γ-氨基丁酸、荷包牡丹碱和L-谷氨酸钠对猫和家兔同侧和对侧图形视觉诱发电位的影响

在猫和家兔大脑半球一侧视区17/18交界处施加γ—氨基丁酸(GABA)、荷包牡丹碱和L—谷氨酸钠,以及用氯化钾和冷冻阻遏的方法,记录对侧和同侧皮层相应处图形视觉诱发电位(PVEP)的变化。讨论了GABA、荷包牡丹碱和L—谷氨酸钠对猫和兔的对侧和同侧PVEP的影响。     

兴奋大鼠延髓A1区引起降压、降心率效应的机制

在水合氯醛麻醉、箭毒化、人工呼吸的大鼠,观察到:(1) A_1区注入谷氨酸钠引起明显的血压下降和心率减慢。(2) 切断双侧颈迷走神经明显衰减A_1区的降压,降心率效应。(3) 延髓头端腹外侧区(RVL)预先注射酚妥拉明或心得安,均能明显衰减谷氨酸钠兴奋A_1区的降压效应,A_1区的降心率作用基本不受影响,将纳洛酮注入RVL后,A_1区的降压和降心率效应均无明显变化;注射荷包牡丹碱入RVL则使A_1区的降压、降心率效应反转。(4) RVL内注入酚妥拉明或心得安本身使基础血压降低,注射荷包牡丹碱入RVL则使基础血压升高(提示RVL内的α-,β-受体中介对RVE加压神经元的紧张性兴奋作用,GABA受体中介紧张性抑制作用);另一方面,RVL内注入心得安使基础心率减慢、注入纳洛酮或荷包牡丹碱使基础心率加快(说明β-受体中介紧张性心加速效应,阿片受体和GABA受体中介紧张性心抑制效应)。     

大鼠脊髓蛛网膜下腔注射γ-氨基丁酸受体激动剂对降低血压和徐缓心率的作用

给大鼠脊髓蛛网膜下腔注射γ-氨基丁酸(GABA)受体激动剂异鹅羔胺(0.125—0.25μg)能显著降低动物的动脉血压和心率。这种作用可被 GABA 受体阻断剂氯甲基荷包牡丹碱(1.0μg)所翻转,且具有剂量-效应关系。另一种 GABA 受体激动剂 THIP(5μg)以及GABA(500μg)也同样具有降低血压和心率的作用。说明激活脊髓内 GABA 受体具有降低血压和减慢心率的作用。肾上腺素α受体阻断剂育亨宾(30μg)能翻转可乐宁(0.25μg)的降压作用,但不能对抗异鹅羔胺的作用;GABA 受体阻断剂氯甲基荷包牡丹碱可翻转异鹅羔胺的作用,对可乐宁则无效。说明脊髓内异鹅羔胺和可乐宁降血压和减慢心率的作用没有相互的依存关系。     

脑内γ—氨基丁酸（GABA）在急性失血性低血压时对血压的影响

本实验通过大鼠和家兔侧脑室注射GABA受体阻断剂荷包牡丹碱(Bicuculline)研究正常血压和急性失血性低血压时,中枢GABA对血压的调节作用。结果表明:在两种情况下,荷包牡丹碱均有明显的升压作用,但后者显著大于前者,且这种升压效应不被去肾或去肾上腺所影响。同时发现:急性失血性低血压时,兔脑脊液中GABA含量明显增加,提示在急性失血性低血压时,中枢GABA具有阻止血压回升的作用,这种作用是通过对中枢交感神经系统的抑制引起的。     

