具有共同感受野的外膝体神经元的反应相位互补特性

用微电极在猫外膝体进行记录时,有时同一支微电极能同时记录到两个神经元放电,通常是一个给光中心细胞和一个撤光中心细胞。这一对神经元具有共同的感受野,并且对光刺激的反应类型也相同(同属于瞬变型细胞,或者同属于持续型细胞)。当正弦调制的光点投射在它们的感受野中心时,在不同的刺激强度下,给光中心细胞和撤光中心细胞的反应相位彼此相差半个周期(180°)。在低的刺激频率(5Hz)下,给光中心和撤光中心细胞的反应峰值延迟时间(相对于光调制信号的最大和最小值)也相同,表明它们具有相同的反应潜伏期。这种相位互补特性使具有共同感受野的一对细胞工作于“推挽”方式。对于瞬变型细胞来说,尽管它们在单独活动时显示半波整流特性,然而组成互补对以后则能传递全周期光调制信号。     

瞳孔控制系统非线性的频率特性与固有频率

本文用实验方法从时域和频域上揭示了瞳孔对光反应的非线性特性.在亮度以正弦变化的光刺激下,瞳孔反应波形呈同步倍频现象;描述函数的频率-振幅特性曲线呈多峰的锯齿形;具有1.2Hz左右的系统固有频率和极限环现象.     

平均亮度对猫外膝体瞬变细胞和持续细胞时间调谐曲线的影响

用正弦波调制的光点刺激麻痹的清醒猫外膝体神经元感受野中心,当平均亮度改变时,瞬变细胞的时间频率调谐曲线的形状和敏感频率没有或很少变化,与此相应,这些细胞的自发发放也不随未调制的光照水平而改变。持续细胞的调谐曲线的调幅大体随对未调制光照的平均发放水平的升降而增大或减小,但敏感峰不变。衰减平均亮度1—2对数单位,可使多数呈双峰的调谐曲线的高调频峰消失,对产生此变化的原因,曾加以讨论。     

猫外膝体神经元时间频率调谐特性的研究

用示波器产生亮度受正弦波调制的小光点刺激清醒猫外膝体神经元的感受野,以不同调制频率下神经元放电的平均频率为指标,分析了126个细胞感受野中心的时间频率调谐特性,主要结果如下。(1)大多数(93.7%)细胞呈调制-兴奋型反应,即刺激光的时间调制在一定频率范围内使放电频率增加;少数(6.3%)细胞呈调制-抑制型反应,即在一定频率范围内,时间调制使放电减少。(2)根据调谐曲线的形状和通带宽度,调制-兴奋型反应包括带通滤波器和低通滤波器两种类型,其110个调谐曲线的峰值分布接近正态曲线,多数细胞对7Hz 的调谐最敏感。调制一抑制型反应包括带除滤波器和低除滤波器两类。(3)调制-兴奋型曲线的通带旁边较當出现抑制性侧带,调制-抑制型曲线出现兴奋性侧带。(4)感受野中心区与外周区的时间频率调谐曲线的带宽和形状有所不同。     

猫外膝体细胞和视网膜神经节细胞对正弦调制光刺激反应的相位特性

记录了猫外膝体细胞和视交叉纤维对正弦调制光点刺激的反应,作成反应时间直方图(PSTH)。用博里叶分析方法测量不同时间频率下反应的基波相位,作相位-频率特性曲线(PFC)。在暗适应条件下用锥系统的阈下刺激分离出杆系统的反应,这时外膝体细胞的相-频特性为一条负斜率的直线。由斜率所推算的潜伏期平均为81ms。在间视条件下,用 Stiles的二色阈法,分离出锥系统的反应,在这种情况下,相-频特性出现一个十分明显的转折。低频段回归线所对应的潜伏期平均为 107ms,高频段为 39ms。用同样方法分析了神经节细胞(视交叉纤维)的相位-频率特性,结果与外膝体细胞相似,说明与锥系统及杆系统活动有关的时间频率通道在视网膜就已经形成。     

