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Tonic activation of presynaptic GABA_B receptors in the opener neuromuscular junction of crayfish

JOURNAL OF NEUROPHYSIOLOGY 1999年第3期81卷 1184-1191页

作者： Parnas, I Rashkovan, G Ong, J Kerr, DIB Hebrew Univ Jerusalem Otto Loewi Minerva Ctr Cellular & Mol Neurobiol Dept Neurobiol Jerusalem Israel Univ Adelaide Dept Anaesthesia & Intens Care Adelaide SA 5005 Australia

Release of excitatory transmitter from boutons on crayfrsh nerve terminals was inhibited by (R,S)-baclofen, an agonist at GABA(B) receptors. Baclofen had no postsynaptic actions as it reduced quantal content without affecting quantal amplitude, The effect of baclofen increased with concentration producing 18% inhibition at 10 mu M EC50, 50% inhibition at 30 mu M;maximal inhibition, 85% at 100 mu M and higher. There was no desensitization. even with 200 or 320 mu M baclofen. Phaclofen, an antagonist at GABA(B) receptors, competitively antagonized the inhibitory action of baclofen (K-D = 50 mu M, equivalent to a pA(2) = 4.3 +/- 0.1). Phaclofen on its own at concentrations below 200 mu M had no effect on release, whereas at 200 mu M phaclofen itself increased the control level of release by 60%, as did 2-hydroxy-saclofen (200 mu M), another antagonist at GABA(B) receptors. This increase was evidently due to antagonism of a persistent level of GABA in the synaptic cleft, since the effect was abolished by destruction of the presynaptic inhibitory fiber, using intra-axonal pronase;We conclude that presynaptic GABA(B) receptors, with a pharmacological profile similar to that of mammalian GABA(B) receptors, are involved in the control of transmitter release at the crayfish neuromuscular junction.

关键词：螯虾总科轴突/药物作用巴氯芬/类似物和衍生物巴氯芬/药理学 GABA激动剂/药理学 GABA拮抗剂/药理学 Logistic模型神经抑制/药物作用神经肌肉接头/药物作用神经肌肉接头/生理学膜片钳术链霉蛋白酶量子论受体 GABA-B/药物作用受体 GABA-B/生理学受体突触前/药物作用受体突触前/生理学动物

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Effects of GABA receptor antagonist on trigeminal caudalis nociceptive neurons in normal and neonatally capsaicin-treated rats

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JOURNAL OF NEUROPHYSIOLOGY 1999年第5期82卷 2154-2162页

作者： Chiang, CY Kwan, CL Ku, JW Sessle, BJ Univ Toronto Fac Dent Toronto ON M5G 1G6 Canada

We have recently demonstrated that significant increases in cutaneous mechanoreceptive field (RF) size and spontaneous activity occur in nociceptive neurons of trigeminal subnucleus caudalis (Vc, the medullary dorsal horn) of adult rats depleted of C-fiber afferents by neonatal treatment with capsaicin. These neuronal changes in capsaicin-treated (CAP) rats are suggestive of central neuroplasticity and involve N-methyl-D-aspartic acid (NMDA) receptor mechanisms. The present study examined whether the GABA(A) receptor antagonist bicuculline (BIC) or the GABA(B) receptor antagonist 2-hydroxysaclofen (SAC) can influence the RF properties and activity of Ve nociceptive neurons classified as either nociceptive-specific or wide-dynamic range in CAP adult rats or in neonatally vehicle-treated (CON) rats. C-fiber depletion was confirmed in the CAP rats by a significant decrease in plasma extravasation of Evans blue dye in a skin area receiving topical application of mustard oil, a small-fiber excitant and inflammatory irritant As previously reported, marked increases in cutaneous RF size and spontaneous activity occurred in Vc nociceptive neurons of adult CAP rats, compared with CON rats. GABA(A) receptor blockade by BIC (i.t.) in CON rats produced a significant increase in spontaneous activity and in pinch RF size and tactile RF size (or appearance of a tactile area in the RF of nociceptive-specific neurons), as well as a significant lowering of the mechanical threshold and a significant enhancement of responses to pinch stimuli applied to the RF. In CAP rats, GABA(B) receptor blockade also produced significant changes similar to those documented in CON rats, except for a paradoxical and significant decrease in pinch RF size and no noticeable changes in responses to pinch stimuli. GABA(A) receptor blockade by SAC (i.t.) did not produce any significant changes in Vc nociceptive neurons in either CON or CAP rats. These results suggest that GABA(A) receptor-mediated inhibitio

