GABA介导杏仁外侧核对皮层A Ⅰ区神经元声反应的抑制:在体微电泳研究

在SD大鼠上应用多顺利完成微电极方法,观察微电泳CABA及其受体的拮抗剂或激动剂对杏仁外侧核（LA）抑制皮层AⅠ神经元声反应效应的影响。结果显示,电泳GABA能抑制皮层AⅠ区神经元的电活动,电泳GABAA受体拮抗剂bicuculline（BIC）则能易化其反应;电刺激LA能抑制皮层AⅠ区听神经元声反应,电泳GABA产生类拟于刺激LA的抑制效应;LA对皮层AⅠ区神经的抑制效应能被BIC所翻转,而不能被什氨酸受体拮抗剂strychnine所翻转,电泳GABAB型受体例激动剂baclofen对神经元声反应无影响。上术结果表明,GABA可能是介民LA抑制皮层AⅠ区神经元声反应的最终递质,并且是通过GABAA受体作用的。     

Effects of 17beta-estradiol on blood-brain barrier disruption in focal ischemia during GABA(A) receptor inhibition.

We performed this study to determine whether gamma-aminobutyric acid (GABA(A)) receptor inhibition could reverse the effect of 17beta-estradiol on blood-brain barrier (BBB) disruption in focal cerebral ischemia. Young ovariectomized rats were implanted with a 500 microg 17beta-estradiol 21-day release pellet or with a vehicle pellet 21 days before the experiments. Forty-five minutes after middle cerebral artery (MCA) occlusion, half of each group was infused with bicuculline (a GABA(A) receptor antagonist) 1 mg/kg/min for 2 min followed by 0.1 mg/kg/min up to the end of experiments. The other half was infused with the same volume of normal saline. The transfer coefficient (Ki) of 14C-alpha-aminoisobutyric acid and the volume of 3H-dextran distribution (70,000 Daltons) were determined to measure the degree of BBB disruption one hour after MCA occlusion. In the control vehicle-treated animals, the Ki in the ischemic cortex (7.2 +/- 2.6 microl/g/min) was higher than in the contralateral cortex (2.5 +/- 1.4 microl/g/min). After bicuculline infusion, the Ki in the ischemic cortex increased (10.6 +/- 5.4 microl/g/min) although the increase was not statistically significant. In the 17beta-estradiol treated animals, the Ki in the ischemic cortex (3.8 +/- 1.6 microl/g/min) was lower than control vehicle-treated rats. With bicuculline infusion, the Ki in the ischemic cortex (14.5 +/- 6.8 microl/g/min) was markedly increased. In the non-ischemic cortex, there was no significant difference in Ki among the experimental groups. The volume of dextran distribution was not significantly different between the experimental groups in the ischemic or non-ischemic cortex. Our data suggests that part of the reason for the decreased BBB disruption in the focal ischemic area after 17beta-estradiol treatment could be due to the interaction between GABA(A) receptors and 17beta-estradiol.     

Changes in ventral respiratory column GABAaR ε- and δ-subunits during hibernation mediate resistance to depression by EtOH and pentobarbital

During hibernation in the 13-lined ground squirrel, Ictidomys tridecemlineatus, the cerebral cortex is electrically silent, yet the brainstem continues to regulate cardiorespiratory function. Previous work showed that neurons in slices through the medullary ventral respiratory column (VRC) but not the cortex are insensitive to high doses of pentobarbital during hibernation, leading to the hypothesis that GABA(A) receptors (GABA(A)R) in the VRC undergo a seasonal modification in subunit composition. To test whether alteration of GABA(A)R subunits are responsible for hibernation-associated pentobarbital insensitivity, we examined an array of subunits using RT-PCR and Western blots and identified changes in ε- and δ-subunits in the medulla but not the cortex. Using immunohistochemistry, we confirmed that during hibernation, the expression of ε-subunit-containing GABA(A)Rs nearly doubles in the VRC. We also identified a population of δ-subunit-containing GABA(A)Rs adjacent to the VRC that were differentially expressed during hibernation. As δ-subunit-containing GABA(A)Rs are particularly sensitive to ethanol (EtOH), multichannel electrodes were inserted in slices of medulla and cortex from hibernating squirrels and EtOH was applied. EtOH, which normally inhibits neuronal activity, excited VRC but not cortical neurons during hibernation. This excitation was prevented by bicuculline pretreatment, indicating the involvement of GABA(A)Rs. We propose that neuronal activity in the VRC during hibernation is unaffected by pentobarbital due to upregulation of ε-subunit-containing GABA(A)Rs on VRC neurons. Synaptic input from adjacent inhibitory interneurons that express δ-subunit-containing GABA(A)Rs is responsible for the excitatory effects of EtOH on VRC neurons during hibernation.     