猫外膝体神经元时间频率调谐特性的非序列脉冲间隔分析

用正弦调制的光点,刺激清醒猫外膝体神经元感受野中心,对25个细胞的非序列脉冲间隔直方图进行了分析,观察到在黑暗和恒定光照条件下,具有均匀、单模和多模三种分布类型。随着闪光频率的变化,在所有直方图上第二模出现的时程等于闪光周期,在细胞各自特有的敏感频率时,直方图上的模数最少,第一模频数最大。这些结果不仅与平均放电频率的变化相对应,也表明闪光所引起的细胞簇形放电,对其敏感频率同步最佳,脉冲数最多,密度最高。细胞放电图的这种闪光调制,有利于该细胞传递其偏爱频率的亮度变化信息。     

猫外膝体神经元兴奋和抑制过程的相互作用

用神经脉冲自动计数的方法,定量地研究了猫外膝体神经元兴奋与抑制过程在时间和空间上的相互作用。1.时间上的相互作用:在亮度变化瞬间,神经细胞的兴奋或抑制过程增强,表现为放电频率暂时地明显增加或减少。这一作用持续的时间(适应时间),瞬变细胞约0.1秒,持续性小感受野细胞约4～8秒,持续性大感受野细胞约40～80秒。2.空间上的相互作用:改变被照射视网膜面积的大小,同时计算神经元的平均放电频率,可以确定外周抑制区的存在、范围和强度。外周抑制可以同时作用于给-撤细胞的给光反应和撤光反应,也可以选择地只抑制其中某一种反应。纯撤光细胞没有外周抑制区。具有大感受野的外膝体神经元,其感受野的大小与背景光的强度有关。在高亮度情况下,感受野变小,有利于改善分辨率;在低亮度下,感受野扩大,有利于提高灵敏度。     

猫外膝体神经元兴奋和抑制过程的相互作用

用神经脉冲自动计数的方法,定量地研究了猫外膝体神经元兴奋与抑制过程在时间和空间上的相互作用。1.时间上的相互作用:在亮度变化瞬间,神经细胞的兴奋或抑制过程增强,表现为放电频率暂时地明显增加或减少。这一作用持续的时间(适应时间),瞬变细胞约0.1秒,持续性小感受野细胞约4～8秒,持续性大感受野细胞约40～80秒。2.空间上的相互作用:改变被照射视网膜面积的大小,同时计算神经元的平均放电频率,可以确定外周抑制区的存在、范围和强度。外周抑制可以同时作用于给-撤细胞的给光反应和撤光反应,也可以选择地只抑制其中某一种反应。纯撤光细胞没有外周抑制区。具有大感受野的外膝体神经元,其感受野的大小与背景光的强度有关。在高亮度情况下,感受野变小,有利于改善分辨率;在低亮度下,感受野扩大,有利于提高灵敏度。     

不同时间频率光栅刺激引起的视觉诱发电位(VEP)方位效应的差异

以人视觉诱发电位(VEP)反应为指标,在不同的时间频率下测定了 VEP 对方波光栅刺激的反应幅度与光栅方位的关系。当光栅方位固定时,光栅闪烁的时间频率不同,VEP 反应的波形、潜伏期和反应频率差别很大,但其反应幅度均呈现方位选择性。当光栅的时间频率为9.1Hz时,光栅为垂直和水平方位时引起的 VEP 反应幅度比倾斜方位时都大,对任何光栅方位,VEP反应幅度与光栅对比度的对数呈线性关系;与此相反,当光栅时间频率为0.4Hz 时,光栅为倾斜方位时引起的 VEP 反应幅度比垂直和水平方位时更大。     

华虻小叶神经元运动敏感性的研究

用电生理细胞内记录的方法记录了１０个以上小叶神经元对闪光、运动光斑及运动光栅刺激的电生理反应特点,结果表明：（１）小叶神经元对闪光刺激具有特征性反应,细胞对给光和撤光刺激都会表现出不同程度的去极化和超极化,反应的波形不随闪光时间的改变而改变,两次去极化之间的时间间隔与闪光刺激的时间长度成线性关系;（２）小叶神经元对运动光斑的运动速度非常敏感,而对光斑的运动方向的改变却不敏感,尽管有的细胞存在一个能使反应的变化更快的优势方向,但并没有明显的运动方向选择性;（３）小叶神经元对运动光栅的响应频率受光栅的空间频率和运动速度的双重调制,与光栅的运动方向无关。     

