Cross-talk and regulation between glutamate and GABAB receptors

Pathological mechanisms of amyotrophic lateral Sclerosis

Amyotrophic lateral sclerosis refers to a neurodegenerative disease involving the motor system, the cause of which remains unexplained despite several years of research. Thus, the journey to understanding or treating amyotrophic lateral sclerosis is still a long one. According to current research, amyotrophic lateral sclerosis is likely not due to a single factor but rather to a combination of mechanisms mediated by complex interactions between molecular and genetic pathways. The progression of the disease involves multiple cellular processes and the interaction between different complex mechanisms makes it difficult to identify the causative factors of amyotrophic lateral sclerosis. Here, we review the most common amyotrophic lateral sclerosis-associated pathogenic genes and the pathways involved in amyotrophic lateral sclerosis, as well as summarize currently proposed potential mechanisms responsible for amyotrophic lateral sclerosis disease and their evidence for involvement in amyotrophic lateral sclerosis. In addition, we discuss current emerging strategies for the treatment of amyotrophic lateral sclerosis. Studying the emergence of these new therapies may help to further our understanding of the pathogenic mechanisms of the disease.

Distinct GABAergic modulation of timing-dependent LTP in CA1 pyramidal neurons along the longitudinal axis of the mouse hippocampus

Synaptic plasticity in the hippocampus underlies episodic memory formation, with dorsal hippocampus being instrumental for spatial memory whereas ventral hippocampus is crucial for emotional learning. Here, we studied how GABAergic inhibition regulates physiologically relevant low repeat spike timing-dependent LTP (t-LTP) at Schaffer collateral-CA1 synapses along the dorsoventral hippocampal axis. We used two t-LTP protocols relying on only 6 repeats of paired spike-firing in pre- and postsynaptic cells within 10 s that differ in postsynaptic firing patterns. GABAA receptor mechanisms played a greater role in blocking 6× 1:1 t-LTP that recruits single postsynaptic action potentials. 6× 1:4 t-LTP that depends on postsynaptic burst-firing unexpectedly required intact GABAB receptor signaling. The magnitude of both t-LTP-forms decreased along the dorsoventral axis, despite increasing excitability and basal synaptic strength in this direction. This suggests that GABAergic inhibition contributes to the distinct roles of dorsal and ventral hippocampus in memory formation.

Chronic alcohol-induced long-lasting working memory deficits are associated with altered histone H3K9 dimethylation in the prefrontal cortex

Introduction

Epigenetic modifications have emerged as key contributors to the enduring behavioral, molecular and epigenetic neuroadaptations during withdrawal from chronic alcohol exposure. The present study investigated the long-term consequences of chronic alcohol exposure on spatial working memory (WM) and associated changes of transcriptionally repressive histone H3 lysine 9 dimethylation (H3K9me2) in the prefrontal cortex (PFC).

Methods

Male C57BL/6 mice were allowed free access to either 12% (v/v) ethanol for 5 months followed by a 3-week abstinence period or water. Spatial WM was assessed through the spontaneous alternation T-maze test. Alcoholic and water mice received daily injections of GABAB agonist baclofen or saline during alcohol fading and early withdrawal. Global levels of histone modifications were determined by immunohistochemistry.

Results

Withdrawal mice displayed WM impairments along with reduced prefrontal H3K9me2 levels, compared to water-drinking mice. The withdrawal-induced decrease of H3K9me2 occurred concomitantly with increased level of permissive H3K9 acetylation (H3K9ac) in the PFC. Baclofen treatment rescued withdrawal-related WM deficits and fully restored prefrontal H3K9me2 and H3K9ac. Alcohol withdrawal induced brain region-specific changes of H3K9me2 and H3K9ac after testing, with significant decreases of both histone marks in the dorsal hippocampus and no changes in the amygdala and dorsal striatum. Furthermore, the magnitude of H3K9me2 in the PFC, but not the hippocampus, significantly and positively correlated with individual WM performances. No correlation was observed between H3K9ac and behavioral performance. Results also indicate that pre-testing intraperitoneal injection of UNC0642, a selective inhibitor of histone methyltransferase G9a responsible for H3K9me2, led to WM impairments in water-drinking and withdrawal-baclofen mice. Collectively, our results demonstrate that alcohol withdrawal induced brain-region specific alterations of H3K9me2 and H3K9ac, an effect that persisted for at least three weeks after cessation of chronic alcohol intake.

Conclusion

The findings suggest a role for long-lasting decreased H3K9me2 specifically in the PFC in the persistent WM impairments related to alcohol withdrawal.

Current Review of the Function and Regulation of Tuberoinfundibular Dopamine Neurons

Tuberoinfundibular dopamine (TIDA) neurons have cell bodies located in the arcuate nucleus of the mediobasal hypothalamus. They project to the external zone of the median eminence, and the dopamine (DA) released there is carried by the hypophysial portal vasculature to the anterior pituitary. The DA then activates D2 receptors to inhibit prolactin (PRL) secretion from lactotrophs. The TIDA neuronal population is the principal regulatory factor controlling PRL secretion. The neuroendocrine role subserved by TIDA neurons sets them apart from other dopaminergic populations like the nigrostriatal and mesolimbic DA neurons. TIDA neurons exhibit intrinsic oscillatory fluctuations in their membrane potential that give rise to phasic firing and bursting activity. TIDA neuronal activity is sexually differentiated and modulated by gonadal hormones and PRL, as well as an array of small molecule and peptide neurotransmitters. This review covers these characteristics.

Paeonol ameliorates hippocampal neuronal damage by inhibiting GRM5/GABBR2/β-arrestin2 and activating the cAMP-PKA signaling pathway in premenstrual irritability rats

Premenstrual dysphoric disorder (PMDD) is a periodic psychiatric disorder with high prevalence in women of childbearing age, seriously affecting patients' work and life. Currently, the international first-line drugs for PMDD have low efficiency and increased side effects. Paeonol, a major component of the traditional Chinese medicine Cortex Moutan, has been applied in treating PMDD in China with satisfactory results, but the therapeutic mechanism is not fully understood. This study aims to evaluate the therapeutic effects and pharmacological mechanisms of paeonol on the main psychiatric symptoms and hippocampal damage in PMDD. We established a premenstrual irritability rat model by the resident-intruder paradigm and performed elevated plus maze and social interactions. And we employed the HE and Nissl staining techniques to observe the therapeutic effect of paeonol on hippocampal damage in PMDD rats. Subsequently, Elisa, qRT-PCR Array, Western Blotting, and cell models were utilized to elucidate the underlying molecular mechanisms through which paeonol intervenes in treating PMDD. In this study, we demonstrated the therapeutic effects of paeonol on irritability, anxiety, and social withdrawal behaviors in rats. In addition, we found that paeonol significantly reduced the serum corticosterone (CORT) level, improved hippocampal morphological structure and neuron number, and reduced hippocampal neuron apoptosis in PMDD rats. Paeonol reduced GRM5, GABBR2, β-arrestin2, and GRK3 expression levels in hippocampal brain regions of PMDD rats and activated the cAMP/PKA signaling pathway. Inhibitor cell experiments showed that paeonol specifically ameliorated hippocampal injury by modulating the β-arrestin2/PDE4-cAMP/PKA signaling pathway. The present study demonstrates, for the first time, that paeonol exerts a therapeutic effect on periodic psychotic symptoms and hippocampal injury in PMDD through inhibiting GRM5/GABBR2/β-arrestin2 and activating cAMP-PKA signaling pathway. These findings enhance our understanding of the pharmacological mechanism underlying paeonol and provide a solid scientific foundation for its future clinical application.

