Inhibitory Amino Acid Neurotransmitters Research Articles

Ligustrazine alleviates spinal cord injury-induced neuropathic pain by inhibiting the TLR4/NF-κB signaling pathway.

To investigate the effects of ligustrazine on neuropathic pain (NPP) in rats with sciatic nerve injury and to provide new scientific insight for broadening the clinical application of ligustrazine. Human spinal cord cell line STR cells were transfected with TLR4-mimic or mimic negative control (mimic-NC). After transfection, the STR cells were treated with different concentrations of ligustrazine (0, 0.25, 0.5, 1, 2 μm) for 24 h or 48 h. Cell proliferation was detected by MTT assay and colony formation assay. A rat model was further constructed to evaluate mechanical and cold pain sensitivity behaviors by fiber mechanical stimulation and freezing spray. The extracellular fluids of medial prefrontal cortex (mPFC) and central amygdala (CeA) were collected by intracranial dual-site simultaneous microdialysis. The contents of glutamic acid (Glu), aspartate (Asp), glycine (Gly), and γ-aminobutyric acid (GABA) in extracellular fluids were detected by HPLC. Compared to the 0 μm group, ligustrazine concentration at 0.5 μm significantly decreased the relative cell viability of STR cells and promoted the cell apoptosis rate. Ligustrazine at 0.25 μm significantly reduced the colony number of STR cells (all P<0.05). Compared to the control group, 1 μM ligustrazine significantly increased the protein expression of Bax and cleaved caspase 3 in STR cells but decreased the protein expression of Bcl-2 (all P<0.001). Compared to the control group, 2 μM ligustrazine treatments significantly reduced the protein levels of TLR4 and p-Akt in STR cells (all P<0.001). However, 2 μM ligustrazine treatments did not change the protein expression of Akt (P>0.05). Compared to the control group, the level of TLR4 in STR cells transfected with TLR4-mimic was significantly increased (P<0.001). Compared to the control group, transfection of TLR4-mimic reversed the anti-proliferative and pro-apoptotic effects of ligustrazine on STR cells (all P<0.001). The analgesic effect of Ligustrazine on neuropathic pain caused by spinal cord injury may be related to its inhibition of the release of excitatory amino acid transmitters Glu and Gly through the TLR4/NF-κB pathway, regulation of the dynamic balance of excitatory and inhibitory amino acid neurotransmitters, and alleviation of the central sensitization effect caused by the excitotoxicity of Glu.

Cerebrolysin restores balance between excitatory and inhibitory amino acids in brain following concussive head injury. Superior neuroprotective effects of TiO2 nanowired drug delivery.

Concussive head injury (CHI) often associated with military personnel, soccer players and related sports personnel leads to serious clinical situation causing lifetime disabilities. About 3-4k head injury per 100k populations are recorded in the United States since 2000-2014. The annual incidence of concussion has now reached to 1.2% of population in recent years. Thus, CHI inflicts a huge financial burden on the society for rehabilitation. Thus, new efforts are needed to explore novel therapeutic strategies to treat CHI cases to enhance quality of life of the victims. CHI is well known to alter endogenous balance of excitatory and inhibitory amino acid neurotransmitters in the central nervous system (CNS) leading to brain pathology. Thus, a possibility exists that restoring the balance of amino acids in the CNS following CHI using therapeutic measures may benefit the victims in improving their quality of life. In this investigation, we used a multimodal drug Cerebrolysin (Ever NeuroPharma, Austria) that is a well-balanced composition of several neurotrophic factors and active peptide fragments in exploring its effects on CHI induced alterations in key excitatory (Glutamate, Aspartate) and inhibitory (GABA, Glycine) amino acids in the CNS in relation brain pathology in dose and time-dependent manner. CHI was produced in anesthetized rats by dropping a weight of 114.6g over the right exposed parietal skull from a distance of 20cm height (0.224N impact) and blood-brain barrier (BBB), brain edema, neuronal injuries and behavioral dysfunctions were measured 8, 24, 48 and 72h after injury. Cerebrolysin (CBL) was administered (2.5, 5 or 10mL/kg, i.v.) after 4-72h following injury. Our observations show that repeated CBL induced a dose-dependent neuroprotection in CHI (5-10mL/kg) and also improved behavioral functions. Interestingly when CBL is delivered through TiO2 nanowires superior neuroprotective effects were observed in CHI even at a lower doses (2.5-5mL/kg). These observations are the first to demonstrate that CBL is effectively capable to attenuate CHI induced brain pathology and behavioral disturbances in a dose dependent manner, not reported earlier.

