学习过程中MF－CA3与PP－CA3突触传递效应的变化

应用慢性电极埋植技术以电生理学结合行为学的方法,探查在学习过程中大鼠海马ＣＡ３区两种不同输入突触（ＭＦ－ＣＡ３突触和ＰＰ－ＣＡ３突触）的可塑性变化及其相互关系。结果如下：（１）在分辨反应的建立过程中,在ＣＡ３区由ＭＦ诱发（ＭＦ－ＣＡ３）的群体锋电位（ｐｏｐｕｌａｔｉｏｎｓｐｉｋｅ,ＰＳ）和由ＰＰ诱发（ＰＰ－ＣＡ３）的群体锋电位,两者的峰值同步增大,同步达最高水平,且ＰＳ峰值达最高水平先于行为反应达学会标准;（２）在自然消退过程中,两者的ＰＳ峰值也是同步恢复至训练前水平的。结果表明,在ＣＡ３区这两种输入突触的习得性ＬＴＰ的产生和消退都是同步的,提示了它们之间可能具有协同作用。     

噪声对幼年和老年大鼠海马CA_3区习得性长时程突触增强的影响

经强噪声重复暴露(96 dB,2h/d,25 d)后,幼年和老年大鼠在条件反应的建立和再建立过程中,其海马CA_3区习得性长时程突触增强(LTP)的发展均受到明显阻抑,相应地动物达到学会标准需更多的训练。但幼年鼠受阻抑的程度更为严重。对习得性LTP的消退则在幼年和老年大鼠均无明显影响。本研究从突触功能的可塑性方面揭示幼年功物特别容易受到强噪声重复暴露的危害,提示应重视环境噪声对人类婴幼儿脑功能的损害作用的研究。     

幼年和老年大鼠学习中海马CA_3区长时程突触增强的年龄特征

研究发现幼年和老年大鼠在条件性饮水反应的建立、消退和再建立过程中,海马CA_3区有习得性长时程突触增强(LTP)的形成、消退和再形成现象。在它的形成和再形成以及每实验日训练作业后习得性LTP的发展上,幼年鼠明显快于老年鼠,而习得性LTP的消退,在两组间无明显差异。这既表明海马CA_3区的习得性LTP具年龄特征,也为论证习得性LTP可能是学习和记忆的神经基础之一提供了新的证据。     

电休克对海马 CA_3区习得性长时程突触增强的影响

每天训练作业结束后对动物进行一次电休克处理,较多的动物(4/6)虽用了比对照组约多一倍的训练次数,但仍未能产生长时程突触增强(LTP),相应地条件反应也未能建立;部分动物(2/6)的突触效应不受影响,能产生LTP,并相应地条件反应亦能建立,且 LTP 发展超前于条件性行为的发展。在条件反应巩固后给大鼠一次电休克,可使它的海马 CA_3区的习得性 LIP—时性地下降,条件反应率也相应地下降。经1—4h,LTP 完全恢复,条件反应率也相应地恢复到电休克前的水平。表明习得性 LTP 受影响,可使条件性行为随之相应改变。它为论证习得性 LTP 可能是记忆的神经基础之一提供了进一步的证据。     

大鼠海马CA3区的习得性长时程突触增强

本实验应用慢性埋植电极技术以电生理学结合行为学的方法,观察大鼠条件性饮水反应的建立、消退和再建立过程中,其海马CA_3区突触效应的变化规律。以刺激内嗅区的穿通纤维(PP)诱发的单突触的群体锋电位(PS)及群体兴奋性突触后电位(EPSPs)为指标,经叠加处理分析,发现随着条件反应的建立,海马CA_3锥体细胞出现突触效应的长时程增强(LTP),它随行为反应的实验性消退而消退,而在随后再次建立条件反应时,又重新出现;且无论此LTP达最高水平还是它的完全消退均超前于条件性行为反应的水平。又在一个实验日训练作业结束时PS并未立即随之增大,在24h内它随时间而发展,但到第4小时已达最高水平,且条件反应率是与PS的水平相应的,对PS与EPSPs的斜率进行相关分析表明,PS的变化主要是突触传递功效的变化。上述结果表明,海马CA_3区随着行为训练有习得性LTP产生。从其发神变化特点及其与条件性行为的关系,提示此习得性LTP极其可能是本实验中学习和记忆的展经基础。     

Unique Induction of CA1 LTP Components After Intake of Theanine, an Amino Acid in Tea Leaves and its Effect on Stress Response

