ability to form complexes with several associated proteins, GABA_BRs display heterogeneity with regard to their function, which makes them a promising target for pharmacological interventions. This review will describe (i) the latest results concerning GABA_BRs/GABA_BR-complex structures, their function, and the developmental time course of their appearance and functional integration in the brain, (ii) their involvement in manifestation of various pathophysiological conditions, and (iii) the current status of preclinical and clinical studies involving GABA_BR-targeting drugs.

Cocaine restricts nucleus accumbens feedforward drive through a monoamine-independent mechanism

Parvalbumin-expressing fast-spiking interneurons (PV-INs) within feedforward microcircuits in the nucleus accumbens (NAc) coordinate goal-directed motivational behavior. Feedforward inhibition of medium spiny projection neurons (MSNs) is initiated by glutamatergic input from corticolimbic brain structures. While corticolimbic synapses onto MSNs are targeted by the psychostimulant, cocaine, it remains unknown whether cocaine also exerts acute neuromodulatory actions at collateralizing synapses onto PV-INs. Using whole-cell patch-clamp electrophysiology, optogenetics, and pharmacological tools in transgenic reporter mice, we found that cocaine decreases thalamocortical glutamatergic drive onto PV-INs by engaging a monoamine-independent mechanism. This mechanism relies on postsynaptic sigma-1 (σ₁) activity, leading to the mobilization of intracellular Ca²⁺ stores that trigger retrograde endocannabinoid signaling at presynaptic type-1 cannabinoid receptors (CB₁R). Cocaine-evoked CB₁R activity occludes the expression of CB₁R-dependent long-term depression (LTD) at this synaptic locus. These findings provide evidence that acute cocaine exposure targets feedforward microcircuits in the NAc and extend existing models of cocaine action on mesolimbic reward circuits.

Kappa opioid receptor modulation of excitatory drive onto nucleus accumbens fast-spiking interneurons

The dynorphin/kappa opioid receptor (KOR) system within the nucleus accumbens (NAc) contributes to affective states. Parvalbumin fast-spiking interneurons (PV-FSIs), a key component of feedforward inhibition, participate in integration of excitatory inputs to the NAc by robustly inhibiting select populations of medium spiny output neurons, therefore greatly influencing NAc dependent behavior. How the dynorphin/KOR system regulates feedforward inhibition in the NAc remains unknown. Here, we elucidate the molecular mechanisms of KOR inhibition of excitatory transmission onto NAc PV-FSIs using a combination of whole-cell patch-clamp electrophysiology, optogenetics, pharmacology, and a parvalbumin reporter mouse. We find that postsynaptic KOR stimulation induces long-term depression (LTD) of excitatory synapses onto PV-FSI by stimulating the endocytosis of AMPARs via a PKA and calcineurin-dependent mechanism. Furthermore, KOR regulation of PV-FSI synapses are input specific, inhibiting thalamic but not cortical inputs. Finally, following acute stress, a protocol known to elevate dynorphin/KOR signaling in the NAc, KOR agonists no longer inhibit excitatory transmission onto PV-FSI. In conclusion, we delineate pathway-specific mechanisms mediating KOR control of feedforward inhibitory circuits in the NAc and provide evidence for the recruitment of this system in response to stress.

Neuroplasticity and Multilevel System of Connections Determine the Integrative Role of Nucleus Accumbens in the Brain Reward System

A growing body of evidence suggests that nucleus accumbens (NAc) plays a significant role not only in the physiological processes associated with reward and satisfaction but also in many diseases of the central nervous system. Summary of the current state of knowledge on the morphological and functional basis of such a diverse function of this structure may be a good starting point for further basic and clinical research. The NAc is a part of the brain reward system (BRS) characterized by multilevel organization, extensive connections, and several neurotransmitter systems. The unique role of NAc in the BRS is a result of: (1) hierarchical connections with the other brain areas, (2) a well-developed morphological and functional plasticity regulating short- and long-term synaptic potentiation and signalling pathways, (3) cooperation among several neurotransmitter systems, and (4) a supportive role of neuroglia involved in both physiological and pathological processes. Understanding the complex function of NAc is possible by combining the results of morphological studies with molecular, genetic, and behavioral data. In this review, we present the current views on the NAc function in physiological conditions, emphasizing the role of its connections, neuroplasticity processes, and neurotransmitter systems.