Ethanol potentiates the effect of gamma-aminobutyric acid on medial vestibular nucleus neurons responding to horizontal rotation

Electrophysiological studies were performed to determine whether or not ethanol potentiates the inhibitory effects of gamma-aminobutyric acid (GABA) on medial vestibular nucleus (MVN) neurons responding to horizontal sinusoidal rotation using alpha-chloralose anesthetized cats. The MVN neurons were classified into types I, II, III and IV neurons according to the responses to the horizontal rotation of the animal placed on the turntable in directions ipsilateral and contralateral to the recording site. In addition, the effects of ethanol and GABA on type I neurons were also examined. Micro-osmotic application of ethanol up to 100 nA did not affect the spontaneous firing or the rotation-induced increase in firing of type I neurons. However, the inhibitory effects of GABA up to 50 nA on the rotation-induced increase in firing were potentiated during simultaneous application of ethanol up to 100 nA. This potentiated inhibition was blocked by iontophoretic application of bicuculline (25-150 nA) and picrotoxin (45-150 nA). These results suggest that ethanol potentiates the inhibitory effects of GABA on MVN type I neurons by acting on the GABA receptor and/or receptor-coupled chloride ion channel.     

γ—氨基丁酸在联合皮层抑制C类纤维皮层诱发电位效应中的作用

电刺激猫大脑皮层前外侧回联合区(ALA)对隐神经C类纤维传入引起的体感皮层(SI)诱发电位(C-CEP)有明显的抑制作用;侧脑室注射γ-氨基丁酸(GABA)能使C-CEP的幅值显著变小,潜伏期延长,表明GABA对C-CEP也有抑制作用;侧脑室注射GABA受体拮抗剂荷包牡丹硷后,电刺激ALA对C-CEP的抑制作用明显减弱,提示内源性GABA的释放可能参与大脑皮层联合区对C-CEP的调制过程。     

Decreased GABA Receptor Binding in the Cerebral Cortex of Insulin Induced Hypoglycemic and Streptozotocin Induced Diabetic Rats

Hypoglycemia is the major problem to blood glucose homeostasis in treatment of diabetes and is associated with severe irreversible consequences including seizures, coma and death. GABAergic inhibitory function in the cerebral cortex plays an important role in controlling the excitability and responsiveness of cortical neurons. Present study analysed effects of insulin induced hypoglycemia and streptozotocin induced diabetes on the cortical GABA receptor binding, GABA_Aά1, GABA_B receptor subtype expression, GAD and GLUT3 expression. Diabetic rats showed decreased [³H] GABA binding in the cerebral cortex compared to control while hypoglycemia exacerbated the decrease. GABA receptor subunits; GABA_Aά1, GABA_B and GAD expression significantly decreased in diabetic rats whereas hypoglycemia significanly decreased the expression compared to diabetic. GLUT3 expression significantly up regulated during both hypo and hyperglycemia. Our results showed that hypoglycemia and hyperglycemia decreased GABAergic neuroprotective function in the cerebral cortex, which account for the increased vulnerability of cerebral cortex to subsequent neuronal damage during hypo/hyperglycemia.     

Excess of taurine supplementation in rat: effects on GABA-related amino acids in developing nervous tissues.

