低频刺激诱发海马突触传递去长时程增强的特性研究

目的和方法：以频率为1、3或5Hz,脉冲数为300或900,与高频刺激（HFS）时间间隔是20min或100min的低频刺激（LFS）作用于大鼠海马脑片,分别观察其对CA1区突触传递去长时程增强（DP）形成的影响。结果：HFS（100Hz,100脉冲的串刺激两串,串间隔30s)可诱发突触传递效率的长时程增强（LTP）。HFS经20min给予3Hz900脉冲的LFS可翻转LTP,产生DP,该作用可为NMDA受体阻断剂AP5（50μmol/L)所阻断,1Hz、5Hz、低脉冲数或与HFS时间间隔长的LFS,其诱发DP的效率减弱。结论：诱发海马CA1区DP的产生,对LFS的参数有较强的依从性。该作用可能是通过激活NMDA受体而实现的。     

Protective effect of interleukin-10 on the development of epileptiform activity induced by brief hypoxic episodes in the rat hippocampal slices

The aim of the study was to investigate the effect of interleukin-10 (IL-10) (1 and 10 ng/ml) on the development of epileptiform activity induced by brief hypoxic episodes in CA1 area of rat hippocampal slices. Three three-minute hypoxic episodes induced a sustained decrease in the threshold of evoked population spike (PS) burst and an increase in the number of PSs in the PS response. IL-10 (1 ng/ml) completely abolished the development of epileptiform activity whereas the effect of IL-10 (10 ng/ml) was weaker. The protective effect of IL-10 on the hyperexcitability of the local neuronal network in hippocampal slices indicate that this cytokine can function as an intercellular mediator in the brain. The present results are the first experimental evidence of a protective role of anti-inflammatory IL-10 in the development of epileptiform events induced by brief episodes of hypoxia in the hippocampus.     

腺苷抑制海马神经元自发放电和谷氨酸所致癫痫样放电

应用细胞外记录单位放电技术,在大鼠海马脑片上观察腺苷（ａｄｃｎｏｓｉｎｅ,Ａｄｏ）对ＣＡ１区神经元自发和谷氨酸所致癫痫样放电的影响。实验结果如下：⑴２０个海刀ＣＡ１神经元在给予Ａｄｏ（０．０１－０．１μｍｏｌ／Ｌ）时自发放电频率降低,且呈明显的剂量依赖性;⑵在２２个ＣＡ１单位,应用腺苷受体非选择性拮抗剂８－苯茶碱（８－ｐｈｅｎｙｌ－ｔｈｅｏｐｈｙｌｌｉｎｅ,８－ＰＴ,０．５ｍｍｏｌ／Ｌ）和腺苷Ａ１     

Glycine receptor activation regulates short-term plasticity in CA1 area of hippocampal slices of rats

Functional glycine receptors (GlyRs) are enriched in the hippocampus, but their roles in synaptic transmission are unclear. In this study, we examined the effect of GlyR activation on paired-pulse stimulation of the whole-cell postsynaptic currents (PSCs) in the Schaffer-CA1 synapses in rat hippocampal slices. Bath application of glycine reduced the amplitude of PSCs, accompanied by an increase in holding current and resting conductance. Moreover, glycine application increased the paired-pulse ratio (PPR) of PSCs significantly, an effect largely abolished by the GlyR specific antagonist strychnine. Interestingly, glycine application had no significant effect on either the amplitude or the PPR of excitatory postsynaptic currents (EPSCs). Our findings suggest that GlyR activation regulates hippocampal short-term plasticity by altering GABAergic neurotransmission.     

成年大鼠海马CA1区锥体细胞KATP通道的特性

为了解成年大鼠海马CA1区锥体细胞KATP通道的特性,实验采用膜片钳技术的内面向外式记录法,在急性分离的CA1区锥体神经元上,研究了可被胞浆侧ATP所抑制的钾离子单通道的特性,当细胞膜内外两侧的K^ 浓度均为140mmol/L时,通道的电导为63pS,翻转电位为1．71mV,通道呈弱向内向整流性,在负钳制电位时,通道开放时常被短时的关闭所打断,而在正钳制电位时,这种短时程的关闭状态明显少于负钳制电位时,但通道开放概率未见明显的电压依赖性,ATP对通道活动的抑制作用呈浓度依赖性,抑制通道活动50％的ATP浓度为0．1mmol/L.KATP通道的特异性阻断剂tolbutamide(甲糖宁,1mmol/L)可完全阻断通道的活动,而KATP通道开放剂diazoxide(二氮嗪,1mmol/L）则不增强通道的活动。     

