组胺能与γ-氨基丁酸能神经传递在间位核神经元信息加工中的作用(英文)

小脑间位核(interpositus nucleus,IN)主要接受γ-氨基丁酸(GABA)能纤维支配,同时接受组胺能纤维的调节.本研究在小脑脑片上研究了GABA和组胺对单个IN神经元电活动的共同作用.持续灌流组胺或同时施加组胺和GABA,81.2%(69/85)神经元,GABA及其激动剂的效应都被组胺削弱(持续灌流n=33;同时施加n=36).这种削弱效应能够被组胺H2受体阻断剂ranitidine(n=10)和PKA抑制剂H-89阻断(n=8),fors-kolin模拟组胺的效应(n=9).结果表明组胺和GABA对IN神经元的电活动具有交互调节作用:通过激活H2受体偶联的G-protein-AC-PKA信号通路,磷酸化GABAB和GABAA受体,降低受体功能.推测受体间的对话的工作模式,可能是整个大脑神经元活动的某些药理作用和生理活动调节的基础;如果对话紊乱,可能导致大脑功能障碍.     

鹌鹑中脑GABA能神经元的分布

以非鸣禽鹌鹑（Coturnix coturnix japonica）为实验材料，使用GABA单克隆抗体进行免疫组化实验，实验结果显示，在鹌鹑中脑存在GABA样免疫反应神经元．讨论了GABA能神经元在中脑的分布特点及其在听觉、视觉中的作用。     

GABA能抑制参与弱噪声对下丘频率调谐的前掩蔽

在自由声场条件下，选用强度相当于纯音阈上5dB SPL、80ms的弱包络白噪声作为前掩蔽声，观察加入掩蔽声后神经元频率调谐的变化．对发生锐化的神经元导入荷包牡丹碱（Bicuculline，BIC），观察去GABA能抑制后前掩蔽效应的变化．结果显示：弱噪声前掩蔽使大部分神经元的频率调谐曲线（frequency tuning curve，FTC）锐化（P〈0．01），导入BIC后，弱噪声的抑制率下降．研究结果证实GABA能抑制参与了弱噪声所致的下丘神经元前掩蔽．     

巨细胞网状核5-HT能纤维对小脑浦肯野细胞自发电活动的影响

用电生理学方法、观察了小脑皮层第Ⅵ—Ⅶ小叶蚓部的浦肯野细胞（Purkinje cell,PC）对巨细胞网状核（Gigantocellularis reticularis nucleus,GI）刺激的反应特性,并观察了颈静脉注射5-羟色胺（5-HT）受体阻断剂二甲麦新碱（Methysergide）后GI刺激的效应。 结果表明:（1）刺激GI对小脑皮层Ⅵ—Ⅶ小叶PC自发放电的影响有抑制（41％）、兴奋（27％）及无明显作用（32％）三种形式,其中以抑制性作用为主。（2）GI刺激引起的PC反应在小脑皮层上呈区域性差异,表现为由VIA（64.3％）、VTB（65.3％）、VIC（71.4％）至Ⅶ小叶（74.2％）PC反应比率逐渐升高。（3）颈静脉注射二甲麦角新碱后,由GI刺激引起的PC自发放电的抑制性效应可逐渐被消除,而兴奋性效应则不被减弱。 结果提示:GI—小脑之间存在着5-HT能纤维投射,这些5-HT能纤维可能以“非突触释放”的形式调节着PC的机能活动。PC对GI刺激反应的区域性差异,可能与GI—小脑5-HT能纤维投射的解剖学分布特性有关。     