The effects of taurine supplementation on GABA-related amino acid homeostasis in developing nervous tissues of suckling rats were studied. In the first two weeks of postnatal growth, cerebral cortex and cerebellum appear more accessible to taurine supplementation in comparison to retina; in addition, different changes in excitatory/inhibitory amino acids were observed. After the 5th day of life, in the retina and cerebellum of taurine-supplemented pups a decrease in GABA levels was found; in contrast, in cerebral cortex GABA content significantly increased throughout 20 days of postnatal growth. In all nervous tissues studied (except for cerebellum) glutamine concentration increased at the 5th day; then in cerebellum and in retina, but not in cerebral cortex, a significant decrease until the 20th day occurred. Furthermore, in cerebellum and retina taurine supplementation decreased glutamate levels, in comparison to controls, at the 10th and until the 20th day of postnatal life, respectively, whereas in cerebral cortex an increase in glutamate level was observed only at the 5th day. In conclusion, taurine supplementation, in excess to the usual amount from the mother's milk, affected the glutamate compartments in various cell types. The changes in GABA-related amino acid concentrations in cerebral cortex, cerebellum, and retina may depend on the different pattern of the metabolic processes at different maturative stages.     

GABA对小鼠大脑皮质中GABA受体胚胎发育的调节

本文用ＧＡＢＡ及其受体激动剂和拮抗剂处理培养的胚胎小鼠大脑皮层神经细胞以及精确计时的妊娠小鼠,用放射配体结合法检测ＧＡＢＡＡ及ＧＡＢＡＢ的结合位点数目,研究了ＧＡＢＡ对小鼠大脑皮层ＧＡＢＡ受体胚胎发育的调节作用,结果表明：①ＧＡＢＡ可使培养１５—１７天妊龄的胚胎小鼠大脑皮层神经细胞及出生第１天的仔鼠大脑皮层中的ＧＡＢＡＡ及ＧＡＢＡＢ受体数目增加,这种作用可被蝇蕈醇（Ｍｕｓ）及巴氯芬（Ｂａｃ）分别模拟,对ＧＡＢＡＡ受体的作用可为荷包牡丹碱（Ｂｉｃ）所阻断;②用ＧＡＢＡ处理妊娠７—１３天的小鼠,仔鼠出生第１天其大脑皮层的ＧＡＢＡＡ及ＧＡＢＡＢ受体数目均无变化;③用ＧＡＢＡ处理妊娠１４—１９天的小鼠,仔鼠出生的第１天其大脑皮层中的ＧＡＢＡＡ受体数目增加而ＧＡＢＡＢ受体数目不变;④用ＧＡＢＡ处理妊娠７－１９天的小鼠,仔鼠出生第１天其大脑皮层中ＧＡＢＡＡ及ＧＡＢＡＢ受体数目增加。这说明在胚胎发育的特定时期内,ＧＡＢＡ可诱导其受体数目的增加,这个作用是由ＧＡＢＡ受体调节的。     

Decreased GABA receptor in the cerebral cortex of epileptic rats: effect of Bacopa monnieri and Bacoside-A

Abstact

Background

Gamma amino butyric acid (GABA), the principal inhibitory neurotransmitter in the cerebral cortex, maintains the inhibitory tones that counter balances neuronal excitation. When this balance is perturbed, seizures may ensue.

Methods

In the present study, alterations of the general GABA, GABA_A and GABA_B receptors in the cerebral cortex of the epileptic rat and the therapeutic application of Bacopa monnieri were investigated.

Results

Scatchard analysis of [³H]GABA, [³H]bicuculline and [³H]baclofen in the cerebral cortex of the epileptic rat showed significant decrease in B_max (P < 0.001) compared to control. Real Time PCR amplification of GABA receptor subunits such as GABA_Aά1, GABA_Aγ, GABA_Aδ, GABA_B and GAD where down regulated (P < 0.001) in epileptic rats. GABA_Aά5 subunit and Cyclic AMP responsible element binding protein were up regulated. Confocal imaging study confirmed the decreased GABA receptors in epileptic rats. Epileptic rats have deficit in radial arm and Y maze performance.

Conclusions

Bacopa monnieri and Bacoside-A treatment reverses epilepsy associated changes to near control suggesting that decreased GABA receptors in the cerebral cortex have an important role in epileptic occurrence; Bacopa monnieri and Bacoside-A have therapeutic application in epilepsy management.     

