Increased GABA Levels Research Articles

In situ production of γ-aminobutyric acid in breakfast cereals

Breakfast cereals are an important part of an equilibrated diet in the Western world, making them extremely suited for carrying health benefits. Intake of γ-aminobutyric acid (GABA), a major inhibitory neurotransmitter of the nervous system, has been related to blood pressure lowering in hypertensive individuals. In vivo, GABA is formed from glutamic acid (GA) by glutamic acid decarboxylase (GAD), a widely distributed enzyme in prokaryotic and eukaryotic species. We here enriched breakfast cereals with GABA by recipe and process optimisation. The dynamics of GA and GABA were monitored throughout the production process. Addition of exogenous recombinantly produced GAD of Yersinia intermedia increased GABA levels by 2- to 5-fold. As only trace levels of GABA (<15ppm) and relatively low levels of its precursor (GA, <100ppm) are present in the wheat and rice flour used, a well-thought ingredient choice (inclusion of quinoa flour (ca. 90ppm GABA and 700ppm GA) or bran enrichment (ca. 66ppm GABA and 500ppm GA)) also significantly increases the GABA content in the final flakes. Finally, a strict control of the heating steps during the production process reduces GA and GABA losses. Consumption of one portion (30g) of the here produced enriched breakfast cereals can even meet up to 55% of the daily intake earlier reported to lower blood pressure (ca. 10mg).

Ultrastructural GABA immunocytochemistry in the mossy fiber terminals of Wistar and genetic absence epileptic rats receiving amygdaloid kindling stimulations

The existence of absence epilepsy and temporal lobe epilepsy in the same patient is not common in clinical practice. The reason why both types of seizures are rarely seen in the same patient is not well understood. Therefore, we aimed to investigate kindling in a well known model of human absence epilepsy, genetic absence epilepsy rats from Strasbourg (GAERS). In the present study, we analyzed whether the GABA content of GAERS that received kindling stimulations was altered in the hippocampal mossy fiber terminals compared to non-epileptic control (NEC) Wistar rats. For this purpose, we used an immunocytochemical technique at the ultrastructural level. Ultrathin sections were immunolabeled with anti-GABA antibody and transmission electron microscopy was used for the ultrastructural examination. The number of gold particles per nerve terminal was counted and the area of the nerve terminal was determined using NIH image analysis program. The GABA density was found to be higher in sham-operated GAERS than sham-operated Wistar rats. The density was increased in kindling Wistar group compared to sham-operated Wistar and kindling GAERS groups. No statistical difference was observed between sham-operated GAERS and kindling GAERS groups. The increase in GABA levels in stimulated Wistar rats may be a result of a protective mechanism. Furthermore, there may be strain differences between Wistar rats and GAERS and our findings addressing different epileptogenesis mechanisms in these strains might be a basis for future experimental studies.

Binge toluene exposure alters glutamate, glutamine and GABA in the adolescent rat brain as measured by proton magnetic resonance spectroscopy

Despite the high incidence of toluene abuse in adolescents, little is known regarding the effect of binge exposure on neurochemical profiles during this developmental stage. In the current study, the effects of binge toluene exposure during adolescence on neurotransmitter levels were determined using high-resolution proton magnetic resonance spectroscopy ex vivo at 11.7T. Adolescent male Sprague-Dawley rats were exposed to toluene (0, 8000, or 12,000ppm) for 15min twice daily from postnatal day 28 (P28) through P34 and then euthanized either 1 or 7 days later (on P35 or P42) to assess glutamate (GLU), glutamine, and GABA levels in intact tissue punches from the medial prefrontal cortex (mPFC), anterior striatum and hippocampus. In the mPFC, toluene reduced GLU 1 day after exposure, with no effect on GABA, while after 7 days, GLU was no longer affected but there was an increase in GABA levels. In the hippocampus, neither GABA nor GLU was altered 1 day after exposure, whereas 7 days after exposure, increases were observed in GABA and GLU. Striatal GLU and GABA levels measured after either 1 or 7 days were not altered after toluene exposure. These findings show that 1 week of binge toluene inhalation selectively alters these neurotransmitters in the mPFC and hippocampus in adolescent rats, and that some of these effects endure at least 1 week after the exposure. The results suggest that age-dependent, differential neurochemical responses to toluene may contribute to the unique behavioral patterns associated with drug abuse among older children and young teens.