Optimization of Ultra-High-Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry Detection of Glutamine-FMOC Ad-Hoc Derivative by Central Composite Design

Glutamine (Gln) is converted to excitatory (glutamate, aspartate) and inhibitory (γ-amino butyric acid) amino acid neurotransmitters in brain, and is a source of energy during glucose deprivation. Current research utilized an Analytical Quality by Design approach to optimize levels and combinations of critical gas pressure (sheath, auxiliary, sweep) and temperature (ion transfer tube, vaporizer) parameters for high-sensitivity mass spectrometric quantification of brain tissue glutamine. A Design of Experiments (DOE) matrix for evaluation of relationships between these multiple independent variables and a singular response variable, e.g. glutamine chromatogram area, was developed by statistical response surface methodology using central composite design. A second-order polynomial equation was generated to identify and predict singular versus combinatory effects of synergistic and antagonistic factors on chromatograph area. Predicted versus found outcomes overlapped, with enhanced area associated with the latter. DOE methodology was subsequently used to evaluate liquid chromatographic variable effects, e.g. flow rate, column temperature, and mobile phase composition on the response variable. Results demonstrate that combinatory AQbD-guided mass spectrometric/liquid chromatographic optimization significantly enhanced analytical sensitivity for Gln, thus enabling down-sized brain tissue sample volume procurement for quantification of this critical amino acid.

An evaluation of the reproducibility of 1H-MRS GABA and GSH levels acquired in healthy volunteers with J-difference editing sequences at varying echo times

Recent advances in J-difference-edited proton magnetic resonance spectroscopy (1H MRS) data acquisition and processing have led to the development of Hadamard Encoding and Reconstruction of MEGA-Edited Spectroscopy (HERMES) techniques, which enable the simultaneous measurement of ɣ-aminobutyric acid (GABA), the primary inhibitory amino acid neurotransmitter in the central nervous system, and of glutathione (GSH), the most abundant antioxidant in living tissue, at the commonly available magnetic field strength of 3 T. However, the reproducibility of brain levels of GABA and GSH measured across multiple scans in human subjects using HERMES remains to be established. In the present study, twelve healthy volunteers completed two consecutive HERMES scans of the dorsal anterior cingulate cortex (dACC) to assess the test-retest reproducibility of the technique for GABA and GSH measurements at TE = 80 ms. Eleven of the twelve participants additionally completed two consecutive MEGA-PRESS scans at TE = 120 ms, with editing pulses configured for GSH acquisition, to compare the reliability of GSH in the same voxel measured using the standard MEGA-PRESS at TE = 120 ms. The primary findings of study were that, 1) the coefficient of variation (CV) of measuring GABA with HERMES was 16.7%, which is in agreement with the reliability we previously reported for measuring GABA using MEGA-PRESS; and 2) the reliability of measuring GSH with MEGA-PRESS at TE = 120 ms was more than twice as high as that for measuring the antioxidant with HERMES at TE = 80 ms (CV = 7.3% vs. 19.0% respectively). These findings suggest that HERMES and MEGA-PRESS offer similar reliabilities for measuring GABA, while MEGA-PRESS at TE = 120 ms is more reliable for measuring GSH relative to HERMES at TE = 80 ms.

A contemporary review of obstructive sleep apnea.

This review provides a contemporary review of sleep apnea with emphasis on definitions, epidemiology, and consequences. Amyloid β-42 is one of the main peptides forming amyloid plaques in the brains of Alzheimer patients. Poorer sleep quality and shorter sleep duration have been associated with a higher amyloid burden. Decreased sleep time in the elderly is a precipitating factor in amyloid retention. Studies have shown that the dysregulation of the homeostatic balance of the major inhibitory and excitatory amino acid neurotransmitter systems of gamma-aminobutyric acid (GABA) and glutamate play a role in sleep disordered breathing (SDB). Untreated sleep disordered breathing (obstructive sleep apnea and/or central sleep apnea) are an important cause of medical mortality and morbidity. OSA is characterized by recurrent episodes of partial or complete collapse of the upper airway during sleep followed by hypoxia and sympathetic activation. Apneic events are terminated by arousal, followed by increases in pulse and blood pressure, and re-oxygenation and the release of inflammatory factors. Individuals with OSA have an increased risk of developing atrial fibrillation. Hypoxemia and poor sleep quality because of OSA increase the risk of cognitive decline in the elderly.