II. Effect of aminooxyacetic acid and bicuculline on prolactin release in castrated male rats

To investigate the role of gamma aminobutyric acid (GABA) on prolactin secretion, castrated male rats were infused with aminooxyacetic acid (AOAA) or bicuculline, two drugs that affect GABA metabolism or its binding to the receptors, respectively. The infusion of AOAA or bicuculline for 2 hr did not significantly modify serum prolactin levels. A quick iv injection of sulpiride, a drug that induces hyperprolactinemia, brought about a significantly lower release of prolactin in rats infused with AOAA than in control rats, infused with saline. The response to sulpiride in rats infused with bicuculline was significantly greater, in terms of prolactin release, than in control rats. These results suggest that GABA may have an inhibitory role on the regulation of prolactin release.     

In Vivo Changes in γ-Aminobutyric Acid Output from the Cerebral Cortex Induced by Inhibitors of γ-Aminobutyric Acid Uptake and Metabolism

Abstract: The effects of inhibitors of γ-aminobutyric acid (GABA) metabolism or uptake on GABA output from the cerebral cortex was studied by means of a collecting cup placed on the exposed cortex of rats anaesthetized with urethane. GABA was identified and quantified by a mass-fragmentographic method. Ethanolamine-O-sulphate (10⁻² M ) applied directly on the cerebral cortex caused a long-lasting twofold increase in GABA output, whereas dl -2, 4-diaminobutyric acid (5 × 10⁻³ M ) caused a sevenfold increase and β -alanine was inactive. The results indicate that glial uptake has little effect on GABA inactivation in the cerebral cortex. The inhibition of neuronal uptake seems a more effective tool to increase GABA concentration in the synaptic cleft, and consequently also in GABA output, than the inhibition of GABA metabolism.     

GABA参与兔杏仁体抑制内膝体神经元电活动

本文采用多管微电极胞外记录技术观察了短纯音引起兔内膝神经元的声反应及刺激杏仁体对声反应的影响,并在此基础上观察电泳ＧＡＢＡ及其拮抗剂Ｂｉｃｕｃｕｌｌｉｎｅ的效应。实验结果表明：ＧＡＢＡ可以抑制ＭＧＢ神经元的声反应及自发放电活动,而ＧＡＢＡＡ拮抗剂Ｂｉｃｕｃｕｌｌｉｎｅ的作用则相反;电泳ＧＡＢＡ对ＭＧＢ神经元产生同刺激杏仁体一样的抑制产应,并且这种影响可被Ｂｉｃｕｃｕｌｌｉｎｅ翻转;嗅鼻沟后缘听区农     

Effects of anticonvulsant agents and ethanol on the complexes of epileptic foci created by applications of bicuculline, strychnine, and penicillin in the rat brain cortex

Anticonvulsive effects of direct agonists of the GABA receptor system, medinal and phenazepam, as well as ethanol, on the complexes of epileptic foci created in the rat brain cortex by applications of various convulsant agents (bicuculline, strychnine, or penicillin) were studied. Ethanol, as well as phenazepam and medinal, were shown to possess high anti-epileptic activity in relation to the complexes. It was shown, using an i.v. infusion technique, that threshold doses of strychnine and bicuculline depend, in a linear and a nonlinear fashion, respectively, on the alcohol doses administered. A specific feature was found in the pharmacolgoical effect of ethanol: anticonvulsive activity of ethanol was pronounced within the postinjection interval from 5 min to 4 h, while within the following interval, from 4 to 24 h, the animals turned into a seizure-ready state. The subseizure phase was observed under the conditions when the penicillin complex was induced, and also following i.v. injections of strychnine and bicuculline.     