GABAB1 receptor knockdown in prefrontal cortex induces behavioral aberrations associated with autism spectrum disorder in mice

Autism spectrum disorder (ASD) is a set of heterogeneous neurodevelopmental disorders, characterized by social interaction deficit, stereotyped or repetitive behaviors. Apart from these core symptoms, a great number of individuals with ASD exhibit higher levels of anxiety and memory deficits. Previous studies demonstrate pronounced decrease of γ-aminobutyric acid B1 receptor (GABAB1R) protein level of frontal lobe in both ASD patients and animal models. The aim of the present study was to determine the role of GABAB1R in ASD-related behavioral aberrations. Herein, the protein and mRNA levels of GABAB1R in the prefrontal cortex (PFC) of sodium valproic acid (VPA)-induced mouse ASD model were determined by Western blot and qRT-PCR analysis, respectively. Moreover, the behavioral abnormalities in naive mice with GABAB1R knockdown mediated by recombinant adeno-associated virus (rAAV) were assessed in a comprehensive test battery consisted of social interaction, marble burying, self-grooming, open-field, Y-maze and novel object recognition tests. Furthermore, the action potential changes induced by GABAB1R deficiency were examined in neurons within the PFC of mouse. The results show that the mRNA and protein levels of GABAB1R in the PFC of prenatal VPA-induced mouse ASD model were decreased. Concomitantly, naive mice with GABAB1R knockdown exhibited ASD-like behaviors, such as impaired social interaction and communication, elevated stereotypes, anxiety and memory deficits. Patch-clamp recordings also revealed that GABAB1R knockdown provoked enhanced neuronal excitability by increasing action potential discharge frequencies. Overall, these findings support a notion that GABAB1R deficiency might contribute to ASD-like phenotypes, with the pathogenesis most likely resulting from enhanced neuronal excitability. SUBHEADINGS: GABAB1 Knockdown Induces Behavioral Aberrations with ASD.

A high ratio of linoleic acid (n-6 PUFA) to alpha-linolenic acid (n-3 PUFA) adversely affects early stage of human neuronal differentiation and electrophysiological activity of glutamatergic neurons in vitro

Introduction: There is a growing interest in the possibility of dietary supplementation with polyunsaturated fatty acids (PUFAs) for treatment and prevention of neurodevelopmental and neuropsychiatric disorders. Studies have suggested that of the two important classes of polyunsaturated fatty acids, omega-6 (n-6) and omega-3 (n-3), n-3 polyunsaturated fatty acids support brain development and function, and when used as a dietary supplement may have beneficial effects for maintenance of a healthy brain. However, to date epidemiological studies and clinical trials on children and adults have been inconclusive regarding treatment length, dosage and use of specific n-3 polyunsaturated fatty acids. The aim of this study is to generate a simplified in vitro cell-based model system to test how different n-6 to n-3 polyunsaturated fatty acids ratios affect human-derived neurons activity as a cellular correlate for brain function and to probe the mechanism of their action. Methods: All experiments were performed by use of human induced pluripotent stem cells (iPSCs). In this study, we examined the effect of different ratios of linoleic acid (n-6) to alpha-linolenic acid in cell growth medium on induced pluripotent stem cell proliferation, generation of neuronal precursors and electrophysiology of cortical glutamatergic neurons by multielectrode array (MEA) analysis. Results: This study shows that at a n-6:n-3 ratio of 5:1 polyunsaturated fatty acids induce stem cell proliferation, generating a large increase in number of cells after 72 h treatment; suppress generation of neuronal progenitor cells, as measured by decreased expression of FOXG1 and Nestin in neuronal precursor cells (NPC) after 20 days of development; and disrupt neuronal activity in vitro, increasing spontaneous neuronal firing, reducing synchronized bursting receptor subunits. We observed no significant differences for neuronal precursor cells treated with ratios 1:3 and 3:1, in comparison to 1:1 control ratio, but higher ratios of n-6 to n-3 polyunsaturated fatty acids adversely affect early stages of neuronal differentiation. Moreover, a 5:1 ratio in cortical glutamatergic neurons induce expression of GABA receptors which may explain the observed abnormal electrophysiological activity.

Calcium Homeostasis, Transporters, and Blockers in Health and Diseases of the Cardiovascular System

Calcium is a highly positively charged ionic species. It regulates all cell types' functions and is an important second messenger that controls and triggers several mechanisms, including membrane stabilization, permeability, contraction, secretion, mitosis, intercellular communications, and in the activation of kinases and gene expression. Therefore, controlling calcium transport and its intracellular homeostasis in physiology leads to the healthy functioning of the biological system. However, abnormal extracellular and intracellular calcium homeostasis leads to cardiovascular, skeletal, immune, secretory diseases, and cancer. Therefore, the pharmacological control of calcium influx directly via calcium channels and exchangers and its outflow via calcium pumps and uptake by the ER/SR are crucial in treating calcium transport remodeling in pathology. Here, we mainly focused on selective calcium transporters and blockers in the cardiovascular system.

Reduction in GABAB on glia induce Alzheimer's disease related changes

Alzheimer's Disease (AD) is a neurodegenerative disorder characterized by beta-amyloid plaques (Aβ), neurofibrillary tangles (NFT), and neuroinflammation. Data have demonstrated that neuroinflammation contributes to Aβ and NFT onset and progression, indicating inflammation and glial signaling is vital to understanding AD. A previous investigation demonstrated a significant decrease of the GABAB receptor (GABABR) in APP/PS1 mice (Salazar et al., 2021). To determine if changes in GABABR restricted to glia serve a role in AD, we developed a mouse model with a reduction of GABABR restricted to macrophages, GAB/CX3ert. This model exhibits changes in gene expression and electrophysiological alterations similar to amyloid mouse models of AD. Crossing the GAB/CX3ert mouse with APP/PS1 resulted in significant increases in Aβ pathology. Our data demonstrates that decreased GABABR on macrophages leads to several changes observed in AD mouse models, as well as exacerbation of AD pathology when crossed with existing models. These data suggest a novel mechanism in AD pathogenesis.