关键词：动物新生巴氯芬/类似物和衍生物巴氯芬/药理学荷包牡丹碱/类似物和衍生物荷包牡丹碱/药理学脑图辣椒辣素/投药和剂量辣椒辣素/药理学功能偏侧化 GABA拮抗剂/药理学 GABA-A受体拮抗剂延髓/药物作用延髓/生理学微量注射神经元可塑性/药物作用神经元可塑性/生理学神经元/药物作用神经元/生理学疼痛感受器/药物作用疼痛感受器/生理学疼痛/病理生理学物理刺激大鼠 Sprague-Dawley 触觉三叉神经/药物作用三叉神经/生理学三叉神经/病理生理学动物男(雄)性大鼠

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A subtype of the γ-aminobutyric acid_B receptor regulates cholinergic twitch response in the guinea pig ileum

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JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS 2000年第1期293卷 42-47页

作者： Marcoli, M Scarrone, S Maura, G Bonanno, G Raiteri, M Dipartimento Med Sperimentale Sez Farmacol & Tossicol I-16148 Genoa Italy

The pharmacological profile of the gamma-aminobutyric acid (GABA), receptor regulating cholinergic twitch contraction in the guinea pig ileum myenteric plexus-longitudinal muscle preparation was investigated. GABA and (-)-baclofen inhibited the contraction, exhibiting quite close potencies (pD(2) for GABA = 5.70;pD(2) for (-)-baclofen = 5.33). The compound CGP 47656 also reduced the cholinergic twitch concentration (pD(2) = 5.42), but its efficacy was significantly lower than that of (-)-baclofen or GABA. Added at varying concentrations, CGP 47656 modified the concentration-response curve of (-)-baclofen as expected for a partial agonist. Phaclofen, CGP 36742, CGP 35348, and CGP 52432 behaved as competitive antagonists of (-)-baclofen, exhibiting the following pA(2) values: 3.90, 4.88, 5.02, and 7.82, respectively. The compound CGP 56999 behaved as a potent noncompetitive GABA, receptor antagonist. In comparing the pharmacological profile of the ileal receptor with those of the previously characterized pharmacological subtypes of the GABA, receptor present in the central nervous system, it can be seen that the GABA, receptor inhibiting cholinergic twitch contraction in guinea pig ileum myenteric plexus-longitudinal muscle mostly resembles the receptor located on somatostatin human neocortex nerve terminals.

关键词：巴氯芬/类似物和衍生物巴氯芬/拮抗剂和抑制剂巴氯芬/药理学结合竞争性/药物作用电刺激 GABA激动剂/药理学 GABA拮抗剂/药理学回肠/药物作用回肠/生理学配体肌收缩/药物作用肌平滑/药物作用肌平滑/生理学肠肌丛/药物作用副交感神经系统/药物作用副交感神经系统/生理学受体 GABA-B/药物作用受体 GABA-B/代谢脊髓/药物作用脊髓/代谢动物豚鼠男(雄)性

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Novel mechanism for presynaptic inhibition:: GABA_A receptors affect the release machinery

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JOURNAL OF NEUROPHYSIOLOGY 2000年第3期84卷 1240-1246页

作者： Parnas, I Rashkovan, G Ravin, R Fischer, Y Hebrew Univ Jerusalem Dept Neurobiol Otto Loewi Minerva Ctr Cellular & Mol Neurobiol IL-91904 Jerusalem Israel

Presynaptic inhibition is produced by increasing Cl- conductance, resulting in an action potential of a smaller amplitude at the excitatory axon terminals. This, in turn, reduces Ca2+ entry to produce a smaller release. For this mechanism to operate, the "inhibitory" effect of shunting should last during the arrival of the "excitatory" action potential to its terminals, and to achieve that, the inhibitory action potential should precede the excitatory action potential. Using the crayfish neuromuscular preparation which is innervated by one excitatory axon and one inhibitory axon, we found, at 12 degrees C, prominent presynaptic inhibition when the inhibitory action potential followed the excitatory action potential by 1, and even 2, ms. The presynaptic excitatory action potential and the excitatory nerve terminal current (ENTC) were not altered, and Ca2+ imaging at single release boutons showed that this "late" presynaptic inhibition did not result from a reduction in Ca2+ entry. Since 50 mu M picrotoxin blocked this late component of presynaptic inhibition, we suggest that gamma- aminobutyric acid-A (GABA(A)) receptors reduce transmitter release also by a mechanism other than affecting Ca2+ entry.

