GABAB受体对牛横酸调节突触体氨基酸释放的影响

目的 牛磺酸（Tau）调节大鼠大脑皮层突触体Asp、Glu、GABA的释放的机制尚不清楚,本研究从GABA受体的角度进行探讨。方法 将phaclofen、biculline、baclofen加入悬浮有突触体的KRB液中,氨基酸测定采用Dans-C1柱前衍生,高效液相测定。结果 Tau对GABA释放的抑制作用能有效被Phaclofen所拮抗,而它们对Glu Asp的释放均无影响。结论 Tau抑制去极化引发GABA的释放是通过激发突触体前膜GABAB受体而起作用的。同时还作用于Asp、Glu神经末梢的突触体前膜,从而抑制去极化引发的Asp、Glu的释放。     

氯胺酮麻醉期间大鼠脑内氨基酸递质水平的变化

氨基酸类递质是主要的中枢神经递质之一,对于精神意识活动的调整起着关键作用.现认为全麻药(尤吸入全麻药)可通过抑制突触前谷氨酸(Glu)的释放、增强谷氨酸的再摄取及阻滞突触后兴奋性氨基酸受体而发挥全麻作用[1].药物对于天冬氨酸(Asp)、γ-氨基丁酸(GABA)和甘氨酸(Gly)的突触前作用则较为复杂,不如谷氨酸明显和统一[2],可能不是全麻药的主要作用部位.有些学者认为氯胺酮对各类氨基酸类递质的摄取与释放过程无明显影响[2],这些都是离体实验的结论,活体动物在麻醉状态下,中枢神经系统中的氨基酸类递质水平是否会有所改变,随麻醉时相的不同,递质的水平会呈怎样的变化规律,尚未见报道.     

青羊参总甙对小鼠脑突触体中某些氨基酸含量和脑中某些有关酶活性的影响

COS青羊参的氟仿提取物,有抗惊厥作用。本文报道ip COS可升高小鼠脑突触体中GABA含量及降低Glu、Asp含量,抑制全脑GDH、谷氨酰胺酶及门冬酰胺酶活性。对突触体中Gln含量和脑中GOT、GPT和谷氨酰胺合成酶活性无明显影响。COS对上述氨基酸含量和酶活性的影响可能与其抗惊厥作用有关。     

γ-氨基丁酸转运体与疼痛

氨酪酸（γ-氨基丁酸,γ-aminobutyric acid,GA-BA）是中枢神经系统内重要的抑制性神经递质,只有与突触后膜上的受体结合后才可以发挥生物学活性。突触间隙内的GABA浓度过高或过低都不利于细胞间信号的传递。位于突触前膜上的γ-氨基丁酸转运体（γ-aminobutyric acid transporter,GAT）可以逆浓度梯度将GABA重吸收回细胞内,因此可以维持突触间隙内GABA的浓度。     

大鼠脊髓背角浅层GABA能轴突与SP受体阳性神经元的突触联系(英文)

目的:研究大鼠脊髓背角浅层内GABA能神经元与P物质受体(SPR)阳性神经元之间的相互关系.方法:应用SPR包埋前免疫电镜结合GABA胶体金技术.结果:SPR样免疫阳性神经元主要分布于脊髓背角Ⅰ层和Ⅱ层背侧部的内侧半.电镜下,浅层内SPR样免疫反应阳性产物主要定位于细胞体和树突.免疫反应产物在树突呈片或颗粒状,常常与线粒体外膜表面、粗面内质网、高尔基氏体、树突膜、胞浆膜内面和核膜外表面等相连.双标记显示SPR样免疫反应树突接受GABA样免疫金标记的轴突传入,形成对称性轴-树突触.此外,GABA还可与SPR共存于同一树突中.结论:GABA和P物质受体在脊髓背角神经元的突触联系,为以往GABA调制脊髓伤害感受功能的药理学研究提供了形态学证据.     