Endocannabinoid Modulation of Nucleus Accumbens Microcircuitry and Terminal Dopamine Release

The nucleus accumbens (NAc) is located in the ventromedial portion of the striatum and is vital to valence-based predictions and motivated action. The neural architecture of the NAc allows for complex interactions between various cell types that filter incoming and outgoing information. Dopamine (DA) input serves a crucial role in modulating NAc function, but the mechanisms that control terminal DA release and its effect on NAc neurons continues to be elucidated. The endocannabinoid (eCB) system has emerged as an important filter of neural circuitry within the NAc that locally shapes terminal DA release through various cell type- and site-specific actions. Here, we will discuss how eCB signaling modulates terminal DA release by shaping the activity patterns of NAc neurons and their afferent inputs. We then discuss recent technological advancements that are capable of dissecting how distinct cell types, their afferent projections, and local neuromodulators influence valence-based actions.

GABAB Receptors and Cognitive Processing in Health and Disease

GABA_B receptors are implicated in numerous central nervous system-based behaviours and mechanisms, including cognitive processing in preclinical animal models. Homeostatic changes in the expression and function of these receptors across brain structures have been found to affect cognitive processing. Numerous preclinical studies have focused on the role of GABA_B receptors in learning, memory and cognition per se with some interesting, although sometimes contradictory, findings. The majority of the existing clinical literature focuses on alterations in GABA_B receptor function in conditions and disorders whose main symptomatology includes deficits in cognitive processing. The aim of this chapter is to delineate the role of GABA_B receptors in cognitive processes in health and disease of animal models and human clinical populations. More specifically, this review aims to present literature on the role of GABA_B receptors in animal models with cognitive deficits, especially those of learning and memory. Further, it aims to capture the progress and advances of research studies on the effects of GABA_B receptor compounds in neurodevelopmental and neurodegenerative conditions with cognitive dysfunctions. The neurodevelopmental conditions covered include autism spectrum disorders, fragile X syndrome and Down's syndrome and the neurodegenerative conditions discussed are Alzheimer's disease, epilepsy and autoimmune anti-GABA_B encephalitis. Although some findings are contradictory, results indicate a possible therapeutic role of GABA_B receptor compounds for the treatment of cognitive dysfunction and learning/memory impairments for some of these conditions, especially in neurodegeneration. Moreover, future research efforts should aim to develop selective GABA_B receptor compounds with minimal, if any, side effects.

Blockade of pre-synaptic and post-synaptic GABAB receptors in the lateral habenula produces different effects on anxiety-like behaviors in 6-hydroxydopamine hemiparkinsonian rats

Although the output of the lateral habenula (LHb) controls the activity of midbrain dopaminergic and serotonergic systems, which are implicated in the pathophysiology of anxiety, it is not known how blockade of GABA_B receptors in the region affects anxiety-like behaviors, particularly in Parkinson's disease-related anxiety. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta in rats induced anxiety-like behaviors, led to hyperactivity of LHb neurons and decreased the level of extracellular dopamine (DA) in the basolateral amygdala (BLA) compared to sham-lesioned rats. Intra-LHb injection of pre-synaptic GABA_B receptor antagonist CGP36216 produced anxiolytic-like effects, while the injection of post-synaptic GABA_B receptor antagonist CGP35348 induced anxiety-like responses in both groups. Further, intra-LHb injection of CGP36216 decreased the firing rate of the neurons, and increased the GABA/glutamate ratio in the LHb and release of DA and serotonin (5-HT) in the BLA; conversely, CGP35348 increased the firing rate of the neurons and decreased the GABA/glutamate ratio and release of DA and 5-HT in sham-lesioned and the lesioned rats. However, the doses of the antagonists producing these behavioral effects in the lesioned rats were lower than those in sham-lesioned rats, and the duration of action of the antagonists on the firing rate of the neurons and release of the neurotransmitters was prolonged in the lesioned rats. Collectively, these findings suggest that pre-synaptic and post-synaptic GABA_B receptors in the LHb are involved in the regulation of anxiety-like behaviors, and degeneration of the nigrostriatal pathway up-regulates function and/or expression of these receptors.