Dynamics of turtle horizontal cell response

The small- and large-field (cone) horizontal cells produce similar dynamic responses to a stimulus whose mean luminance is modulated by a white-noise signal. Nonlinear components increase with an increase in the mean luminance and may produce a mean square error (MSE) of up to 15%. Increases in the mean luminance of the field stimulus bring about three major changes: the incremental sensitivity defined by the amplitude of the kernels decreases in a Weber-Fechner fashion; the waveforms of the kernels are transformed from monophasic (integrating) to biphasic (differentiating); the peak response time of the kernels becomes shorter and the cells respond to much higher-frequency inputs. The dynamics of the horizontal cell response also depend on the area of the retina stimulated. Smaller spots of light produce monophasic kernels of a longer peak response time. The presence of a steady background produces three major changes in the spot kernels: the kernel's amplitude becomes larger (incremental sensitivity increases); the peak response times become shorter; the waveform of the kernels changes in a fashion similar to that observed with an increase in the mean luminance of the field stimulus. A similar enhancement in the incremental sensitivity by a steady background has also been observed in catfish, which shows that this phenomenon is a common feature of the horizontal cells in the lower vertebrate retina.     

背景光对图形视网膜电图空间调谐特性的影响

本工作应用背景光压抑闪光视网膜电图(FERG),考察对图形视网膜电图(PERG)的空间调谐特性的影响,并与无背景光时的结果进行比较。背景光使全屏幕闪光诱发的FERG基本压抑。在这种条件下,同屏幕的图形刺激所诱发的PERG的振幅显示一定的低空间频率衰减(LSFA)。FFT分析表明,当时间频率为3.91Hz时,PERG的二次谐波呈现十分明显的LS-FA,与无背景光时的结果吻合得很好;当时间频率为7.81Hz时,也表现出LSFA,而无背景光时则缺如。这些结果表明,无背景光时记录的PERG振幅在低空间频率区偏高确实是由于混杂有亮度特异性成分—FERG。但是,PERG振幅所显示的LSFA仍不如二次谐波那么明显,这可能是因为FERG中存在的非线性成分未为背景光所完全压抑,仍然混杂在低频区的PERG反应中。     

Intensity Coding in the Frog Retina : Quantitative relations between impulse and graded activity

The impulse discharge of single on-off neurons and a graded field potential, the proximal negative response (PNR), were simultaneously recorded with an extracellular microelectrode in the inner frog retina. Normalized amplitude-intensity functions for the on-response of the PNR and the neuron's post-stimulus time histogram (PSTH) were nearly coincident and typically showed a dynamic range spanning approximately 2 log units of intensity. Thus a nearly linear relation is found between the amplitude of the PNR and the neuron's PSTH. A neuron's PSTH amplitude and maximum instantaneous frequency of discharge were usually highly correlated, but occasional marked disparities indicate that temporal jitter of the first spike latency is an additional, relatively independent variable influencing PSTH amplitude. It typically changes by a factor of 20–30 over the intensity range. These and other findings have implications for the functional significance of the PNR and the PSTH, for a possible linear link between amacrine and on-off ganglion cells, and for a mechanism of intensity coding in which temporal jitter of latency exerts a major role.     

Superimposing noise linearizes the responses of primary muscle spindle afferents to sinusoidal muscle stretch

Experiments were conducted in anaesthetized and spinalized cats to measure the extent to which the non-linear response of Ia afferent fibers to sinusoidal muscle stretch as expressed by the peristimulus-time-histograms, PSTHs, can be transformed into a linear one by means of the superposition of random stretch ("mechanical noise"). The gastrocnemius muscles of one hind leg were stretched and the response to sinewave muscle stretch (amplitudes between 0.01 and 4.0 mm, frequencies between 0.1 and 20 Hz) were investigated while band-limited mechanical noise was superimposed on the sinewave stretch. The random stretch upper cut-off frequency was varied between 60 and 300 Hz; the displacements were normally distributed. The noise amplitude sigma, i.e. the standard deviation of the displacement distributions, was varied systematically between 0.002 and 0.4 mm. Mechanical noise was very effective in raising the mean discharge rate. Added to the sinusoidal stretch it prevented the cessation of firing during the release phase of the stretch cycle, or at least reduced the duration of discharge pauses, i.e., a linearization occurred. In general, the larger the noise amplitude, the more the amplitude of the fundamental harmonic component was attenuated and the phase lead reduced. Apart from this rule the particular combination of superimposing small noise (sigma less than 0.02 mm) on small sinewave stretch (A less than 0.02 mm) could enhance the depth of sinusoidal modulation of cycle histograms (compared with responses to pure sinusoids). Linearizing the sinewave response by additional noise allowed the estimation of frequency response characteristics in the otherwise non-linear range of amplitudes (sinewave amplitude 0.5-1.0 mm).(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamics of the ganglion cell response in the catfish and frog retinas

