GABA Signaling Research Articles

The effect of exercise on GABA signaling pathway in the model of chemically induced seizures

AimsGamma amino butyric acid (GABA) imbalance plays a critical role in most neurological disorders including epilepsy. This study assessed the involvement of mild exercise on GABA imbalance following by seizure induction in rats. Main methodsSeizure was induced by pentylentetrazole (PTZ) injection. Animals were divided into sham, seizure, exercise (EX), co-seizure-induced exercise (Co-SI EX) and Pre-SI EX groups. In the Co-SI EX group, doing exercise and seizure induction was carried out during four weeks. Animals in the Pre-SI EX group exercised in week 1 to week 8 and seizures were induced in week 5 to week 8. Seizure properties, neural viability and expressions of glutamic acid decarboxylase 65 (GAD65) and GABAA receptor α1 in the hippocampus were assessed. Key findingsSeizure severity reduced and latency increased in the Co-SI EX and Pre-SI EX groups compared to seizure group.The mean number of dark neurons decreased in all exercise groups compared to seizure group in both CA1 and CA3 areas.The gene level of GAD65 and GABAA receptor α1 was highly expressed in the Co-SI EX group in the hippocampal area.Distribution of GAD65 in the both CA1 and CA3 areas increased in the EX and Co-SI EX groups.GABAA receptor α1 was up-regulated in the CA3 area of Co-SI EX group and down-regulated in the CA1 and CA3 areas of Pre-SI EX group. SignificanceThese findings suggest that exercise develop anti-epileptic as well as neuroprotective effects by modulating of GABA disinhibition.

KCC2 Regulates Neuronal Excitability and Hippocampal Activity via Interaction with Task-3 Channels

KCC2 regulates neuronal transmembrane chloride gradients and thereby controls GABA signaling in the brain. KCC2 downregulation is observed in numerous neurological and psychiatric disorders. Paradoxical, excitatory GABA signaling is usually assumed to contribute to abnormal network activity underlying the pathology. We tested this hypothesis and explored the functional impact of chronic KCC2 downregulation in the rat dentate gyrus. Although the reversal potential of GABAA receptor currents is depolarized in KCC2 knockdown neurons, this shift is compensated by depolarization of the resting membrane potential. This reflects downregulation of leak potassium currents. We show KCC2 interacts with Task-3 (KCNK9) channels and is required for their membrane expression. Increased neuronal excitability upon KCC2 suppression altered dentate gyrus rhythmogenesis, which could be normalized by chemogenetic hyperpolarization. Our data reveal KCC2 downregulation engages complex synaptic and cellular alterations beyond GABA signaling that perturb network activity thus offering additional targets for therapeutic intervention.

The Impact of the Ketogenic Diet on Glial Cells Morphology. A Quantitative Morphological Analysis

Ketogenic diet is reported to protect against cognitive decline, drug-resistant epilepsy, Alzheimer's Disease, damaging effect of ischemic stroke and many neurological diseases. Despite mounting evidence that this dietary treatment works, the exact mechanism of its protective activity is largely unknown. Ketogenic diet acts systemically, not only changing GABA signaling in neurons, but also influencing the reliance on mitochondrial respiration, known to be disrupted in many neurological diseases. Normally, human body is driven by glucose while ketogenic diet mimics starvation and energy required for proper functioning comes from fatty acids oxidation. In the brain astrocytes are believed to be the sole neural cells capable of fatty oxidation. Here we try to explain that not exclusively neurons, but also morphological changes of astroglia and/or microglia due to different metabolic state are important for the mechanism underlying the protective role of ketogenic diet. By quantifying different parameters describing cellular morphology like ramification index or fractal dimension and using Principal Component Analysis to discover the regularities between them, we demonstrate that in normal adult rat brain, ketogenic diet itself is able to change glial morphology, indicating an important role of these underappreciated cells in the brain metabolism.

Peripheral GABA receptors regulate colonic afferent excitability and visceral nociception.