Effects of Melissa officinalis L. (Lemon Balm) Extract on Neurogenesis Associated with Serum Corticosterone and GABA in the Mouse Dentate Gyrus

Lemon balm, leaves of Melissa officinalis L., has been used for anti-anxiety and spasmolytics. We observed the extract of Melissa officinalis L. (MOE) on cell proliferation and neuroblast differentiation in the hippocampal dentate gyrus (DG) of middle-aged mice (12 months of age) using Ki67 and doublecortin (DCX), respectively. We also observed changes in corticosterone, GAD67 and GABA-transaminase (GABA-T) to check their possible mechanisms related to neurogenesis. We administered 50 or 200 mg/kg MOE to the animals once a day for 3 weeks. For labeling of newly generated cells, we also administered 5-bromodeoxyuridine (BrdU) twice a day for 3 days from the day of the first MOE treatment. Administration of 50 or 200 mg/kg MOE dose-dependently increased Ki67 positive nuclei to 244.1 and 763.9% of the vehicle-treated group, respectively. In addition, 50 or 200 mg/kg MOE significantly increased DCX positive neuroblasts with well-developed (tertiary) dendrites. Furthermore, MOE administration significantly increased BrdU/calbindin D-28 k double labeled cells (integrated neurons into granule cells in the DG) to 245.2% of the vehicle-treated group. On the other hand, administration of MOE reduced corticosterone levels in serum and decreased GABA-T levels in the DG homogenates. These results suggest that MOE increases cell proliferation, neuroblast differentiation and integration into granule cells by decreasing serum corticosterone levels as well as by increasing GABA levels in the mouse DG.

Effects of valproate on neurotransmission associated with ryanodine receptors

To clarify the antiepileptic mechanisms of valproate (VPA), we determined the effects of acute and sub-acute administrations of VPA on ryanodine receptor (RyR)-associated hippocampal releases of GABA and glutamate using microdialysis, as well expression of mRNA and protein of RyR subtypes in the rat hippocampus. Acute administration of therapeutic-relevant VPA did not affect the hippocampal extracellular levels of GABA or glutamate, whereas sub-acute administration increased GABA level without affecting that of glutamate. Perfusion with ryanodine increased the hippocampal extracellular level of glutamate (ryanodine concentration range: 1–1000 μM) concentration-dependently; however, that of GABA was increased by 1–100 μM ryanodine concentration-dependently but the stimulatory effects of 1000 μM ryanodine on GABA release was not observed. Both acute and sub-acute administrations of therapeutic-relevant VPA inhibited ryanodine-induced responses of hippocampal extracellular glutamate level without affecting that of GABA. Especially, both acute and sub-acute administrations of VPA prevented the breakdown of GABA release induced by 1000 μM ryanodine. Sub-acute administration of therapeutically-relevant dose VPA weakly increased RyR mRNA expression but we could not detect the changes of RyR protein expression in rat hippocampus. These results suggest that VPA inhibited the neurotransmitter release associated with RyR without affecting the expression of RyR protein. Therefore, the antiepileptic action of VPA seems to be mediated, at least in part, by an increase in basal GABA release and inhibition of RyR-associated glutamate release.

High γ-aminobutyric acid content, a novel component associated with resistance to abamectin in Tetranychus cinnabarinus (Boisduval)