谷氨酸对家鸽顶盖脑片Ⅱa？f亚层神经元自发电活动的影响

应用离体脑片技术,胞外记录观察了家鸽顶盖Ⅱa～f亚层神经元的自发放电特征,以及灌流和微电泳给予谷氨酸（glutamate,Glu）及其受体措抗剂谷氨酸二乙酯（glutamatediethylester,GDEE）对自发电活动的影响．在46例脑片上观察了80个Ⅱa～f亚层神经元的自发放电活动,其放电形式有3种：慢而不规则型（50个,占62．5％）;连续重复放电型（24,占30．0％）;周期性簇状放电型（6个,占7．5％）．分别用灌流和微电泳方式给予Glu后,受试神经元均出现明显的增频反应,且呈现剂量一效应关系．GDEE对自发放电有抑制作用,且能阻断Glu的兴奋作用一以上结果提示,家鸽顶盖Ⅱa～f亚层内存在Glu敏感神经元,外源性的Glu对这些神经元有兴奋作用,Glu可能作为神经递质参与了家鸽顶盖Ⅱa～f亚层神经元的活动．     

中华鳖心的肾上腺素能受体类型

采用改良的八木氏插管法在３２个离体灌流的鳖心上，重点研究了对３种肾上腺素能受体激动剂的变时性反应．其亲和力顺序：ＩＳＯ＞Ｅ≥ＮＥ．ＮＥ（３．３３×１０－８ｇ）的正变时性作用可被ＰＲＯ（３．３３×１０－６ｇ）所阻断，ＰＨＥＮＴ（３．３３×１０－６ｇ）则无效．同浓度（３．３３×１０－８ｇ）的Ｅ与ＮＥ正变时性作用相近，明显强于ＳＡＬ．选择性α－受体激动剂ＭＥＴＨＯ无明显作用或略抑制．夏季与冬季的鳖心反应基本相同．提示鳖心的肾上腺素能受体主要为β－亚型而无α－受体．     

γ-氨基丁酸参与家鸽顶盖的视网膜抑制性传入作用的离体研究

在６０例家鸽顶盖脑片上,利用胞外记录研究了γ－氨基丁酸（γ－ａｍｉｎｏｂｕｔｙｒｉｃ ａｃｉｄ,ＧＡＢＡ）和荷包牡丹碱（ｂｉｃｕｃｕｌｌｉｎｅ,ＢＩＣ）对顶盖视网膜接受区神经元自发放电及刺激Ⅰ层诱发的抑制反应的影响,灌流ＧＡＢＡ（１－１０ｍｍｏｌ／Ｌ）抑制了６０个神经元中的５２个神经元的电活动,这些抑制效应呈剂量依赖关系,ＧＡＢＡ的抑制效应绝大部分可被ＧＡＢＡＡ受体拮抗剂ＢＩＣ所阻断。单独灌流ＢＩ     

β-淀粉样蛋白31—35及25—35片段对海马CA1细胞兴奋性和抑制性受体通道电流的影响

在Alzheimer病（AD）出现神经变性前的早期记忆功能障碍中,可溶性β-淀粉样蛋白（Aβ）发挥了重要作用,Aβ及其活性片段对海马长时程增强（LTP）的压抑效应与其对学习记忆认知行为的伤害作用具有密切联系,但其机制仍不清楚．鉴于突触后兴奋性和抑制性受体／通道在突触传递、包括LTP的诱导中起着关键性调制作用,利用全细胞膜片钳技术观察了β-淀粉样蛋白31—35片段（Aβ31-35）和25-35片段（Aβ25-35）对急性分离的海马CA1区锥体细胞谷氨酸（Glu）受体、N-甲基-D-天冬氨酸（NMDA）受体和γ-氨基丁酸（GABA）受体通道电流的影响．结果显示：急性给予Aβ25-35或Aβ31-35可对Glu受体电流和GABA受体电流产生相反的调制作用．Aβ25-35预处理剂量依赖性地减小了Glu和NMDA引起的全细胞内向电流,相反,GABA受体电流被明显增强;小片段的Aβ31-35也选择性抑制了Glu和NMDA受体电流,增强了GABA受体电流;然而,给予Aβ31-35的反序列Aβ35-31刊预处理后,Glu,NMDA和GABA引起的受体电流均未出现明显改变．这些结果表明,Aβ25-35和Aβ31-35片段急性处理可导致海马锥体细胞NMDA受体和GABAn受体分别受到抑制和易化影响,这可能有助于解释AD早期可溶性Aβ对海马LTP及认知行为造成的伤害作用．同时,Aβ25-35和Aβ31-35片段具有的类似效应提示,31—35序列很可能是Aβ发挥神经毒性作用的活性中心．     

