Explore the vast range of titles available.

The neurotransmitters glutamate and γ-aminobutyric acid (GABA) transmit synaptic signals by activating fast-acting ligand-gated ion channels and more slowly acting G-protein-coupled receptors (GPCRs). The GPCRs for these neurotransmitters, metabotropic glutamate (mGlu) and GABA B receptors, are atypical GPCRs with a large extracellular domain and a mandatory dimeric structure. Recent studies have revealed how these receptors are activated through multiple allosteric interactions between subunit domains. It emerges that the molecular complexity of these receptors is further increased through association with trafficking, effector and regulatory proteins. The structure and composition of these receptors present opportunities for therapeutic intervention in mental health and neurological disorders. This Review discusses current knowledge of the structure, function and interactions of the metabotropic glutamate and GABA B receptors and the potential to target receptor subunits for future therapeutic intervention in neurological and mental health disorders. Activation of mGlu and GABA B receptors The two main neurotransmitters in the brain, glutamate and γ-aminobutyric acid (GABA), transmit synaptic signals by activating fast-acting ligand-gated ion channels and more slowly acting mGlu and GABA B receptors. mGlu and GABA B are G-protein-coupled receptors (GPCRs) and attractive drug targets for neurological disorders. In this Review, Jean-Philippe Pin and Bernhard Bettler discuss biophysical and structural studies that have shown the activation mechanisms of mGlu and GABA B , as well as proteomic approaches that have revealed interacting proteins and downstream signalling pathways. These studies are leading to new opportunities for drug discovery.

Key Points GABA B receptors (GABA B Rs) are the G protein-coupled receptors for the inhibitory neurotransmitter GABA. Activation of these receptors is involved in pre- and postsynaptic inhibition, regulation of Ca 2+ and K + channels and rhythmic network activity. GABA B Rs are composed of principal GABA B1a , GABA B1b and GABA B2 subunits, which form the core of the receptor, and auxiliary KCTD8, KCTD12, KCTD12b and KCTD16 subunits, which differentially modulate receptor properties. Principal subunits form functional GABA B(1a,2) and GABA B(1b,2) heterodimers that form higher-order oligomers and bind tetramers of KCTD proteins. The principal subunits regulate the surface expression and the axonal versus dendritic distribution of GABA B Rs, whereas the auxiliary subunits determine agonist potency and the kinetics of the receptor response. Phosphorylation of the principal subunits is a prime mechanism regulating GABA B R endocytosis, recycling and degradation. GABA B Rs engage in intracellular signalling crosstalk with metabotropic and NMDA-type glutamate receptors, allowing integration of inhibitory and excitatory signals at a cellular level. GABA B Rs are implicated in a variety of neurological and psychiatric conditions. Drugs that target receptor subtypes, defined by the KCTD proteins present, may allow more-specific therapeutic interference of GABA B R-mediated signalling. GABA B receptor activity is integral to the proper functioning of many neural systems. In this Review, Gassmann and Bettler examine our understanding of the subunit composition of such receptors and how this affects GABA B receptor properties, neuronal processes and higher brain functions. GABA B receptors (GABA B Rs) are G protein-coupled receptors for GABA, the main inhibitory neurotransmitter in the CNS. In the past 5 years, notable advances have been made in our understanding of the molecular composition of these receptors. GABA B Rs are now known to comprise principal and auxiliary subunits that influence receptor properties in distinct ways. The principal subunits regulate the surface expression and the axonal versus dendritic distribution of these receptors, whereas the auxiliary subunits determine agonist potency and the kinetics of the receptor response. This Review summarizes current knowledge on how the subunit composition of GABA B Rs affects the distribution of these receptors, neuronal processes and higher brain functions.

Targeting receptor proteins, such as ligand-gated ion channels and G protein-coupled receptors, has directly enabled the discovery of most drugs developed to modulate receptor signalling. However, as the search for novel and improved drugs continues, an innovative approach — targeting receptor complexes — is emerging. Receptor complexes are composed of core receptor proteins and receptor-associated proteins, which have profound effects on the overall receptor structure, function and localization. Hence, targeting key protein–protein interactions within receptor complexes provides an opportunity to develop more selective drugs with fewer side effects. In this Review, we discuss our current understanding of ligand-gated ion channel and G protein-coupled receptor complexes and discuss strategies for their pharmacological modulation. Although such strategies are still in preclinical development for most receptor complexes, they exemplify how receptor complexes can be drugged, and lay the groundwork for this nascent area of research.Targeting protein complexes, including those containing G protein-coupled receptors or ligand-gated ion channels, could provide opportunities to increase the target and functional selectivity of novel drugs compared with existing therapies, which only target the receptors. This Review discusses the landscape of ligand-gated ion channel and G protein-coupled receptor complexes as therapeutic targets, as well as strategies for their pharmacological modulation.