An abamectin-resistant strain of Tetranychus cinnabarinus (Boisduval) (Rf=25.3) was selected in laboratory. We compared the γ-aminobutyric acid (GABA) content in abamectin-susceptible T. cinnabarinus individuals with that in resistant individuals and investigated its relationship to abamectin resistance. High performance liquid chromatography (HPLC) was used to ascertain GABA content in abamectin-susceptible (SS) and resistant (AR) strains of T. cinnabarinus. The results indicate that GABA content in the AR was significantly higher than that in the SS (1.39-fold). AR individuals treated with a sublethal dose of abamectin did not show significant differences in GABA levels compared with AR individuals that were not treated with abamectin. However in the SS, abamectin treated individuals had a significantly higher GABA content than those that were untreated (1.52-fold). Individuals in the SS that survived from selection with LC95 of abamectin (SS–AR) showed significantly higher GABA levels compared to SS (1.41-fold). Similarly, progenies of the SS–AR parental generation (SS–ARF1) also showed increased GABA levels (1.51-fold) compared to SS. In addition, behavioral observations have shown that all individuals from the AR, SS–AR and SS–ARF1, which had more GABA content than the SS, demonstrated a significant decrease in crawling speed compared with SS individuals. This observation is consistent with excessive GABA levels had inhibitory effect on the central nervous system. Thus, we postulate that increasing GABA content in T. cinnabarinus is associated with resistance against abamectin.

Effects of chronic administration of Melissa officinalis L. extract on anxiety-like reactivity and on circadian and exploratory activities in mice

This study aimed to determine the effects of chronic (15 consecutive days of treatment) per os administration of Melissa officinalis L. extract (Cyracos, Naturex) on anxiety-like reactivity in mice. As measured by HPLC, Cyracos contains significant amounts of rosmarinic acid and the triterpenoids oleanolic acid and ursolic acid, which inhibit gamma-aminobutyric acid transaminase (GABA-T) activity and increase GABA levels in the brain (Awad et al., 2007; Awad et al., 2009). Thus, we evaluated Cyracos use in independent groups of C57BL/6 mice with regard to anxiety-like reactivity in an elevated plus maze and an open field task. We found that Cyracos significantly reduced anxiety-like reactivity in the elevated plus maze dose-dependently, but no significant effect was observed in the open field task. Parallel experiments in independent groups of mice showed that the Cyracosdose at which it exerted anxiolytic-like effects in the elevated plus maze did not alter exploratory or circadian activities. Therefore, our results demonstrate that Cyracos has anxiolytic-like effects under moderate stress conditions and does not alter activity levels.

Pharmacological characterization of GABAA receptors in taurine-fed mice

BackgroundTaurine is one of the most abundant free amino acids especially in excitable tissues, with wide physiological actions. Chronic supplementation of taurine in drinking water to mice increases brain excitability mainly through alterations in the inhibitory GABAergic system. These changes include elevated expression level of glutamic acid decarboxylase (GAD) and increased levels of GABA. Additionally we reported that GABAA receptors were down regulated with chronic administration of taurine. Here, we investigated pharmacologically the functional significance of decreased / or change in subunit composition of the GABAA receptors by determining the threshold for picrotoxin-induced seizures. Picrotoxin, an antagonist of GABAA receptors that blocks the channels while in the open state, binds within the pore of the channel between the β2 and β3 subunits. These are the same subunits to which GABA and presumably taurine binds.MethodsTwo-month-old male FVB/NJ mice were subcutaneously injected with picrotoxin (5 mg kg-1) and observed for a) latency until seizures began, b) duration of seizures, and c) frequency of seizures. For taurine treatment, mice were either fed taurine in drinking water (0.05%) or injected (43 mg/kg) 15 min prior to picrotoxin injection.ResultsWe found that taurine-fed mice are resistant to picrotoxin-induced seizures when compared to age-matched controls, as measured by increased latency to seizure, decreased occurrence of seizures and reduced mortality rate. In the picrotoxin-treated animals, latency and duration were significantly shorter than in taurine-treated animas. Injection of taurine 15 min before picrotoxin significantly delayed seizure onset, as did chronic administration of taurine in the diet. Further, taurine treatment significantly increased survival rates compared to the picrotoxin-treated mice.ConclusionsWe suggest that the elevated threshold for picrotoxin-induced seizures in taurine-fed mice is due to the reduced binding sites available for picrotoxin binding due to the reduced expression of the beta subunits of the GABAA receptor. The delayed effects of picrotoxin after acute taurine injection may indicate that the two molecules are competing for the same binding site on the GABAA receptor. Thus, taurine-fed mice have a functional alteration in the GABAergic system. These include: increased GAD expression, increased GABA levels, and changes in subunit composition of the GABAA receptors. Such a finding is relevant in conditions where agonists of GABAA receptors, such as anesthetics, are administered.