大鼠延髓A5区降压、降心率效应的机制及其与A1区之比较

在与上一篇论文(关于A_1区)相同的条件下,(1) 用谷氨酸钠兴奋大鼠A_5区,和A_1区类似,也产生明显的降压、降心率效应。(2) 切断双侧颈迷走神经也明显衰减兴奋A_5区的心血管作用。(3) 将不同受体阻断剂注入延髓头端腹外侧区对兴奋A_5区引起的降压,降心率反应之影响,与A_1区比较有所不同:酚妥拉明、心得安、纳洛酮和荷包牡丹碱均能明显衰减A_5区的降压、降心率效应(心得安和荷包牡丹碱甚至反转之),表明除α-,β-,GABA受体之外,阿片受体也中介A_5区的降压降心率作用。     

家兔延髓腹外侧区内注射荷包牡丹碱对安定降低心脏功能的影响

家兔48只,用乌拉坦(1g/kg)静脉麻醉,三碘季铵酚制动,在人工呼吸下进行实验。静脉注射安定(0.5mg/kg)以及侧脑室注射氟安定(2mg溶于50μl人工脑脊液中)或γ-氨基丁酸(GABA)(300μg溶于50μl人工脑脊液中)都可降低心室内压峰值(PLVP),减少心力环面积(ACFL)和心室内压最大上升速率(dp/dt_(max))。安定和氟安定对PLVP、ACFL和dp/dt_(max)的抑制作用可被预先在侧脑室注射GABA受体拮抗剂印防己毒素(15μg溶于50μl人工脑脊液中)或双侧延髓腹外侧头端区(γVLM)微量注射GABA受体拮抗剂荷包牡丹碱(3μg溶于0.5μl生理盐水)所阻断。而在延髓网状巨细胞核中间部、网状小细胞核、孤束核或面神经核内注射同样剂量的荷包牡丹碱则不能阻断。 这些结果提示:延髓腹侧部GABA受体的激活可抑制心脏功能,安定对心脏功能的抑制作用可能通过激活延髓腹侧区GABA受体而实现。     

GABA对大鼠下丘脑正中隆起LHRH释放调节的研究

本研究应用大鼠下丘脑正中隆起(ME),观察 γ-氨基丁酸(GABA)和去甲肾上腺素(NA)对下丘脑促黄体生成激素释放激素(LHRH)神经元末梢分泌作用的影响。结果发现:GABA(10~(-6)mol/L)可显著促进 ME 的 LHRH 和 NA 的释放,即 LHRH 释放量由27.3±2.5pg/100ul 增加至150.4±27.9pg/100μl;NA 释放量由50.9±4.2pg/100μl 增加至105.5±19.1pg/100ul,两者与对照组相比有显著差异(P<0.01)。GABA 这些作用可被受体拮抗剂荷包牡丹碱(Bicuculline)所翻转。当荷包牡丹碱和 GABA(10~(-6)mol/L)同时存在于 ME 的培灌液中,LHRH 的分泌量下降为18.2±1.9pg/100μl,而 NA 分泌量下降为43.9±3.4pg/100μl。在内源性 NA 被利血平耗竭时,LHRH 的释放量仅增加26.5%,而 GABA 能使正常大鼠 LHRH 释放量增加451.9%。本研究提示:GABA 可促进下丘脑 ME 释放 LHRH,这一作用可能通过 NA 中介。     

γ-氨基丁酸及其GABAA受体参与家鸽顶盖前核神经元方向选择性的形成

研究了-氨基丁酸(GABA)及其拮抗剂荷包牡丹碱和2-hydroxysaclofen对家鸽中脑扁豆核神经元视觉反应的影响. 结果指出, GABA能明显减小扁豆核神经元的自发活动和视觉反应, 其GABAA拮抗剂荷包牡丹碱则能增强视觉反应, 并可消除无效方向上的抑制性反应, 但GABAB拮抗剂2-hydroxysaclofen对视觉反应和抑制反应均无效. 由此可见, 家鸽中脑扁豆核方向敏感神经元无效方向上的抑制主要由GABA和GABAA受体介导. 这种抑制作用至少部分是视动震颤方向不对称性的基础.     

