组胺能与y-氨基丁酸能神经传递在问位核神经元信息加工中的作用

小脑间位核（interpositusnucleus,IN）主要接受1一氨基丁酸（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纽胺H,受体阻断剂ranitidine（n=10）和PK。抑制剂H一89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H：受体偶联的G—protein—AC—PK。信号通路,磷酸化GABAB和GABA^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．     

孕烯醇酮和孕烯醇酮硫酸盐对小鼠不同脑区~3H-GABA与GABA_B 受体结合的影响

采用放射配体受体结合分析法 ,研究了孕烯醇酮 (Pe)和孕烯醇酮硫酸盐 (Pes)对小鼠不同脑区3H GABA与GABAB 受体结合的影响 .结果显示 ,Pe对小鼠下丘脑、大脑皮层、海马、小脑GABAB 受体的结合均有抑制效应 ,且能被GABAB 受体激动剂巴氯芬 (Bac)所阻断并翻转 .Pes对大脑皮层、海马、小脑GABAB 受体的结合有抑制作用 ,而对下丘脑则有促进作用 .Bac能阻断Pes的抑制作用 (海马除外 ) ,加强Pes的促进作用 .实验结果提示 ,Pe ,Pes对各脑区GABAB 受体的结合具有一定的影响作用 ,且多为抑制效应     

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。     

5-HT_(2C)受体对帕金森病模型大鼠外侧缰核谷氨酸能神经元电活动的影响

为探讨帕金森病(PD)模型大鼠外侧缰核(LHb)中谷氨酸能神经元的电活动变化及其对5-羟色胺2C(5-HT_(2C))受体刺激的反应,阐明LHb和5-HT_(2C)受体在PD神经生物学机制中发挥的作用,通过6-羟多巴胺(6-OHDA)损毁单侧黑质致密部(substantia nigra pars compacta,SNc)建立PD模型,采用细胞外记录的方法,观察假手术组与单侧SNc损毁组大鼠LHb中谷氨酸能神经元的电活动。结果显示:与假手术组大鼠相比,损毁组大鼠LHb中谷氨酸能神经元的电活动增强,表现为爆发式放电活动增强(P0.05);LHb中局部注射5-HT_(2C)受体激动剂Ro60-0175后,两组大鼠的神经元放电频率虽均升高(P0.05),但损毁组大鼠LHb中谷氨酸能神经元放电频率升高持续时间显著长于假手术组,且给药前后神经元的放电形式更趋向于爆发式活动(P0.05),变异系数明显升高(P0.05)。结果提示单侧SNc损毁使LHb中谷氨酸能神经元爆发式电活动增强,可能与PD相关抑郁行为发生有关,5-HT_(2C)受体参与了对LHb中谷氨酸能神经元电活动的调节。     

GABA引起正常和病理性疼痛大鼠DRG神经元去极化反应的比较

为探究GABA在痛觉信息传递中的作用,观察分析了γ-氨基丁酸(GABA)在神经病理性疼痛中的作用。制备神经病理性疼痛大鼠模型,取其L4-L5背根神经节(dorsal root ganglion,DRG),运用细胞内微电极记录技术观察在灌流GABA及其受体阻断剂的情况下,引起DRG神经元膜电位的变化。结果表明,病理性疼痛模型组大鼠的DRG神经元对不同浓度GABA引起的去极化反应均明显小于正常对照组大鼠(P0.05),这说明神经病理性疼痛可通过减弱GABA介导的突触前抑制易化痛觉信息的传递。     

D_2受体激动剂R(一)—NPA对DRG神经元GABA-激活电流的抑制作用

应用全细胞膜片钳记录技术在大鼠新鲜分离DRG神经元上,观察预加多巴胺D_2受体选择性激动剂R(—)—NPA对GABA—激活电流的调制作用.绝大部分受检细胞86.2%(50/58)对外加GABA敏感.10~(-6)～10~(-3)mol/LGABA 引起一剂量依赖性有明显去敏感作用的内向电流.对GABA敏感的50个受检细胞中13个细胞引起一较大的无明显去敏感的内向电流,其他的无反应.预加R(一)—NPA30秒后再加GABA,则对GABA—激活电流幅值的影响如下:抑制的为76%(38/5O),增强的为2%(1/50),无明显作用的为22%(11/5O).在其浓度为10~(-4)mol/L、10~(-5)mol/L、10~(-6)mol/L、10~(-7)moV/L时抑制(X±SE)分别为19.1%12.8(n=6)、42.49%±3.2(n=6)、83.6%±1.2(n=6)、8.69%±1.8(n=6).细胞内加蛋白激酶抑制剂H7后,R(—)—NPA对GABA的抑制作用完全消除(n=16).     