马桑内酯激活的星形胶质细胞条件培养液对正常大鼠脑内谷氨酸和GABA的影响

目的探讨星形胶质细胞对大鼠脑内谷氨酸(Glu)和γ-氨基丁酸(GABA)的影响及其在癫痫发病中的作用。方法将马桑内酯激活的星形胶质细胞条件培养液(astrocyte-conditioned medium,ACM)注射入正常SD大鼠侧脑室,观察大鼠的行为变化,运用免疫组织化学及HPLC的方法,观察大鼠大脑皮质、海马内Glu和GABA免疫反应的变化及脑组织匀浆、脑脊液内Glu和GABA含量的变化。结果ACM组大鼠在注射ACM后30min出现癫痫行为,2h恢复正常。免疫组织化学显示:ACM作用后2h,大鼠大脑皮质及海马内Glu免疫反应阳性神经元数和平均光密度值明显增高,4h达高峰(P<0.05),12h恢复正常水平;ACM作用后2h,大鼠大脑皮质及海马GABA免疫反应阳性神经元数和平均光密度值明显减弱(P<0.05),12h恢复正常水平。HPLC方法显示:ACM作用后2h大鼠大脑皮质、海马及脑脊液中Glu含量均开始增加,4h达高峰(P<0.05);ACM作用后2h大脑皮质、海马及脑脊液中GABA含量均开始降低,4h达最低(P<0.05)。结论马桑内酯激活的星形胶质细胞条件培养液可影响大鼠脑内Glu和GABA的表达,并导致动物痫性发作。     

Foot-Shock Stress and Anxiogenic β-Carbolines Increase t-[35S]Butylbicyclophosphorothionate Binding in the Rat Cerebral Cortex, an Effect Opposite to Anxiolytics and γ-Aminobutyric Acid Mimetics

The effect of foot-shock stress on t-[35S]butylbicyclophosphorothionate [( 35S]TBPS) binding to fresh unwashed membrane preparations from rat cerebral cortex was studied and was compared to those of GABAA receptor agonists and antagonists and to positive and negative modulators of the GABAergic transmission. [35S]TBPS binding was increased in the cerebral cortex of rats exposed to foot shock compared to that of nonstressed rats. Scatchard analysis revealed that the effect of foot shock was due to an increase in the total number of [35S]TBPS binding sites. In contrast, the in vitro addition of muscimol or GABA induced a dose-dependent inhibition of [35S]TBPS binding, an effect abolished by the concomitant addition of the GABA receptor antagonist, bicuculline, which, per se, enhanced [35S]TBPS binding by 73%. Thus, bicuculline, similar to stress, increased [35S]TBPS binding in the same membrane preparation. In contrast to stress, the anxiolytic and positive modulators of the GABAergic transmission (ZK 93423, ZK 91296, and diazepam) inhibited the specific binding of [35S]TBPS in a concentration-dependent manner. The greatest inhibitory effect was produced by ZK 93423 at 30 microM (31% of control), followed by diazepam (54% of control) and by the partial agonist ZK 91296 (61% of control). Scatchard plot analysis indicated that the inhibition induced by ZK 93423 and diazepam was due to a decrease in the density of [35S]TBPS recognition sites. On the other hand, the anxiogenic beta-carbolines DMCM and FG 7142 mimicked the effect of stress. Thus, at a 10 microM concentration, DMCM and FG 7142 increased [35S]TBPS binding by 22% and 26%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of short-lasting bilateral clamping of carotid arteries (BCCA) on GABA turnover in rat brain structures

We have previously shown that short-lasting reduction of cerebral blood flow by bilateral clamping of carotid arteries (BCCA) results in long-lasting increase in regional GABA concentration and decrease in seizure susceptibility in rats. In the present experiments, the effect of BCCA on GABA turnover and the enzymes involved in GABA synthesis and degradation were studied in rats. Regional GABA turnover was measured by means of GABA accumulation induced by the GABA-transaminase (GABA-T) inhibitor aminooxyacetic acid (AOAA). Fourteen days after BCCA, GABA turnover was significantly increased in hippocampus, substantia nigra and cortex, but not different from sham-operated controls in several other brain regions, including striatum, hypothalamus and cerebellum. The activity of glutamate decarboxylase (GAD) measured ex vivo did not show any changes in investigated structures, while the activity of GABA-T was slightly increased in hippocampus. The increased GABA turnover in some brain regions may explain our previous findings of increased GABA content in these brain regions and decreased sensitivity of BCCA treated animals to the GABA_A-receptor antagonist bicuculline.     