溴氰菊酯对大鼠脊髓中递质氨基酸含量的影响

本文观察了溴氰菊酯对大鼠脊髓中递质氨基酸:天冬氨酸(Asp)、谷氨酸(Glu)γ-氨基丁酸(GABA)、甘氨酸(Gly)和牛磺酸(Tau)含量的影响。实验结果表明,大鼠用溴氰菊酯150mg/kg 灌胃染毒后,脊髓中递质氨基酸:Asp、Glu和GABA 含量显著增加,但在急性中毒的不同阶段,这些递质氨基酸的含量变化是不同的。Asp含量增加不仅与中毒症状有关,而且与溴氰菊酯染毒剂量呈明显相关;而Glu和GABA 含量增加仅出现在抽搐阶段。实验结果提示溴氰菊酯引起的毒性症状与脊髓中递质氨基酸的释放有关。     

突触前肾上腺素受体

自从70年代初正式命名突触前受体以来,其发展异常迅速.本文综述突触前肾上腺素受体(侧重α-受体)的分类、功能、作用机理、生理意义和药理意义等方面的一些进展.对α-受体的传统的解剖学分类已为药理学分类所取代;突触前受体参与信息的突触调节、非突触调节和跨突触调节;突触前-受体激活后可通过抑制神经末梢(膨体)的去极化程度和反应性或抑制膨体去极化-分泌耦联而抑制递质释放;突触前受体具有重要的生理意义和药理意义.     

神经肌肉接头前阻断剂川楝素抑制大鼠大脑皮层突触体谷氨酸释放(英文)

目的　阐释川楝素的作用机制 ,为了解递质解释的基本过程提供线索。方法　以大鼠大脑皮层匀浆经密度梯度离心分离获得的突触体作为研究标本 ,分别施加 5 0mmol·L- 1KCl,1.5 μmol·L- 1卡西霉素或 7.5mmol·L- 14 氨基吡啶触发谷氨酸 (Glu)释放。通过检测由Glu氧化脱氢反应与NAD+ 生成的NADH荧光变化测定Glu释放量。结果　川楝素浓度、时间依赖地显著抑制由KCl诱发的Glu释放 ,并主要抑制钙依赖性释放 ;由卡西霉素直接提升胞内钙离子浓度而诱发的Glu释放也被川楝素明显抑制。结论川楝素抑制中枢突触Glu释放 ,该效应与其导致的递质释放机制中钙离子敏感性降低有关。     

AMG-1和腺苷对大鼠脑突触体谷氨酸释放的影响

观察了腺苷类化合物AMG-1对大鼠脑突触体前膜谷氨酸(glu)释放的影响。AMG-1在0.1～0.3 mmol·L^-1能明显抑制突触前膜Ca²⁺-依赖性glu的释放,并呈现剂量—效应关系。其作用强度与腺苷基本相似。提示AMG-1对脑保护作用可能与它激活腺苷A₁受体,从而抑制兴奋性氨基酸释放有关。     

几种静脉麻醉药对GABA能神经元的Phasic／Tonic抑制的影响

γ-氨基丁酸（gama-amino butyic acid ,GABA ）是广泛存在于中枢神经系统中一种重要的抑制性神经递质,参与调控睡眠和镇静等作用,主要通过作用于 GABAA 离子型亚基受体发挥生理效用。GABAA 受体属配体门控离子通道受体,通过增加神经细胞膜对氯离子和碳酸根离子的通透性,使细胞膜外高浓度的阴离子顺浓度梯度产生内向流动,从而引起突触后的超极化反应,导致神经元的兴奋性降低,这种由突触内的GABAA 型受体短暂的或“阶段性”的激活突触囊泡释放GABA ,从而产生的抑制,称为Phasic抑制,也是 GABAA 受体介导抑制性作用的经典途径。而近年来,研究者们提出了一种GABAA 受体介导的新型抑制作用即Tonic抑制［1］,它是由于轴突末梢保持一种持续少量的GA-BA释放,细胞外低浓度GABA 的环境能持续性的激活突触外的GABAA 受体引起的生理效应。本篇拟综述突触内和突触外GABAA 受体在控制神经元兴奋性的独特作用以及与全麻机制相关的最新研究进展。     

4-氨基吡啶对牛磺酸调节突触体氨基酸释放的影响

AIM　To elucidate the mechanism of taurine-regulated amino acid release from synaptosomes. METHODS　Endogenous aspartate, glutamate and GABA release from cortical synaptosomes were measured by high performance liquid chromatography using stepwise elution system, Glutamate release was monitored by continuous fluorometry. RESULTS　4-Aminopyridine (3.0×10^-2 mol*L^-1) counteracted the taurine-induced inhibition of glutamate overflow (P<0.05), while aspartate and GABA release was not affected. Nimodipine (10^-5 mol*L^-1) combined with 4-aminopyridine was shown to decrease glutamate release (P<0.05). CONCLUSION　Taurine may regulate glutamate release through presynaptic L-type calcium channel and aslo act on Asp-and GABA-nereve terminal to regulate Asp and GABA release in rat cortex.     