甘氨酸和γ-氨基丁酸对小鼠游离脊髓的初级传入终末兴奋性的作用

本工作在正常离体小鼠(天龄10—15d)脊髓进行。实验结果表明:电刺激邻近记录电极的背根,微电泳GABA及GABA的协同剂Thip、Thiomuscimol和甘氨酸(Glycine)均能引起小鼠脊髓单一初级传入纤维终末的兴奋阈值下降,兴奋性增高,说明终末发生了去极化的变化。同时电泳荷包牡丹碱(Bicuculline)能逆转GABA及其协同剂的去极化作用,但对Glycine的去极化作用无效。而士的宁(Strychnine)能逆转Glycine的去极化作用,对GABA的去极化作用无效。说明在小鼠脊髓初级传入终末存在GABA_A受体及Glycine受体,而且在传入终末区Glycine受体类型可能与脊髓内其它部位的相同。     

霉菌毒素 Dihydroxyaflavinine 非竞争性抑制在爪蟾卵母细胞内表达的 GABA_A 受体通道

Dihydroxyaflavinine 是黄曲霉菌(Aspergillus flavus)的吲哚类代谢物。我们将鸡脑mRNA 注入爪蟾卵母细胞表达得到 GABA_A 受体通道,然后用电压箝记录方法定量研究了dihydroxyaflavinine 对 GABA 电流反应的作用。Dihydroxyaflavinine 非竞争性阻断GABA 电流反应(K_I=12μmol/L),撤药后反应迅速恢复。作为比较,青霉素对 GABA_A受体的抑制作用随 GABA 浓度的升高而增加。浓度高达1μmol/L 苯二氮(艹卓)位点配体 Ro 15-1788(KD=0.6—2nmol/L)不能阻断10μmol/L dihydroxyaflavinine 的作用,说明 dihy-droxyaflavinine 不作用于 GABA_A 受体的苯二氮(艹卓)位点。Dihydroxyaflavinine 类似印防已毒素,表观上加速 GABA_A 受体的脱敏过程,而青霉素和荷包牡丹碱与此相反。     

The modulation of somatosensory evoked potentials during the foreperiod of a forewarned reaction time task

During the foreperiod of a forewarned reaction time (RT) task reflexes in the executing limb increase to a lesser extent than those in the contralateral limb. This is possibly due to input modulation. The present study investigates the possibility of cutaneous sensory modulation during motor preparation by studying the amplitudes of somatosensory evoked potentials (SEPs). Eighteen subjects performed a forewarned RT task with the same fingers as the ones which were electrically stimulated. SEPs evoked during the 4 sec preparatory period were compared to those evoked during movement execution and during the resting period after the motor response respectively. During response execution most SEP components showed smaller amplitudes, i.e., they were gated, which agrees with other studies. In the first part of the foreperiod no SEP modulation was observed. Towards the end of the foreperiod, 500 msec before the response stimulus (RS), the amplitude of the contralateral parietal N70-P100 was significantly decreased, while the P45-N70 showed a similar tendency. However, at the same time the P100-N140 was increased in amplitude. The decrease of the intermediate latency components towards the end of the foreperiod is discussed in terms of gating, while the increase in the long latency component is discussed with respect to a decrease in RT on trials where the fingers were stimulated just before the RS, pointing to the role of attentional mechanisms.     

Frontal distribution of early cortical somatosensory evoked potentials to median nerve stimulation

The topography of early frontal SEPs (P20 and N26) to left median nerve stimulation was studied in 30 normal subjects and 3 patients with the left frontal bone defect. The amplitudes of P20 and N26 were maximum at the frontal electrode (F4) contralateral to the stimulation and markedly decreased at frontal electrodes ipsilateral to the site of stimulation. There was, however, no latency difference of P20 and N26 between ipsilateral and contralateral frontal electrodes. These results suggest that the origin of the ipsilateral and contralateral P20 and N26 is the same. The wide distribution of P20 and N26 over both frontal areas could be explained by assuming a smearing effect from generators actually located in the rolandic fissure and motor cortex.     