Axo-axonic synapses: Diversity in neural circuit function

The chemical synapse is the principal form of contact between neurons of the central nervous system. These synapses are typically configured as presynaptic axon terminations onto postsynaptic dendrites or somata, giving rise to axo-dendritic and axo-somatic synapses, respectively. Beyond these common synapse configurations are less-studied, non-canonical synapse types that are prevalent throughout the brain and significantly contribute to neural circuit function. Among these are the axo-axonic synapses, which consist of an axon terminating on another axon or axon terminal. Here, we review evidence for axo-axonic synapse contributions to neural signaling in the mammalian nervous system and survey functional neural circuit motifs enabled by these synapses. We also detail how recent advances in microscopy, transgenics, and biological sensors may be used to identify and functionally assay axo-axonic synapses.

Calcium-Permeable AMPA Receptors Promote Endocannabinoid Signaling at Parvalbumin Interneuron Synapses in the Nucleus Accumbens Core

Synaptic plasticity is a key mechanism of learning and memory. Synaptic plasticity mechanisms within the nucleus accumbens (NAc) mediate differential behavioral adaptations. Feedforward inhibition in the NAc occurs when glutamatergic afferents onto medium spiny neurons (MSNs) collateralize onto fast-spiking parvalbumin (PV)-expressing interneurons (PV-INs), which exert GABAergic control over MSN action potential generation. Here, we find that feedforward glutamatergic synapses onto PV-INs in the NAc core selectively express Ca²⁺-permeable AMPA receptors (CP-AMPARs). Ca²⁺ influx by CP-AMPARs on PV-INs triggers long-term depression (LTD) mediated by endocannabinoid (eCB) signaling at presynaptic cannabinoid type-1 (CB₁) receptors (CB₁Rs). Moreover, CP-AMPARs authorize tonic eCB signaling to negatively regulate glutamate release probability. Blockade of CP-AMPARs in the NAc core in vivo is sufficient to disinhibit locomotor output. These findings elucidate mechanisms by which PV-IN-embedded microcircuits in the NAc undergo activity-dependent shifts in synaptic strength.

Manz et al. show that CP-AMPARs are expressed at glutamatergic synapses onto PV-INs but not D1- or D2-expressing MSNs in the NAc core. Ca²⁺ influx through CP-AMPARs triggers endocannabinoid-dependent tone and synaptic plasticity. Intra-NAc blockade of CP-AMPARs in vivo increases basal locomotion.

Neurexins regulate presynaptic GABAB-receptors at central synapses

Diverse signaling complexes are precisely assembled at the presynaptic active zone for dynamic modulation of synaptic transmission and synaptic plasticity. Presynaptic GABA_B-receptors nucleate critical signaling complexes regulating neurotransmitter release at most synapses. However, the molecular mechanisms underlying assembly of GABA_B-receptor signaling complexes remain unclear. Here we show that neurexins are required for the localization and function of presynaptic GABA_B-receptor signaling complexes. At four model synapses, excitatory calyx of Held synapses in the brainstem, excitatory and inhibitory synapses on hippocampal CA1-region pyramidal neurons, and inhibitory basket cell synapses in the cerebellum, deletion of neurexins rendered neurotransmitter release significantly less sensitive to GABA_B-receptor activation. Moreover, deletion of neurexins caused a loss of GABA_B-receptors from the presynaptic active zone of the calyx synapse. These findings extend the role of neurexins at the presynaptic active zone to enabling GABA_B-receptor signaling, supporting the notion that neurexins function as central organizers of active zone signaling complexes.

Neurexins are evolutionarily conserved cell adhesion molecules that tune synapse formation and specification. Here the authors show that neurexins play similar roles in regulating presynaptic GABA_B receptors at multiple CNS synapses.

Patch-clamp and multi-electrode array electrophysiological analysis in acute mouse brain slices

Patch-clamp and multi-electrode array electrophysiology techniques are used to measure dynamic functional properties of neurons. Whole-cell and cell-attached patch-clamp recordings in brain slices can be performed in voltage-clamp and current-clamp configuration to reveal cell-type-specific synaptic and cellular parameters governing neurotransmission. Multi-electrode array electrophysiology can provide spike activity recordings from multiple neurons, enabling larger sample sizes, and long-term recordings. We provide our guide to preparing acute rodent brain slices with example experiments and analyses intended for novice and expert electrophysiologists.

For complete details on the use and execution of this protocol, please refer to Manz et al. (2020b).