Cortical neural circuits are complex but very precise networks of balanced excitation and inhibition. Yet, the molecular and cellular mechanisms that form the balance are just beginning to emerge. Here, using conditional γ-aminobutyric acid receptor B1- deficient mice we identify a γ-aminobutyric acid/tumor necrosis factor superfamily member 12-mediated bidirectional communication pathway between parvalbumin-positive fast spiking interneurons and oligodendrocyte precursor cells that determines the density and function of interneurons in the developing medial prefrontal cortex. Interruption of the GABAergic signaling to oligodendrocyte precursor cells results in reduced myelination and hypoactivity of interneurons, strong changes of cortical network activities and impaired social cognitive behavior. In conclusion, glial transmitter receptors are pivotal elements in finetuning distinct brain functions. Early postnatal interruption of the bidirectional GABA/TNFSF12 signaling between parvalbumin-positive interneurons and oligodendrocyte precursor cells impairs correct prefrontal cortical network activity and social cognitive behavior later in life.

GABA B receptors (GBRs) are key regulators of synaptic release but little is known about trafficking mechanisms that control their presynaptic abundance. We now show that sequence-related epitopes in APP, AJAP-1 and PIANP bind with nanomolar affinities to the N-terminal sushi-domain of presynaptic GBRs. Of the three interacting proteins, selectively the genetic loss of APP impaired GBR-mediated presynaptic inhibition and axonal GBR expression. Proteomic and functional analyses revealed that APP associates with JIP and calsyntenin proteins that link the APP/GBR complex in cargo vesicles to the axonal trafficking motor. Complex formation with GBRs stabilizes APP at the cell surface and reduces proteolysis of APP to Aβ, a component of senile plaques in Alzheimer’s disease patients. Thus, APP/GBR complex formation links presynaptic GBR trafficking to Aβ formation. Our findings support that dysfunctional axonal trafficking and reduced GBR expression in Alzheimer’s disease increases Aβ formation. The mechanisms that control the presynaptic abundance of GABAB receptors (GBRs) remains unclear. This study shows that sequence-related epitopes in APP, AJAP-1 and PIANP bind with nanomolar affinities to the N-terminal sushi-domain of presynaptic GBRs, and that selective loss of APP impaired GBR-mediated presynaptic inhibition and axonal GBR expression

Interneurons are critical for proper neural network function and can activate Ca2+ signaling in astrocytes. However, the impact of the interneuron-astrocyte signaling into neuronal network operation remains unknown. Using the simplest hippocampal Astrocyte-Neuron network, i.e., GABAergic interneuron, pyramidal neuron, single CA3-CA1 glutamatergic synapse, and astrocytes, we found that interneuron-astrocyte signaling dynamically affected excitatory neurotransmission in an activity- and time-dependent manner, and determined the sign (inhibition vs potentiation) of the GABA-mediated effects. While synaptic inhibition was mediated by GABAA receptors, potentiation involved astrocyte GABAB receptors, astrocytic glutamate release, and presynaptic metabotropic glutamate receptors. Using conditional astrocyte-specific GABAB receptor (Gabbr1) knockout mice, we confirmed the glial source of the interneuron-induced potentiation, and demonstrated the involvement of astrocytes in hippocampal theta and gamma oscillations in vivo. Therefore, astrocytes decode interneuron activity and transform inhibitory into excitatory signals, contributing to the emergence of novel network properties resulting from the interneuron-astrocyte interplay.