Responses were evoked from ganglion cells in catfish and frog retinas by a Gaussian modulation of the mean luminance. An algorithm was devised to decompose intracellularly recorded responses into the slow and spike components and to extract the time of occurrence of a spike discharge. The dynamics of both signals were analyzed in terms of a series of first-through third-order kernels obtained by cross-correlating the slow (analog) or spike (discrete or point process) signals against the white-noise input. We found that, in the catfish, (a) the slow signals were composed mostly of postsynaptic potentials, (b) their linear components reflected the dynamics found in bipolar cells or in the linear response component of type-N (sustained) amacrine cells, and (c) their nonlinear components were similar to those found in either type-N or type-C (transient) amacrine cells. A comparison of the dynamics of slow and spike signals showed that the characteristic linear and nonlinear dynamics of slow signals were encoded into a spike train, which could be recovered through the cross-correlation between the white-noise input and the spike (point process signals. In addition, well-defined spike correlates could predict the observed slow potentials. In the spike discharges from frog ganglion cells, the linear (or first-order) kernels were all inhibitory, whereas the second-order kernels had characteristics of on-off transient excitation. The transient and sustained amacrine cells similar to those found in catfish retina were the sources of the nonlinear excitation. We conclude that bipolar cells and possibly the linear part of the type-N cell response are the source of linear, either excitatory or inhibitory, components of the ganglion cell responses, whereas amacrine cells are the source of the cells' static nonlinearity.     

Differentiation of the bimodal stimuli in a frog's retina

In work electric activity of frog's retina was investigated by silent substitution technique. Electroretinogram was recorded as a response to abrupt exchange of the referent stimulus-line with fixed values of luminance and orientation to test lines with varied luminance and orientations. As a result of the analysis it has been allocated two types of responses of a retina. The response to onset-offset of a stimulus-line was similar to the response at homogeneous illumination of a retina (ERG), and was characterized by both the high amplitude of b-wave (hundreds mkV) and significant asymmetry of b- and d-waves. Whereas the same waves in response to substitution of the same stimuli were more symmetric and had on ten times smaller amplitudes. Such activity of frog's retina was referred as pattern electroretinogram (PERG) recorded in a high vertebrate's retina as response to stimuli whose contrast was temporally modulated. The analysis of interaction of luminance and line orientation channels in retina was carried out on the base of construction V-shaped functions of stimuli differentiation. It has shown, that activities of both channels are linearly summarized in PERG. It means independent and parallel functioning of these mechanisms. However, it takes the short subdivision of luminance, namely, when luminance of test line not far from luminance of referent line. At the same time, from the moment of the double prevalence of test line in relation to referent line, growth of PERG amplitude has nonlinearly form. Such two-stage changing of PERG amplitude speaks presence in a retina of a frog of two mechanisms of coding of luminance. One mechanism coding light intensity by power of the discharge, it forms the information on an absolute level of light in the environment. Its activity is caused basically, by receptors and cells of external plexiform layer and is submitted by b-wave of electroretinogram. Other mechanism submitted in PERG, is based on the vector code of stimulus, it forms the information on spatial and time differentiation of a light in the visual field and is connected, basically, with cells of internal plexiform layer of frog's retina.     

Negative feedback regulation is responsible for the non-linear modulation of photosynthetic activity in plants and cyanobacteria exposed to a dynamic light environment