Central nervous system interaction and crosstalk between nAChRs and other ionotropic and metabotropic neurotransmitter receptors

Neuronal nicotinic acetylcholine receptors (nAChRs) are widely distributed in both the peripheral and the central nervous systems. nAChRs exert a crucial modulatory influence on several brain biological processes; they are involved in a variety of neuronal diseases including Parkinson's disease, Alzheimer's disease, epilepsy, and nicotine addiction. The influence of nAChRs on brain function depends on the activity of other neurotransmitter receptors that co-exist with nAChRs on neurons. In fact, the crosstalk between receptors is an important mechanism of neurotransmission modulation and plasticity. This may be due to converging intracellular pathways but also occurs at the membrane level, because of direct physical interactions between receptors. In this line, this review is dedicated to summarizing how nAChRs and other ionotropic and metabotropic receptors interact and the relevance of nAChRs cross-talks in modulating various neuronal processes ranging from the classical modulation of neurotransmitter release to neuron plasticity and neuroprotection.

Changes in Acupuncture-Induced Specific Acupoint Neurotransmitters are Possibly Related to Their Physiological Functions in Rats

This study investigated changes in neurotransmitters induced by the application of electroacupuncture (EA) at Zusanli (ST36) and Neiguan (PC6). A total of 30 rats were divided into five groups: sham, ST (EA at bilateral ST36 and ST37), ScT (ST plus previous neurectomy of the bilateral sciatic nerves), ScS (sham plus previous neurectomy of the bilateral sciatic nerve), and PC (EA at bilateral PC6 and PC7). The P2X2 receptor expression was stronger in the sham group than in the ST and PC groups (both p < 0.05) but similar between the sham and ScT groups (p > 0.05). Dopamine levels in the extracellular fluid surrounding the acupoints were higher in the PC group than in the sham and ST groups during the postacupuncture period (both p < 0.05). Glutamate levels in the extracellular fluid surrounding the acupoints were higher in the ST group than in the sham group during the acupuncture period (p < 0.05) and higher in the ST group than in the sham and PC groups during the postacupuncture period (both p < 0.05). Serum adrenaline and noradrenaline levels were higher in the PC group than in the sham, ST, and ScT groups (all p < 0.05). Glutamate levels in the CSF were higher in the ST group than in the sham, ScS, and PC groups (all p < 0.05). GABA levels in the CSF were higher in the ST group than in the sham, ScT, and PC groups (all p < 0.05). EA at ST36 and ST37 and PC6 and PC7 exerted an analgesic effect, EA at PC6 and PC7 can enhance heart function, and EA at ST36 and ST37 modulates the cerebral cortex. However, the study needs an evaluation of direct pain behavior, heart function, and brain function in the future.

Cell-Type Specific Inhibition Controls the High-Frequency Oscillations in the Medial Entorhinal Cortex

The medial entorhinal cortex (mEC) plays a critical role for spatial navigation and memory. While many studies have investigated the principal neurons within the entorhinal cortex, much less is known about the inhibitory circuitries within this structure. Here, we describe for the first time in the mEC a subset of parvalbumin-positive (PV+) interneurons (INs)-stuttering cells (STUT)-with morphological, intrinsic electrophysiological, and synaptic properties distinct from fast-spiking PV+ INs. In contrast to the fast-spiking PV+ INs, the axon of the STUT INs also terminated in layer 3 and showed subthreshold membrane oscillations at gamma frequencies. Whereas the synaptic output of the STUT INs was only weakly reduced by a μ-opioid agonist, their inhibitory inputs were strongly suppressed. Given these properties, STUT are ideally suited to entrain gamma activity in the pyramidal cell population of the mEC. We propose that activation of the μ-opioid receptors decreases the GABA release from the PV+ INs onto the STUT, resulting in disinhibition of the STUT cell population and the consequent increase in network gamma power. We therefore suggest that the opioid system plays a critical role, mediated by STUT INs, in the neural signaling and oscillatory network activity within the mEC.

GABA Receptor Agonists Protect From Excitotoxic Damage Induced by AMPA in Oligodendrocytes

Oligodendrocytes are the myelin forming cells of the central nervous system, and their vulnerability to excitotoxicity induced by glutamate contributes to the pathogenesis of neurological disorders including brain ischemia and neurodegenerative diseases, such as multiple sclerosis. In addition to glutamate receptors, oligodendrocytes express GABA receptors (GABAR) that are involved in their survival and differentiation. The interactions between glutamate and GABAergic systems are well documented in neurons, under both physiological and pathological conditions, but this potential crosstalk in oligodendrocytes has not been studied in depth. Here, we evaluated the protective effect of GABAR agonists, baclofen (GABA_B) and muscimol (GABA_A), against AMPA-induced excitotoxicity in cultured rat oligodendrocytes. First, we observed that both baclofen and muscimol reduced cell death and caspase-3 activation after AMPA insult, proving their oligoprotective potential. Interestingly, analysis of the cell-surface expression of calcium-impermeable GluR2 subunits in oligodendrocytes revealed that GABAergic agonists significantly reverted GluR2 internalization induced by AMPA. We determined that baclofen and muscimol also impaired AMPA-induced intracellular calcium increase and subsequent mitochondrial membrane potential alteration, ROS generation, and calpain activation. However, AMPA-triggered activation of Src, Akt, JNK and CREB was not affected by baclofen or muscimol. Overall, our results suggest that GABAR activation initiates alternative molecular mechanisms that attenuate AMPA-mediated apoptotic excitotoxicity in oligodendrocytes by interfering with expression of GluR subunits in membranes and with calcium-dependent intracellular signaling pathways. Together, these findings provide evidence of GABAR agonists as potential oligodendroglial protectants in central nervous system disorders.

Cardiovascular deconditioning increases GABA signaling in the nucleus tractus solitarii

The nucleus tractus solitarii (nTS) is the major integrative brainstem region for autonomic modulation and processing of cardiovascular reflexes. GABA and glutamate are the main inhibitory and excitatory neurotransmitters, respectively, within this nucleus. Alterations in the GABA-glutamate regulation in the nTS are related to numerous cardiovascular comorbidities. Bedridden individuals and people exposed to microgravity exhibit dysautonomia and cardiovascular deconditioning that are mimicked in the hindlimb unloading (HU) rat model. We have previously shown in the nTS that HU increases glutamatergic neurotransmission yet decreases neuronal excitability. In this study, we investigated the effects of HU on nTS GABAergic neurotransmission. We hypothesized that HU potentiates GABA signaling via increased GABAergic release and postsynaptic GABA receptor expression. Following HU or control postural exposure, GABAergic neurotransmission was assessed using whole cell patch clamp whereas the magnitude of GABA release was evaluated via an intensity-based GABA sensing fluorescence reporter (iGABASnFR). In response to GABA interneuron stimulation, the evoked inhibitory postsynaptic current (nTS-IPSC) amplitude and area, as well as iGABASnFR fluorescence, were greater in HU than in control. HU also elevated the frequency but not the amplitude of spontaneous miniature IPSCs. Picoapplication of GABA produced similar postsynaptic current responses in nTS neurons of HU and control. Moreover, HU did not alter GABA_A receptor α1 subunit expression, indicating minimal alterations in postsynaptic membrane receptor expression. These results indicate that HU increases GABAergic signaling in the nTS likely via augmented release of GABA from presynaptic terminals. Altogether, our data indicate GABA plasticity contributes to the autonomic and cardiovascular alterations following cardiovascular deconditioning (CVD).NEW & NOTEWORTHY Gravity influences distribution of blood volume and autonomic function. Microgravity and prolonged bed rest induce cardiovascular deconditioning (CVD). We used hindlimb unloading (HU), a rat analog for bed rest, to investigate CVD-induced neuroplasticity in the brainstem. Our data demonstrate that HU increases GABA modulation of nucleus tractus solitarii (nTS) neurons via presynaptic plasticity. Given the importance of nTS in integrating cardiovascular reflexes, this study provides new evidence on the central mechanisms behind CVD following HU.