Inputs to midbrain dopamine neurons control rewarding and drug-related behaviors. The authors found that nucleus accumbens inputs and local GABA neurons inhibit dopamine neurons through distinct populations of GABA receptors. Furthermore, genetic deletion of GABA B receptors from dopamine neurons selectively increased behavioral sensitivity to cocaine. Afferent inputs to the ventral tegmental area (VTA) control reward-related behaviors through regulation of dopamine neuron activity. The nucleus accumbens (NAc) provides one of the most prominent projections to the VTA; however, recent studies have provided conflicting evidence regarding the function of these inhibitory inputs. Using optogenetics, cell-specific ablation, whole cell patch-clamp and immuno-electron microscopy, we found that NAc inputs synapsed directly onto dopamine neurons, preferentially activating GABA B receptors. GABAergic inputs from the NAc and local VTA GABA neurons were differentially modulated and activated separate receptor populations in dopamine neurons. Genetic deletion of GABA B receptors from dopamine neurons in adult mice did not affect general or morphine-induced locomotor activity, but markedly increased cocaine-induced locomotion. Collectively, our findings demonstrate notable selectivity in the inhibitory architecture of the VTA and suggest that long-range GABAergic inputs to dopamine neurons fundamentally regulate behavioral responses to cocaine.

The signaling diversity of GABAergic interneurons to post-synaptic neurons is crucial to generate the functional heterogeneity that characterizes brain circuits. Whether this diversity applies to other brain cells, such as the glial cells astrocytes, remains unexplored. Using optogenetics and two-photon functional imaging in the adult mouse neocortex, we here reveal that parvalbumin- and somatostatin-expressing interneurons, two key interneuron classes in the brain, differentially signal to astrocytes inducing weak and robust GABA B receptor-mediated Ca 2+ elevations, respectively. Furthermore, the astrocyte response depresses upon parvalbumin interneuron repetitive stimulations and potentiates upon somatostatin interneuron repetitive stimulations, revealing a distinguished astrocyte plasticity. Remarkably, the potentiated response crucially depends on the neuropeptide somatostatin, released by somatostatin interneurons, which activates somatostatin receptors at astrocytic processes. Our study unveils, in the living brain, a hitherto unidentified signaling specificity between interneuron subtypes and astrocytes opening a new perspective into the role of astrocytes as non-neuronal components of inhibitory circuits. Interneurons in the neocortex have functional and morphological subtypes. Here, Mariotti and colleagues show that activation of parvalbumin-expressing interneurons evokes depressing calcium responses in astrocytes while somatostatin-expressing interneurons evoke potentiating astrocytic responses.

GABA B receptors are the most abundant inhibitory G protein–coupled receptors in the mammalian brain. Using high-resolution proteomics, the authors show that native GABA B receptors are macromolecular complexes with previously unknown complexity in subunit composition. This molecular diversity in structure and assembly encodes the diversity of GABA B physiology in the CNS. GABA B receptors, the most abundant inhibitory G protein–coupled receptors in the mammalian brain, display pronounced diversity in functional properties, cellular signaling and subcellular distribution. We used high-resolution functional proteomics to identify the building blocks of these receptors in the rodent brain. Our analyses revealed that native GABA B receptors are macromolecular complexes with defined architecture, but marked diversity in subunit composition: the receptor core is assembled from GABA B1a/b , GABA B2 , four KCTD proteins and a distinct set of G-protein subunits, whereas the receptor's periphery is mostly formed by transmembrane proteins of different classes. In particular, the periphery-forming constituents include signaling effectors, such as Cav2 and HCN channels, and the proteins AJAP1 and amyloid-β A4, both of which tightly associate with the sushi domains of GABA B1a . Our results unravel the molecular diversity of GABA B receptors and their postnatal assembly dynamics and provide a roadmap for studying the cellular signaling of this inhibitory neurotransmitter receptor.

Amyloid-β precursor protein (APP) regulates neuronal activity through the release of secreted APP (sAPP) acting at cell surface receptors. APP and sAPP were reported to bind to the extracellular sushi domain 1 (SD1) of GABA B receptors (GBRs). A 17 amino acid peptide (APP17) derived from APP was sufficient for SD1 binding and shown to mimic the inhibitory effect of sAPP on neurotransmitter release and neuronal activity. The functional effects of APP17 and sAPP were similar to those of the GBR agonist baclofen and blocked by a GBR antagonist. These experiments led to the proposal that sAPP activates GBRs to exert its neuronal effects. However, whether APP17 and sAPP influence classical GBR signaling pathways in heterologous cells was not analyzed. Here, we confirm that APP17 binds to GBRs with nanomolar affinity. However, biochemical and electrophysiological experiments indicate that APP17 does not influence GBR activity in heterologous cells. Moreover, APP17 did not regulate synaptic GBR localization, GBR-activated K + currents, neurotransmitter release, or neuronal activity in vitro or in vivo. Our results show that APP17 is not a functional GBR ligand and indicate that sAPP exerts its neuronal effects through receptors other than GBRs.