GABA in pedunculopontine tegmentum increases rapid eye movement sleep in freely moving rats: possible role of GABA-ergic inputs from substantia nigra pars reticulata

Pedunculopontine tegmentum (PPT) has GABA-ergic neurons and receives GABA-ergic projections from substantia nigra pars reticulata (SNrpr). Based on the recent studies from our and other laboratories, it was hypothesized that GABA in PPT promotes rapid eye movement (REM) sleep. In order to further study the role of GABA in PPT in REM sleep regulation, we microinjected GABA-A agonist, muscimol (200 nL, 3.5 mM), into the PPT. Muscimol in PPT significantly enhanced the amount of REM sleep by increasing the mean number of REM sleep bouts. Besides the local interneurons, GABA-ergic afferents from SNrpr are another source of GABA in PPT. In order to understand the contribution of GABA-ergic inputs from SNrpr into PPT for REM sleep regulation, SNrpr was electrically stimulated either alone or simultaneously along with the infusion of GABA-A antagonist, picrotoxin (200 nL, 0.86 mM), into the PPT. The experiment was designed with the premise that stimulation of SNrpr should increase GABA levels in PPT which should increase REM sleep comparable to that after muscimol microinjection in PPT. Further, the effect of stimulation of SNrpr on REM sleep should be antagonized by simultaneous infusion of picrotoxin into PPT. The electrical stimulation of SNrpr did not produce any significant change in sleep–wake states although it was sufficient to counter the effect of picrotoxin injection into the PPT. To overcome the limitations and confounds of electrical stimulation, SNrpr was pharmacologically stimulated by glutamate microinjection (200 nL, 5.34 mM). Infusion of glutamate into SNrpr enhanced REM sleep by increasing the mean number of REM sleep bouts, which was similar and comparable to the effect of muscimol injection into the PPT. The results confirm that GABA in PPT either from local neurons or from SNrpr promotes REM sleep.

Vigabatrin: effect on brain GABA levels measured by nuclear magnetic resonance spectroscopy.

Vigabatrin is undoubtedly one of the most exciting anti-epilepsy drugs in use today. Many open and controlled clinical trials have confirmed that it is particularly effective in controlling partial epileptic seizures with or without secondary generalization. Vigabatrin acts to increase GABA levels in the presynaptic nerve terminal by inhibiting the activity of GABA-transaminase. There is no direct correlation between the blood or brain concentration of vigabatrin and its clinical effect, so monitoring vigabatrin levels is not predictive of patient response. However, it is possible to relate the activity of vigabatrin to levels of GABA in the brain, measured by nuclear magnetic resonance spectroscopy (NMRS). NMRS studies show that following administration of vigabatrin, brain concentrations of GABA rise to about 2-3 times their baseline values. This 'extra' GABA is held within the nerve terminal, and is only released during synaptic transmission. Although there appears to be a clear dose-response relationship up to 3 g/day, it is not well documented if higher doses result in proportionately higher brain GABA levels. This finding seems to support the results of clinical studies suggesting that the optimal dose of vigabatrin may be 3 g/day. There is also some evidence for a correlation between the concentration of GABA in the brain and the clinical outcome. Continuing investigations using NMRS aim to confirm these preliminary findings, and to determine the time course and extent of changes in brain GABA levels after vigabatrin administration.