Presynaptic inhibition by clonidine of neurotransmitter amino acid release in various brain regions.

The release of endogenous aspartic acid (Asp), glutamic acid (Glu) and gamma-aminobutyric acid (GABA) was investigated in synaptosomes prepared from various regions of the rat brain. The basal release of Asp, Glu and GABA from various regions was 12-35, 24-107 and 15-43 pmol/min per mg protein, respectively. Exposure to a depolarizing concentration of KCl (30 mM) resulted in 1.7 to 3.6-fold increases in Asp, Glu and GABA release. When clonidine (10(-4) M) was added to the perfusion medium, the K(+)-evoked overflow of both Asp and Glu was inhibited by 50-90% in the anterior cortex, thalamus and hypothalamus. Clonidine inhibited the K(+)-evoked Glu overflow by 30-40% in the posterior cortex and hippocampus. No significant effects were observed in the other brain regions (olfactory bulb, striatum, midbrain, cerebellum, pons, medulla oblongata). The inhibitory effects of clonidine were counteracted by an alpha 2-adrenoceptor antagonist, rauwolscine. The data suggest that the basal and K(+)-evoked release of Asp, Glu and GABA from nerve terminals is different in rat brain regions and that the presynaptic alpha 2-adrenoceptors which regulate the release of excitatory amino acids are mainly distributed in the anterior cerebral cortex, thalamus and hypothalamus of the rat brain.     

Reduced inhibition of cortical glutamate and GABA release by halothane in mice lacking the K+ channel, TREK-1

BACKGROUND AND PURPOSE: Deletion of TREK-1, a two-pore domain K(+) channel (K(2P)) activated by volatile anaesthetics, reduces volatile anaesthetic potency in mice, consistent with a role for TREK-1 as an anaesthetic target. We used TREK-1 knockout mice to examine the presynaptic function of TREK-1 in transmitter release and its role in the selective inhibition of glutamate vs GABA release by volatile anaesthetics. EXPERIMENTAL APPROACH: The effects of halothane on 4-aminopyridine-evoked and basal [(3)H]glutamate and [(14)C]GABA release from cerebrocortical nerve terminals isolated from TREK-1 knockout (KO) and littermate wild-type (WT) mice were compared. TREK-1 was quantified by immunoblotting of nerve terminal preparations. KEY RESULTS: Deletion of TREK-1 significantly reduced the potency of halothane inhibition of 4-aminopyridine-evoked release of both glutamate and GABA without affecting control evoked release or the selective inhibition of glutamate vs GABA release. TREK-1 deletion also reduced halothane inhibition of basal glutamate release, but did not affect basal GABA release. CONCLUSIONS AND IMPLICATIONS: The reduced sensitivity of glutamate and GABA release to inhibition by halothane in TREK-1 KO nerve terminals correlates with the reduced anaesthetic potency of halothane in TREK-1 KO mice observed in vivo. A presynaptic role for TREK-1 was supported by the enrichment of TREK-1 in isolated nerve terminals determined by immunoblotting. This study represents the first evidence for a link between an anaesthetic-sensitive 2-pore domain K(+) channel and presynaptic function, and provides further support for presynaptic mechanisms in determining volatile anaesthetic action.     

Effects of baclofen on amino acid release.

This study showed the effects of baclofen on endogenous excitatory (Glu and Asp) and non-excitatory (Tau, Gly and Ala) amino acid release. (A) Release was stimulated by K+ 30 mM in rat frontal cortex slices in vitro (evoked release in ng/g tissue per 5 min): 3739 +/- 215 (Asp), 3429 +/- 357 (Glu), 763 +/- 181 (Tau), 945 +/- 71 (Ala), 468 +/- 44 (Gly). (B) Release was largely Ca(2+)-dependent for all amino acids but Ca(2+)-independent release was observed for Asp and Glu (29 and 32%, of total evoked release respectively). (C) Ca(2+)-dependent release was inhibited by baclofen 100 microM (% of inhibition taking as 100%, the Ca(2+)-dependent release in the absence of baclofen): 46 (Asp), 96 (Glu) (85% inhibition by baclofen 10 microM), 100 (Tau), 77 (Ala). Ca(2+)-independent release was inhibited: 87 and 88% (Asp), 85 and 95% (Glu) by baclofen 10 and 100 microM respectively. It is concluded that baclofen at a high concentration inhibits the evoked release of Glu, Asp, Tau and Ala due to inhibition of the Ca(2+)-dependent fraction and also of the Ca(2+)-independent component in the case of Glu and Asp. Baclofen at a low concentration inhibits only Glu- and Asp-evoked release (total release) due to inhibition of both Ca(2+)-dependent and -independent fractions in the case of Glu and to inhibition of the Ca(2+)-independent fraction in the case of Asp. The possibility that baclofen might affect the Ca(2+)-independent carrier-mediated release of Glu-Asp is discussed.     

