Effects of GABA natriuresis induced centrally by cholinergic stimulation

Sodium and potassium excretion and urine output have been studied in rats following water loading and intracerebroventricular (i.c.v.) injection of isotonic saline (NaCl-0.15M), gamma-amino butyric acid (GABA), picrotoxin, carbachol, GABA plus picrotoxin, GABA plus carbachol and GABA plus atropine. GABA injection decreased sodium and potassium excretion. Picrotoxin or carbachol injection elicited natriuresis and kaliuresis. GABA injection decreased the effects of the carbachol and atropine injection decreased the effects of the GABA on sodium and potassium excretion. These results suggest an interaction between gabaergic and cholinergic pathways in the control of sodium and potassium excretion.     

Induction of oral dyskinesias in naive rats by D1 stimulation

Repetitious opening and closing of the mouth and high frequency clonic jaw movements were observed in rats challenged with dopamine agonists after acute treatment with sulpiride or a low dose of spiroperidol. SKF 38393, a specific D1 receptor agonist, alone, also induced these behaviors and cis-flupenthixol blocked them, evidence suggesting D1 dopamine receptor mediation.     

GABA concentrations in the striatum following repetitive cerebral ischemia

GABAergic neurons in the striatum are very sensitive to the effects of ischemia. The progressive decline in striatal GABA following transient forebrain ischemia in gerbils may be secondary to either a decreased production or an increase in reuptake mechanisms or both. The current experiment was designed to evaluate release of GABA by stimulation with K+ or inhibition of its uptake with nipecotic acid or their combination (K+ nipecotic) after repetitive forebrain ischemia in gerbils by in-vivo microdialysis on Days 1, 3, 5, and 14 following the insult. Infusion of nipecotic acid or potassium chloride, resulted in a significant increase in extracellular GABA. This response was significantly decreased in the post-ischemic animals. The synergistic effect of increased GABA concentrations by the infusion of nipecotic acid+potassium chloride seen in the controls was not evident in the post-ischemic animals. In conclusion, though there is a reduction in the extracellular GABA concentrations in the first week following an ischemic insult, restorative mechanisms are operative in the second week as seen by the increasing GABA concentrations.     

甲醛致炎痛对大鼠远位触液神经元γ-氨基丁酸表达的影响

目的：观察甲醛致炎痛对大鼠远位触液神经元的γ-氨基丁酸（GABA）表达。方法：SD大鼠甲醛致痛后,观察行为学变化,并采用CB-HRP/GABA双重标记技术分别观察大鼠远位触液神经元中GABA表达的变化。结果：甲醛致痛后,6h远位触液神经元内GABA增加,24h最为显著,48h恢复至正常水平。与空白对照组相比有显著差异（P〈0.05）。结论：甲醛致炎痛后大鼠远位触液神经元内在一定时间内GABA表达增加,提示远位触液神经元内GABA这种表达变化可能参与了机体对炎性痛的信息调控。     

AT1受体在脑胆碱能刺激引起的蓝斑TH免疫反应活性变化中的作用

目的：探讨大鼠侧脑室注射胆碱能激动剂氨甲酰胆碱（carbachol,CBC）后蓝斑儿茶酚胺能神经元活性和血管紧张素能AT1受体表达的变化以及阻断ATl受体对上述变化的影响。方法：选用SD雄性大鼠,利用免疫组织化学方法,观察侧脑室注射氨甲酰胆碱（0．5μg）和／或losartan（20μg）后40min,蓝斑的酪氨酸羟化酶（tyrosine hydroxylase,TH）及AT1受体免疫反应活性的变化。结果：侧脑室注射氨甲酰胆碱（0．5pg）后40min,蓝斑的TH及ATl受体免疫反应阳性神经元数目明显增多（P〈0．05）,免疫染色强度明显增强（P〈0．05）。losartan预处理后蓝斑的TH免疫反应活性和AT1受体表达明显下降（P〈0．05）。结论：侧脑室注射胆碱能激动剂氨甲酰胆碱对蓝斑儿茶酚胺能神经元具有兴奋作用,AT1受体表达增强;阻断脑血管紧张素能AT1受体可下调氨甲酰胆碱在蓝斑诱导的上述变化。     