Ethanol-induced changes in synaptic amino acid neurotransmitter levels in the nucleus accumbens of differentially sensitized mice.

Ethanol-induced behavioural sensitization (EBS) does not occur uniformly in mice exposed to the sensitization paradigm. This suggests innate differential responses to ethanol (EtOH) in the reward circuitry of individual animals. To better characterize the adaptive differences between low-sensitized (LS) and high-sensitized (HS) mice, we examined excitatory amino acid (EAA) and inhibitory amino acid (IAA) neurotransmitter levels in the nucleus accumbens (NAc) during EBS expression. Male DBA/2J mice received five ethanol (EtOH) (2.2g/kg) or saline injections, and locomotor activity (LMA) was assessed during EBS induction. EtOH mice were classified as LS or HS on the basis of final LMA scores. Following an EtOH challenge (1.8g/kg) 2weeks later, LMA was re-evaluated and in vivo microdialysis samples were collected from the NAc. Most differences in amino acid levels were observed within the first 20min after EtOH challenge. LS mice exhibited similar glutamate levels compared with acutely treated (previously EtOH naïve) mice, and generally increased levels of the IAAs GABA, glycine, and taurine. By contrast, HS mice exhibited increased glutamate and attenuated levels of GABA, glycine, and taurine. These data suggest that the profile of amino acid neurotransmitters in the NAc of LS and HS mice significantly differs. Elucidating these adaptive differences contributes to our understanding of factors that confer susceptibility/resilience to alcohol use disorder.

EFFECTS OF DRINKING WATER CONTAINING ALUMINUM AND FLUORIDE SALTS ON THE LEARNING BEHAVIOR AND BRAIN NEUROTRANSMITTERS OF MALE RAT OFFSPRING

The widely existence of aluminum and fluoride in the environment makes the exposure to these pollutants unavoidable. Few studies reported the toxic impact of these pollutants separately on the neurotransmitters involved in the cognitive behavior of rodent offspring. The present study aimed to evaluate the potential impact of these pollutants together on the amino acid neurotransmitters of different brain regions (cerebral cortex, hypothalamus and hippocampus) and the learning ability of male rat offspring. The rat offspring were exposed to deionized water containing 0.5 g AlCl3/L, 0.15 g NaF/L, or their combination throughout the prenatal period of brain growth in the uterus (via the placenta) and the postnatal period until 70 days old (via lactation and drinking water). The results indicated that the levels of most excitatory and inhibitory amino acid neurotransmitters were significantly affected in the three brain regions of exposed male offspring to AlCl3 and/or NaF, as compared with the control male offspring. In addition, the learning ability was more affected in the male offspring exposed to AlCl3 plus NaF, a finding that indicates a synergistic effect. The alteration in the learning ability of rat offspring exposed to AlCl3 plus NaF was concomitant with the increase in the cerebral cortical glycine, hypothalamic and hippocampal γ-aminobutyric acid, and hippocampal glutamate. In conclusion, administration of the AlCl3 plus NaF was more neurotoxic than each salt alone.

Isoniazid-induced hepatotoxicity and neurotoxicity in rats investigated by 1H NMR based metabolomics approach

Isoniazid (INH) is a well-known therapeutic and preventive agent against tuberculosis. However, high rates of side effects with various symptoms concerning hepatotoxicity and neurotoxicity have been reported, hindering its wide and safe application in clinic. In this investigation, rats were intoxicated with INH by gavage at doses of 200 and 400 mg/kg for 7 consecutive days to develop a rat model of acute INH-induced toxicity, which was investigated by a 1H NMR-based metabolomics complemented with clinical assays, histopathological inspection and western blotting. INH decreased the weights of dosed rats and induced seizure and hepatic steatosis dose-dependently. Orthogonal signal correction partial least-squares discriminant analysis (OSC-PLS-DA) of the NMR profiles of rat livers, brains and serum revealed that INH dose-dependently induced oxidative stress, disorders of excitatory and inhibitory amino acid neurotransmitters, and disturbances of energy metabolism and osmotic balance, which could help clarify the mechanisms of INH-induced hepatotoxicity and neurotoxicity. This integrated metabolomics approach showcased its ability to characterize the global metabolic status of organism, providing a powerful and feasible tool to probe drug induced toxicity or side effects.