硫酸镁对大鼠海马CA1区神经元钠电流的抑制作用

利用全细胞膜片钳技术研究了硫酸镁 (MgSO4 )对大鼠海马CA1区神经元钠电流的影响。结果表明 ,MgSO4 可浓度依赖和电压依赖地抑制钠电流 ,半数抑制浓度为 4 0 5mmol/L。这一抑制作用与刺激频率无关。结果还表明 ,4mmol/LMgSO4 不影响钠电流的失活过程 ,却使半数激活电压由 - 5 5 8± 6 8mV变为 - 3 4 2± 6 2mV (n =8,P <0 0 1) ,而激活曲线的斜率因子不变。结果提示 ,MgSO4 抑制大鼠海马CA1区神经元的钠电流可能是其抗缺血缺氧造成的中枢神经系统损伤的机制之一     

KATP通道对缺氧海马CA1区神经元损伤保护作用的机制

目的:探讨KATP通道在缺氧中对海马CA1区神经元的保护作用机制。方法:比较对照组、单纯缺氧组、KATP通道激动剂 缺氧组、KATP通道阻断剂 缺氧组中神经元p53 mRNA的表达、DNA断裂、以及神经元存活情况。结果:将神经元暴露在氧浓度为0%的缺氧环境中12h,KATP通道的激动剂二氮嗪(diazoxide,100μmol/L)显著降低p53 mRNA的表达量及细胞的凋亡数量。KATP通道的阻断剂甲糖宁(tolbutamide,100μmol/L)使p53mR-NA表达量显著增加,细胞的凋亡数量也随之显著增加。p53的特异性阻断剂曲古抑菌素(trichostatin,TSA)可以逆转甲糖宁(tolbutamide,100μmol/L)的作用。结论:KATP通道可以通过下调p53 mRNA的表达水平,对缺氧中的海马CA1区神经元起到保护作用。     

Comparative analysis of neuronal impulse activity in the CA1 and CA3 hippocampal fields in various typological groups of rats under exposure to emotional stimuli

Hippocampal unit activity in the right and left CA1 and CA3 fields was studied in rats divided in two groups by the method of "emotional resonance": the animals which did ("A") and did not stop ("E") crying of a partner rat. The rate of neuronal firing was studied in the state of hunger, satiation, and under exposure to intracranial electrical stimulation of the emotional positive and negative structures of the brain. It was shown that units increasing their activity after satiation prevailed in the CA1 field, whereas, in the CA3 field, the majority of neurons decreased the firing rate under these conditions. Intracranial stimulation, especially positive, increased the rate of firing in both hippocampal fields. Under exposure to emotional stimuli, "A" rats displayed asymmetric unit activity only in the CA1 field, whereas in "E" rats, activity was asymmetric only in the CA3 field. Under these conditions in both groups of animals, the left-side activity was more intense than the right-side activity independently of the emotion sign.     

Phencyclidine actions measured intracellularly in hippocampal CA1 neurons

The electrophysiological effects of phencyclidine (PCP) were measured intracellularly in guinea pig hippocampal CA1 neurons in vitro. At all doses tested (0.2 microM - 10 mM), PCP increased the width of action potentials (APs). Doses of 10 microM and higher were associated with decreased action potential amplitude. PCP decreased inhibitory postsynaptic potentials and excitatory postsynaptic potentials but did not alter responses to focally applied GABA. At the lowest dose (0.2 microM), PCP decreased the input resistance (Rin), while at all other doses Rin was increased. PCP decreased post-spike train afterhyperpolarizations at low and medium doses. PCP effects persisted in low calcium medium and also in medium containing 10(-6) M tetrodotoxin. It is concluded that in these central neurons, PCP primarily blocks potassium conductances at all doses and, at anesthetic doses, depresses sodium-dependent spikes.     

羟基马桑毒素所致的大鼠海马锥体细胞痫样放电活动

本研究采用离体海马脑片电生理研究技术,细胞外记录海马锥体细胞群体锋电位(population spike,PS),观察羟基马桑毒素(tutin)对大鼠海马脑片CA1区锥体细胞电活动的影响,探讨tutin是否具有致痛作用及其致痫机制。结果如下:(1)用40、30和20μg/ml浓度的tutin灌流海马脑片,可显著增高由顺向刺激Schaffer侧支所诱发的PS的幅度,灌流tutin 30min时,PS第一个波的幅度分别为对照的(388.7±20.1)%、(317.2±19.1)%和(180.9±11.6)%(各组n=5,P<0.05)。(2)伴随PS波幅的增高,可出现成串痫样放电波,波数4～11个不等。(3)灌流tutin后的部分脑片(n=9/34),在未刺激Schaffer侧支时也出现自发的成串、高幅痫样放电。(4)灌流CNQX阻断非NMDA受体后,再灌流tutin,PS幅度和放电波数均无显著性变化,即CNQX可完全抑制tutin所致的痫样放电;灌流AP-5阻断NMDA受体后,tutin仍可使PS幅度增高但放电波数无显著性增加,即AP-5可部分抑制tutin所致的痫样放电。上述结果表明,tutin可使海马脑片锥体细胞兴奋活动增强,具有致痫作用;兴奋性谷氨酸受体尤其是非NMDA受体可能介导tutin的致痫作用。     