Theanine, γ-glutamylethylamide, is one of the major amino acid components in green tea. This study was undertaken to evaluate the effect of theanine intake on long-term potentiation (LTP) induction at hippocampal CA1 synapses and exposure to acute stress. Young rats were fed water containing 0.3% theanine after birth. Key findings: Serum corticosterone level was markedly decreased by theanine intake. Because this decrease can modify synaptic plasticity, the effect of theanine intake was examined focused on CA1 LTP induction. CA1 LTP induced by a 100-Hz tetanus for 1 s was almost the same extent in hippocampal slices from theanine-administered rats, whereas that induced by a 200-Hz tetanus for 1 s was significantly attenuated. 2-Amino-5-phosphonovalerate (APV), an N-methyl-d-aspartate (NMDA) receptor antagonist, significantly attenuated CA1 LTP induced by a 200-Hz tetanus in the control rats, but not in theanine-administered rats. Interestingly, APV completely blocked CA1 LTP induced by a 100-Hz tetanus in the control rats, while scarcely blocking it in theanine-administered rats. These results indicate that theanine intake reduces NMDA receptor-dependent CA1 LTP, while increasing NMDA receptor-independent CA1 LTP. Furthermore, neither 100-Hz tetanus-induced LTP nor 200-Hz tetanus-induced LTP was attenuated in theanine-administered rats after exposure to tail suspension stress, suggesting that the lack of NMDA receptor-dependent CA1 LTP by theanine intake is involved in ameliorating the attenuation of CA1 LTP after tail suspension. This study is the first to indicate that theanine intake modifies the mechanism of CA1 LTP induction.     

NMDA-dependent and NMDA-independent neuronal processes in the cat motor cortex,disinhibited by bicuculline,during forepaw placement conditioning

Neuronal activity associated with a conditioned forepaw placing reaction was recorded in the cat's motor cortex locally disinhibited by bicuculline spontaneously diffused from the recording pipette. Electrical stimulation of the parieral cortex (area 5) with 3-5 pulses was used as a conditioned stimulus. In both naive and trained cats, adding of APV (NMDA receptor blocker) led to disappearance of the late (30-120 ms) secondary excitatory responses from the pattern of the neuronal reaction to the parietal stimulation recorded in the motor cortex. At the same time, the APV administration did not change the excitatory reactions (recorded, predominantly, in the deep cortical layers) time-locked to the execution of the conditioned movement. The conditioning resulted in a statistically significant increase in the amplitude and duration of the late secondary responses as well as in a shortening of their latency. In some cases (after a long period of training), the late secondary responses to the conditioned stimulus transformed into paroxysmal epileptiform bursts. A hypothesis is discussed that the increase in synaptic strength of the backward horizontal collaterals of layer-II/III pyramidal neurons is responsible for the learning-related changes in the neuronal reactions in the disinhibited motor cortex.     

大鼠内侧隔核对齿状回习得性LTP的调制

本工作观察到高频刺激自由活动的大鼠内侧隔核,对海马齿状回的群体蜂电位有一时性（１－２ｈ）的抑制作用。在明暗辨别学习中每次训练作业后立即给予ＭＳ ＨＦＳ,导致ＤＧ习得性长时程增强,（Ｌｏｎｇ－ｔｅｒｍ ｐｏｔｅｎｔｉａｔｉｏｎ,ＬＴＰ）的形成显著延缓,并且ＰＳ峰值增强的最高水平显著降低（Ｐ＜０．００１）,辨别反应的习得相应延迟,但对ＤＧ习得性ＬＴＰ的保持无影响。表明ＭＳ对ＤＧ习得性ＬＴＰ的形成有抑制     

Role of excitatory amino acid receptors in synaptic transmission in area CA1 of rat hippocampus

The new antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), which blocks responses to kainate and quisqualate, has been used in conjunction with D-2-amino-5-phosphonovalerate (APV), which blocks selectively responses to N-methyl-D-aspartate (NMDA), to determine the role of excitatory amino acid receptors in synaptic transmission. An excitatory postsynaptic potential (EPSP)-inhibitory postsynaptic potential (IPSP) sequence was evoked in CA1 neurons by stimulation of the Schaffer collateral-commissural pathway in rat hippocampal slices. CNQX (10 microM) substantially reduced the EPSP without having any effect on input resistance or membrane potential. The IPSP was also reduced provided that the stimulating electrode was place approximately 1 mm from the recording electrode. The EPSP that remained in the presence of CNQX had characteristics of an NMDA receptor-mediated potential; it had a slow timecourse, summated at high frequencies, was blocked reversibly by APV, increased greatly in size in Mg2+-free medium, and showed an anomalous voltage dependence in Mg2+-containing medium. In the presence of CNQX, an APV-sensitive polysynaptic GABAergic IPSP could be evoked, indicating that NMDA receptors can mediate suprathreshold EPSPS in inhibitory interneurons. It is suggested that either NMDA or non-NMDA receptors can, under different circumstances, mediate the synaptic excitation of pyramidal neurons and inhibitory interneurons in area CA1 of the hippocampus.     

Evoked potentials during the elaboration of a conditioned reflex to hippocampal stimulation in rats

In experiments on 9 rats, the study of evoked potentials (EPs) of the CA1 field of the dorsal hippocampus to stimulation of its symmetrical part serving as a signal of drinking conditioned reflex (CR) showed that during reflex elaboration, the amplitude of the main EP components significantly decreased; CR did not appear when the population spike (PS) was absent in the hippocampal response. PS always accompanying CR was not specific only of it, it was also recorded at other behavioural reactions. Changes of fascia dentata EPs in the process of CR elaboration to stimulation of its symmetrical part consisted in decrease of the initial negative wave and increase of the positive one. The obtained data point to a significant reconstruction of excitatory and inhibitory inputs to the hippocampus and fascia dentata under the influence of conditioned activity.