This Month in Anesthesiology

Mechanisms underlying the alleged cancer-promoting effects of blood transfusion are unknown, including the involvement of donors' leukocytes, erythrocytes, and soluble factors. Two tumor models were used in rats to study the impact of blood transfusion on the host ability to clear circulating cancer cells and host survival rates. The potential deleterious characteristics of the transfusion were also studied. Blood transfusion, in conjunction with blood storage time, was found to be an independent and significant risk factor for cancer progression, and aged erythrocytes mediated the effects. In rats, transfusion of fresh blood is less harmful than transfusion of stored blood. These results have implications for cancer patients receiving erythrocyte transfusions. See the accompanying Editorial View on page 951 This study examined the effect of isoflurane on γ-aminobutyric acid (GABA) levels in pontine reticular formation and the effect of drugs that increase or decrease GABA levels in the pontine reticular formation in experimental animals. Compared with wakefulness, GABA levels were significantly decreased by isoflurane. Nipecotic acid increased GABA levels and increased isoflurane induction time, whereas 3-mercaptopropionic acid decreased GABA levels and decreased isoflurane induction time. These results indicate that decreasing rather than increasing pontine reticular formation GABA levels is one mechanism by which isoflurane causes loss of consciousness and altered cortical excitability. See the accompanying Editorial View on page 948 Using a new risk scale developed for children, the effect size was calculated for treatments recommended for the pediatric population in the new Guidelines for the Management of Postoperative Nausea and Vomiting. Six single-drug therapies and five combination treatments were analyzed for risk reduction. With single-agent therapy using the 5-hydroxytryptamine receptor antagonists or dexamethasone, a 50–60% relative risk reduction is expected. Droperidol offers only a 40% decrease. With the combinations of a 5-hydroxytryptamine receptor antagonist and dexamethasone, a relative risk reduction in vomiting of about 80% is expected.In the senescent heart, β-adrenergic responsiveness is altered in parallel with β1- and β2-adrenoceptor down-regulation. This study tested the hypothesis that the β3-adrenoceptor plays a role in β-adrenergic receptor dysfunction in the senescent heart. β-adrenergic responses were investigated in vivo using echocardiography and in vitro using isolated left ventricular papillary muscle in young adult and senescent rats. An impaired positive inotropic effect in parallel with β3-adrenoceptor up-regulation was confirmed in senescent hearts both in vivo and in vitro . In the senescent group, the positive inotropic effect of β-adrenergic agonists was partially restored by nitric oxide synthase inhibitors. This was not the case in the young adult group. These results indicate β3-adrenoceptor overexpression plays a role in the altered β-adrenergic response in senescent cardiomyopathy via the induction of nitric oxide. See the accompanying Editorial View on page 956 Supervision of anesthesia residents by an attending anesthesiologist is associated with a decreased incidence of complications during emergent intubations outside the operating room. See the accompanying Editorial View on page 945 Training for fiberoptic orotracheal intubation using a high-fidelity simulator was not different than training with a low-fidelity simulator.Desmopressin is associated with a significant reduction in transfusion of blood products.This review evaluates different methods for determination of sympathetic nervous system activity and describes its role in human neurohumoral circulatory control. The effects of general anesthesia on sympathetic nervous system activity and their relevance for clinical anesthesia are discussed.

Interaction between GABA and norepinephrine in interleukin-1β-induced suppression of the luteinizing hormone surge

Interleukin-1β (IL-1β), a cytokine that is closely associated with inflammation and immune stress, is known to interfere with reproductive functions. Earlier studies have demonstrated that IL-1β inhibits the luteinizing hormone (LH) surge during the afternoon of proestrus in female rats. We have shown that this effect is most probably mediated through a reduction in norepinephrine (NE) levels in the medial preoptic area (MPA) of the hypothalamus. However, the mechanism by which IL-1β decreases NE levels in the MPA is unclear. We hypothesized that the inhibitory neurotransmitter, GABA could play a role in decreasing NE levels in the MPA. To test this, ovariectomized, steroid-primed rats were injected (i.p.) with either PBS–BSA (control) or 5 μg of IL-1β, alone or in combination with i.c.v. administration of GABA-A and GABA-B receptor antagonists, Bicuculline and CGP 35348 (CGP) respectively. Animals were subjected to push–pull perfusion of the MPA and perfusates collected at 30 min intervals were analyzed for both NE and GABA levels using HPLC-EC. Simultaneously, serial plasma samples were obtained through jugular catheters and were analyzed for LH levels using RIA. Compared to control rats, NE levels decreased significantly in the MPA in IL-1β-treated rats ( p < 0.05). Concurrently, there was a significant increase in GABA levels in the MPA ( p < 0.05). The GABA-A receptor antagonist, bicuculline, was able to reverse the effect of IL-1β on NE and LH, while the GABA-B receptor antagonist, CGP 35348 was without any effect. This leads us to conclude that the IL-1β-induced suppression of the LH surge is most probably mediated through an increase in GABA levels in the MPA which causes a reduction in NE levels. This is probably one of the mechanisms by which IL-1β inhibits reproductive functions.