关键词：动作电位/药物作用螯虾总科巴氯芬/类似物和衍生物巴氯芬/药理学钙/代谢剂量效应关系药物电刺激 Fura-2 GABA拮抗剂/药理学 GABA-A受体拮抗剂细胞内液/代谢镁/代谢镁/药理学神经抑制/药物作用神经抑制/生理学神经肌肉接头/药物作用神经肌肉接头/生理学膜片钳术印防己毒素/药理学突触前末梢/药物作用突触前末梢/代谢反应时间/生理学受体 GABA-A/代谢突触传递/药物作用突触传递/生理学温度 γ氨基丁酸/代谢 γ氨基丁酸/药理学动物

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Activation of peripheral GABA_A receptors inhibits temporomandibular joint-evoked jaw muscle activity

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JOURNAL OF NEUROPHYSIOLOGY 1999年第4期81卷 1966-1969页

作者： Cairns, BE Sessle, BJ Hu, JW Univ Toronto Fac Dent Dept Oral Physiol Toronto ON M5G 1G6 Canada

We have previously shown that injection of mustard oil or glutamate into rat temporomandibular joint (TMJ) tissues, an experimental model of acute TMJ injury, can reflexly induct a prolonged increase in the activity of both digastric (jaw-opener) and masseter (jaw-closer) muscles. In this study, GABA was applied to the TMJ region by itself or in combination with glutamate, and the magnitude of evoked jaw muscle electromyographic (EMG) activity was measured. Application of GABA alone to the TMJ region did not evoke significant jaw muscle EMG activity when compared with normal saline controls. In contrast, co-application of GABA and glutamate into the TMJ region decreased the magnitude of glutamate-evoked EMG activity. This GABA-mediated inhibition of glutamate-evoked EMG activity followed an inverse dose-response relationship with an estimated median inhibitory dose (ID50) of 0.17 +/- 0.05 (SE) mu mol and 0.031 +/- 0.006 mu mol for the digastric and masseter muscles, respectively. Go-administration of the GABA(A) receptor antagonist bicuculline (0.05 mu mol) but not the GABA(B) receptor antagonist phaclofen (0.05 or 0.15 mu mol) reversed the suppressive actions of GABA, indicating that this action of GABA may be mediated by peripheral GABA(A) receptors located within the TMJ region. Our results suggest that activation of peripheral GABA(A) receptors located within the TMJ region could act to decrease the transmission of nociceptive information.

关键词：巴氯芬/类似物和衍生物巴氯芬/药理学荷包牡丹碱/药理学剂量效应关系药物肌电描记术 GABA拮抗剂/药理学谷氨酸/药理学咬肌/神经支配咬肌/生理学运动神经元/药物作用运动神经元/生理学大鼠 Sprague-Dawley 受体 GABA-A/生理学颞下颌关节/神经支配颞下颌关节/生理学 γ氨基丁酸/药理学动物男(雄)性大鼠

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GABA_B receptor-mediated regulation of glutamate-activated calcium transients in hypothalamic and cortical neuron development

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JOURNAL OF NEUROPHYSIOLOGY 1999年第1期82卷 94-102页

作者： Obrietan, K van den Pol, A Yale Univ Sch Med Dept Neurosurg New Haven CT 06520 USA Stanford Univ Dept Biol Sci Stanford CA 94305 USA