Dorsolateral prefrontal cortex GABA deficit in older adults with sleep-disordered breathing

Sleep-disordered breathing (SDB) is a common disorder in aging that is associated with cognitive decline, including significant executive dysfunction, for which the neurobiological underpinnings remain poorly understood. Using proton magnetic resonance spectroscopy (1H MRS), this study assessed whether dysregulation of the homeostatic balance of the major inhibitory and excitatory amino acid neurotransmitter systems of γ-aminobutyric acid (GABA) and glutamate, respectively, play a role in SDB. Levels of GABA and those of the combined resonances of glutamate and glutamine (Glx), were measured by 1H MRS in the left dorsolateral prefrontal cortex (l-DLPFC) and bilateral hippocampal regions of 19 older adults (age ± SD: 66.1 ± 1.9 years) with moderate to severe SDB, defined as having an Apnea-Hypopnea Index (AHI) greater than 15 as assessed by polysomnography, and in 14 older adults (age ± SD: 62.3 ± 1.3 years) without SDB (AHI < 5). In subjects with SDB, levels of l-DLPFC GABA, but not Glx, were significantly lower than in control subjects (P < 0.0002). Additionally, there was a negative correlation between l-DLPFC GABA levels, but not Glx, and SDB severity by AHI (r = -0.68, P < 0.0001), and a positive correlation between l-DLPFC GABA levels, but not Glx, and minimal oxygen saturation during sleep (r = 0.62, P = 0.0005). By contrast, no group differences or oxygenation associations were found for levels of GABA or Glx in right or left hippocampal region. These findings are interpreted in terms of a pathophysiological model of SDB in which hypoxia-mediated inhibitory neurotransmission deficit in DLPFC could lead to hyperexcitability and, potentially neuronal dysfunction and cognitive decline.

Alterations in hypoglossal motor neurons due to GAD67 and VGAT deficiency in mice

There is an emerging body of evidence that glycinergic and GABAergic synaptic inputs onto motor neurons (MNs) help regulate the final number of MNs and axonal muscle innervation patterns. Using mutant glutamate decarboxylase 67 (GAD67) and vesicular inhibitory amino acid transporter (VGAT) deficient mice, we describe the effect that deficiencies of presynaptic GABAergic and/or glycinergic release have on the post-synaptic somato-dendritic structure of motor neurons, and the development of excitatory and inhibitory synaptic inputs to MNs. We use whole-cell patch clamp recording of synaptic currents in E18.5 hypoglossal MNs from brainstem slices, combined with dye-filling of these recorded cells with Neurobiotin™, high-resolution confocal imaging and 3-dimensional reconstructions. Hypoglossal MNs from GAD67- and VGAT-deficient mice display decreased inhibitory neurotransmission and increased excitatory synaptic inputs. These changes are associated with increased dendritic arbor length, increased complexity of dendritic branching, and increased density of spiny processes. Our results show that presynaptic release of inhibitory amino acid neurotransmitters are potent regulators of hypoglossal MN morphology and key regulators of synaptic inputs during this critical developmental time point.

Neurochemical impact of bisphenol A in the hippocampus and cortex of adult male albino rats.

Bisphenol A (BPA), an endocrine-disrupting chemical, is widely used in the manufacture of polycarbonated plastics and epoxy resins and line metal beverage cans. Growing evidence suggests that BPA acts directly on neuronal functions as it is lipophilic and could accumulate in the brain. The present study aims to investigate the effect of two doses of BPA (10 mg/kg for 6 and 10 weeks and 25 mg/kg for 6 weeks) on excitatory (glutamate and aspartate) and inhibitory (γ-aminobutyric acid, glycine, and taurine) amino acid neurotransmitter levels in the cortex and hippocampus. This study extends to investigate the effect of BPA on acetylcholinesterase (AchE) activity and some oxidative stress parameters in the two regions. In the cortex, a significant increase in the excitatory and a significant decrease in the inhibitory amino acids occurred after BPA (10 mg/kg for 10 weeks and 25 mg/kg for 6 weeks). This was accompanied by a significant increase in lipid peroxidation, nitric oxide, and reduced glutathione after 6 weeks of BPA (25 mg/kg). In the hippocampus, a significant increase in the excitatory and inhibitory amino acid neurotransmitters occurred after 6 weeks of BPA. Hippocampal lipid peroxidation increased significantly after BPA exposure and hippocampal reduced glutathione increased significantly after 6 weeks of BPA exposure (10 mg/kg). BPA induced a significant increase in cortical and hippocampal AchE activity. The present neurochemical changes in the cortex and hippocampus suggest that BPA induced a state of excitotoxicity and oxidative stress. This may raise concerns about the exposure of humans to BPA due to its wide applications in industry.