18-β甘草次酸抑制KCl对大鼠脑中动脉的收缩作用

为讨论缝隙连接阻断剂18β—GA在脑血管收缩反应中的可能作用。采用压力肌动图技术,在急性分离的Wistar大鼠的大脑中动脉（直径〈300μm）,观察18β—GA干预前后不同浓度的收缩剂KCl对血管直径的影响。结果显示,KCl可以浓度依赖性的引起脑中动脉收缩,且30～80mmol／L引起的收缩与血管静息状态下的直径相比具有统计学差异（P〈0．05,n=7）。18βGA也可浓度依赖性的引起脑中动脉收缩,且10～100〉mol／L引起的收缩与未加药前相比具有统计学差异（P％0．05,n=8）。预灌流18β—GA（100／amol／L）后,50～80mmol／L KCl引起血管收缩幅度减小,拟合曲线下移,且差异具有统计学意义（P〈0．05,n=7）。由此可知：18B—GA可抑制KCl对脑血管的收缩作用,提示细胞问缝隙连接参与脑血管收缩活动。     

γ-氨基丁酸对家鸽(Columba livia)顶盖脑片Ⅲ层神经元电活动的影响

在２５只家鸽的离体顶盖脑片上,用玻璃微电极胞外记录到顶盖Ⅲ层神经元自发放电单位５５个,观察了γ氨基丁酸（ｇａｍｍａａｍｉｎｏｂｕｔｙｒｉｃ,ＧＡＢＡ）及其拮抗剂以及电刺激Ⅱａ～ｆ亚层对Ⅲ层神经元电活动的作用．作用显示：脑片灌流ＧＡＢＡ（１０－６ｍｏｌ／Ｌ,３ｍｉｎ）后,１６／２１个单位（占７６．２％）放电频率减少,１／２１个单位（占４．８％）放电频率增加,４／２１个单位（占１９．６％）放电频率无变化．ＧＡＢＡ的这种减频作用可被１０－６ｍｏｌ／Ｌ荷包牡丹碱（ｂｉｃｕｃｕｌｉｎｅ,ＢＩＣ）逆转．１４个被Ⅱａ～ｆ亚层刺激传入减频的Ⅲ层神经元,其中１１个单位（占７８．６％）的减频作用可被ＢＩＣ阻断,另３个单位则不产生阻遏作用．上述药物的作用具有可逆性和重复性．结果表明：家鸽顶盖Ⅲ层中可能有ＧＡＢＡ能纤维的到达,Ⅲ层内存在ＧＡＢＡ敏感神经元．顶盖Ⅱａ～ｆ亚层与Ⅲ层神经元间的抑制性突触传递过程中有ＧＡＢＡ及其相应的ＧＡＢＡＡ型受体参与     

Excitatory effect of histamine on neuronal activity of rat cerebellar fastigial nucleus in vitro

The cerebellar fastigial nucleus (FN) holds an important role in motor control and body balance. Previous studies have revealed that the nucleus is innervated by direct hypothalamocerebellar histaminergic fibers. However, the functional role of histaminergic projection in cerebellar FN has never been established. In this study, we investigated the effect of histamine on neuronal firing of cerebellar FN by using slice preparations. Sixty-five FN cells were recorded from 47 cerebellar slices, and a vast majority of the cells responded to histamine stimulation with an excitatory response (58/65, 89.2%). Perfusing slices with low-Ca2 /high-Mg2 medium did not block the histamine-induced excitation (n=10), supporting a direct postsynaptic action of histamine on the cells. Furthermore, the excitatory effect of histamine on FN neurons was not blocked by selective histamine H1 receptor antagonist triprolidine (n=15) or chlorpheniramine (n=10), but was effectively suppressed by ranitidine (n=15), a highly selective histamine H2 receptor antagonist. On the other hand, highly selective histamine H2 receptor agonist dimaprit (n=20) instead of histamine H1 receptor agonist 2-pyridylethylamine (n=16) mimicked the ex- citatory effect of histamine on FN neurons. The dimaprit-induced FN neuronal excitation was effectively antagonized by selective histamine H2 receptor antagonist ranitidine (n=13) but not influenced by se- lective histamine H1 receptor antagonist triprolidine (n=15). These results demonstrate that histamine excites cerebellar FN cells via the histamine H2 receptor mechanism and suggest that the hypotha- lamocerebellar histaminergic fibers may modulate cerebellar FN-mediated sensorimotor integration through their excitatory innervations on FN neurons.     