The role of calcium in the stimulation of gluconeogenesis by catecholamines

In hepatocytes isolated from fasted normal rats and incubated without albumin or gelatin, norepinephrine stimulated gluconeogenesis from fructose or dihydroxyacetone only in the absence of added calcium and from sorbitol or glycerol only in the presence of added calcium. The effects of calcium, norepinephrine, or calcium in combination with norepinephrine on the concentration of intermediary metabolites were therefore studied in hepatocytes metabolizing fructose or sorbitol as the representative oxidized or reduced substrate, respectively. With fructose as the substrate, addition of calcium increased the concentrations of lactate, pyruvate, glyceraldehyde 3-phosphate, and β-hydroxybutyrate, but decreased the concentrations of phosphoenolpyruvate, 2-phosphoglycerate, 3-phosphoglycerate, glucose 6-phosphate, malate, citrate, and α-oxoglutarate. With sorbitol as the substrate, calcium increased the concentrations of pyruvate, malate, β-hydroxybutyrate, and glucose. With either substrate, calcium caused a decrease in the lactate/ pyruvate ratio and an increase in the β-hydroxybutyrate/acetoacetate ratio, indicating the stimulation of transfer of reducing equivalents from cytosol to mitochondria. With sorbitol as the substrate, and with calcium present, norepinephrine promoted further electron transfer from cytosolic to mitochondrial NAD. Enhanced cytosolic calcium concentrations, when cells are exposed to catecholamines in the presence of medium calcium, stimulate the mitochondrial α-glycerophosphate dehydrogenase and thus the transfer of electrons between cell compartments.     

The role of GABA in human motor learning

GABA modification plays an important role in motor cortical plasticity. We therefore hypothesized that interindividual variation in the responsiveness of the GABA system to modification influences learning capacity in healthy adults. We assessed GABA responsiveness by transcranial direct current stimulation (tDCS), an intervention known to decrease GABA. The magnitude of M1 GABA decrease induced by anodal tDCS correlated positively with both the degree of motor learning and the degree of fMRI signal change within the left M1 during learning. This study therefore suggests that the responsiveness of the GABAergic system to modification may be relevant to short-term motor learning behavior and learning-related brain activity.     

The role of catecholaminergic group-A5 neurons in analgesia induced by auricular electroacupuncture and in electrodermal pain stimulation

The activity of antinociceptive mechanisms of auricular electroacupuncture (AEA) and footshock (FS) was studied on rats with bilaterally lesioned group A5 neurones. It was shown that the activity of the antinociceptive mechanisms triggered in experimental rats as compared to control rats. The data reveal the involvement of A5-nuclei in the antinociceptive mechanisms of AEA and FS.     

Toxicity induced by chemical warfare agents: Insights on the protective role of melatonin

Chemical Warfare Agents (CWAs) are substances that can be used to kill, injure or incapacitate an enemy in warfare, but also against civilian population in terrorist attacks. Many chemical agents are able to generate free radicals and derived reactants, excitotoxicity process, or inflammation, and as consequence they can cause neurological symptoms and damage in different organs. Nowadays, taking into account that total immediate decontamination after exposure is difficult to achieve and there are not completely effective antidotes and treatments against all CWAs, we advance and propose that medical countermeasures against CWAs poisoning would benefit from a broad-spectrum multipotent molecule.     

A new role for FcgammaRIIA in the potentiation of human platelet activation induced by weak stimulation

The low affinity receptor for immunoglobulin G, FcgammaRIIA, is expressed in human platelets, mediates heparin-induced thrombocytopenia and participates to platelet activation induced by von Willebrand factor. In this work, we found that stimulation of platelets with agonists acting on G-protein-coupled receptors resulted in the tyrosine phosphorylation of FcgammaRIIA, through a mechanism involving a Src kinase. Treatment of platelets with the blocking monoclonal antibody IV.3 against FcgammaRIIA, but not with control IgG, inhibited platelet aggregation induced by TRAP1, TRAP4, the thromboxane analogue U46619, and low concentrations of thrombin. By contrast, platelet aggregation induced by high doses of thrombin was unaffected by blockade of FcgammaRIIA. We also found that the anti-FcgammaRIIA monoclonal antibody IV.3 inhibited pleckstrin phosphorylation and calcium mobilization induced by low, but not high, concentrations of thrombin. In addition, thrombin- or U46619-induced tyrosine phosphorylation of several substrates typically involved in FcgammaRIIA-mediated signalling, such as Syk and PLCgamma2, was clearly reduced by incubation with anti-FcgammaRIIA antibody IV.3. Upon stimulation with thrombin, FcgammaRIIA relocated in lipid rafts, and thrombin-induced tyrosine phosphorylation of FcgammaRIIA occurred within these membrane domains. Controlled disruption of lipid rafts by depleting membrane cholesterol prevented tyrosine phosphorylation of FcgammaRIIA and impaired platelet aggregation induced by U46619 or by low, but not high, concentrations of thrombin. These results indicate that FcgammaRIIA can be activated in human platelets downstream G-protein-coupled receptors and suggest a novel general mechanism for the reinforcement of platelet activation induced by low concentrations of agonists.     