Effects of Propofol on Excitatory and Inhibitory Amino Acid Neurotransmitter Balance in Rats with Neurogenic Pulmonary Edema Induced by Subarachnoid Hemorrhage

Propofol exhibits neuroprotective effects mediated by the inhibition of excitatory amino acid (EAA) neurotransmitter release and potentiation of inhibitory amino acid (IAA) neurotransmitters. To our knowledge, this is the first study to investigate the effects of propofol on the EAA and IAA balance in neurogenic pulmonary edema (NPE). Sixty male Wistar rats were randomized to Sham, NPE, Low-dose propofol, and High-dose propofol groups. NPE was induced via rapid injection of autologous blood (0.5ml) into the cisterna magna. The Low- and High-dose propofol groups were pretreated with boluses of 2 and 5mgkg(-1), respectively, prior to blood injection, followed by continuous propofol infusion at 6 and 15mgkg(-1)h(-1), respectively. The mean arterial pressure (MAP), heart rate, intracranial pressure (ICP), peak inspiratory pressure (PIP), and arterial blood gases were continuously recorded. After 2h, the lung wet-to-dry weight ratio, total protein concentration in the bronchoalveolar lavage fluid (BALF), brain water content, cortical EAA and IAA levels, chest X-ray, and histological staining of lung sections were evaluated. Blood injections into the cisterna magna induced NPE and hemodynamic changes. Propofol alleviated the increases in the MAP, ICP, and PIP, improved oxygenation and histopathological changes, ameliorated pulmonary and cerebral edema, increased the IAA brain levels, and decreased the ratio of Glu to γ-aminobutyric acid. The current findings suggest that propofol improves NPE likely via IAA accumulation and the regulation of EAA and IAA balance, which may represent an effective treatment for NPE.

Expressions of retinal γ-aminobutyric acid and its receptors in retina of guinea pig eyes after lens induction

Background Researches showed that gamma aminobutyric acid (GABA),an inhibitory amino acid neurotransmitter,plays a critical role in myopia refractive development.The inhibitory roles of GABA and its receptors antagonists have been confirmed.However,the study on whether GABA participates in the mechanisms of lens-induced myopia (LIM) in guinea pigs is rare. Objective The aim of this study was to explore the alteration of expression of GABA and its three receptor subtypes in the retinas of guinea pigs with LIM. Methods Three-week-old healthy guinea pigs were randomized into the normal control group and the model group.The right eyes of the guinea pigs in the normal control group served as the normal control eyes,and the right eyes of the guinea pigs in the model group monocularly fitted with -10 D lens as the experimental eyes,and the fellow eyes of the model group were used as the self-control eyes.The refraction and axial length of eyes were measured by A-sonography and streak retinoscopy before and 4 weeks after modeling.The guinea pigs were sacrificed at the fourth week after modeling,and the retinas were isolated.GABA content in the retinas was assayed by high performance liquid chromatography (HPLC) and the relative expression levels of subtypes of GABA receptors were detected by real-time PCR.All the results were compared among the groups.All experimental protocols and animal handling procedures were approved by the Animal Care and Use Committee of Shandong University of Traditional Chinese Medicine,and were in accordance with the statement of the Association for Research in Vision and Ophthalmology for the use of animals. Results At the fourth week after modeling,the mean diopter of the model eyes was (-3.39±0.70)D,which was significantly higher than (1.03±0.68)D of the normal control eyes and (0.77±0.64)D of the self-control eyes in the model group (t=-16.382,-17.113,both at P 0.05). Conclusions The expressions of GABA as well as the mRNA of GABAA and GABAC receptor up-regulate, but there is no obvious alteration in the expression of mRNA of GABAB receptor in the LIM eyes. Key words: Myopia/lens-induced; Gamma aminobutyric acid; Gamma aminobutyric acid receptor; Retina

Inhibitory and excitatory amino acid neurotransmitters are utilized by the projection from the dorsal deep mesencephalic nucleus to the sublaterodorsal nucleus REM sleep induction zone