In the mature nervous system excitatory neurotransmission mediated by glutamate is balanced by the inhibitory actions of GABA. However, during early development, GABA acting at the ligand-gated GABA(A) Cl- channel also exerts excitatory actions. This raises a question as to whether GABA can exert inhibitory activity during early development, possibly by a mechanism that involves activation of the G protein-coupled GABA(B) receptor. To address this question we used Ca2+ digital imaging to assess the modulatory role of GABA(B) receptor signaling in relation to the excitatory effects of glutamate during hypothalamic and cortical neuron development. Ca2+ transients mediated by synaptic glutamate release in neurons cultured from embryonic rat were dramatically depressed by the administration of the GABA(B) receptor agonist baclofen in a dose-dependent manner. The inhibitory effects of GABA(B) receptor activation persisted for the duration of baclofen administration (>10 min). Preincubation with the Gi protein inhibitor pertussis toxin resulted in a substantial decrease in the inhibitory actions of baclofen, confirming that a Gi-dependent mechanism mediated the effects of the GABA(B) receptor. Go-administration of the GABA(B) receptor antagonist 2-hydroxy-saclofen eliminated the inhibitory action of baclofen. Alone, GABA(B) antagonist application elicited a marked potentiation of Ca2+ transients mediated by glutamatergic neurotransmission, suggesting that tonic synaptic GABA release exerts an inhibitory tone on glutamate receptor-mediated Ca2+ transients via GABA(B) receptor activation. In the presence of TTX to block action potential-mediated neurotransmitter release, stimulation with exogenously applied glutamate triggered a robust postsynaptic Ca2+ rise that was dramatically depressed (>70% in cortical neurons, >40% in hypothalamic neurons) by baclofen. Together these data suggest both a pre- and postsynaptic component for the modulatory actions of the GABA(B) receptor

关键词： 2-氨基-5-膦酰基戊酸盐/药理学 6-氰-7-硝基喹喔啉-2 3-二酮/药理学巴氯芬/类似物和衍生物巴氯芬/药理学荷包牡丹碱/药理学钙/代谢细胞培养的大脑皮质/细胞学大脑皮质/生理学阿糖胞苷/药理学药物协同作用胚胎哺乳动物兴奋性氨基酸拮抗剂/药理学 GABA拮抗剂/药理学谷氨酸/药理学谷氨酸/生理学下丘脑中/细胞学下丘脑中/生理学膜电位/药物作用膜电位/生理学神经元/细胞学神经元/药物作用神经元/生理学百白咳毒素大鼠 Sprague-Dawley 受体 GABA-B/生理学河豚毒素/药理学毒力因子鲍特菌属/药理学动物大鼠

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GABA receptor antagonists modulate postmitotic cell migration in slice cultures of embryonic rat cortex

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CEREBRAL CORTEX 2000年第9期10卷 899-909页

作者： Behar, TN Schaffner, AE Scott, CA Greene, CL Barker, JL NINDS Neurophysiol Lab NIH Bethesda MD 20892 USA

Recent studies indicate that GABA acts as a chemoattractant during rat cortical histogenesis. In vivo, GABA localizes in appropriate locations for a chemoattractant, along migratory routes and near target destinations for migrating cortical neurons. In vitro, GABA induces dissociated embryonic cortical neurons to migrate. Here, embryonic rat cortical slices were cultured in the presence or absence of GABA receptor (GABA-R) antagonists to assess GABA's Effects on neuronal migration in situ. Gestational day 18 (E18) cortical slices were incubated overnight in bromodeoxyuridine (BrdU)-containing medium to label ventricular zone (vz) cells as they underwent terminal mitosis. The slices were then cultured in BrdU-free medium with or without GABA-R antagonists. In control slices, most BrdU(+) cells were observed in the cortical plate (cp) after 48 h. in contrast, cultures maintained in either saclofen (a GABA(B)-R antagonist) or picrotoxin (a GABA(A/C)-R antagonist) had few BrdU-labeled cp cells. However, the effects of the two antagonists were distinct. In the picrotoxin-treated slices, nearly half of all BrdU(+) cells remained in the vz and subventricular zone (svz), whereas saclofen treatment resulted in an accumulation of BrdU(+) cells in the intermediate zone (iz). Bicuculline, a GABA(A)-R antagonist, did not block, but rather enhanced migration of BrdU(+) cells into the cp. These results provide evidence that picrotoxin-sensitive receptors promote the migration of vz/svz cells into the it, while saclofen sensitive receptors signal cells to migrate into the cp. Thus, as cortical cells differentiate, changing receptor expression appears to modulate migratory responses to GABA.