Ghrelin对大鼠孤束核葡萄糖反应神经元的影响

采用玻璃微电极记录神经元活动的实验方法,研究大鼠孤束核(NTS)微量注射ghrelin对孤束核内葡萄糖反应神经元的活动的调节作用;在孤束核中记录到的82个神经元中,有37(45.13%)个葡萄糖反应神经元中,其中11个给予葡萄糖后电活动增强,26个电活动减弱,分别称之为葡萄糖受体神经元(GRNs)和葡萄糖敏感神经元(GSNs)。在11个GRNs中有9个(81.81%)给予ghrelin后电活动减弱,1个(9.095%)电活动增强;在26个GSNs中23个(88.46%)给予ghrelin后电活动减弱,1个(16.67%)电活动增强。结果提示,ghrelin可以通过改变NTS内葡萄糖反应神经元的电活动来调节能量代谢和摄食活动。     

GABA能回路在听皮层神经元频率调谐中的作用

为了解神经抑制在听中枢神经元频率调谐过程中的作用,本研究采用多管玻璃微电极胞外记录单单位反应的方法观察了去r-氨基丁酸能抑制后大棕蝠(Eptesicusfuscus)听皮层神经元频率调谐特性的变化,结果显示:(1)97.9%的神经元频率调谐曲线扩宽,Qn值下降(p<0.0001);(2)绝大部分神经元的最小阈值下降(p<0.0001);(3)兴奋性调谐曲线面积增加(p<0.0001).该结果提供了GABA能回路参与蝙蝠听皮层神经元频率调谐的直接证据.     

SKF38393对DRG神经元GABA-激活电流的抑制

在大鼠新鲜分离DRG神经元标本上应用全细胞膜片作记录,观察了多巴胺D_1受体的选择性激动剂(±)SKF38393HCI对GABA-激活电流的作用。大部分受检细胞(60/70)对GABA敏感。10~(-6)～10~(-3)mol/L GABA可引起呈剂量依赖性的明显去敏感作用的内向电流。在60个对GABA敏感的细胞中,预加SKF38393引起的膜反应如下:(1)外向电流(7/60);(2)内向电流(5/60);(3)无反应(48/60)。与GABA激活的内向电流相比,SKF38393激活电流幅值较小,无明显去敏感现象。预加SKF38393 30秒对GABA-激活电流幅值的影响如下:产生抑制作用的为88.33％(53/60),增强的为1.66％(1/60),无明显作用的为10.0％(6/0)。SKF38393对10~(-4)mol/L的GABA-激活电流的抑制作用依赖于SKF38393的浓度,在其浓度为10~(-4)、10~(-5)、10~(-6)、10~(-7)mol/L时对GABA-激活电流的抑制(±)分别为46.5％±2.3(n=8)、35.5％±1.2(n=8)、26.8％±1.5(n=7)、24.8％±2.6(n=7)。通过应用二次膜片作(repatch)技术在同一细胞(n=2)以及不同细胞组间(n=14)进行对比,证明:细胞内加蛋白激酶抑制剂H-7后,SKF38393对GABA的抑制作用完全清除。结果提示:SKF38393对GABA-激活电流的抑制作用可能是由于SKF38393激活D_1受体后通过胞内转导机制,使GABA受体通道复合体胞内磷酸化所致。     

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。     

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.     

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.     

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.     

Regulation of AMPA receptor lateral movements

An essential feature in the modulation of the efficacy of synaptic transmission is rapid changes in the number of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors at post-synaptic sites on neurons. Regulation of receptor endo- and exocytosis has been shown to be involved in this process. Whether regulated lateral diffusion of receptors in the plasma membrane also participates in receptor exchange to and from post-synaptic sites remains unknown. We analysed the lateral mobility of native AMPA receptors containing the glutamate receptor subunit GluR2 in rat cultured hippocampal neurons, using single-particle tracking and video microscopy. Here we show that AMPA receptors alternate within seconds between rapid diffusive and stationary behaviour. During maturation of neurons, stationary periods increase in frequency and length, often in spatial correlation with synaptic sites. Raising intracellular calcium, a central element in synaptic plasticity, triggers rapid receptor immobilization and local accumulation on the neuronal surface. We suggest that calcium influx prevents AMPA receptors from diffusing, and that lateral receptor diffusion to and from synaptic sites acts in the rapid and controlled regulation of receptor numbers at synapses.     

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.     

Protein kinase C reduces Mg2+ block of NMDA-receptor channels as a mechanism of modulation.

The roles of N-methyl-D-aspartate (NMDA) receptors and protein kinase C (PKC) are critical in generating and maintaining a variety of sustained neuronal responses. In the nociceptive (pain-sensing) system, tissue injury or repetitive stimulation of small-diameter afferent fibres triggers a dramatic increase in discharge (wind-up) or prolonged depolarization of spinal cord neurons. This central sensitization can neither be induced nor maintained when NMDA receptor channels are blocked. In the trigeminal subnucleus caudalis (a centre for processing nociceptive information from the orofacial areas), a mu-opioid receptor agonist causes a sustained increase in NMDA-activated currents by activating intracellular PKC. There is also evidence that PKC enhances NMDA-receptor-mediated glutamate responses and regulates long-term potentiation of synaptic transmission. Despite the importance of NMDA-receptors and PKC, the mechanism by which PKC alters the NMDA response has remained unclear. Here we examine the actions of intracellularly applied PKC on NMDA-activated currents in isolated trigeminal neurons. We find that PKC potentiates the NMDA response by increasing the probability of channel openings and by reducing the voltage-dependent Mg2+ block of NMDA-receptor channels.     

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.     

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.