While the presence of GABA receptors on primary afferents has been well described, most functional analyses have focused on the regulation of transmitter release from central terminals and/or signalling in the sensory neuron cell body. Evidence that GABA receptors are transported to peripheral terminals and that there are several sources of GABA in the colon raise the possibility that GABA signalling in the periphery may influence colonic afferent excitability. GABAA and GABAB are present and functional in the colon, where exogenous agonists decrease the excitability of colonic afferents and suppress visceral nociception. Endogenous GABA release within the colon is sufficient to establish the resting excitability of colonic afferents as well as the behavioural response to noxious stimulation of the colon, primarily via GABAA receptors. Peripheral GABA receptors may serve as a viable target for the treatment of visceral pain. It is well established that GABA receptors at the central terminals of primary afferent fibres regulate afferent input to the superficial dorsal horn. However, the extent to which peripheral GABA signalling may also regulate afferent input remains to be determined. The colon was used to explore this issue because of the numerous endogenous sources of GABA that have been described in this tissue. The influence of GABA signalling on colonic afferent excitability was assessed in an ex vivo mouse colorectum pelvic nerve preparation where test compounds were applied to the receptive field. The visceromotor response (VMR) evoked by noxious colorectal distension was used to assess the impact of GABA signalling on visceral nociception, where test compounds were applied directly to the colon. Application of either GABAA or GABAB receptor agonists attenuated the colonic afferent response to colon stretch. Conversely, GABAA and GABAB receptor antagonists increased the stretch response. However, while the noxious distension-induced VMR was attenuated in the presence of GABAA and GABAB receptor agonists, the VMR was only consistently increased by GABAA receptor antagonists. These results suggest that GABA receptors are present and functional in the peripheral terminals of colonic afferents and activation of these receptors via endogenous GABA release contributes to the establishment of colonic afferent excitability and visceral nociception. These results suggest that increasing peripheral GABA receptor signalling could be used to treat visceral pain.

Pulmonary Neuroendocrine Cells Secrete γ-Aminobutyric Acid to Induce Goblet Cell Hyperplasia in Primate Models.

Mucus overproduction is a major contributor to morbidity and mortality in asthma. Mucus overproduction is induced by orchestrated actions of multiple factors that include inflammatory cytokines and γ-aminobutyric acid (GABA). GABA is produced only by pulmonary neuroendocrine cells (PNECs) in the mouse lung. Recent studies in a neonatal mouse model of allergic inflammation have shown that PNECs play an essential role in mucus overproduction by GABA hypersecretion. Whether PNECs mediate dysregulated GABA signaling for mucus overproduction in asthma is unknown. In this study, we characterized the cellular source of GABA in the lungs of nonhuman primates and humans and assessed GABA secretion and signaling in primate disease models. We found that like in mice, PNECs were the major source of GABA in primate lungs. In addition, an infant nonhuman primate model of asthma exhibited an increase in GABA secretion. Furthermore, subjects with asthma had elevated levels of expression of a subset of GABA type α (GABAα) and type β (GABAβ) receptors in airway epithelium compared with those of healthy control subjects. Last, employing a normal human bronchial epithelial cell model of preinduced mucus overproduction, we showed pharmaceutical blockade of GABAα and GABAβ receptor signaling reversed the effect of IL-13 on MUC5AC gene expression and goblet cell proliferation. Together, our data demonstrate an evolutionarily conserved intraepithelial GABA signaling that, in concert with IL-13, plays an essential role in mucus overproduction. Our findings may offer new strategies to ameliorate mucus overproduction in patients with asthma by targeting PNEC secretion and GABA signaling.