Photosynthetic organisms exposed to a dynamic light environment exhibit complex transients of photosynthetic activities that are strongly dependent on the temporal pattern of the incident irradiance. In a harmonically modulated light of intensity I approximately const.+sin(omegat), chlorophyll fluorescence response consists of a steady-state component, a component modulated with the angular frequency of the irradiance omega and several upper harmonic components (2omega, 3omega and higher). Our earlier reverse engineering analysis suggests that the non-linear response can be caused by a negative feedback regulation of photosynthesis. Here, we present experimental evidence that the negative feedback regulation of the energetic coupling between phycobilisome and Photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC6803 indeed results in the appearance of upper harmonic modes in the chlorophyll fluorescence emission. Dynamic changes in the coupling of the phycobilisome to PSII are not accompanied by corresponding antiparallel changes in the Photosystem I (PSI) excitation, suggesting a regulation limited to PSII. Strong upper harmonic modes were also found in the kinetics of the non-photochemical quenching (NPQ) of chlorophyll fluorescence, of the P700 redox state and of the CO(2) assimilation in tobacco (Nicotiana tabaccum) exposed to harmonically modulated light. They are ascribed to negative feedback regulation of the reactions of the Calvin-Benson cycle limiting the photosynthetic electron transport. We propose that the observed non-linear response of photosynthesis may also be relevant in a natural light environment that is modulated, e.g., by ocean waves, moving canopy or by varying cloud cover. Under controlled laboratory conditions, the non-linear photosynthetic response provides a new insight into dynamics of the regulatory processes.     

2-ns Electrostimulation of Ca2+ Influx into Chromaffin Cells: Rapid Modulation by Field Reversal

Cellular effects of nanosecond-pulsed electric field exposures can be attenuated by an electric field reversal, a phenomenon called bipolar pulse cancellation. Our investigations of this phenomenon in neuroendocrine adrenal chromaffin cells show that a single 2-ns, 16 MV/m unipolar pulse elicited a rapid, transient rise in intracellular Ca²⁺ levels due to Ca²⁺ influx through voltage-gated calcium channels. The response was eliminated by a 2-ns bipolar pulse with positive and negative phases of equal duration and amplitude and fully restored (unipolar-equivalent response) when the delay between each phase of the bipolar pulse was 30 ns. Longer interphase intervals evoked Ca²⁺ responses that were greater in magnitude than those evoked by a unipolar pulse (stimulation). Cancellation was also observed when the amplitude of the second (negative) phase of the bipolar pulse was half that of the first (positive) phase but progressively lost as the amplitude of the second phase was incrementally increased above that of the first phase. When the amplitude of the second phase was twice that of the first phase, there was stimulation. By comparing the experimental results for each manipulation of the bipolar pulse waveform with analytical calculations of capacitive membrane charging/discharging, also known as accelerated membrane discharge mechanism, we show that the transition from cancellation to unipolar-equivalent stimulation broadly agrees with this model. Taken as a whole, our results demonstrate that electrostimulation of adrenal chromaffin cells with ultrashort pulses can be modulated with interphase intervals of tens of nanoseconds, a prediction of the accelerated membrane discharge mechanism not previously observed in other bipolar pulse cancellation studies. Such modulation of Ca²⁺ responses in a neural-type cell is promising for the potential use of nanosecond bipolar pulse technologies for remote electrostimulation applications for neuromodulation.     

Negative feedback regulation is responsible for the non-linear modulation of photosynthetic activity in plants and cyanobacteria exposed to a dynamic light environment

Photosynthetic organisms exposed to a dynamic light environment exhibit complex transients of photosynthetic activities that are strongly dependent on the temporal pattern of the incident irradiance. In a harmonically modulated light of intensity I≈const.+sin(ωt), chlorophyll fluorescence response consists of a steady-state component, a component modulated with the angular frequency of the irradiance ω and several upper harmonic components (2ω, 3ω and higher). Our earlier reverse engineering analysis suggests that the non-linear response can be caused by a negative feedback regulation of photosynthesis. Here, we present experimental evidence that the negative feedback regulation of the energetic coupling between phycobilisome and Photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC6803 indeed results in the appearance of upper harmonic modes in the chlorophyll fluorescence emission. Dynamic changes in the coupling of the phycobilisome to PSII are not accompanied by corresponding antiparallel changes in the Photosystem I (PSI) excitation, suggesting a regulation limited to PSII. Strong upper harmonic modes were also found in the kinetics of the non-photochemical quenching (NPQ) of chlorophyll fluorescence, of the P700 redox state and of the CO₂ assimilation in tobacco (Nicotiana tabaccum) exposed to harmonically modulated light. They are ascribed to negative feedback regulation of the reactions of the Calvin-Benson cycle limiting the photosynthetic electron transport. We propose that the observed non-linear response of photosynthesis may also be relevant in a natural light environment that is modulated, e.g., by ocean waves, moving canopy or by varying cloud cover. Under controlled laboratory conditions, the non-linear photosynthetic response provides a new insight into dynamics of the regulatory processes.