Auto-inhibition of brain histamine release mediated by a novel class (H3) of histamine receptor

Although histaminergic neurones have not yet been histochemically visualized, there is little doubt that histamine (HA) has a neurotransmitter role in the invertebrate and mammalian central nervous system. For example, a combination of biochemical, electrophysiological and lesion studies in rats have shown that histamine is synthesized in and released from a discrete set of neurones ascending through the lateral hypothalamic area and widely projecting in the telencephalon. Histamine acts on target cells in mammalian brain via stimulation of two classes of receptor (H1 and H2) previously characterized in peripheral organs and probably uses Ca2+ and cyclic AMP, respectively, as second messengers. It is well established that several neurotransmitters affect neuronal activity in the central nervous system through stimulation not only of postsynaptic receptors, but also of receptors located presynaptically which often display distinct pharmacological specificity and by which they may control their own release. Such 'autoreceptors' have been demonstrated (or postulated) in the case of noradrenaline, dopamine, serotonin, acetylcholine and gamma-aminobutyric acid (GABA) neurones but have never been demonstrated for histamine. We show here that histamine inhibits its own release from depolarized slices of rat cerebral cortex, an action apparently mediated by a class of receptor (H3) pharmacologically distinct from those previously characterized, that is, the H1 and H2 receptors.     

Benzodiazepine actions mediated by specific gamma-aminobutyric acid(A) receptor subtypes.

GABA(A) (gamma-aminobutyric acid(A)) receptors are molecular substrates for the regulation of vigilance, anxiety, muscle tension, epileptogenic activity and memory functions, which is evident from the spectrum of actions elicited by clinically effective drugs acting at their modulatory benzodiazepine-binding site. Here we show, by introducing a histidine-to-arginine point mutation at position 101 of the murine alpha1-subunit gene, that alpha1-type GABA(A) receptors, which are mainly expressed in cortical areas and thalamus, are rendered insensitive to allosteric modulation by benzodiazepine-site ligands, whilst regulation by the physiological neurotransmitter gamma-aminobutyric acid is preserved. alpha1(H101R) mice failed to show the sedative, amnesic and partly the anticonvulsant action of diazepam. In contrast, the anxiolytic-like, myorelaxant, motor-impairing and ethanol-potentiating effects were fully retained, and are attributed to the nonmutated GABA(A) receptors found in the limbic system (alpha2, alpha5), in monoaminergic neurons (alpha3) and in motoneurons (alpha2, alpha5). Thus, benzodiazepine-induced behavioural responses are mediated by specific GABA(A) receptor subtypes in distinct neuronal circuits, which is of interest for drug design.     