Microionophoretic study of the mechanism of action of gamma-hydroxybutyrate

The effect of gamma-hydroxybutyric acid (GHBA) on the extracellularly registered spontaneous electrical activity of nervous cells of the rabbit brain sensomotor cortex was studied using the microionophoretic technique. GHBA decreased the frequency of action potential in the majority of the neurons studied. A specific gamma-aminobutyric acid (GABA) blocking agent bicuculline prevented GBHA inhibitory effect. GHBA is suggested to interact with central GABA-receptors. The frequency of discharges increased in some neutrons due to GHBA, while GHBA prevented the development of GABA inhibitory effect. This is indicative of probable competitive relations between GHBA and GABA during their interaction with the same receptor. The conditions for the development of such relations are discussed.     

Differential effects of ethanol ingestion on somatostatin content, somatostatin receptors and adenylyl cyclase activity in the frontoparietal cortex of virgin and parturient rats

Chronic ethanol ingestion decreases the number of somatostatin (SRIF) receptors in the rat frontoparietal cortex and female sex hormones modulate the effects of ethanol in the brain. Therefore, we investigated the differential effects of ethanol consumption on the SRIFergic system in the frontoparietal cortex of virgin and parturient rats given ethanol in their drinking water before and during gestation. In parturient rats, ethanol consumption decreased the density of SRIF receptors (25%, p<0.01 vs control parturient group) whereas the SRIF-like immunoreactivity (SRIF-LI) content was increased (140%, p<0.01). In virgin rats, ethanol ingestion decreased the density of SRIF receptors (42%, p<0.01) more than in alcoholic parturient rats. SRIF-LI levels were unaffected. The inhibitory effect of SRIF on basal and forskolin-stimulated adenylyl cyclase was significantly lower in alcoholic virgin rats as compared to alcoholic parturient rats. No differences in the levels of the G inhibitory (Gi) alpha1 and Gialpha2 proteins were observed among the experimental groups. These results suggest that gestation may confer partial resistance to the ethanol-induced effect on the SRIFergic system.     

Social isolation-induced increase in alpha and delta subunit gene expression is associated with a greater efficacy of ethanol on steroidogenesis and GABA receptor function

Previously we have demonstrated that social isolation of rats reduces both the cerebrocortical and plasma concentrations of 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG), and potentiates the positive effects of acute ethanol administration on the concentrations of this neurosteroid. We now show that the ethanol-induced increase in 3alpha,5alpha-TH PROG is more pronounced in the brain than in the plasma of isolated rats. The ability of ethanol to inhibit isoniazid-induced convulsions is greater in isolated rats than in group-housed animals and this effect is prevented by treatment with finasteride. Social isolation modified the effects of ethanol on the amounts of steroidogenic regulatory protein mRNA and protein in the brain. Moreover, ethanol increased the amplitude of GABA(A) receptor-mediated miniature inhibitory postsynaptic currents recorded from CA1 pyramidal neurones with greater potency in hippocampal slices prepared from socially isolated rats than in those from group-housed rats, an effect inhibited by finasteride. The amounts of the alpha(4) and delta subunits of the GABA(A) receptor in the hippocampus were increased in isolated rats as were GABA(A) receptor-mediated tonic inhibitory currents in granule cells of the dentate gyrus. These results suggest that social isolation results in changes in GABA(A) receptor expression in the brain, and in an enhancement of the stimulatory effect of ethanol on brain steroidogenesis, GABA(A) receptor function and associated behaviour.     

葆包牡丹碱对垂体前叶组织块释放促肾上腺皮质激素的刺激效应

本实验利用垂体组织块离体灌流技术,观察到γ－氨基丁酸Ａ受体拮抗剂荷包牡丹笃切除双侧肾上腺９６ｈ后的大鼠垂体前叶ＡＣＴＨ的分泌具有强烈的刺激作用。但同样浓度的荷包牡丹笃分离的垂体前叶细胞的ＡＣＴＨ分泌无影响,提示肾上腺切除后,γ－氨基丁酸在垂体前叶直接或通过间接途径抑制ＡＣＴＨ分泌。