Chronic nicotine modifies the effects of morphine on extracellular striatal dopamine and ventral tegmental GABA

Previously, we have shown that 7-week oral nicotine treatment enhances morphine-induced behaviors and dopaminergic activity in the mouse brain. In this study, we further characterized the nicotine-morphine interaction in the mesolimbic and nigrostriatal dopaminergic systems, as well as in the GABAergic control of these systems. In nicotine-pretreated mice, morphine-induced dopamine release in the caudate putamen and nucleus accumbens was significantly augmented, as measured by microdialysis. Chronic nicotine treatment did not change basal extracellular concentrations of dopamine and its metabolites in the caudate putamen and nucleus accumbens, nor did it affect the rate of dopamine synthesis, as assessed by 3-hydroxybenzylhydrazine dihydrochloride-induced DOPA accumulation. GABAergic control of dopaminergic activity was studied by measuring extracellular GABA in the presence of nipecotic acid, an inhibitor of GABA uptake. Acute (0.3 mg/kg or 0.5 mg/kg i.p.) and chronic nicotine, as well as morphine (15 mg/kg s.c.) in control mice decreased nipecotic acid-induced increase in extracellular GABA in the ventral tegmental area/substantia nigra (VTA/SN). In contrast, in nicotine-treated mice, morphine increased GABA levels in the presence of nipecotic acid. We did not find any alterations in GABA(B)-receptor function after chronic nicotine treatment. Thus, our data show that chronic nicotine treatment sensitizes dopaminergic systems to morphine and affects GABAergic systems in the VTA/SN.

Extracellular levels of brain aspartate, glutamate and GABA during an inhibitory avoidance response in the rat

The extracellular levels of aspartate, glutamate and GABA were measured by microdialysis, coupled with an HPLC method, in rat prefrontal cortex (mPFC) and ventral hippocampus (VH) before and during the performance of a step-down inhibitory task. The basal levels of glutamate were about 50% higher than those of aspartate, and GABA levels were about 20-folds smaller than those of the excitatory amino acids. There were no significant differences in the basal levels of any of the three amino acids between the two brain regions. The extracellular levels of aspartate increased during acquisition and recall trials in both VH and mPFC, whereas those of glutamate increased in the VH during acquisition only. A significant increase in GABA levels was also detected during acquisition but only in the mPFC. The neuronal origin of the increased extracellular levels of aspartate, glutamate and GABA was demonstrated by administering tetrodotoxin directly into the mPFC or VH by reverse dialysis. These findings, together with previous evidence from our and other laboratories, indicate a differential release of aspartate and glutamate from excitatory neurons during the performance of behavioral responses, and therefore, distinct roles for the two excitatory amino acids should be envisaged.

Tiagabine Increases [11C]flumazenil Binding in Cortical Brain Regions in Healthy Control Subjects

Accumulating evidence indicates that synchronization of cortical neuronal activity at gamma-band frequencies is important for various types of perceptual and cognitive processes and that GABA-A receptor-mediated transmission is required for the induction of these network oscillations. In turn, the abnormalities in GABA transmission postulated to play a role in psychiatric conditions such as schizophrenia might contribute to the cognitive deficits seen in this illness. We measured the ability to increase GABA in eight healthy subjects by comparing the binding of [(11)C]flumazenil, a positron emission tomography (PET) radiotracer specific for the benzodiazepine (BDZ) site, at baseline and in the presence of an acute elevation in GABA levels through the blockade of the GABA membrane transporter (GAT1). Preclinical work suggests that increased GABA levels enhance the affinity of GABA-A receptors for BDZ ligands (termed 'GABA shift'). Theoretically, such an increase in the affinity of GABA-A receptors should be detected as an increase in the binding of a GABA-A BDZ-receptor site-specific PET radioligand. GAT1 blockade resulted in significant increases in mean (+/- SD) [(11)C]flumazenil-binding potential (BP(ND)) over baseline in brain regions representing the major functional domains of the cerebral cortex: association cortex +15.2+/-20.2% (p=0.05), sensory cortex +13.5+/-15.5% (p=0.03) and limbic (medial temporal lobe, MTL) +16.4+/-20.2% (p=0.03). The increase in [(11)C]flumazenil-BP(ND) was not accounted for by differences in the plasma-free fraction (f(P); paired t-test p=0.24) or changes in the nonspecific binding (pons V(T), p=0.73). Moreover, the ability to increase GABA strongly predicted (r=0.85, p=0.015) the ability to entrain cortical networks, measured through EEG gamma synchrony during a cognitive control task in these same subjects. Although additional studies are necessary to further validate this technique, these data provide preliminary evidence of the ability to measure in vivo, with PET, acute fluctuations in extracellular GABA levels and provide the first in vivo documentation of a relationship between GABA neurotransmission and EEG gamma-band power in humans.