The sublaterodorsal nucleus (SLD) in the pons of the rat is a locus supporting short-latency induction of a REM sleep-like state following local application of a GABAA receptor antagonist or kainate, glutamate receptor agonist. One putatively relevant source of these neurotransmitters is from the region of the deep mesencephalic nucleus (DpMe) just ventrolateral to the periaquiductal gray, termed the dorsal DpMe (dDpMe). Here, the amino acid neurotransmitter innervation of SLD from dDpMe was studied utilizing anterograde tract-tracing with biotinylated dextranamine (BDA) and fluorescence immunohistochemistry visualized with laser scanning confocal microscopy. Both markers for inhibitory and excitatory amino acid neurotransmitters were found in varicose axon fibers in SLD originating from dDpMe. Vesicular glutamate transporter2 (VGLUT2) represented the largest number of anterogradely labeled varicosities followed by vesicular GABA transporter (VGAT). Numerous VGAT and VGLUT2 labeled varicosities were observed apposed to dDpMe-labeled axon fibers indicating both excitatory and inhibitory presynaptic, local modulation within the SLD. Some double-labeled BDA/VGAT varicosities were seen apposed to small somata labeled for glutamate consistent with being presynaptic to the phenotype of REM sleep-active SLD neurons. Results found support the current theoretical framework of the interaction of dDpMe and SLD in control of REM sleep, while also indicating operation of mechanisms with a greater level of complexity.

Compound Formula Rehmannia alleviates levodopa-induced dyskinesia in Parkinson's disease.

Compound Formula Rehmannia has been shown to be clinically effective in treating Parkinson's disease and levodopa-induced dyskinesia; however, the mechanisms remain unclear. In this study, we established a model of Parkinson's disease dyskinesia in rats, and treated these animals with Compound Formula Rehmannia. Compound Formula Rehmannia inhibited the increase in mRNA expression of N-methyl-D-aspartate receptor subunits 1 and 2 and excitatory amino acid neurotransmitter genes, and it inhibited the reduction in expression of γ-aminobutyric acid receptor B1, an inhibitory amino acid neurotransmitter gene, in the corpus striatum. In addition, Compound Formula Rehmannia alleviated dyskinesia symptoms in the Parkinson's disease rats. These experimental findings indicate that Compound Formula Rehmannia alleviates levodopa-induced dyskinesia in Parkinson's disease by modulating neurotransmitter signaling in the corpus striatum.

Ketamine reverses stress-induced depression-like behavior and increased GABA levels in the anterior cingulate: An 11.7T 1H-MRS study in rats

Gamma-aminobutyric acid (GABA) is the major inhibitory amino acid neurotransmitter in the brain and is primarily responsible for modulating excitatory tone. Clinical neuroimaging studies show decreased GABA levels in the anterior cingulate of patients with mood disorders, including major depressive disorder. Chronic unpredictable stress (CUS) is an animal model thought to mimic the stressful events that may precipitate clinical depression in humans. In this study male Sprague-Dawley rats were subjected to a modified CUS paradigm that used a random pattern of unpredictable stressors twice daily for 10 days to explore the early developmental stages of depression-like endophenotypes. Control rats were handled daily for 10 days. Some rats from each treatment group received an injection of ketamine (40 mg/kg) after the final stressor. One day following the final stressor rats were tested for behavioral effects in the forced swim test and then euthanized to collect trunk blood and anterior cingulate brain samples. GABA levels were measured in anterior cingulate samples ex vivo using proton magnetic resonance spectroscopy ((1)H-MRS) at 11.7 T. Animals subjected to CUS had lower body weights, higher levels of blood corticosterone, and increased immobility in the forced swim test; all of which suggest that the stress paradigm induced a depression-like phenotype. GABA levels in the anterior cingulate were significantly increased in the stressed animals compared to controls. Administration of ketamine on the last day of treatment blunted the depression-like behavior and increased GABA levels in the anterior cingulate following CUS. These data indicate that stress disrupts GABAergic signaling, which may over time lead to symptoms of depression and ultimately lower basal levels of cortical (1)H-MRS GABA that are seen in humans with depression. Furthermore, the data suggests that ketamine modulates cortical GABA levels as a mechanism of its antidepressant activity.