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Viable and efficient preparation of mouse brain tissue

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Comprehensive material source for acute brain slice electrophysiology

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Detailed approach to whole-cell patch-clamp recording of neurons

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Utility and application of multi-electrode array electrophysiology in mouse brain

Noradrenergic Signaling Disengages Feedforward Transmission in the Nucleus Accumbens Shell

The nucleus accumbens shell (NAcSh) receives extensive monoaminergic input from multiple midbrain structures. However, little is known how norepinephrine (NE) modulates NAc circuit dynamics. Using a dynamic electrophysiological approach with optogenetics, pharmacology, and drugs acutely restricted by tethering (DART), we explored microcircuit-specific neuromodulatory mechanisms recruited by NE signaling in the NAcSh of parvalbumin (PV)-specific reporter mice. Surprisingly, NE had little direct effect on modulation of synaptic input at medium spiny projection neurons (MSNs). In contrast, we report that NE transmission selectively modulates glutamatergic synapses onto PV-expressing fast-spiking interneurons (PV-INs) by recruiting postsynaptically-localized α₂-adrenergic receptors (ARs). The synaptic effects of α₂-AR activity decrease PV-IN-dependent feedforward inhibition onto MSNs evoked via optogenetic stimulation of cortical afferents to the NAcSh. These findings provide insight into a new circuit motif in which NE has a privileged line of communication to tune feedforward inhibition in the NAcSh.SIGNIFICANCE STATEMENT The nucleus accumbens (NAc) directs reward-related motivational output by integrating glutamatergic input with diverse neuromodulatory input from monoamine centers. The present study reveals a synapse-specific regulatory mechanism recruited by norepinephrine (NE) signaling within parvalbumin-expressing interneuron (PV-IN) feedforward inhibitory microcircuits. PV-IN-mediated feedforward inhibition in the NAc is instrumental in coordinating NAc output by synchronizing the activity of medium spiny projection neurons (MSNs). By negatively regulating glutamatergic transmission onto PV-INs via α₂-adrenergic receptors (ARs), NE diminishes feedforward inhibition onto MSNs to promote NAc output. These findings elucidate previously unknown microcircuit mechanisms recruited by the historically overlooked NE system in the NAc.

Histamine H3 Receptor Function Biases Excitatory Gain in the Nucleus Accumbens

BACKGROUND

Histamine (HA), a wake-promoting monoamine implicated in stress-related arousal states, is synthesized in histidine decarboxylase-expressing hypothalamic neurons of the tuberomammillary nucleus. Histidine decarboxylase-containing varicosities diffusely innervate striatal and mesolimbic networks, including the nucleus accumbens (NAc). The NAc integrates diverse monoaminergic inputs to coordinate motivated behavior. While the NAc expresses various HA receptor subtypes, mechanisms by which HA modulates NAc circuit dynamics are undefined.

METHODS

Using male D1tdTomato transgenic reporter mice, whole-cell patch-clamp electrophysiology, and input-specific optogenetics, we employed a targeted pharmacological approach to interrogate synaptic mechanisms recruited by HA signaling at glutamatergic synapses in the NAc. We incorporated an immobilization stress protocol to assess whether acute stress engages these mechanisms at glutamatergic synapses onto D₁ receptor-expressing [D1(+)] medium spiny neurons (MSNs) in the NAc core.

RESULTS

HA negatively regulates excitatory gain onto D1(+)-MSNs via presynaptic H₃ receptor-dependent long-term depression that requires G_βγ-directed Akt-GSK3β signaling. Furthermore, HA asymmetrically regulates glutamatergic transmission from the prefrontal cortex and mediodorsal thalamus, with inputs from the prefrontal cortex undergoing robust HA-induced long-term depression. Finally, we report that acute immobilization stress attenuates this long-term depression by recruiting endogenous H₃ receptor signaling in the NAc at glutamatergic synapses onto D1(+)-MSNs.

CONCLUSIONS

Stress-evoked HA signaling in the NAc recruits H₃ heteroreceptor signaling to shift thalamocortical input onto D1(+)-MSNs in the NAc. Our findings provide novel insight into an understudied neuromodulatory system within the NAc and implicate HA in stress-associated physiological states.

Temperature regulates synaptic subcellular specificity mediated by inhibitory glutamate signaling

Environmental factors such as temperature affect neuronal activity and development. However, it remains unknown whether and how they affect synaptic subcellular specificity. Here, using the nematode Caenorhabditis elegans AIY interneurons as a model, we found that high cultivation temperature robustly induces defects in synaptic subcellular specificity through glutamatergic neurotransmission. Furthermore, we determined that the functional glutamate is mainly released by the ASH sensory neurons and sensed by two conserved inhibitory glutamate-gated chloride channels GLC-3 and GLC-4 in AIY. Our work not only presents a novel neurotransmission-dependent mechanism underlying the synaptic subcellular specificity, but also provides a potential mechanistic insight into high-temperature-induced neurological defects.