Artesunate Alleviates Paclitaxel-Induced Neuropathic Pain in Mice by Decreasing Metabotropic Glutamate Receptor 5 Activity and Neuroinflammation in Primary Sensory Neurons

Experimental studies on the pathogenetic process of paclitaxel-induced neuropathic pain (PINP) have been initially carried out, but PINP still has no effective therapy. Recently reported studies have highlighted the involvement of glutamate receptors and neuroinflammation in peripheral and central nociceptive transmission in PINP. Artesunate is a first-line antimalarial drug with established efficacy in alleviating pain in a variety of pathologies. The current work assessed whether artesunate inhibits PINP by modulating metabotropic glutamate receptor 5 (mGluR5) and neuroinflammation in mice. The anti-hyperalgesic effect of artesunate was verified by assessing mechanical frequency and thermal latency in the paw withdrawal test as well as spontaneous pain. The expression levels of mGluR5, pain-related receptors and neuroinflammatory markers in dorsal root ganglion (DRG) were examined. In addition, treatment with CHPG and 2-methyl-6-(phenyl ethynyl) pyridine (MPEP) (mGluR5 agonist and antagonist, respectively) was performed to determine mGluR5’s role in the anti-hyperalgesic properties of artesunate. We demonstrated artesunate prevented PINP in a dose-dependent manner, while exerting a clear anti-hyperalgesic effect on already existing PINP. Artesunate normalized paclitaxel-related expression changes in DRG mGluR5, NR1, and GluA2, as well as six paclitaxel related neuroinflammation markers. Intrathecal application of MPEP treated PINP by reversing NR1 and GluA2 expression changes but had no effects on chemokines and inflammatory factors. Furthermore, artesunate treatment reversed acute pain following CHPG application. In conclusion, this study revealed that artesunate alleviates paclitaxel-induced hyperalgesia and spontaneous pain by decreasing DRG mGluR5 expression and neuroinflammation in the mouse model of PINP.

Crosstalk Between GABAergic Neurotransmission and Inflammatory Cascades in the Post-ischemic Brain: Relevance for Stroke Recovery

Adaptive plasticity processes are required involving neurons as well as non-neuronal cells to recover lost brain functions after an ischemic stroke. Recent studies show that gamma-Aminobutyric acid (GABA) has profound effects on glial and immune cell functions in addition to its inhibitory actions on neuronal circuits in the post-ischemic brain. Here, we provide an overview of how GABAergic neurotransmission changes during the first weeks after stroke and how GABA affects functions of astroglial and microglial cells as well as peripheral immune cell populations accumulating in the ischemic territory and brain regions remote to the lesion. Moreover, we will summarize recent studies providing data on the immunomodulatory actions of GABA of relevance for stroke recovery. Interestingly, the activation of GABA receptors on immune cells exerts a downregulation of detrimental anti-inflammatory cascades. Conversely, we will discuss studies addressing how specific inflammatory cascades affect GABAergic neurotransmission on the level of GABA receptor composition, GABA synthesis, and release. In particular, the chemokines CXCR4 and CX3CR1 pathways have been demonstrated to modulate receptor composition and synthesis. Together, the actual view on the interactions between GABAergic neurotransmission and inflammatory cascades points towards a specific crosstalk in the post-ischemic brain. Similar to what has been shown in experimental models, specific therapeutic modulation of GABAergic neurotransmission and inflammatory pathways may synergistically promote neuronal plasticity to enhance stroke recovery.

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.

GABAB receptors constrain glutamate presynaptic release and postsynaptic actions in substantia gelatinosa of rat spinal cord

The substantia gelatinosa (SG, lamina II of spinal cord gray matter) is pivotal for modulating nociceptive information from the peripheral to the central nervous system. γ-Aminobutyric acid type B receptors (GABA_BRs), the metabotropic GABA receptor subtype, are widely expressed in pre- and postsynaptic structures of the SG. Activation of GABA_BRs by exogenous agonists induces both pre- and postsynaptic inhibition. However, the actions of endogenous GABA via presynaptic GABA_BRs on glutamatergic synapses, and the postsynaptic GABA_BRs interaction with glutamate, remain elusive. In the present study, first, using in vitro whole-cell recordings and taking minimal stimulation strategies, we found that in rat spinal cord glutamatergic synapses, blockade of presynaptic GABA_BRs switched "silent" synapses into active ones and increased the probability of glutamate release onto SG neurons; increasing ambient GABA concentration mimicked GABA_BRs activation on glutamatergic terminals. Next, using holographic photostimulation to uncage glutamate on postsynaptic SG neurons, we found that postsynaptic GABA_BRs modified glutamate-induced postsynaptic potentials. Taken together, our data identify that endogenous GABA heterosynaptically constrains glutamate release via persistently activating presynaptic GABA_BRs; and postsynaptically, GABA_BRs modulate glutamate responses. The results give new clues for endogenous GABA in modulating the nociception circuit of the spinal dorsal horn and shed fresh light on the postsynaptic interaction of glutamate and GABA.