314-OR: Mechanisms of AgRP Neuron-Induced Hunger

Neural circuits express a remarkable diversity of neuropeptides, yet the specific function of most of these peptides remains unclear. Agouti-Related Peptide (AgRP) neurons in the arcuate nucleus are critical for the regulation of energy balance. These cells are activated by food deprivation and their activity promotes food seeking and consumption. When food is discovered, AgRP neurons are inhibited within seconds, yet their potentiation of feeding persists for tens of minutes. The mechanisms underlying this sustained hunger drive remain unknown. I will describe data showing that Neuropeptide Y (NPY) is uniquely required for the long-lasting effects of AgRP neurons on feeding behavior. We systematically blocked the ability of AgRP neurons to signal through AgRP, NPY, and GABA, and then stimulated these cells using an optogenetic paradigm that mimics their natural regulation. We found that genetic deletion of NPY abolished optically stimulated food intake and lever-pressing for food, whereas inactivation of AgRP or GABA signaling had no effect. Re-expression of NPY selectively in AgRP neurons rescued these deficits. These findings reveal that NPY plays a critical role in enabling AgRP neurons to drive feeding behavior, due its unique ability to sustain hunger in the interval between food discovery and consumption. Disclosure Z. Knight: None. Funding American Diabetes Association/Pathway to Stop Diabetes (1-16-ACE-29 to Z.K.); National Institutes of Health; Howard Hughes Medical Institute

143-LB: Calorie Restriction in Combination with GABA Ameliorates Type 2 Diabetes

Dysfunction of adipocytes and β-cells are crucial in the progression of obesity-related insulin resistance and type 2 diabetes (T2D). γ-Aminobutyric Acid (GABA) is a key neurotransmitter and is secreted by β-cells. It exerts protective and regenerative effects on β-cells. At the metabolic level, Calorie Restriction (CR) has been shown to improve insulin sensitivity, reduces Fasting Blood Glucose (FBG) and increases insulin levels. GABA and CR are speculated to show an additive effect on insulin secretion and β-cell regeneration via GABA signaling and enhance insulin sensitivity ameliorating T2D manifestations. We have evaluated the effect of GABA and CR combination on β-cell regeneration and insulin sensitivity in High Fat Diet (HFD) and streptozotocin (STZ) induced late stage T2D mouse model. Our results show favorable changes in the measured parameters. GABA+CR group showed reduced FBG levels and improved whole-body insulin responsiveness indicated by increased insulin levels, insulin sensitivity, and glucose tolerance. The combination therapy improved the lipid profile by significantly reducing triglycerides, total cholesterol, and LDL levels and increased HDL levels. The transcript expression profile of metabolic enzymes in the liver indicates a significant decrease in gluconeogenesis and glycogenolysis. The transcript levels indicate decreased lipolysis and increased fatty acid synthesis in the adipose tissue. The transcript levels of mitochondrial biogenesis in the skeletal muscle indicate increased effect of combination therapy, thereby promoting insulin sensitivity. Also, combination therapy promoted β-cell proliferation. In conclusion, calorie restriction in combination with GABA ameliorates T2D in the mouse model by inducing β-cell regeneration mediated by GABA and increased insulin sensitivity by CR diet. Disclosure N.N. Rathwa: None. R. Patel: None. S. Pramanik: None. N.R. Parmar: None. R. A.v.: None. R. Begum: None. Funding Department of Biotechnology, New Delhi, India (BT/PR21242/MED/30/1750/2016)

Synapse-specific opioid modulation of thalamo-cortico-striatal circuits.

The medial thalamus (MThal), anterior cingulate cortex (ACC) and striatum play important roles in affective-motivational pain processing and reward learning. Opioids affect both pain and reward through uncharacterized modulation of this circuitry. This study examined opioid actions on glutamate transmission between these brain regions in mouse. Mu-opioid receptor (MOR) agonists potently inhibited MThal inputs without affecting ACC inputs to individual striatal medium spiny neurons (MSNs). MOR activation also inhibited MThal inputs to the pyramidal neurons in the ACC. In contrast, delta-opioid receptor (DOR) agonists disinhibited ACC pyramidal neuron responses to MThal inputs by suppressing local feed-forward GABA signaling from parvalbumin-positive interneurons. As a result, DOR activation in the ACC facilitated poly-synaptic (thalamo-cortico-striatal) excitation of MSNs by MThal inputs. These results suggest that opioid effects on pain and reward may be shaped by the relative selectivity of opioid drugs to the specific circuit components.