The neuropharmacology of the age-old sedative/hypnotic, ethanol

Ethyl alcohol (ethanol) is produced by the process of fermentation whereby plant sugars are converted to ethanol by yeast. Products of fermentation include mead from honey, wine from grapes, sake from rice, and beer from grains. Fermented products can also be distilled, for example when whisky is distilled from grains (Herbst and Herbst, 2003). The history of voluntary ethanol use by humans dates as far back as 8000 years ago for wine and possibly earlier for beer, as barley may have been the oldest cultivated grain (Pendell, 2010). It is also documented that ethanol was an extremely important staple to ancient civilizations such as the Egyptians and the Maya (Johnson, 1994), as well as more modern societies such as the original American colonies (Pendell, 2010). It seems that modern society's interest in alcohol has certainly not waned, and from the standpoint of neuropharmacology, has probably increased. During the past several decades, there has been a concerted effort to determine the neuropharmacological mechanism of action(s) of ethanol. Ethanol has been reported to produce its effects via modulation of neural cell membrane fluidity as well as modulation of several neurotransmitter systems, including γ-amino butyric acid (GABA), glutamate, dopamine, and opioid systems (for reviews, see Koob et al., 1998; Kumar et al., 2009). GABA is an inhibitory amino acid neurotransmitter that is ubiquitously distributed in the mammalian brain, and ethanol's effects on the GABA system are thought to be mediated primarily by activating the GABAA receptor, a 5-subunit receptor that gates Cl− ions (for a review, see Kumar et al., 2009). Thus, GABA receptor activation produces CNS inhibition via Cl− influx. It has also been reported that specific GABAA receptor subunits mediate specific effects. For example, the α1 subunit is associated with sedation, whereas the α2 and α3 subunits are associated with anti-anxiety effects (Licata and Rowlett, 2008; Ator et al., 2010). Many types of sedative-hypnotic compounds (drugs producing dose-dependent sedation and ultimately sleep), including the benzodiazepines, barbiturates, and ethanol, bind to and activate the GABAA receptor, and it is reasonable to assume that the sedative effects of these agents are mediated, at least in part, by the α1 subunit. It is known that neurotransmitters, including GABA, bind to their receptors as “first messengers,” and initiate a complex cascade of intra-cellular events. In the case of GABA, part of this cellular cascade includes modulation of the “second messenger” systems Ca++ and cAMP that ultimately modulate two protein kinases, PKC and PKA, resulting in myriad effects in the cell, including changes to gene expression (Moss et al., 1992; Diamond and Gordon, 1997; Brandon et al., 2000 for a review, see Kumar et al., 2009). Leslie Morrow and colleagues have been exploring the complex cascade of downstream cellular events mediated by ethanol-induced GABAA receptor activation. In their recent Frontiers in Neuroscience report (Kumar et al., 2012), this research team determined the effects of acute ethanol exposure on PKA-mediated GABAA receptor expression. Although chronic ethanol exposure has been reported to produce down-regulation and/or desensitization of GABAA receptors, Morrow and colleagues reported an interesting finding of acute ethanol exposure. Specifically, acute intracerebroventricular administration of ethanol produced dose-dependent increases in expression of PKA and GABAA receptor α1 subunits. In addition, antagonism studies revealed that blockade of PKA blocked the ethanol-induced increases in GABAA receptor α1 subunit expression, providing further evidence for a PKA-GABAA receptor network communication. An additional manipulation showed that enhancing PKA activity actually enhanced ethanol-induced loss of righting reflex. Together with earlier reports from this research group, these data indicate that PKA (Kumar et al., 2012) and PKC (Kumar et al., 2006) may have antagonistic effects on GABAA receptor α1 subunit expression, thus delineating specific potential pathway(s) for mediation of ethanol effects on cell function and overt organismal behavior. This group's current report represents a comprehensive analysis of the specific effects of ethanol on kinase activity and receptor subunit expression levels, and adds another layer of knowledge about the neuropharmacological mechanisms of ethanol. It is quite possible that further elucidation of the complex molecular “systems level” analysis of ethanol's actions in nerve cells may yield important “systems level” approaches and advances for the treatment of alcohol abuse and dependence.