The translocator protein gene is associated with endogenous pain modulation and the balance between glutamate and γ-aminobutyric acid in fibromyalgia and healthy subjects: a multimodal neuroimaging study

ABSTRACT

A cerebral upregulation of the translocator protein (TSPO), a biomarker of glial activation, has been reported in fibromyalgia subjects (FMS). The TSPO binding affinity is genetically regulated by the Ala147Thr polymorphism in the TSPO gene (rs6971) and allows for a subject classification into high affinity binders (HABs) and mixed/low affinity binders (MLABs). The aim of the present multimodal neuroimaging study was to examine the associations of the TSPO polymorphism with: (1) conditioned pain modulation, (2) expectancy-modulated pain processing assessed during functional magnetic resonance imaging, and (3) the concentration and balance of glutamate and γ-aminobutyric acid in the rostral anterior cingulate cortex and thalamus using proton magnetic resonance spectroscopy in FMS (n = 83) and healthy controls (n = 43). The influence of TSPO on endogenous pain modulation presented in the form of TSPO HABs, as opposed to MLABs, displaying less efficient descending pain inhibition and expectancy-induced reduction of pain. Translocator protein HABs in both groups (FM and healthy controls) were found to have higher thalamic glutamate concentrations and exhibit a pattern of positive correlations between glutamate and γ-aminobutyric acid in the rostral anterior cingulate cortex, not seen in MLABs. Altogether, our findings point to TSPO-related mechanisms being HAB-dependent, brain region-specific, and non-FM-specific, although in FMS the disadvantage of an aberrant pain regulation combined with an HAB genetic set-up might hamper pain modulation more strongly. Our results provide evidence for an important role of TSPO in pain regulation and brain metabolism, thereby supporting the ongoing drug development targeting TSPO-associated mechanisms for pain relief.

GABAB receptor modulation of visual sensory processing in adults with and without autism spectrum disorder

[Figure: see text].

Dopaminergic input from the posterior hypothalamus to the raphe pallidus area inhibits brown adipose tissue thermogenesis

Systemic administration of dopamine (DA) receptor agonists leads to falls in body temperature. However, the central thermoregulatory pathways modulated by DA have not been fully elucidated. Here we identified a source and site of action contributing to DA's hypothermic action by inhibition of brown adipose tissue (BAT) thermogenesis. Nanoinjection of the type 2 and type 3 DA receptor (D2R/D3R) agonist, 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT), in the rostral raphe pallidus area (rRPa) inhibits the sympathetic activation of BAT evoked by cold exposure or by direct activation of N-methyl-d-aspartate (NMDA) receptors in the rRPa. Blockade of D2R/D3R in the rRPa with nanoinjection of SB-277011A increases BAT thermogenesis, consistent with a tonic release of DA in the rRPa contributing to inhibition of BAT thermogenesis. Accordingly, D2Rs are expressed in cold-activated and serotonergic neurons in the rRPa, and anatomical tracing studies revealed that neurons in the posterior hypothalamus (PH) are a source of dopaminergic input to the rRPa. Disinhibitory activation of PH neurons with nanoinjection of gabazine inhibits BAT thermogenesis, which is reduced by pretreatment of the rRPa with SB-277011A. In conclusion, the rRPa, the site of sympathetic premotor neurons for BAT, receives a tonically active, dopaminergic input from the PH that suppresses BAT thermogenesis.

Vocal and physical phenotypes of calsyntenin2 knockout mouse pups model early-life symptoms of the autism spectrum disorder

This study discovered a novel acoustic phenotype in Calsyntenin2 deficient knockout (Clstn2-KO) pups in the neurodevelopment period of 5-9 postnatal days (PND 5-9). The narrowband ultrasonic calls (nUSVs) were less complex (mostly one-note, shorter in duration and higher in peak frequency) in Clsnt2-KO than in wild-type (WT) C57BL/6 J pups. The wideband ultrasonic calls (wUSVs) were produced substantially more often by Clstn2-KO than WT pups. The clicks were longer in duration and higher in peak frequency and power quartiles in Clstn2-KO pups. The elevated discomfort due to additional two-minute maternal separation coupled with experimenter's touch, resulted in significantly higher call rates of both nUSVs and clicks in pups of both genotypes and sexes compared to the previous two-minute maternal separation, whereas the call rate of wUSVs was not affected. In Clstn2-KO pups, the prevalence of emission of wUSVs retained at both sex and both degrees of discomfort, thus providing a reliable quantitative acoustic indicator for this genetic line. Besides the acoustic differences, we also detected the increased head-to-body ratio in Clstn2-KO pups. Altogether, this study demonstrated that lack of such synaptic adhesion protein as calsyntenin2 affects neurodevelopment of vocalization in a mouse as a model organism.

Alterations of GABA B receptors in the APP/PS1 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the progressive decline of memory and cognitive function. The disease is characterized by the presence of amyloid plaques, tau tangles, altered inflammatory signaling, and alterations in numerous neurotransmitter signaling systems, including γ-aminobutyric acid (GABA). Given the extensive role of GABA in regulating neuronal activity, a careful investigation of GABA-related changes is needed. Further, given persistent inflammation has been demonstrated to drive AD pathology, the presence of GABA B receptor expressed on glia that serve a role regulation of the immune response adds to potential implications of altered GABA in AD. There has not previously been a systematic evaluation of GABA-related changes in an amyloid model of AD that specifically focuses on examining changes in GABA B receptors. In the present study, we examined alterations in several GABA-specific targets in the APP/PS1 mouse model at different ages. In the 4-month-old cohort, no significant deficits in spatial learning and memory or alterations in any of the GABAergic targets were observed compared with wild-type controls. However, we identified significant alterations in several GABA-related targets in the 6-month-old cohort that exhibited spatial learning deficits that include changes in glutamic acid decarboxylase 65, GABA transporter type 3, and GABA B receptors protein and mRNA levels. This was the same cohort at which learning and memory deficits and significant amyloid pathology was observed. Overall, our study provides evidence of altered GABAergic signaling in an amyloid model of AD at a time point consistent with AD-related deficits.

Transcranial magnetic stimulation and magnetic resonance spectroscopy: Opportunities for a bimodal approach in human neuroscience

Over the last decade, there has been an increasing number of studies combining transcranial magnetic stimulation (TMS) and magnetic resonance spectroscopy (MRS). MRS provides a manner to non-invasively investigate molecular concentrations in the living brain and thus identify metabolites involved in physiological and pathological processes. Particularly the MRS-detectable metabolites glutamate, the major excitatory neurotransmitter, and gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter, are of interest when combining TMS and MRS. TMS is a non-invasive brain stimulation technique that can be applied either as a neuromodulation or neurostimulation tool, specifically targeting glutamatergic and GABAergic mechanisms. The combination of TMS and MRS can be used to evaluate alterations in brain metabolite levels following an interventional TMS protocol such as repetitive TMS (rTMS) or paired associative stimulation (PAS). MRS can also be combined with a variety of non-interventional TMS protocols to identify the interplay between brain metabolite levels and measures of excitability or receptor-mediated inhibition and facilitation. In this review, we provide an overview of studies performed in healthy and patient populations combining MRS and TMS, both as a measurement tool and as an intervention. TMS and MRS may reveal complementary and comprehensive information on glutamatergic and GABAergic neurotransmission. Potentially, connectivity changes and dedicated network interactions can be probed using the combined TMS-MRS approach. Considering the ongoing technical developments in both fields, combined studies hold future promise for investigations of brain network interactions and neurotransmission.