SAT-427 Low Chloride Transporter Expression in Vasopressin Neurons

Several membrane proteins function as ion pumps/transporters that work to maintain the relative ionic concentrations necessary for neuronal signaling. The potassium-chloride co-transporter two (KCC2) is a symporter that actively pumps K+ and Cl- out of the cell in order to maintain a low intracellular [Cl-], while the sodium-potassium-chloride cotransporters one and two (NKCC1/NKCC2) are symporters that actively pump Na+, K+, and Cl- into the cell. KCC2 and NKCC1/2, therefore, have opposing actions on Cl- transport. In the adult, high KCC2 expression leads to low intracellular [Cl-], which causes GABAA receptor Cl- channels to flux Cl- into the neuron, causing a membrane hyperpolarization. Early in development however, low KCC2 expression reverses the Cl- gradient and causes GABAA receptors to flux Cl- out of the neuron, leading to membrane depolarization and neuronal excitation. The change in the polarity of GABA signaling during development is, in part, due to a shift in KCC2 expression from low to high with the maturation of synaptic circuits. Our previous studies have demonstrated an excitatory GABAA receptor-mediated response due to a GABA equilibrium potential (EGABA) that is shifted positive, like that seen early in development, in adult vasopressin (VP)-secreting neurons of the rat hypothalamus. In the current study, we used immunohistochemistry to compare expression levels of the main Cl- transporters, KCC2, NKCC1, and NKCC2, between VP- and oxytocin (OT)-secreting neurons of the hypothalamic paraventricular and supraoptic nuclei. We found that, in adult male Wistar rats, expression of all three transporters is uniformly lower in VP neurons than in adjacent OT neurons in the hypothalamus. Because the phosphorylation state of KCC2 affects membrane trafficking and stabilization, we are also using Western blot to analyze phosphorylation of KCC2 under different osmotic conditions. Finally, we are using Cre-dependent viral transduction to express a light-activatable Cl- channel conditionally in vasopressin-secreting neurons to test for the effect of Cl- flux on vasopressin secretion.

SAT-411 Prepubertal Tonic Gamma-Amino Butyric Acid (GABA) Inhibition Is Upstream of Neurokinin B (NKB), Kisspeptin, and Gonadotropin Releasing Hormone (GnRH) Neuronal Network in Male Rhesus Monkeys

The concept that GnRH release during the prepubertal period is under tonic central inhibition is well established in primates. Although it has been reported that the makorin RING finger protein 3 (MKRN3) gene plays a role in this process (1), neuronal substrates responsible for prepubertal tonic inhibition remain unclear. A series of studies in this lab have shown that GABA neurons are consistently inhibitory to GnRH and kisspeptin neurons in female prepubertal rhesus monkeys (2, 3, 4). Because we recently found that release of GnRH, kisspeptin and NKB in prepubertal male monkeys is significantly lower than those in pubertal monkeys and the pubertal increase in release of these neuropeptides is gonadal steroid independent, in the present study, we ask the question of whether GABA neurons play a role in central inhibition of GnRH release before puberty onset in male monkeys. As described previously, a microdialysis probe was inserted into the median eminence of the hypothalamus in 4 gonadally intact prepubertal male monkeys (15.1 ± 1.9 months of age) and the effects of GABAA receptor antagonist, bicuculline, on release of GnRH, kisspeptin and NKB were examined. The results indicate that bicuculline at 1 µM, but not vehicle, dramatically stimulated release of GnRH, kisspeptin, and NKB in prepubertal male monkeys. Subsequently, we examined whether the bicuculline-induced release of GnRH and kisspeptin was affected by the presence of NKB antagonist, SB222200, as previously we found that NKB signaling is upstream of kisspeptin and GnRH neurons in male monkeys (5). We found that inhibition of NKB signaling attenuated the bicuculline-induced release of GnRH and kisspeptin, suggesting that NKB neurons, in part, relay inhibitory GABA signals to GnRH and kisspeptin neurons. These results are interpreted to mean that in male monkeys, inhibitory GABA signaling plays a role in central inhibition during the prepubertal period and that inhibitory GABA signaling is upstream of the NKB, kisspeptin, and GnRH neuronal pathway. How “Central GABA Inhibition” is regulated by genes involved in this process, such as MKRN3, remains to be investigated.