Systemic administration of baclofen and the GABAB antagonist,CGP 35348, does not affect GABA,glutamate or aspartate in microdialysates of the striatum of conscious rats

Summary Previous in vitro experiments have shown that the GABA_B agonist, baclofen, and the antagonist, CGP 35348, respectively, decrease and increase the autoreceptor-mediated release of GABA in brain slices and synaptosomes. Since it is not clear whether these autoreceptors are operative in vivo, an attempt was made to reproduce these results in brain dialysis experiments, knowing that only positive results would permit a conclusion in view of the doubts expressed in the literature with respect to the origin of extracellular GABA. Because of older reports of an inhibitory action of baclofen on the in vitro release of glutamate, which might be ascribed to the action of presynaptic GABA_B heteroreceptors, extracellular glutamate and aspartate were also measured.Neither (–)-baclofen, administered systemically at a dose of 20 mg/kg i.p., nor the GABA_B antagonist, CGP 35348 (300 mg/kg i.p.) had significant effects on basal overflow of GABA, glutamate, or aspartate nor on that evoked by 100 mmol/l K⁺ in the striatum of the conscious, freely moving rat. To ascertain this result, (–)-baclofen was also administered between two K⁺ stimulations, so that the first stimulation could serve as an intraindividual control of the second. The compound did not significantly affect K⁺ evoked overflow of any of the three transmitter amino acids under these conditions.It must be emphasized that these data do not exclude the operativity of presynaptic GABA_B auto- and hetero-receptors in vivo. They only suggest that this question must, in all probability, be addressed by other techniques than brain dialysis. Send offprint requests to P. Waldmeier at the above address     

Weak effects of local and systemic administration of the GABA uptake inhibitor,SK&F 89976, on extracellular GABA in the rat striatum

Summary The effects of local and systemic administration of the potent GABA uptake inhibitor, SK&F 89976, on GABA overflow from the striatum of conscious rats were investigated in brain dialysis experiments. Administration of the compound via the dialysis probe at concentrations of 25 or 100 gmol/l significantly increased basal GABA overflow about 2-fold. Overflow evoked by 104 mmol/l K⁺ remained unaltered at the lower and was almost doubled at the higher concentration; this increase did, however, not reach statistical significance.Given systemically at 50 mg/kg i.p., a dose which is severalfold higher than those which exhibit anticonvulsant effects, SK&F 89976 caused a significant enhancement of K⁺-stimulated GABA overflow by about a factor of 2; the lower dose of 20 mg/kg i.p. was not effective. Basal GABA overflow was not significantly increased by either dose. These results suggest that the marked effects of nipecotic acid on basal GABA overflow reported by several authors seem to be related to GABA displacement rather than uptake inhibition, and that uptake inhibition does not improve the interpretability of measurements of GABA release by brain dialysis. They neither support the idea that the relative insensitivity of extracellular GABA to low Ca²⁺ and tetrodotoxin is indirectly due to very efficient removal of GABA by neuronal and/or glial uptake, leaving only residual amounts to be measured. Send offprint requests to P. Waldmeier at the above address     

Paradoxical antagonism by bicuculline of the inhibition by baclofen of the electrically evoked release of [3H]GABA from rat cerebral cortex slices

The presynaptic regulation of the electrically evoked release of [3H]GABA was studied in the rat cerebral cortex. Among the GABA receptor agonists tested (GABA, SL 75102, muscimol, THIP, isoguvacine, (+/-)-baclofen), only (+/-)-baclofen inhibited the stimulation-evoked release of [3H]GABA. This effect of baclofen was stereoselective in favor of the (-) enantiomer. The inhibition by (+/-)-baclofen of the electrically evoked release of [3H]GABA was antagonized by bicuculline and picrotoxin. Our results suggest that the release of [3H]GABA in vitro can be modulated by a receptor-mediated mechanism which is sensitive to baclofen, bicuculline and picrotoxin but not to GABA, muscimol or THIP.     