Effects of intrathecal baclofen therapy in subjects with disorders of consciousness: a reappraisal

Baclofen is a structural analogue of gamma-amino-butyric acid (GABA), which reduces spastic hypertonia of striated muscle due to a mechanism of GABA_B-ergic inhibition of mono- and polysynaptic reflexes at the spinal level. There are reports of patients with severe disorders of consciousness that presented a substantial improvement following intrathecal baclofen (ITB) administration for severe spasticity. The neural mechanisms underlying the clinical recovery after ITB have not yet been clarified. Baclofen could modulate sleep-wake cycles that may be dysregulated and thus interfere with alertness and awareness. The diminished proprioceptive and nociceptive sensory inputs may relieve thalamo-cortical neural networks involved in maintaining the consciousness of the self and the world. ITB treatment might also promote the recovery of an impaired GABAergic cortical tone, restoring the balance between excitatory and inhibitory cortical activity. Furthermore, glutamatergic synapses are directly or indirectly modulated by GABA_B-ergic receptors. Neurophysiological techniques (such as transcranial magnetic stimulation, electroencephalography, or the combination of both) can be helpful to explore the effects of intrathecal or oral baclofen on the modulation of neural cortical circuits in humans with disorders of consciousness.

Muscarinic M1 receptors stimulated by intracerebroventricular administration of McN-A-343 reduces the nerve injury-induced mechanical hypersensitivity via GABAB receptors rather than GABAA receptors in mice

Cholinergic neurons play an important role in the higher functions of the brain, such as the memory, cognition, and nociception. However, the exact mechanism behind how the stimulation of all the muscarinic M₁ receptors in the entire brain results in the alleviation of partial sciatic nerve ligation (PSNL)-induced mechanical hypersensitivity has not been investigated. Thus, we examined which subtype of GABA receptor was involved in the alleviation of PSNL-induce mechanical hypersensitivity produced by an intracerebroventricular administration of a muscarinic M₁ receptor agonist, McN-A-343. Administering a GABA_A receptor antagonist, bicuculline, resulted in no changes to the McN-A-343-induced anti-hypersensitivity in PSNL mice whereas a GABA_B receptor antagonist, CGP35348, dose-dependently inhibited the anti-hypersensitivity. Furthermore, CGP35348 increased mechanical hypersensitivity in naïve mice, and the hypersensitivity was blocked by NMDA receptor antagonists, MK-801 and D-AP5. Additionally, muscarinic M₁ receptors colocalized with GABA_B1 receptors and an NMDA receptor subunit, GluN2A, in a large region of the brain. Consequently, these results suggest that the activation of muscarinic M₁ receptors in the entire brain reduces nerve injury-induced mechanical hypersensitivity via the GABA_B receptors, and the activation of the GABA_B receptors regulates glutamatergic transmission via NMDA receptors.

Bi-directional Acceleration of Alcohol Use and Opioid Use Disorder

Alcohol is the most widely used addictive substance. Severe alcohol abuse is diagnosed as "alcohol use disorder" (AUD). A common and harmful drinking pattern is binge drinking that elevates a person's blood alcohol concentration to ≥ 0.08%. Such drinking may be an early indicator of AUD. Opioid misuse and dependence have become worldwide crises. Patterned consumption of various opioids can develop into opioid use disorder (OUD). An intertwined epidemic exists between opioid abuse, alcohol addiction, and binge drinking. Currently, studies on the interaction of AUD and OUD are limited and the underlying mechanisms linking these disorders remains unclear. We reviewed studies on AUD and OUD and utilized Ingenuity Pathway Analysis (IPA) to identify mechanisms of AUD and OUD interaction and potential gene targets for therapeutic agents. According to IPA Canonical Pathways Analysis, Gamma-aminobutyric Acid (GABA) Receptor Signaling, Neuroinflammation Signaling Pathway, Opioid Signaling Pathway and Dopamine-DARPP32 Feedback in cAMP Signaling are potential contributors to the interaction of AUD and OUD.

Defective Excitatory/Inhibitory Synaptic Balance and Increased Neuron Apoptosis in a Zebrafish Model of Dravet Syndrome

Dravet syndrome is a type of severe childhood epilepsy that responds poorly to current anti-epileptic drugs. In recent years, zebrafish disease models with Scn1Lab sodium channel deficiency have been generated to seek novel anti-epileptic drug candidates, some of which are currently undergoing clinical trials. However, the spectrum of neuronal deficits observed following Scn1Lab depletion in zebrafish larvae has not yet been fully explored. To fill this gap and gain a better understanding of the mechanisms underlying neuron hyperexcitation in Scn1Lab-depleted larvae, we analyzed neuron activity in vivo using combined local field potential recording and transient calcium uptake imaging, studied the distribution of excitatory and inhibitory synapses and neurons as well as investigated neuron apoptosis. We found that Scn1Lab-depleted larvae displayed recurrent epileptiform seizure events, associating massive synchronous calcium uptakes and ictal-like local field potential bursts. Scn1Lab-depletion also caused a dramatic shift in the neuronal and synaptic balance toward excitation and increased neuronal death. Our results thus provide in vivo evidence suggesting that Scn1Lab loss of function causes neuron hyperexcitation as the result of disturbed synaptic balance and increased neuronal apoptosis.

LC-MS/MS-based quantification of tryptophan metabolites and neurotransmitters in the serum and brain of mice

l-Tryptophan (Trp) metabolites and related neurotransmitters play crucial roles in physiological functions, and their imbalances are implicated in the pathology of depression, Alzheimer's disease and other diseases. Measurement of Trp metabolites and related neurotransmitters possesses a great potential to elucidate the disease mechanisms and evaluate the outcomes of therapeutic interventions. A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for simultaneous determination of Trp, l-kynurenine (Kyn), kynurenic acid (Kyna), 3-hydroxykynurenine (3-HK), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine (NE), l-glutamic acid (Glu), γ-aminobutyric acid (GABA) and acetylcholine (ACh) in mice serum and the brain tissues in a single chromatographic run. Samples were spiked with the internal standard, mixed with trifluoroacetic acid to precipitate protein and analyzed by LC-MS/MS. Chromatographic separation was achieved using a Restek Ultra Aqueous C18 column in combination with a gradient elution within 8 min. Mass spectrometric detection was performed using multiple reaction monitoring with electrospray ionization source in positive mode. The method exhibited good selectivity and correlation coefficient values for the calibration curves of each analyte were >0.99. The limit of detection and quantification ranged from 0.96 to 24.48 nmol/L and 3.42 to 244.82 nmol/L, respectively. The intra- and inter-day precision were ≤13.92%. All analytes were stable in prepared samples at room temperature in the autosampler for 24 h. This method was successfully applied to the analysis of biological samples from control and chronic mild stress (CMS) induced depression mice. It was found that Kyn and 3-HK pathways were enhanced by CMS, while the levels of Trp, Kyna, 5-HIAA, Glu, GABA and ACh were significantly reduced. The changes in 5-HT and NE levels were not uniform in the periphery and the brain. This method can therefore be applied to analyze Trp metabolites and related neurotransmitters levels to monitor disease states, study the mechanisms and outcomes of therapeutic interventions.