Enhanced Social Dominance and Altered Neuronal Excitability in the Prefrontal Cortex of Male KCC2b Mutant Mice.

The K-Cl cotransporter KCC2 is essential in the development of the "GABA switch" that produces a change in neuronal responses to GABA signaling from excitatory to inhibitory early in brain development, and alterations in this progression have previously been hypothesized to play a causal role in autism spectrum disorder (ASD). We investigated the KCC2b (Slc12a5) heterozygous knockout mouse using a battery of rodent behavioral tests relevant to core and comorbid ASD symptoms. Compared to wild-type littermates, KCC2+/- mice were normal in standard measures of locomotor activity, grooming and digging behaviors, and social, vocalization, and anxiety-like behaviors. However, KCC2+/- mice exhibited increased social dominance behaviors and increased amplitude of spontaneous postsynaptic currents in the medial prefrontal cortex (PFC) that were previously implicated in governing social hierarchy and dominance behaviors. Treatment of wild-type mouse brain slices with the KCC2 inhibitor VU0240511 increased the amplitude and frequency of excitatory postsynaptic currents, partially recapitulating the phenotype of KCC2+/- mice. These findings indicate that the activity of KCC2 plays a role in social dominance, in parallel with effects on PFC signaling, further suggesting that KCC2 function has some relevance to social behavior but without the breadth of impact on autism-like behavior suggested by previous studies. Further testing could assess whether KCC2 alters other circuits and whether additional factors such as environmental insults may precipitate autism-related behavioral phenotypes. Autism Research 2019, 12: 732-743. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: A mouse model of altered chloride transporter expression was used to look for a role in behaviors and brain function relevant to autism. There was an imbalance in signaling in the prefrontal cortex, and increased social dominance behavior, although other autism-related behaviors were not changed. These findings indicate that altered chloride transporter function affects prefrontal cortex function and social dominance without a broader impact on autism-like behaviors.

Glutamate versus GABA in neuron-oligodendroglia communication.

In the central nervous system (CNS), myelin sheaths around axons are formed by glial cells named oligodendrocytes (OLs). In turn, OLs are generated by oligodendrocyte precursor cells (OPCs) during postnatal development and in adults, according to a process that depends on the proliferation and differentiation of these progenitors. The maturation of OL lineage cells as well as myelination by OLs are complex and highly regulated processes in the CNS. OPCs and OLs express an array of receptors for neurotransmitters, in particular for the two main CNS neurotransmitters glutamate and GABA, and are therefore endowed with the capacity to respond to neuronal activity. Initial studies in cell cultures demonstrated that both glutamate and GABA signaling mechanisms play important roles in OL lineage cell development and function. However, much remains to be learned about the communication of glutamatergic and GABAergic neurons with oligodendroglia in vivo. This review focuses on recent major advances in our understanding of the neuron-oligodendroglia communication mediated by glutamate and GABA in the CNS, and highlights the present controversies in the field. We discuss the expression, activation modes and potential roles of synaptic and extrasynaptic receptors along OL lineage progression. We review the properties of OPC synaptic connectivity with presynaptic glutamatergic and GABAergic neurons in the brain and consider the implication of glutamate and GABA signaling in activity-driven adaptive myelination.

GABARAPs dysfunction by autophagy deficiency in adolescent brain impairs GABAA receptor trafficking and social behavior.