Lamina-specific differences in GABA(B) autoreceptor-mediated regulation of spontaneous GABA release in rat entorhinal cortex

Spontaneous synaptic inhibition plays an important role in regulating the excitability of cortical networks. Here we have investigated the role of GABA(B) autoreceptors in regulating spontaneous GABA release in the entorhinal cortex (EC), a region associated with temporal lobe epilepsies. We have previously shown that the level of spontaneous inhibition in superficial layers of the EC is much greater than that seen in deeper layers. In the present study, using intracellular and whole cell patch clamp recordings in rat EC slices, we have demonstrated that evoked GABA responses are controlled by feedback inhibition via GABA(B) autoreceptors. Furthermore, recordings of spontaneous, activity-independent inhibitory postsynaptic currents in layer II and layer V neurones showed that the GABA(B) receptor agonist, baclofen, reduced the frequency of GABA-mediated currents indicating the presence of presynaptic GABA(B) receptors in both layers. Application of the antagonist, CGP55845, blocked the effects of baclofen and also increased the frequency of GABA-mediated events above baseline, but the latter effect was restricted to layer V. This demonstrates that GABA(B) autoreceptors are tonically activated by synaptically released GABA in layer V, and this may partly explain the lower level of spontaneous GABA release in the deep layer.     

GABA transporter type 1 (GAT-1) uptake inhibition reduces stimulated aspartate and glutamate release in the dorsal spinal cord in vivo via different GABAergic mechanisms

Mechanisms through which the reported antinociceptive activity of GABA re-uptake inhibitors is mediated (and where on the sensory neuraxis) have not been defined. Here, microdialysis in the anaesthetised rat was used to examine the effect of selective GABA transporter type 1 (GAT-1) inhibition on basal and evoked amino acid release in the dorsal spinal cord. Reverse dialysis of the selective GAT-1 inhibitor NO-711 (10–300 μM) induced a concentration-related increase in extracellular GABA (maximal threefold of basal levels) without affecting other amino acids. Employing an S2/S1 paradigm, release evoked by brief high (45 mM) K⁺-induced depolarisation of aspartate and glutamate, but not GABA or glycine, was found to be significantly reduced by reverse dialysis of NO-711 (300 μM). Co-administration of selective antagonists for GABA_A or GABA_B receptors ((+)-bicuculline (100 μM) or SCH 50911 (100 μM), respectively) prevented the GAT-1 inhibition-induced reduction of evoked aspartate. In contrast, while (+)-bicuculline also antagonised the reduction of evoked glutamate, SCH 50911 (up to 1 mM) was without effect. Inhibition of GAT-1 re-uptake was further found to play a permissive role in autoinhibitory effects on GABA release mediated through GABA_A and GABA_B receptors. These data demonstrate that augmentation of GABAergic neurotransmission by re-uptake inhibition activates pharmacologically distinguishable inhibitory influences on aspartate and glutamate release in the dorsal spinal cord. Thus, inhibition of spinal pro-nociceptive neurotransmitter release may contribute to the analgesic action of this drug class.     

The effect of 3-mercaptopropionate,an inhibitor of glutamate decarboxylase,on the levels of GABA and other amino acids,and on presynaptic inhibition in the rat cuneate nucleus

Rats were anaesthetized with urethane and treated with the reversible competitive glutamate decarboxylase (GAD) inhibitor 3-mercaptopropionate (3-MP: 150mg/kg) in order to lower the endogenous levels of GABA. Within 15min GAD activity and GABA levels had decreased by about 50 and 30% respectively in the region of the caudal medulla containing the dorsal column nuclei (den). The decreased GABA levels were subsequently maintained for at least 45 min. In unanaesthetized animals, running fits and tonic clonic convulsions occur within 15 min coincident with the rapid fall in GABA levels. Urethane appeared to protect against such convulsant activity without itself altering GABA levels or the decrease in levels produced by 3-MP. Taurine and glycine levels were unaffected by 3-MP, glutamine levels rose progressively, glutamate levels rose transiently, aspartate and serine levels fell progressively and alanine levels fell sharply within 5 min, subsequently rising to the pre-treatment level. The level of presynaptic inhibition in the dcn was also decreased by 3-MP, as assessed from the size of the surface recorded P-wave produced by supramaximal, electrical stimulation of the ipsilateral forepaw. The observed similarity in time course between the alteration of GABA levels and the decrease in presynaptic inhibition supports previous studies suggesting that GABA is the transmitter mediating synaptic inhibition in the den.