Stress in Regulation of GABA Amygdala System and Relevance to Neuropsychiatric Diseases

The amygdala is an almond-shaped nucleus located deep and medially within the temporal lobe and is thought to play a crucial role in the regulation of emotional processes. GABAergic neurotransmission inhibits the amygdala and prevents us from generating inappropriate emotional and behavioral responses. Stress may cause the reduction of the GABAergic interneuronal network and the development of neuropsychological diseases. In this review, we summarize the recent evidence investigating the possible mechanisms underlying GABAergic control of the amygdala and its interaction with acute and chronic stress. Taken together, this study may contribute to future progress in finding new approaches to reverse the attenuation of GABAergic neurotransmission induced by stress in the amygdala.

TMS evoked N100 reflects local GABA and glutamate balance

BACKGROUND

Animal studies suggest that synchronized electrical activities in the brain are regulated by the primary inhibitory and excitatory neurotransmitters gamma-aminobutyric acid (GABA) and glutamate, respectively. Identifying direct evidence that this same basic chemical-electrical neuroscience principle operates in the human brains is critical for translation of neuroscience to pathological research.

OBJECTIVE/HYPOTHESIS

We hypothesize that the background neurochemical concentrations may affect the cortical excitability probed by transcranial magnetic stimulation (TMS).

METHODS

We used TMS with simultaneous evoked potential recording to probe the cortical excitability and determined how background frontal cortical GABA and glutamate levels measured using magnetic resonance spectroscopy (MRS) modulate frontal electrical activities.

RESULTS

We found that TMS-evoked N100 reflects a balance between GABA-inhibitory and glutamate-excitatory levels. About 46% of individual variances in frontal N100 can be explained by their glutamate/GABA ratio (r = -0.68, p = 0.001). Both glutamate (r = -0.51, p = 0.019) and GABA (r = 0.55, p = 0.01) significantly contributed to this relationship but in opposite directions.

CONCLUSION

The current finding encourages additional mechanistic studies to develop TMS evoked N100 as a potential electrophysiological biomarker for translating the known inhibitory GABAergic vs. excitatory glutamatergic chemical-electrical principle from animal brain studies to human brain studies.

Effects of GABAB receptor activation on spatial cognitive function and hippocampal neurones in rat models of type 2 diabetes mellitus

The present study was conducted with the aim being to investigate the effect γ-aminobutyric acid type B (GABAB) receptor activation have on spatial cognitive function and hippocampal neurones found in the rat models of type 2 diabetes mellitus (T2DM). T2DM rat models were then established, randomized, and subsequently assigned into normal control (NC), T2DM, T2DM + chemical grade propylene (CGP), T2DM + baclofen, and T2DM + CGP + baclofen groups. T2DM rats’ weight and blood sugar concentrations were monitored. The DMS-2 Morris water maze testing system was performed in order to figure out the spatial cognitive function of these rats. Reverse-transcription quantitative PCR (RT-qPCR) and Western blotting were also performed in order to detect GABAB mRNA and protein expressions. We used the Nissl staining method in order to detect the number of hippocampal neurones, TUNEL (terminal deoxyribonucleotidy transferase-mediated dUTP nick labeling) staining to detect cell apoptosis, and Western blotting method in order to measure the expressions of the apoptosis-related proteins (Bax, cytochrome c (Cyt-c), Caspase-3, and Bcl-2). In comparison with the T2DM group, the weight decreased, blood sugar concentration increased, and spatial cognitive function as well as hippocampal neurones were both impaired in the T2DM + CGP group, contrary to the rats in the T2DM + baclofen group who showed an opposite trend. The situation in the T2DM + CGP + baclofen group was better than that found in the T2DM + CGP group while proving to be more serious than that of the NC and T2DM + baclofen groups. Conclusively, activating the GABAB receptor improved spatial cognitive function and hippocampal neurones in the T2DM rats.

Diversity of structure and function of GABAB receptors: a complexity of GABAB-mediated signaling

γ-aminobutyric acid type B (GABA_B) receptors are broadly expressed in the nervous system and play an important role in neuronal excitability. GABA_B receptors are G protein-coupled receptors that mediate slow and prolonged inhibitory action, via activation of Gαi/o-type proteins. GABA_B receptors mediate their inhibitory action through activating inwardly rectifying K⁺ channels, inactivating voltage-gated Ca²⁺ channels, and inhibiting adenylate cyclase. Functional GABA_B receptors are obligate heterodimers formed by the co-assembly of R1 and R2 subunits. It is well established that GABA_B receptors interact not only with G proteins and effectors but also with various proteins. This review summarizes the structure, subunit isoforms, and function of GABA_B receptors, and discusses the complexity of GABA_B receptors, including how receptors are localized in specific subcellular compartments, the mechanism regulating cell surface expression and mobility of the receptors, and the diversity of receptor signaling through receptor crosstalk and interacting proteins.

Female-specific myoinhibitory peptide neurons regulate mating receptivity in Drosophila melanogaster

Upon mating, fruit fly females become refractory to further mating for several days. An ejaculate protein called sex peptide (SP) acts on uterine neurons to trigger this behavioural change, but it is still unclear how the SP signal modifies the mating decision. Here we describe two groups of female-specific local interneurons that are important for this process—the ventral abdominal lateral (vAL) and ventral abdominal medial (vAM) interneurons. Both vAL and vAM express myoinhibitory peptide (Mip)-GAL4. vAL is positive for Mip neuropeptides and the sex-determining transcriptional factor doublesex. Silencing the Mip neurons in females induces active rejection of male courtship attempts, whereas activation of the Mip neurons makes even mated females receptive to re-mating. vAL and vAM are located in the abdominal ganglion (AG) where they relay the SP signal to other AG neurons that project to the brain. Mip neuropeptides appear to promote mating receptivity both in virgins and mated females, although it is dispensable for normal mating in virgin females.

After mating, female flies are not receptive to re-mating with a new male fly, a response triggered by a male seminal protein called sex peptide. Here, the authors work out the downstream circuits and neurons that are important for post-mating receptivity in female flies.

Allicin attenuates tunicamycin-induced cognitive deficits in rats via its synaptic plasticity regulatory activity

Objective(s):

To illuminate the functional effects of allicin on rats with cognitive deficits induced by tunicamycin (TM) and the molecular mechanism of this process.

Materials and Methods:

200–250 g male SD rats were divided into three groups at random: control group (n=12), TM group (5 μl, 50 μM, ICV, n=12), and allicin treatment group (180 mg/kg/d with chow diet, n=12). After 16 weeks of allicin treatment, the learning ability and memory were tested using novel object recognition (NOR) testing on rats with 72 hr TM treatment (5 μl, 50 μM, ICV); meanwhile, the variation of field excitatory postsynaptic potential (fEPSP) in the Schaffer Collateral (SC)-CA1 synapse was detected by extracellular electrophysiological recordings and the morphology of dendritic spine was observed by Golgi staining as well as detecting several synaptic plasticity-related proteins by Western blot.