Dysfunctional mTOR signaling is associated with the pathogenesis of neurodevelopmental and neuropsychiatric disorders. However, it is unclear what molecular mechanisms and pathogenic mediators are involved and whether mTOR-regulated autophagy continues to be crucial beyond neurodevelopment. Here, we selectively deleted Atg7 in forebrain GABAergic interneurons in adolescent mice and unexpectedly found that these mice showed a set of behavioral deficits similar to Atg7 deletion in forebrain excitatory neurons. By unbiased quantitative proteomic analysis, we identified γ-aminobutyric acid receptor-associated protein-like 2 (GABARAPL2) to differentially form high-molecular weight species in autophagy-deficient brains. Further functional analyses revealed a novel pathogenic mechanism involving the p62-dependent sequestration of GABARAP family proteins, leading to the reduction of surface GABAA receptor levels. Our work demonstrates a novel physiological role for autophagy in regulating GABA signaling beyond postnatal neurodevelopment, providing a potential mechanism for the reduced inhibitory inputs observed in neurodevelopmental and neuropsychiatric disorders with mTOR hyperactivation.

GABA is a modulator, rather than a classical transmitter, in the medial nucleus of the trapezoid body-lateral superior olive sound localization circuit.

The lateral superior olive (LSO), a brainstem hub involved in sound localization, integrates excitatory and inhibitory inputs from the ipsilateral and the contralateral ear, respectively. In gerbils and rats, inhibition to the LSO reportedly shifts from GABAergic to glycinergic within the first three postnatal weeks. Surprisingly, we found no evidence for synaptic GABA signalling during this time window in mouse LSO principal neurons. However, we found that presynaptic GABAB Rs modulate Ca2+ influx into medial nucleus of the trapezoid body axon terminals, resulting in reduced synaptic strength. Moreover, GABA elicited strong responses in LSO neurons that were mediated by extrasynaptic GABAA Rs. RNA sequencing revealed highly abundant δ subunits, which are characteristic of extrasynaptic receptors. Whereas GABA increased the excitability of neonatal LSO neurons, it reduced the excitability around hearing onset. Collectively, GABA appears to control the excitability of mouse LSO neurons via extrasynaptic and presynaptic signalling. Thus, GABA acts as a modulator, rather than as a classical transmitter. GABA and glycine mediate fast inhibitory neurotransmission and are coreleased at several synapse types. Here we assessed the contribution of GABA and glycine in synaptic transmission between the medial nucleus of the trapezoid body (MNTB) and the lateral superior olive (LSO), two nuclei involved in sound localization. Whole-cell patch-clamp experiments in acute mouse brainstem slices at postnatal days (P) 4 and 11 during pharmacological blockade of GABAA receptors (GABAA Rs) and/or glycine receptors demonstrated no GABAergic synaptic component on LSO principal neurons. A GABAergic component was absent in evoked inhibitory postsynaptic currents and miniature events. Coimmunofluorescence experiments revealed no codistribution of the presynaptic GABAergic marker GAD65/67 with gephyrin, a postsynaptic marker for GABAA Rs, corroborating the conclusion that GABA does not act synaptically in the mouse LSO. Imaging experiments revealed reduced Ca2+ influx into MNTB axon terminals following activation of presynaptic GABAB Rs. GABAB R activation reduced the synaptic strength at P4 and P11. GABA appears to act on extrasynaptic GABAA Rs as demonstrated by application of 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol, a δ-subunit-specific GABAA R agonist. RNA sequencing showed high mRNA levels for the δ-subunit in the LSO. Moreover, GABA transporters GAT-1 and GAT-3 appear to control extracellular GABA. Finally, we show an age-dependent effect of GABA on the excitability of LSO neurons. Whereas tonic GABA increased the excitability at P4, leading to spike facilitation, it decreased the excitability at P11 via shunting inhibition through extrasynaptic GABAA Rs. Taken together, we demonstrate a modulatory role of GABA in the murine LSO, rather than a function as a classical synaptic transmitter.