GABA regulates synaptic integration of newly generated neurons in the adult brain

Adult neurogenesis, the birth and integration of new neurons from adult neural stem cells, is a striking form of structural plasticity and highlights the regenerative capacity of the adult mammalian brain. Accumulating evidence suggests that neuronal activity regulates adult neurogenesis and that new neurons contribute to specific brain functions. The mechanism that regulates the integration of newly generated neurons into the pre-existing functional circuitry in the adult brain is unknown. Here we show that newborn granule cells in the dentate gyrus of the adult hippocampus are tonically activated by ambient GABA (gamma-aminobutyric acid) before being sequentially innervated by GABA- and glutamate-mediated synaptic inputs. GABA, the major inhibitory neurotransmitter in the adult brain, initially exerts an excitatory action on newborn neurons owing to their high cytoplasmic chloride ion content. Conversion of GABA-induced depolarization (excitation) into hyperpolarization (inhibition) in newborn neurons leads to marked defects in their synapse formation and dendritic development in vivo. Our study identifies an essential role for GABA in the synaptic integration of newly generated neurons in the adult brain, and suggests an unexpected mechanism for activity-dependent regulation of adult neurogenesis, in which newborn neurons may sense neuronal network activity through tonic and phasic GABA activation.     

尼氟灭酸对CCI模型鼠DRG神经元GABA介导膜电流的影响

为观察尼氟灭酸(NFA)对坐骨神经慢性压迫损伤(CCI)所导致的神经病理性痛大鼠的背根神经节(dorsal root ganglion,DRG)神经元上GABAA受体激活电流的影响,探讨尼氟灭酸在神经病理性疼痛时在脊髓水平的作用及可能机制。采用如下方法:(1)制作CCI模型。(2)运用热板实验检测CCI组、假手术组术侧下肢热缩足反射潜伏期的变化。(3)运用全细胞膜片钳技术记录CCI模型组术侧、假手术组术侧、正常组DRG神经元上GABAA受体激活电流的幅度。(4)记录尼氟灭酸对正常组和CCI组术侧DRG神经元上GABAA受体激活电流的调节作用。结果显示,(1)CCI组术侧下肢热缩足反射潜伏期明显缩短。(2)GABA(1~1000μmol/L)可以使DRG神经元产生浓度依赖的内向电流(P0.05,n=10)。(3)CCI组1~100μmol/L GABA激活电流幅值显著小于假手术组和正常对照组(P0.01,n=6)。假手术组和正常对照组GABA电流差异无统计学意义。(4)NFA(1~100μmol/L)对正常组、CCI组的DRG神经元上GABA激活的电流均有抑制作用,该抑制作用具有浓度依赖性,且正常组的抑制作用更明显(P0.01,n=5)。由此可知,NFA对CCI模型大鼠DRG神经元GABA激活电流的抑制作用相比较正常组有所减弱,这可能是由于CCI模型的DRG神经元上钙激活氯通道的数量增加。     

Excitatory effect of histamine on neuronal activity of rat cerebellar fastigial nucleus Jn vitro

The cerebellar fastigial nucleus （FN） holds an important role in motor control and body balance. Previous studies have revealed that the nucleus is innervated by direct hypothalamocerebellar hletaminergic fibers. However, the functional role of histaminergic projection in cerebellar FN has never been established. In this study, we investigated the effect of histamine on neuronal firing of cerebellar FN by using slice preparations. Sixty-five FN cells were recorded from 47 cerebellar slices, and a vast majority of the cells responded to histamine stimulation with an excitatory response （58/65, 89.2%）. Perfusing slices with low-Ca^2＋/high-Mg^2＋ medium did not block the histamine-induced excitation （n=10）, supporting a direct postsynaptic action of histamine on the cells. Furthermore, the excitatory effect of histamine on FN neurons was not blocked by selective histamine H1 receptor antagonist triprolidine （n=15） or chlorpheniramine （n=10）, but was effectively suppressed by ranitidine （n=15）, a highly selective histamine H2 receptor antagonist. On the other hand, highly selective histamine H2 receptor agonist dimaprit （n=20） instead of histamine HI receptor agonist 2-pyridylethylamine （n=16） mimicked the excitatory effect of histamine on FN neurons. The dimaprit-induced FN neuronal excitation was effectively antagonized by selective histamine H2 receptor antagonist ranitidine （n=13） but not influenced by selective histamine H1 receptor antagonist triprolidine （n=15）. These results demonstrate that histamine excites cerebellar FN cells via the histamine H2 receptor mechanism and suggest that the hypothalamocerebellar histaminergic fibers may modulate cerebellar FN-mediated sensorimotor integration through their excitatory innervations on FN neurons.     