Dose-dependent effects of phencyclidine on hippocampal CA1 neurons

The dose-dependent effects of phencyclidine were examined in guinea pig hippocampal slices using intracellular and extracellular recordings. Orthodromically evoked population potentials from the CA1 cell body layer were enhanced by low doses (0.2-0.4 microM) and depressed by high doses (0.01-10 mM). Medium doses of the drug (2.0-10.0 microM) showed little effect. Intracellular recordings from CA1 pyramidal neurons gave similar dose-dependent results. Low doses increased spontaneous firing rates and caused silent cells to fire. Medium doses both increased and decreased firing rates, whereas high doses depressed firing rates. Large transient depolarizing shifts were seen in some phencyclidine-treated cells at medium and high doses. Phencyclidine effects took 15-30 min to develop and were only partially reversible after a washout of up to 1 h.     

Serotonin agonist and antagonist actions in hippocampal CA1 neurons

The actions of serotonin (5-HT) and its putative agonists and antagonists were examined in vitro on hippocampal CA1 neurons using intracellular recordings, demonstrating that the cellular pharmacological effects can not necessarily be predicted from binding characteristics alone. The first response following 5-HT application was often a long-lasting (several minutes) hyperpolarization associated with decreased input resistance. Subsequent 5-HT applications caused only brief hyperpolarizations (30-120 s) and associated decreased input resistance, often followed by membrane depolarization. The post-spike train afterhyperpolarization (AHP) was prolonged for several minutes following the 5-HT induced hyperpolarization. 5-HT1 agonists (8-hydroxy-2-(di-n-propylamino)tetralin, 5-methoxytryptamine, MK-212) caused a prolonged hyperpolarization, decreased input resistance, and enhancement of the AHP. 5-HT applied following agonist application elicited only short-lasting hyperpolarizations. The 5-HT2 antagonists, cyproheptadine and mianserin, and a nonspecific 5-HT antagonist, methysergide, also caused a prolonged hyperpolarization with decreased input resistance. Spiperone, a nonspecific 5-HT antagonist, and ritanserin, a putative specific 5-HT2 receptor antagonist, depolarized CA1 neurons with little or no change in input resistance. The 5-HT-induced short-lasting hyperpolarization was not affected by drop application of 5-HT antagonists, except for methysergide, but perfusion of methysergide, ritanserin, and spiperone attenuated this response. The long-lasting 5-HT hyperpolarization might be mediated by 5-HT1A receptor activation, and the short-lasting hyperpolarization by another serotonergic receptor subtype.     

Identification and two-photon imaging of oligodendrocyte in CA1 region of hippocampal slices

Oligodendrocyte (OL) plays a critical role in myelination and axon maintenance in central nervous system. Recent studies show that OL can also express NMDA receptors in development and pathological situations in white matter. There is still lack of studies about OL properties and function in gray matter of brain. Here we reported that some glial cells in CA1 region of rat hippocampal slices (P15-23) had distinct electrophysiological characteristics from the other glia cells in this region, while they displayed uniform properties with OL from white matter in previous report; therefore, they were considered as OL in hippocampus. By loading dye in recording pipette and imaging with two-photon laser scanning microscopy, we acquired the high spatial resolution, three-dimension images of these special cells in live slices. The OL in hippocampus shows a complex process-bearing shape and the distribution of several processes is parallel to Schaffer fiber in CA1 region. When stimulating Schaffer fiber, OL displays a long duration depolarization mediated by inward rectifier potassium channel. This suggested that the OL in CA1 region could sense the neuronal activity and contribute to potassium clearance.     

成年大鼠海马CA1区锥体细胞K_(ATP)通道的特性

为了解成年大鼠海马CA1区锥体细胞KATP 通道的特性 ,实验采用膜片钳技术的内面向外式记录法 ,在急性分离的CA1区锥体神经元上 ,研究了可被胞浆侧ATP所抑制的钾离子单通道的特性。当细胞膜内外两侧的K 浓度均为 14 0mmol/L时 ,通道的电导为 63pS ,翻转电位为 1 71mV ,通道呈弱内向整流性。在负钳制电位时 ,通道开放时常被短时程的关闭所打断 ,而在正钳制电位时 ,这种短时程的关闭状态明显少于负钳制电位时。但通道开放概率未见明显的电压依赖性。ATP对通道活动的抑制作用呈浓度依赖性 ,抑制通道活动 5 0 %的ATP浓度为 0 1mmol/L。KATP 通道的特异性阻断剂tolbutamide (甲糖宁 ,1mmol/L)可完全阻断通道的活动 ,而KATP 通道开放剂diazoxide (二氮嗪 ,1mmol/L)则不增强通道的活动。     