Hippocampal gene expression patterns linked to late-life physical activity oppose age and AD-related transcriptional decline

Exercise has emerged as a powerful variable that can improve cognitive function and delay age-associated cognitive decline and Alzheimer's disease (AD); however, the underlying mechanisms are poorly understood. To determine if protective mechanisms may occur at the transcriptional level, we used microarrays to investigate the relationship between physical activity levels and gene expression patterns in the cognitively intact aged human hippocampus. In parallel, hippocampal gene expression patterns associated with aging and AD were assessed using publicly available microarray data profiling hippocampus from young (20–59 years), cognitively intact aging (73–95 years) and age-matched AD cases. To identify “anti-aging/AD” transcription patterns associated with physical activity, probesets significantly associated with both physical activity and aging/AD were identified and their directions of expression change in each condition were compared. Remarkably, of the 2210 probesets significant in both data sets, nearly 95% showed opposite transcription patterns with physical activity compared with aging/AD. The majority (>70%) of these anti-aging/AD genes showed increased expression with physical activity and decreased expression in aging/AD. Enrichment analysis of the anti-aging/AD genes showing increased expression in association with physical activity revealed strong overrepresentation of mitochondrial energy production and synaptic function, along with axonal function and myelin integrity. Synaptic genes were notably enriched for synaptic vesicle priming, release and recycling, glutamate and GABA signaling, and spine plasticity. Anti-aging/AD genes showing decreased expression in association with physical activity were enriched for transcription-related function (notably negative regulation of transcription). These data reveal that physical activity is associated with a more youthful profile in the hippocampus across multiple biological processes, providing a potential molecular foundation for how physical activity can delay age- and AD-related decline of hippocampal function.

Pharmacological activation of dopamine D4 receptor modulates morphine-induced changes in the expression of GAD65/67 and GABAB receptors in the basal ganglia

Dopamine D4 receptor (D4R) stimulation, in a putative D4R/μ opioid heteroreceptor (MOR) complex, counteracts the molecular, cellular and behavioural actions of morphine which are associated with morphine addiction, without any effect on its analgesic properties. In the present work, we have evaluated the role of D4R in modulating the effects of a continuous treatment with morphine on the GABAergic system in the basal ganglia. It has been demonstrated that the co-administration of a D4R agonist together with morphine leads to a restoration of GABA signaling by preventing drug-induced changes in GAD65/67 expression in the caudate putamen, globus palidus and substantia nigra. Results from GABABR1 and GABABR2 expression suggest a role of D4R in modulation of the GABAB heteroreceptor complexes along the basal ganglia, especially in the functional divisions of the caudate putamen. These results provide a new proof of the functional interaction between D4R and MOR and we postulate this putative heteroreceptor complex as a key target for the development of a new strategy to prevent the addictive effects of morphine in the treatment of pain.This article is part of the Special Issue entitled ‘Receptor heteromers and their allosteric receptor-receptor interactions’.

Loss of function of NCOR1 and NCOR2 impairs memory through a novel GABAergic hypothalamus-CA3 projection.

Nuclear receptor corepressor 1 (NCOR1) and NCOR2 (also known as SMRT) regulate gene expression by activating histone deacetylase 3 through their Deacetylase Activation Domain (DAD). We show that mice with DAD knock-in mutations have memory deficits, reduced anxiety levels, and reduced social interactions. Mice with NCOR1/2 depletion specifically in GABAergic neurons (NS-V mice) recapitulated the memory deficits and had reduced GABRA2 expression in lateral hypothalamus GABAergic neurons (LHGABA). This was associated with LHGABA neuron hyperexcitability and impaired hippocampal long-term potentiation, through a monosynaptic LHGABA to CA3GABA projection. Optogenetic activation of this projection caused memory deficits, while targeted manipulation of LHGABA or CA3GABA neuron activity reversed memory deficits in NS-V mice. We describe de novo variants in NCOR1, NCOR2 or HDAC3 in patients with intellectual disability or neurodevelopmental defects. These findings identify a hypothalamus–hippocampus projection that may link endocrine signals with synaptic plasticity through NCOR-mediated regulation of GABA signaling.

A physiological function for sAPP?