Diabetes affects the expression of GABA and potassium chloride cotransporter in the spinal cord: A study in streptozotocin diabetic rats

Painful diabetic neuropathy is associated to hyperexcitability and spontaneous hyperactivity of spinal cord neurons. The underlying pathophysiological mechanisms are not clear. Increases in excitatory neurotransmission at the spinal cord, involving glutamate and SP, seem to account for the abnormal neuronal activity, but inhibitory influences were never evaluated. This study aims to analyse the expression of GABA, its synthesizing enzyme glutamic acid decarboxylase (GAD) and the potassium chloride cotransporter (KCC2), in the spinal dorsal horn of streptozotocin (STZ)-induced diabetic rats. Four weeks after saline or STZ (60mg/kg) injection, animals were sacrificed and the spinal segments L2-L3 were removed and immunoreacted for GABA, GAD and KCC2, or processed for western blotting for KCC2. Densitometric quantification was performed in the superficial dorsal horn (laminae I, II and III) of immunoreacted sections and in the immunoblots. STZ rats presented a significant increase of GABA expression in laminae II and III when compared with control animals, while no differences were detected in GAD expression. A significant decrease in KCC2 expression was detected by immunohistochemistry in laminae I and II, which was confirmed by immunoblotting. Increased GABA levels, along with decrease in KCC2 expression, may underlie the abnormal neuronal activity detected in the spinal cord of diabetic rats. Reduction in KCC2 expression was shown to lead to increases in intracellular chloride concentration and, in such condition, GABA binding to GABA(A) receptor induces membrane depolarization, provoking neuronal excitation rather than inhibition. Based on these findings, we propose that a loss of GABA-mediated inhibitory tone at the spinal cord may result in neuronal hyperexcitability and spontaneous hyperactivity during diabetes.

Endocannabinoid Signaling Mediates Cocaine-Induced Inhibitory Synaptic Plasticity in Midbrain Dopamine Neurons

Drugs that increase GABA levels in the brain reduce cocaine seeking in rodents and humans, suggesting that GABAergic inhibition regulates cocaine-seeking behavior. We previously reported that repeated cocaine exposure in vivo facilitates long-term potentiation by reducing the strength of GABAergic inhibition in dopamine neurons of the ventral tegmental area (VTA). Selective blockade of cocaine-induced reduction of GABAergic inhibition in the VTA might diminish cocaine-induced aberrant synaptic plasticity and addictive behavior. Here, we investigated the mechanism for cocaine-induced reduction of GABAergic inhibition. We show that a pathophysiologically relevant concentration of cocaine enables a normally ineffective stimulus to induce long-term depression (LTD) of IPSCs (I-LTD) in VTA dopamine neurons of midbrain slices. Activation of D2 dopamine receptors and group I metabotropic glutamate receptors and subsequent recruitment of endocannabinoid signaling are required for I-LTD induction. We further demonstrate that in vivo pretreatment with antagonists to these receptors blocks cocaine-induced reduction of GABAergic inhibition and that repeated cocaine exposure in vivo occludes the subsequent induction of I-LTD ex vivo. Together, these results suggest that repeated cocaine exposure reduces the strength of GABAergic inhibition in dopamine neurons by inducing I-LTD-like modification in vivo.

Quantitation of brain metabolites by HRMAS-NMR spectroscopy in rats exposed to sublethal irradiation.