An endocannabinoid-regulated basolateral amygdala-nucleus accumbens circuit modulates sociability

Deficits in social interaction (SI) are a core symptom of autism spectrum disorders (ASDs); however, treatments for social deficits are notably lacking. Elucidating brain circuits and neuromodulatory signaling systems that regulate sociability could facilitate a deeper understanding of ASD pathophysiology and reveal novel treatments for ASDs. Here we found that in vivo optogenetic activation of the basolateral amygdala-nucleus accumbens (BLA-NAc) glutamatergic circuit reduced SI and increased social avoidance in mice. Furthermore, we found that 2-arachidonoylglycerol (2-AG) endocannabinoid signaling reduced BLA-NAc glutamatergic activity and that pharmacological 2-AG augmentation via administration of JZL184, a monoacylglycerol lipase inhibitor, blocked SI deficits associated with in vivo BLA-NAc stimulation. Additionally, optogenetic inhibition of the BLA-NAc circuit markedly increased SI in the Shank3B-/- mouse, an ASD model with substantial SI impairment, without affecting SI in WT mice. Finally, we demonstrated that JZL184 delivered systemically or directly to the NAc also normalized SI deficits in Shank3B-/- mice, while ex vivo JZL184 application corrected aberrant NAc excitatory and inhibitory neurotransmission and reduced BLA-NAc-elicited feed-forward inhibition of NAc neurons in Shank3B-/- mice. These data reveal circuit-level and neuromodulatory mechanisms regulating social function relevant to ASDs and suggest 2-AG augmentation could reduce social deficits via modulation of excitatory and inhibitory neurotransmission in the NAc.

Targeting presynaptic H3 heteroreceptor in nucleus accumbens to improve anxiety and obsessive-compulsive-like behaviors

Anxiety commonly co-occurs with obsessive-compulsive disorder (OCD). Both of them are closely related to stress. However, the shared neurobiological substrates and therapeutic targets remain unclear. Here we report an amelioration of both anxiety and OCD via the histamine presynaptic H3 heteroreceptor on glutamatergic afferent terminals from the prelimbic prefrontal cortex (PrL) to the nucleus accumbens (NAc) core, a vital node in the limbic loop. The NAc core receives direct hypothalamic histaminergic projections, and optogenetic activation of hypothalamic NAc core histaminergic afferents selectively suppresses glutamatergic rather than GABAergic synaptic transmission in the NAc core via the H3 receptor and thus produces an anxiolytic effect and improves anxiety- and obsessive-compulsive-like behaviors induced by restraint stress. Although the H3 receptor is expressed in glutamatergic afferent terminals from the PrL, basolateral amygdala (BLA), and ventral hippocampus (vHipp), rather than the thalamus, only the PrL- and not BLA- and vHipp-NAc core glutamatergic pathways among the glutamatergic afferent inputs to the NAc core is responsible for co-occurrence of anxiety- and obsessive-compulsive-like behaviors. Furthermore, activation of the H3 receptor ameliorates anxiety and obsessive-compulsive-like behaviors induced by optogenetic excitation of the PrL-NAc glutamatergic afferents. These results demonstrate a common mechanism regulating anxiety- and obsessive-compulsive-like behaviors and provide insight into the clinical treatment strategy for OCD with comorbid anxiety by targeting the histamine H3 receptor in the NAc core.

My Neighbour Hetero-deconstructing the mechanisms underlying heterosynaptic plasticity

Synapses change in strength following patterns of activity, but in many cases seemingly inactive neighbouring synapses also undergo changes in strength. These heterosynaptic changes occur across developmental time-points in various brain circuits in different species, but their precise molecular mechanisms are not well understood. Additionally, heterosynaptic changes can mirror homosynaptic plasticity or occur in opposition to homosynaptic changes. In this review we consider what useful functionality heterosynaptic dynamics could potentially endow the circuit with, and the underlying signalling events that implement heterosynaptic changes. We discuss what unanswered questions remain, and what the future looks like for understanding the logic of synaptic plasticity.