Results:

The density of dendritic spine was increased significantly in allicin-treated groups and the correspondence slope of fEPSP in TM-induced cognitive deficits group was enhanced and expression of synaptophysin and glutamate receptor-1(GluR1) in hippocampal neurons was up-regulated.

Conclusion:

The results indicate that allicin plays an important role in synaptic plasticity regulation. These finding showed that allicin could be used as a pharmacologic treatment in TM-induced cognitive deficits.

Effects of GABAB receptors in the insula on recognition memory observed with intellicage

BACKGROUND

Insular function has gradually become a topic of intense study in cognitive research. Recognition memory is a commonly studied type of memory in memory research. GABA_BR has been shown to be closely related to memory formation. In the present study, we used intellicage, which is a new intelligent behavioural test system, and a bilateral drug microinjection technique to inject into the bilateral insula, to examine the relationship between GABA_BR and recognition memory.

METHODS

Male Sprague-Dawley rats were randomly divided into control, Sham, Nacl, baclofen and CGP35348 groups. Different testing procedures were employed using intellicage to detect changes in rat recognition memory. The expression of GABA_BR (GB1, GB2) in the insula of rats was determined by immunofluorescence and western blotting at the protein level. In addition, the expression of GABA_BR (GB₁, GB₂) was detected by RT-PCR at the mRNA level.

RESULTS

The results of the intellicage test showed that recognition memory was impaired in terms of position learning, punitive learning and punitive reversal learning by using baclofen and CGP35348. In position reversal learning, no significant differences were found in terms of cognitive memory ability between the control groups and the CGP and baclofen groups. Immunofluorescence data showed GABA_BR (GB1, GB2) expression in the insula, while data from RT-PCR and western blot analysis demonstrated that the relative expression of GB1 and GB2 was significantly increased in the baclofen group compared with the control groups. In the CGP35348 group, the expression of GB1 and GB2 was significantly decreased, but there was no significant difference in GB1 or GB2 expression in the control groups.

CONCLUSIONS

GABA_BR expression in the insula plays an important role in the formation of recognition memory in rats.

Ionomycin-induced calcium influx induces neurite degeneration in mouse neuroblastoma cells: analysis of a time-lapse live cell imaging system

Reactive oxygen species induce neuronal cell death. However, the detailed mechanisms of cell death have not yet been elucidated. Previously, we reported neurite degeneration before the induction of cell death. Here, we attempted to elucidate the mechanisms of neurite degeneration before the induction of cell death using the neuroblastoma N1E-115 cell line and a time-lapse live cell imaging system. Treatment with the calcium ionophore ionomycin induced cell death and neurite degeneration in a concentration- and time-dependent manner. Treatment with a low concentration of ionomycin immediately produced a significant calcium influx into the intracellular region in N1E-115 cells. After 1-h incubation with ionomycin, the fluorescence emission of MitoSOX^TM increased significantly compared to the control. Finally, analysis using a new mitochondrial specific fluorescence dye, MitoPeDPP, indicated that treatment with ionomycin significantly increased the mitochondrial lipid hydroperoxide production in N1E-115 cells. The fluorescence emissions of Fluo-4 AM and MitoPeDPP were detected in the cell soma and neurite regions in ionomycin-treated N1E-115 cells. However, the emissions of neurites were much lower than those of the cell soma. TBARS values of ionomycin-treated cells significantly increased compared to the control. These results indicate that ionomycin induces calcium influx into the intracellular region and reactive oxygen species production in N1E-115 cells. Lipid hydroperoxide production was induced in ionomycin-treated N1E-115 cells. Calcium influx into the intracellular region is a possible activator of neurite degeneration.

Analgesic potential of standardized methanol stem bark extract of Ficus platyphylla in mice: Mechanisms of action

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts of the stem bark of Ficus platyphylla (FP) have been used in traditional the Nigerian medicine to treat psychoses, depression, epilepsy, pain and inflammation. Previous studies have revealed the analgesic and anti-inflammatory effects of FP in different assays including acetic acid-induced writhing, formalin-induced nociception, and albumin-induced oedema.

PURPOSE/METHODS

In this study, we assessed the effects of the standardised extract of FP on hot plate nociceptive threshold and vocalisation threshold in response to electrical stimulation of the tail root in order to confirm its acclaimed analgesic properties. We also investigated the molecular mechanisms underlying these effects, with the focus on opiate receptor binding and the key enzymes of eicosanoid biosynthesis, namely cyclooxygenase (COX) and 5-lipoxygenase (5-LO).

RESULTS

FP (i) increased the hot plate nociceptive threshold and vocalisation threshold. The increase in hot plate nociceptive threshold was detectable over a period of 30min whereas the increase in vocalisation threshold persisted over a period of 90min. (ii) FP showed an affinity for µ opiate receptors but not for δ or κ opiate receptors, and (iii) FP inhibited the activities of COX-2 and 5-LO but not of COX-1.

CONCLUSIONS

We provided evidence supporting the use of FP in Nigerian folk medicine for the treatment of different types of pain, and identified opioid and non-opioid targets. It is interesting to note that the dual inhibition of COX-2 and 5-LO appears favourable in terms of both efficacy and side effect profile.

The key regulator of submergence tolerance, SUB1A, promotes photosynthetic and metabolic recovery from submergence damage in rice leaves

The submergence-tolerance regulator, SUBMERGENCE1A (SUB1A), of rice (Oryza sativa L.) modulates gene regulation, metabolism and elongation growth during submergence. Its benefits continue during desubmergence through protection from reactive oxygen species and dehydration, but there is limited understanding of SUB1A's role in physiological recovery from the stress. Here, we investigated the contribution of SUB1A to desubmergence recovery using the two near-isogenic lines, submergence-sensitive M202 and tolerant M202(Sub1). No visible damage was detected in the two genotypes after 3 d of submergence, but the sublethal stress differentially altered photosynthetic parameters and accumulation of energy reserves. Submergence inhibited photosystem II photochemistry and stimulated breakdown of protein and accumulation of several amino acids in both genotypes at similar levels. Upon desubmergence, however, more rapid return to homeostasis of these factors was observed in M202(Sub1). Submergence considerably restrained non-photochemical quenching (NPQ) in M202, whereas the value was unaltered in M202(Sub1) during the stress. Upon reaeration, submerged plants encounter sudden exposure to higher light. A greater capability for NPQ-mediated photoprotection can benefit the rapid recovery of photosynthetic performance and energy reserve metabolism in M202(Sub1). Our findings illuminate the significant role of SUB1A in active physiological recovery upon desubmergence, a component of enhanced tolerance to submergence.