Puropose : In the event of an acute total-body irradiation, whatever it is therapeutic or accidental, the physiopathology explaining the long-term neurological effects is unknown. We have developed a model of adult rats for which frequent behavioral assays were performed before and after a non-lethal whole-body ionizing radiation (60Co, 4,5 Gy). Learning and memory processing is an aspect of cognition involving mainly the hippocampus. We used high-resolution magic angle spinning (HRMAS) 1H NMR spectroscopy to characterize the biochemistry of four specific brain regions. The biological data for each animal will be compared to their behavioral performances, in order to underline any possible correlations. The best understanding of the physiopathological process in the Central Nervous System (CNS) will allow determining some prevention means or some enhancements for the radio-induced neurological late effects. Experimental procedures: Twenty male Wistar rats were experimented for each sample period, among which ten were gamma radiated (4.5 Gy). The cerebral structures (cortex, striata, anterior and posterior hippocampus, hypothalamus) were removed at three times: 48 hours, 8 days and 30 days after radiation. The HRMAS 1H NMR experiments were performed on a Bruker DRX Avance spectrometer at 9.4 T. Samples were spun at 4 kHz and the temperature maintained at 4°C. A spin-echo sequence with a 30ms total echo time was used. Eighteen metabolites were included in the basis. They were quantitated using the quest procedure of JMRUI software, and statistically analyzed. Moreover, another group of animals was radiated and tested in the same conditions. Then a immuno-histological study of apoptosis and neurogenesis events in the CNS was made at the same removal times. Results: NMR HRMAS results present significant differences (p<0.05) between the radiated group and the non-radiated one. GPC decreased at 48 hours post-radiation whereas Cho and PC increased, potentially with relation to a cerebral oedema. At Day-8, a decrease of Gly and Tau, and an increase in Gln, are observed in the posterior hippocampus. One month after total body irradiation, we observe an increase of GABA in cortex and striatum. Perspectives: The behavioral data, showing a significant difference in the cognitive capacities of the rats between the radiated group and the witnesses at one month, may suggest that relevant correlations are possible with biochemical and morphological modifications of the CNS. For example, the increase in GABA levels in cortex and striatum might explain the least performances of learning test.

The ability to increase extracellular GABA predicts frontal cortical gamma synchrony

Introduction: Accumulating evidence indicates that synchronization of cortical neuronal activity at gamma-band frequencies is important for various types of perceptual and cognitive processes. Experimental models as well as preclinical studies suggest that GABAA receptor-mediated transmission is required for the induction of network oscillations. However, to date, there is no evidence linking GABA transmission with gamma-band oscillations in humans. Here we show that the ability to increase extracellular GABA levels predicts frontal cortical gamma synchrony in healthy controls. Preclinical and prior imaging work suggests that increased GABA levels enhance the affinity of GABAA receptors for benzodiazepine (BDZ) ligands via a conformational change (termed the ‘GABA-shift’). Theoretically, such an increase in affinity of GABAA receptors should be detected as an increase in the binding of a GABAA BDZ-receptor site-specific PET radioligand.

Group III metabotropic glutamate receptors act as hetero-receptors modulating evoked GABA release in the globus pallidus in vivo

In vitro studies suggest that group III metabotropic glutamate (mGlu) receptors function as hetero-receptors to modulate GABA release within the globus pallidus. In the present study we examined this hypothesis in vivo, using microdialysis to assess the ability of locally infused group III mGlu receptor agonists to modulate KCl-evoked GABA release in the globus pallidus of anaesthetised rats. Extra-cellular levels of GABA in dialysate samples were assayed using High Pressure Liquid Chromatography (HPLC) coupled to electrochemical detection. Infusion of KCl (50–100 mM) evoked a dose-dependent increase in GABA levels in the globus pallidus. Addition of the group III mGlu receptor agonists l-AP4 (30 and 300 μM) and l-SOP (3–300 μM) significantly reduced the extra-synaptic levels of GABA that resulted after 100 mM KCl challenge. The effect of l-SOP (30 μM) was almost totally abolished by co-infusion with M-SOP (30 μM). These data confirm that activation of group III mGlu receptors inhibits GABA release in the globus pallidus, thereby supporting their hetero-receptor role in vivo.