化学刺激或电刺激大鼠穹窿下器官诱发的饮水行为和脑内c-fos表达

目的对化学刺激和电刺激穹窿下器官(subfornical organ, SFO)诱发的饮水量和脑内c-fos表达的结果是否不同进行比较. 方法向大鼠SFO内微量注射L-谷氨酸作为化学刺激,用恒流刺激SFO作为电刺激,记录诱发的1 h内饮水量,用免疫组化方法检测脑内Fos蛋白表达.结果电刺激和化学刺激SFO均能诱导相似的饮水行为,其诱饮率分别为75%和85.7%,1 h平均饮水量分别为(0.28±0.22) ml 和(0.31±0.15) ml ,明显高于各自的对照组(P<0.05),并均能使前脑的 11个脑区(终板血管器官, 正中视前核,室旁核,视上核,下丘脑外侧区,丘脑室旁核,联合核和中央内侧核,终纹床核,穹窿周背区和无名质)和后脑的4个脑区(最后区,孤束核,臂旁外侧核和中缝背核)相似的Fos蛋白表达.结论刺激SFO所诱导的饮水行为和脑内Fos蛋白表达是激活其神经元胞体的结果.     

The role of heme and the mitochondrion in the chemical and molecular mechanisms of mammalian cell death induced by the artemisinin antimalarials

The artemisinin compounds are the frontline drugs for the treatment of drug-resistant malaria. They are selectively cytotoxic to mammalian cancer cell lines and have been implicated as neurotoxic and embryotoxic in animal studies. The endoperoxide functional group is both the pharmacophore and toxicophore, but the proposed chemical mechanisms and targets of cytotoxicity remain unclear. In this study we have used cell models and quantitative drug metabolite analysis to define the role of the mitochondrion and cellular heme in the chemical and molecular mechanisms of cell death induced by artemisinin compounds. HeLa ρ(0) cells, which are devoid of a functioning electron transport chain, were used to demonstrate that actively respiring mitochondria play an essential role in endoperoxide-induced cytotoxicity (artesunate IC(50) values, 48 h: HeLa cells, 6 ± 3 μM; and HeLa ρ(0) cells, 34 ± 5 μM) via the generation of reactive oxygen species and the induction of mitochondrial dysfunction and apoptosis but do not have any role in the reductive activation of the endoperoxide to cytotoxic carbon-centered radicals. However, using chemical modulators of heme synthesis (succinylacetone and protoporphyrin IX) and cellular iron content (holotransferrin), we have demonstrated definitively that free or protein-bound heme is responsible for intracellular activation of the endoperoxide group and that this is the chemical basis of cytotoxicity (IC(50) value and biomarker of bioactivation levels, respectively: 10β-(p-fluorophenoxy)dihydroartemisinin alone, 0.36 ± 0.20 μM and 11 ± 5%; and with succinylacetone, >100 μM and 2 ± 5%).     

GABA antagonists potentiate the cardioinhibitory reflex induced by capsaicin in the cat

The GABA antagonists picrotoxin (PX) and bicuculline (BIC) were given intravenously (i.v.) or applied topically to the region of the nucleus of the solitary tract (NTS) in intact or in precollicularly decerebrate cats under chloralose-urethane anaesthesia, and their effects on capsaicin (CAP)-induced reflex bradycardia were studied. The administration of PX or BIC was found to result in a decrease of the resting heart rate and a significant increase of the cardioinhibitory reflex evoked by CAP. The maximum effects of these GABA antagonists developed within 3-10 min and lasted for about 40-60 min. Neither the resting heart rate nor the response to CAP was affected by strychnine. It is concluded that the CAP-sensitive unmyelinated barosensory afferents and/or the interneurons in the NTS are under a tonically active GABA-ergic inhibitory control originating in the brain stem.     

The role of the striatum in aversive learning and aversive prediction errors

Neuroeconomic studies of decision making have emphasized reward learning as critical in the representation of value-driven choice behaviour. However, it is readily apparent that punishment and aversive learning are also significant factors in motivating decisions and actions. In this paper, we review the role of the striatum and amygdala in affective learning and the coding of aversive prediction errors (PEs). We present neuroimaging results showing aversive PE-related signals in the striatum in fear conditioning paradigms with both primary (shock) and secondary (monetary loss) reinforcers. These results and others point to the general role for the striatum in coding PEs across a broad range of learning paradigms and reinforcer types.     