Micromolar concentrations of Zn2+ antagonize NMDA and GABA responses of hippocampal neurons

NMDA (N-methyl-D-aspartate) receptors serve as modulators of synaptic transmission in the mammalian central nervous system (CNS) with both short-term and long-lasting effects. Divalent cations are pivotal in determining this behaviour in that Mg2+ blocks the ion channel in a voltage-dependent manner, and Ca2+ permeates NMDA channels. Zn2+ could also modulate neuronal excitability because it is present at high concentrations in brain, especially the synaptic vesicles of mossy fibers in the hippocampus and is released with neuronal activity. Both proconvulsant and depressant actions of Zn2+ have been reported. We have found that zinc is a potent non-competitive antagonist of NMDA responses on cultured hippocampal neurons. Unlike Mg2+, the effect of Zn2+ is not voltage-sensitive between -40 and +60 mV, suggesting that Zn2+ and Mg2+ act at distinct sites. In addition, we have found that Zn2+ antagonizes responses to the inhibitory transmitter GABA (gamma-aminobutyric acid). Our results provide evidence for an additional metal-binding site on the NMDA receptor channel, and suggest that Zn2+ may regulate both excitatory and inhibitory synaptic transmission in the hippocampus.     

A novel class (H3) of histamine receptors on perivascular nerve terminals

Two types of histamine receptor, the H1- and H2-receptors, are found not only on vascular smooth muscle cells but on the perivascular autonomic nerve terminals. Activation of the prejunctional histamine receptors modifies transmitter release from the nerve terminals. Recently, histamine was shown to inhibit its own release from depolarized slices of rat cerebral cortex. This phenomenon was found to be mediated by a novel class of histamine receptor, the H3-receptor, that was pharmacologically distinct from the H1- and H2-receptors. Up to now, there has been no indication whether this third class of histamine receptor is present in any tissue other than the brain. We report here that histamine depresses sympathetic neurotransmission in the guinea-pig mesenteric artery by interacting with histamine H3-receptors on the perivascular nerve terminals. The pharmacological properties of these receptors are similar to those reported for the H3-receptors in the brain. Our data provide evidence for the existence of H3-receptors in the autonomic nervous system.     

Deciphering a neuronal circuit that mediates appetite

Hypothalamic neurons that co-express agouti-related protein (AgRP), neuropeptide?Y and γ-aminobutyric acid (GABA) are known to promote feeding and weight gain by integration of various nutritional, hormonal, and neuronal signals. Ablation of these neurons in mice leads to cessation of feeding that is accompanied by activation of Fos in most regions where they project. Previous experiments have indicated that the ensuing starvation is due to aberrant activation of the parabrachial nucleus (PBN) and it could be prevented by facilitating GABA(A) receptor signalling in the PBN within a critical adaptation period. We speculated that loss of GABA signalling from AgRP-expressing neurons (AgRP neurons) within the PBN results in unopposed excitation of the PBN, which in turn inhibits feeding. However, the source of the excitatory inputs to the PBN was unknown. Here we show that glutamatergic neurons in the nucleus tractus solitarius (NTS) and caudal serotonergic neurons control the excitability of PBN neurons and inhibit feeding. Blockade of serotonin (5-HT(3)) receptor signalling in the NTS by either the chronic administration of ondansetron or the genetic inactivation of Tph2 in caudal serotonergic neurons that project to the NTS protects against starvation when AgRP neurons are ablated. Likewise, genetic inactivation of glutamatergic signalling by the NTS onto N-methyl D-aspartate-type glutamate receptors in the PBN prevents starvation. We also show that suppressing glutamatergic output of the PBN reinstates normal appetite after AgRP neuron ablation, whereas it promotes weight gain without AgRP neuron ablation. Thus we identify the PBN as a hub that integrates signals from several brain regions to bidirectionally modulate feeding and body weight.