Neuroscience Although the pathological role of the amyloid-β precursor protein (APP) in Alzheimer's disease is well studied, the physiological role of this protein has remained elusive. Rice et al. found that the secreted ectodomain of APP (sAPP) binds to GABABR1a, the metabotropic receptor for the inhibitory neurotransmitter γ-aminobutyric acid (GABA) (see the Perspective by Korte). Binding suppressed synaptic vesicle release and modulated synaptic transmission and plasticity in mice. A short, 17–amino acid peptide in APP bound to GABABR1a's sushi 1 domain, conferring structure to this unstructured domain. Therapeutics targeting this interaction could potentially benefit a range of neurological disorders in which GABA signaling is implicated. Science , this issue p. [eaao4827][1]; see also p. [123][2] [1]: /lookup/doi/10.1126/science.aao4827 [2]: /lookup/doi/10.1126/science.aaw0636

Secreted amyloid-β precursor protein functions as a GABABR1a ligand to modulate synaptic transmission.

Amyloid-β precursor protein (APP) is central to the pathogenesis of Alzheimer's disease, yet its physiological function remains unresolved. Accumulating evidence suggests that APP has a synaptic function mediated by an unidentified receptor for secreted APP (sAPP). Here we show that the sAPP extension domain directly bound the sushi 1 domain specific to the γ-aminobutyric acid type B receptor subunit 1a (GABABR1a). sAPP-GABABR1a binding suppressed synaptic transmission and enhanced short-term facilitation in mouse hippocampal synapses via inhibition of synaptic vesicle release. A 17-amino acid peptide corresponding to the GABABR1a binding region within APP suppressed in vivo spontaneous neuronal activity in the hippocampus of anesthetized Thy1-GCaMP6s mice. Our findings identify GABABR1a as a synaptic receptor for sAPP and reveal a physiological role for sAPP in regulating GABABR1a function to modulate synaptic transmission.

Carbonic anhydrase enzymes: Likely targets for inhalational anesthetics

Inhalational anesthetics such as isoflurane, desflurane and halothane are the mainstay medications for surgical procedures; upon inhalation, they produce anesthesia described as reversible unconsciousness with the features of amnesia, sleep, immobility and analgesia. To date, how they produce anesthesia is unknown. This study proposes that carbonic anhydrase enzymes are likely targets mediating the actions of inhalational anesthetics. Carbonic anhydrase enzymes, commonly expressed in living organisms, utilize carbon dioxide (CO2) as a substrate and can generate H+ and HCO3− from CO2 with a great efficiency. There are remarkable lines of evidence for their likely roles in mediating anesthetic actions. Firstly, carbonic anhydrase enzymes are extensively expressed in the brain and spinal cord, and their importance in the brain activity, especially for the GABA and NMDA receptor signaling pathways, has been demonstrated in numerous studies. According to these studies, they provide HCO3− for GABA-A receptor activities and also buffer HCO3− excess resulting from NMDA receptor activation. Activation of GABA-A and inhibition of NMDA receptors are associated with the induction of anesthesia by the intravenous general anesthetics propofol and ketamine, respectively. Secondly, the carbonic anhydrase inhibitors topiramate and zonisamide are effectively used in the treatment of epilepsy for decades; their chronic use results in the requirement of increased levels of amobarbital in order to produce anesthesia in the epileptic patients during WADA test. In addition, given that CO2 is a substrate for these enzymes, their tertiary structure is likely has a hydrophobic pocket suitable for the anesthetic molecules to bind. Inhalational anesthetic molecules, which are lipophilic and inert in nature, have an ability to cross the membranes and inhibit carbonic anhydrases, which might not be accessible by topiramate and zonisamide. Unlike carbonic anhydrase inhibitors, they could bind to the hydrophobic pocket for CO2 molecules and produce a profound effect called anesthesia. Finally, there is a great deal of similarities between the physiological actions of inhalational anesthetics and carbonic anhydrase inhibitors; moreover well-known side effects of inhalational anesthetics could be associated with the inhibition of carbonic anhydrases. Therefore, this article presents a hypothesis that the anesthetic actions of inhalational anesthetics could be due to their inhibitory effects on the carbonic anhydrases. Investigating this hypothesis might lead to the development of new safer anesthetics, and more importantly it might reveal an endogenous anesthetic pathway, in which the carbonic anhydrase system is a component along with the GABA-A and NMDA receptor systems.