The alterations of rat brain GABA and glutamine induced by the organophosphorus compound cyolane

Levels of the amino acids GABA and glutamine were determined in the whole brain of the white albino rat Rattus norvegicus after daily injection of 1/2, 1/4, 1/8, 1/16, 1/32 and 1/100 LD50 of cyolane. With 1/2 LD50 an increase in the level of both GABA and glutamine in the brain was recorded. Dose levels of 1/4 and 1/8 LD50 caused an increase in the level of GABA and a decrease in glutamine concentration followed by an increase from the 7th and 11th days for 1/4 and 1/8 LD50, respectively. The induced increase in GABA level started from the 2nd week for 1/16 and 1/32 LD50 and from the 3rd week for 1/100 LD50. Dose levels of 1/16, 1/32 and 1/100 LD50 caused a fluctuating increase in glutamine concentration starting from the 2nd, 3rd and 6th weeks, respectively, which was followed by a fluctuating decrease at the 9th week for 1/32 and 1/100 LD50. These findings support previous findings that the enhanced transformation of glutamic acid to GABA and glutamine is a result of a disturbance in the metabolism of the glutamic acid-GABA and the glutamic acid-glutamine systems in the rat brain.     

On the role of the striatum in response inhibition

Background

Stopping a manual response requires suppression of the primary motor cortex (M1) and has been linked to activation of the striatum. Here, we test three hypotheses regarding the role of the striatum in stopping: striatum activation during successful stopping may reflect suppression of M1, anticipation of a stop-signal occurring, or a slower response build-up.

Methodology/Principal Findings

Twenty-four healthy volunteers underwent functional magnetic resonance imaging (fMRI) while performing a stop-signal paradigm, in which anticipation of stopping was manipulated using a visual cue indicating stop-signal probability, with their right hand. We observed activation of the striatum and deactivation of left M1 during successful versus unsuccessful stopping. In addition, striatum activation was proportional to the degree of left M1 deactivation during successful stopping, implicating the striatum in response suppression. Furthermore, striatum activation increased as a function of stop-signal probability and was to linked to activation in the supplementary motor complex (SMC) and right inferior frontal cortex (rIFC) during successful stopping, suggesting a role in anticipation of stopping. Finally, trial-to-trial variations in response time did not affect striatum activation.

Conclusions/Significance

The results identify the striatum as a critical node in the neural network associated with stopping motor responses. As striatum activation was related to both suppression of M1 and anticipation of a stop-signal occurring, these findings suggest that the striatum is involved in proactive inhibitory control over M1, most likely in interaction with SMC and rIFC.     

The role of the striatum in adaptation learning: a computational model

To investigate the functional role of the striatum in visuo-motor adaptation, we extend the DIRECT-model for visuo-motor reaching movements formulated by Bullock et al.(J Cogn Neurosci 5:408–435,1993) through two parallel loops, each modeling a distinct contribution of the cortico–cerebellar–thalamo–cortical and the cortico–striato–thalamo–cortical networks to visuo-motor adaptation. Based on evidence of Robertson and Miall(Neuroreport 10(5): 1029–1034, 1999), we implement the function of the cortico–cerebellar–thalamo–cortical loop as a module that gradually adapts to small changes in sensorimotor relationships. The cortico–striato–thalamo–cortical loop on the other hand is hypothesized to act as an adaptive search element, guessing new sensorimotor-transformations and reinforcing successful guesses while punishing unsuccessful ones. In a first step, we show that the model reproduces trajectories and error curves of healthy subjects in a two dimensional center-out reaching task with rotated screen cursor visual feedback. In a second step, we disable learning processes in the cortico–striato– thalamo–cortical loop to simulate subjects with Parkinson’s disease (PD), and show that this leads to error curves typical of subjects with PD. We conclude that the results support our hypothesis, i.e., that the role of the cortico–striato–thalamo–cortical loop in visuo-motor adaptation is that of an adaptive search element.     

The role of catecholamines in the prolactin release induced by salsolinol

Salsolinol (1,2,3,4-tetrahydro-6,7-dihydroxy-1-methylisoquinoline) is an endogenous prolactin releasing agent. Its action can be inhibited by another isoquinoline, 1-methyl-3,4-dihydroisoquinoline (1MeDIQ), which has a strong norepinephrine releasing activity. Salsolinol does not alter the dopamine release in median eminence in vitro, providing evidence for the lack of interaction with presynaptic D2 dopamine receptors. At the same time, lack of norepinephrine transporter abolishes salsolinol's action. Salsolinol decreases tissue level of dopamine and increases norepinephrine to dopamine ratio in organs innervated by the sympathetic nervous system indicating a possible decrease of norepinephrine release. Enzymes of catecholamine synthesis and metabolism are probably also not the site of action of salsolinol. In summary, based upon all of these observations a physiologically relevant interplay might exist between the sympatho-neuronal system and the regulation of prolactin release.