Modulation of vibrissa-evoked cortical potentials after infraorbital nerve crush in rats

Cortical potentials evoked by unilateral stimulation of the major vibrissae were recorded in 12 rats subjected to unilateral crush of the infraorbital nerve. Immediately after nerve crushing, the latency of the initial positive potential evoked at contralateral scalp sites by stimulating the vibrissae of the nerve-crushed side was increased. In contrast, the latency of the ipsilaterally evoked potential was shortened. The relative amplitude of the negative component to the positive one of the evoked potentials tended, immediately after the nerve crush, to be smaller on the contralateral cortex (N/P-contra) and greater on the ipsilateral cortex (N/P-ipsi). These changes disappeared largely by the 2nd post-operative week. It is suggested that reduction of the tactile signals transmitted through the crossed pathway is responsible for the prolonged latency and the smaller N/P-contra. Shortening of the ipsilateral latency and the enhanced N/P-ipsi may be due to liberation of the ipsilateral sensory system from inhibition by the contralateral one.     

Auditory event-related potentials in well-characterized groups of children

Sixty-eight subjects ranging in age from 6 to 23 years were studied in an ‘auditory oddball’ event-related potential (ERP) paradigm. Our results replicate other studies, finding P3 as the most consistent component of ERPs since childhood, although great variability of this component was found in the 6-year-old group. Separate age/ERP component latency and amplitude linear regressions were computed for subjects 6–14 and 6–23 years old. Our data show in both groups a significant negative and positive correlation between age and P3 latency and N1-P2 amplitude respectively. The age/P3 latency slope for the subjects under 15 years old was −19.00 msec/year versus 8.15 msec/year for all subjects (6–23 years old). Our results indicate that P3 latency during childhood decreases with age, reaching an asymptote after or during the second decade of life. No curvilinear relationship between age and P3 latency was found over the child groups, although a significant curvilinear relationship was found over the entire age range.This study showed no significant gender differences in latency at any age group. However, in the adult group females showed significantly larger amplitudes than males.     

Auditory brain stem responses to monoaural stimulation registered in symmetrical areas of cat's brain cortex

In five anaesthetized cats (Nembutal 35 mg/kg) with 14 chronically implanted recording epidural electrodes the auditory brain stem responses (ABR) to monoaural stimulation (click) in symmetrical areas of the brain cortex were recorded. Each ABR to acoustic stimulus of sufficient intensity is formed by a complex of alternating five positive (P1-P5) and four negative (N1-N4) peaks; two further small peaks often follow on this complex. The amplitude of ABR peaks N3, P4, N4 and P5 to monoaural stimulation in symmetrical areas of cat's cortex was always higher in records from the hemisphere contralateral to the stimulated ear than in records from the ipsilateral one. The amplitude of P3 ABR peak behaved to the contrary--it was higher on ipsilateral hemisphere. On the other hand the amplitude of ABR peaks P1, N1, P2 and N2 to monoaural stimulation in symmetrical areas of the brain cortex showed no degree of lateralization in our experimental animals. The present findings support indirectly the presumption that each peak of the ABR is generated by a particular acoustic brain stem structure.     

Effect of stimulus rate on the cortical posterior tibial nerve SEPs: a topographic study

We performed topographical mapping of somatosensory evoked potentials (SEPs) in response to posterior tibial nerve stimulation delivered at 2, 5 and 7.5 Hz in 15 healthy subjects. P37 was significantly attenuated at 5 and 7.5 Hz and the N50 component attenuated only at 5 Hz, its amplitude remaining stable for further increases in stimulus frequency. Frontal N37 and P50 potentials showed no significant decrease when the stimulus repetition frequency was changed from 2 to 7.5 Hz. P60 showed an attenuation of the amplitude only at 7.5 Hz. Latency and scalp topographies of all cortical components examined remained uncharged for the 3 stimulus rates tested The optimal stimulus rate for mapping of tibial nerve SEPs was lower than 5 Hz. The distinct recovery function of the contralateral N37-P50 and ipsilateral P37-N50 responses suggests that these potentials arise from separate generators     