Mechanism of developing "deprivation" potentiation of population responses of neurons in the CA1 field in hippocampal slices]

In rat hippocampal slices, synaptic transmission from Schaffer collaterals to CA1 neurons was studied by assessment of the effects of cessation of low-frequency testing stimulation to the population spike amplitude. A positive correlation between the duration of the stimulation interruption period (from 10 to 120 min) and the increment of the population spike amplitude (from 30 to 100% above baseline level). The "deprivational" potentiation (DP) offers a property of summation and is able to persist for long (testing was continued up to one hour). Prior induction of the long-term posttetanic potentiation (LPTP) that for 1-3 hours prevents the development of the late rather than the short-term LPTP phase, in our experiments also suppressed the DP induction after 60-min stimulation interruption interval. The same results were obtained in the presence of polymixin B (20 mcM), which is an inhibitor of protein kinase C (PKC) and PKC-dependent phase of the LPTP. This finding provides support for the earlier assumption about the similarity of the mechanisms responsible for the development of the DP and PKC-dependent LPTP phase related with protein phosphorylation.     

Temporal pattern sensitivity of long-term potentiation in hippocampal CA1 neurons

High-frequency electrical stimulation in the hippocampus leads to an increase in synaptic efficacy that lasts for many hours. This long-term potentiation (LTP) of synaptic transmission is presumed to play a crucial role in learning and memory in the brain. However, the frequency of stimulation generally used to obtain LTP is beyond the normal physiological range of activity of hippocampal neurons. We found that LTP can be induced by an electrical stimulation whose frequency is comparable to that of the naturally occurring firing activity of hippocampal neurons if the stimulating pulseinterval train has a special time structure. In the present experiment, we compared the magnitude of LTP induced by the four types of stimuli which have the same pulse number and the same mean frequency but different time structure in interstimulus intervals. One type of stimuli has regular intervals, and this served as a control stimulus. In the other three types of stimuli, the adjacent interstimulus interval had the following statistical properties: in type 1, their correlations are positive; in type 2, negative; and in type 3, independent. The magnitude of LTP induced by these four types of stimuli showed clear order relationships: type 3/type 1 control > type 2. Detailed analysis of the evoked potential during a period of temporal pattern stimulation revealed that the amplitude of the population spikes of repetitive firing, especially of the second and third population spikes, had the same order relationship as the LTP. Because 2-amino-5-phosphonovalerate (APV) (50 M) selectively abolished the second and the third population spikes but not the first, and blocked the formation of LTP, the second and the third peaks which appeared as part of the late component of excitatory postsynaptic potentials (EPSP) must involve LTP formation through the activities of N-methy-D-aspartate (NMDA) channels. From the experimental data, a dynamic induction rule concerning LTP in specific neural networks was derived by which the temporal information of the input stimuli can be extracted and transformed into the weight space of synaptic connections in hippocampal networks (see Fig. 1. CA1).     

The presynaptic modulation of glutamate release and the membrane dysfunction induced by in vitro ischemia in rat hippocampal CA1 neurons

Superfusion with an oxygen and glucose deprived medium (in vitro ischemia) of rat hippocampal CA1 pyramidal neurons in tissue slices produced a rapid depolarization within 5 min and thereafter showed no functional recovery (irreversible membrane dysfunction), even if oxygen and glucose were reintroduced. We previously suggested that such a rapid depolarization is triggered by the accumulation of extracellular glutamate (Glu). As a result, we examined the effects of either the activation or inhibition of presynaptic receptors, which modulate Glu release from the nerve terminal, on the potential change produced by in vitro ischemia. The adenosine A1 receptor antagonist, 8-cyclopenthyl theophylline, A2a receptor antagonist, ZM241385, and A2b receptor antagonist, alloxazine, did not significantly alter either the latency or the maximal slope of the rapid depolarization. In addition, the GABAB receptor antagonist, 2-hydroxysaclofen, or the metabotropic Glu receptor type 4 antagonist, alpha-methylserine-O-phosphate, did not change either the latency or the maximal slope. The adenosine A(1) receptor agonist, 2-chloro-N6-cyclopentyladenosine, A2a receptor agonist, CGS2168, or A2b receptor agonist, 5'-(N-ethylcarboxamido)-adenosine, did not affect these parameters either. None of these drugs restored the membrane potential to the pre-exposure level after the reintroduction of oxygen and glucose. Simultaneous intracellular recordings from CA1 and CA3 pyramidal neurons in the same slices revealed the membrane of the CA3 neurons to be hyperpolarized when a rapid depolarization occurred in the CA1 neurons. These results suggest that presynaptic Glu release does not accelerate during the generation of the rapid depolarization induced by in vitro ischemia.