关键词：巴氯芬/类似物和衍生物巴氯芬/药理学荷包牡丹碱/药理学溴脱氧尿苷/分析细胞运动/药物作用细胞运动/生理学大脑皮质/细胞学大脑皮质/药物作用大脑皮质/胚胎学趋化作用/药物作用 GABA拮抗剂/药理学神经胶质原纤维酸性蛋白质/分析中间丝蛋白质类/分析有丝分裂神经组织蛋白质类神经胶质/细胞学神经元/化学神经元/细胞学神经元/生理学器官培养技术印防己毒素/药理学受体 GABA-A/生理学 γ氨基丁酸/药理学动物女(雌)性妊娠大鼠

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Increased mesolimbic GABA concentration blocks heroin self-administration in the rat

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JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS 2000年第2期294卷 613-619页

作者： Xi, ZX Stein, EA Med Coll Wisconsin Dept Cell Biol Neurobiol & Anat Milwaukee WI 53226 USA Med Coll Wisconsin Dept Psychiat & Behav Med Milwaukee WI 53226 USA Med Coll Wisconsin Dept Pharmacol & Toxicol Milwaukee WI 53226 USA Med Coll Wisconsin Biophys Res Inst Milwaukee WI 53226 USA

Opiate reinforcement has been hypothesized to be mediated by an inhibition of mesolimbic gamma-aminobutyric acid (GABA) release that subsequently disinhibits ventral tegmental area (VTA) dopamine neurons. In support of this hypothesis, this study demonstrates that when administered directly into the lateral ventricle, the VTA, or the ventral pallidum, but not the nucleus accumbens, gamma-vinyl-GABA (GVG, an irreversible GABA-transaminase inhibitor, 20-50 mu g) dose dependently blocked heroin (0.06 mg/kg) self-administration (SA), as assessed by an increase in heroin SA at low doses of GVG and an initial increase followed 1 to 2 h later by a blockade of heroin SA at higher GVG doses. This effect lasted 3 to 5 days. In drug-naive rats, intra-VTA GVG pretreatment also prevented or delayed acquisition of heroin SA for 2 days. This GVG effect was prevented or reversed by systemic or intra-VTA pretreatment with the GABA(B) antagonist 2-hydroxysaclofen, but not the GABA(A) antagonist bicuculline. Similarly, coadministration of heroin with aminooxy-acetic acid (1-4 mg/kg) or ethanolamine-O-sulfate (50-100 mg/kg), two reversible GABA transaminase inhibitors, dose dependently reduced heroin reinforcement. Coadministration of (+/-)-nipecotic acid (0.1-5 mg/kg) with heroin, or intra-VTA or -ventral pallidum pretreatment with (+/-)-nipecotic acid (10 mu g) or NO-711 (2 mu g), two GABA uptake inhibitors, significantly increased heroin SA behavior, an effect also blocked by systemic 2-hydroxysaclofen, but not bicuculline. Taken together, these experiments, for the first time, demonstrate that pharmacological elevation of mesolimbic GABA concentration blocks heroin reinforcement by activating GABA(B) receptors, supporting the GABAergic hypothesis of opiate reinforcement and the incorporation of GABA agents in opiate abuse treatment.

关键词： 4-氨基丁酸转氨酶/拮抗剂和抑制剂巴氯芬/类似物和衍生物巴氯芬/药理学行为动物/药物作用荷包牡丹碱/药理学酶抑制剂/药理学 GABA拮抗剂/药理学苍白球/药物作用苍白球/代谢海洛因/投药和剂量注射脑室内侧脑室/药物作用侧脑室/代谢微量注射麻醉品/投药和剂量神经递质摄取抑制药/药理学伏核/药物作用伏核/代谢阿片相关性障碍/药物疗法阿片相关性障碍/代谢阿片相关性障碍/病理生理学大鼠 Sprague-Dawley 受体 GABA-A/拮抗剂和抑制剂受体 GABA-B/拮抗剂和抑制剂自我遵嘱服药端脑/药物作用端脑/代谢腹侧被盖区/药物作用腹侧被盖区/代谢氨己烯酸/药理学 γ氨基丁酸/代谢 γ氨基丁酸/生理学动物男(雄)性大鼠

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