Replicability of MEG and EEG measures of the auditory N1/N1m-response

We investigated the replicability of the source location, amplitude and latency measures of the auditory evoked N1 (EEG) and N1m (MEG) responses. Each of the 5 subjects was measured 6 times in two recording sessions. Responses to monaural stimuli were recorded from 122 MEG and 64 EEG channels simultaneously. The EEG data were modeled with a symmetrically-located dipole pair. For the MEG data, one dipole in each hemisphere was located independently using a subset of channels. Standard deviation (SD) was used as a measure for replicability. The average SD of the x, y and z coordinates of the contralateral N1m dipole was about 2 mm, whereas the corresponding figures for the ipsilateral N1m and the contra- and ipsilateral N1 were about twice as large. The SDs of the dipole amplitudes and latencies were almost equal with MEG and EEG. The amplitude and latency measures of the MEG field gradient waveforms were almost as replicable as those of the dipole models. The results suggest that both MEG and EEG can be used for investigating the simultaneous activity of the left and right auditory cortices independently, MEG being superior in certain experimental setups.     

Reliability and upper normal variability limits of pattern reversal visual evoked potential parameters.

Twenty healthy volunteers aged 21-48 years (10 males, 10 females) were submitted to pattern reversal visual evoked potentials with 15' and 30' checks. The recordings were repeated after 7 days to assess reliability and upper normal variability limits of the following parameters: latencies of N70, P100, N140 and peak-to peak amplitudes of N70-P100, P100-N140. Reliability was tested with intraclass correlation coefficient, which was excellent or good for all parameters. Test-retest variability limits were computed with = 0.01 for absolute latency differences and relative amplitude differences.     

Pattern ERG: effects of reference electrode site,stimulus mode and check size

We studied monocular pattern ERG (PERG) in 10 normal subjects and a patient with optic neuritis. No clinically significant PERG could be recorded from the occluded eye with any reference (ipsilateral ear or temple, or midfrontal), indicating that cross-contamination is not present with binocular testing. Ipsilateral temple reference minimized VEP (P100/N100) contribution to the PERG N95 which occurred with ipsilateral ear or midfrontal reference. The conclusions were confirmed by results from the patient, who had marked monocular delay of a normal amplitude P100. Twenty-four subjects were tested with monocular and binocular stimulation using an ipsilateral temple reference. There were differences in PERG latencies and amplitudes although the interside amplitude ratio showed smaller differences with binocular stimulation. Increasing check size (17, 35 and 70 min) decreased P50 and N95 latencies and increased P50 amplitude.     

Enhanced amplitude reduction of somatosensory evoked potentials by voluntary movement in the elderly

We studied the effects of aging on modification of the median nerve somatosensory evoked potentials (SEPs) by voluntary movement in 17 aged (66.5±8.9 years, mean±SD) and 12 young normal humans (27.5±5.0 years). The amplitudes of cortical SEP components were generally larger in the aged group than in the young group. Following isometric contraction of the thenar muscle, the aged group showed significant attenuation of the prerolandic P22-N28-P45 and the postrolandic P24-N30-P45, while the young group only demonstrated significant reduction of the prerolandic P22-N28 amplitude. In the prerolandic N28-P45 and the postrolandic P24-N30 and N30-P45, amplitudes reduced by voluntary movement (gated amplitude) significantly correlated with amplitudes at rest (resting amplitude) and with the age of subjects. The effects of stimulus intensity and frequency on gating supported the correlative changes between gated and resting amplitudes. These results suggest that the magnitude of gating depends on SEP amplitudes at rest, and that augmented gating in the aged group is a result of enlarged SEPs. Since the cervical and Erb's potentials were not changed by movement, and passive movement did not significantly affect the SEPs, a centrifugal mechanism is probably responsible for gating in this study.