Transcranial Focused Ultrasound to the Thalamus Is Associated with Reduced Extracellular GABA Levels in Rats

Objective: Transcranial focused ultrasound (FUS), with its ability to non-invasively modulate the excitability of region-specific brain areas, is gaining attention as a potential neurotherapeutic modality. The aim of this study was to examine whether or not FUS administered to the brain could alter the extracellular levels of glutamate and γ-aminobutyric acid (GABA), which are representative excitatory and inhibitory amino acid neurotransmitters, respectively. Methods: FUS, delivered in the form of a train of pulses, was applied to the thalamus of Sprague-Dawley rats transcranially. Glutamate and GABA were directly sampled from the frontal lobe of the rat brain via a direct microdialysis technique before, during, and after the sonication. The dialysate concentrations were determined by high-performance liquid chromatography. Results: The individual levels of the neurotransmitters sampled were normalized to the baseline level for each rat. In terms of the changes in extracellular glutamate levels, there was no difference between the FUS-treated group and the unsonicated control group. However, extracellular GABA levels started to decrease upon sonication and remained reduced (approximately 20% below baseline; repeated-measures ANOVA, p < 0.05, adjusted for multiple comparisons) compared to the control group. Conclusion: The ability to modulate region-specific brain activity, along with the present evidence of the ability to modulate neurotransmission, demonstrates the potential utility of FUS as a completely new non-invasive therapeutic modality.

Coordinated modulation of cellular signaling through ligand-gated ion channels in Hydra vulgaris (Cnidaria, Hydrozoa)

Cnidarians lack well developed organs, but they have evolved the molecular and cellular components needed to assemble a nervous system. The apparent 'simplicity' of the cnidarian nervous net does not occur at the cellular level, but rather in the organisation of conducting systems. Cnidarian neurons are in fact electrically excitable, show the typical extended morphology and are connected by chemical synapses or gap junctions. They have been regarded as peptidergic, given the wealth of neuropeptides generally distributed along neurites and in cell bodies, supporting the hypothesis of a modulatory role in neurotransmission. However, the presence of clear-cored, as well as dense-cored synaptic vesicles in cnidarian neurons suggests both fast and slow synaptic transmission mechanisms. In fact, biochemical and functional evidence indicates that classical neurotransmitters and their metabolic partners are present in cnidarian tissues, where they are involved in coordinating motility and behavior. We have identified and characterized in Hydra tissues receptors to the inhibitory and excitatory amino acid neurotransmitters, GABA, glycine and NMDA, that are similar to mammalian ionotropic receptors in terms of their biochemical and pharmacological properties. These receptors appear to regulate pacemaker activities and their physiological correlates; in the live animal, they also affect feeding behavior, namely the duration and termination of the response elicited by reduced glutathione, with opposite actions of GABA and glycine or NMDA, respectively. These results suggest that modulation of cellular signaling through ligand-gated-ion channels is an ancient characteristic in the animal kingdom, and that the pharmacological properties of these receptors have been highly conserved during evolution.

Anterior Cingulate Cortexγ-Aminobutyric Acid in Depressed Adolescents

Anhedonia, a core symptom of major depressive disorder (MDD) and highly variable among adolescents with MDD, may involve alterations in the major inhibitory amino acid neurotransmitter system of γ-aminobutyric acid (GABA). To test whether anterior cingulate cortex (ACC) GABA levels, measured by proton magnetic resonance spectroscopy, are decreased in adolescents with MDD. The associations of GABA alterations with the presence and severity of anhedonia were explored. Case-control, cross-sectional study using single-voxel proton magnetic resonance spectroscopy at 3 T. Two clinical research divisions at 2 teaching hospitals. Twenty psychotropic medication-free adolescents with MDD (10 anhedonic, 12 female, aged 12-19 years) with episode duration of 8 weeks or more and 21 control subjects group matched for sex and age. Anterior cingulate cortex GABA levels expressed as ratios relative to unsuppressed voxel tissue water (w) and anhedonia scores expressed as a continuous variable. Compared with control subjects, adolescents with MDD had significantly decreased ACC GABA/w (t=3.2; P<.003). When subjects with MDD were categorized based on the presence of anhedonia, only anhedonic patients had decreased GABA/w levels compared with control subjects (t=4.08; P<.001; P(Tukey)<.001). Anterior cingulate cortex GABA/w levels were negatively correlated with anhedonia scores for the whole MDD group (r=-0.50; P=.02), as well as for the entire participant sample including the control subjects (r=-0.54; P<.001). Anterior cingulate cortex white matter was also significantly decreased in adolescents with MDD compared with controls (P=.04). These findings suggest that GABA, the major inhibitory neurotransmitter in the brain, may be implicated in adolescent MDD and, more specifically, in those with anhedonia. In addition, use of a continuous rather than categorical scale of anhedonia, as in the present study, may permit greater specificity in evaluating this important clinical feature.