在双脉冲光刺激下瞳孔系统的采样控制特性

本文用实验揭示了瞳孔对光动态反应具有采样控制特性。实验中采用各种不同时间间隔的双脉冲光,以开环的方式(Maxwellian View)刺激瞳孔,当双脉冲之间间隔较长时,瞳孔反应相当于对双脉冲光的两次脉冲分别产生瞬态收缩;当双脉冲时间间隔短于0.6s 时,其反应就成了一次瞬态收缩,与单个光脉冲所引起的瞳孔反应一样。同—受试者的多次实验结果相同,不同受试者所得结果也基本一致。故瞳孔对脉冲刺激光引起反应后,必须至少约隔0.6s 才能对另一次脉冲光产生反应,这就说明了瞳孔动态反应具有离散的采样控制特性。实验还进一步证明,瞳孔系统的控制机制是双重模式的控制:不同的刺激条件下,瞳孔反应可呈现为瞬态反应(AC)或持续反应(DC),瞬态反应的 AC 通道为离散的采样控制,持续反应的 DC 通道为连续控制。     

吗啡对猕猴瞳孔光反应能力的影响

光照能明显改变正常人和动物瞳孔的大小,而精神疾病及药物滥用则影响人和动物瞳孔对光的反应性.因此,瞳孔对光反应异常可以用作检测精神疾病和药物滥用的指标.有关药物滥用是如何影响瞳孔对光的反应性的研究还很少.为定量地测量成瘾性药物对瞳孔光反应变化的影响,该文采用猕猴为实验对象,通过在黑暗环境中测量猕猴在吗啡给予前和吗啡给予后的不同时间段,其瞳孔直径大小以及其对光反应能力的变化情况,来系统研究吗啡是如何影响这种非自主性反射系统的.研究发现,吗啡给予降低了猕猴在黑暗环境中的扩瞳反应,并且降低了瞳孔对光反应的收缩率.该文为将瞳孔对光反应特征用作鉴定吸毒者的检测手段提供了实验依据.     

瞳孔控制系统采样特性的中枢机制

本文以双脉冲光分眼刺激（ｄｉｃｈｏｐｔｉｃ ｓｔｉｍｕｌａｔｉｎｇ,双脉冲的第一脉冲光刺激一侧眼,第二脉冲光刺激另一侧眼）进行瞳孔采样特性研究。实验结果表明：当双脉冲之间的时间间隔较长时,瞳孔产生两次收缩反应;当时间间隔小于约０．６ｓ时,瞳孔只对第一个脉冲光刺激产生瞬态收缩,对第二个脉冲光刺激不产生反应。这不仅证实了单眼实验研究的结论：瞳孔系统不是在时间上连续进行控制,而是离散的采样控制,它对光刺     

视觉图形诱发的瞳孔反应

以图形变化刺激进行瞳孔反应研究,实验表明：（１）空间平均亮度守恒的光栅或棋盘格图形翻转能激发起瞳孔反应,为瞬态收缩波形,与ｐｕｐｉｌｌａｒｙ ｅｓｃａｐｅ相似;（２）光栅或棋盘格的空间频率的变化也能引起瞳孔反应,且反应幅度随空间频率差别增大而变大;（３）从均匀亮背景变化到棋盘格图形或者从棋盘格图形变化到黑暗背景,虽然不存在任何局部亮度增强,皆能引起瞳孔反应。实验结果明确证明了人的瞳孔反应系统除接收     

用于研究快速扫视对瞳孔光反射调制作用的新方法

瞳孔对光反射系统和快速扫视系统在解剖学和功能上都有着紧密的联系,但是快速扫视系统对瞳孔的光反射系统是否有调制作用尚无报道。研究这两个系统间的调制作用,必须了解光刺激不均匀和近反应对瞳孔直径变化是否有影响。该研究以人为被试,设计了一种全新的实验方法,研究光刺激不均匀和近反应对瞳孔直径变化的影响。实验方法：将被试的一只眼用密闭的眼罩罩住给予脉冲光刺激,刺激由位于眼罩内全视野范围水平排列的一排发光二极管(light emitting diodes,LEDs)给出,被试的另一只眼用来记录眼动和瞳孔直径的变化,研究水平方向的快速扫视对瞳孔对光反射时瞳孔直径变化的影响。实验结果：比较被试注视视野内不同位置的瞳孔对光反射相对收缩率无显著差异（P=0.148, 非配对样本t检验）。结论：本方法消除了光刺激不均匀和近反应对瞳孔直径变化的影响,可用于研究快速扫视系统对瞳孔光反射系统间的调制作用。     

小鼠下丘听神经元的反应潜伏期对特征频率的表达

频率是声音的基本参数之一. 听觉神经元对声音频率的反应可以表现为放电率和反应潜伏期的变化. 大部分神经元放电率随频率的改变呈多种变化, 而神经元对声音反应的放电潜伏期往往比较稳定, 提示潜伏期能有效地表达频率信息. 本文研究了BALB/C小鼠下丘听神经元对纯音频率反应的放电率及潜伏期特性, 实验结果表明: 神经元对特征频率的反应潜伏期通常最短, 随声强的变化改变不大; 而神经元对纯音频率反应的放电率随频率改变呈多种变化, 尤其当声强增强时. 实验结果提示小鼠下丘神经元的反应潜伏期具有较放电率更准确表征特征频率的特性.     

眼睛的新奥秘

科学家们发现了眼睛所具有的一些非视觉功能 ,例如瞳孔见光收缩和设定生物钟。他们发现 ,视网膜系统除了与视觉相关的杆状和圆锥细胞外 ,还有 1个全新的光感受器—— melanopsin。R.J.Lucas和英国、美国的研究小组发现 ,缺少光感受器 melanopsin的小鼠 ,瞳孔见光时没有正常的收缩反应 ,所以 ,正常的瞳孔收缩反应除了需要杆状和圆锥细胞外 ,还需要melanopsin参与。另外 ,Russell Van Gelder和同事发现 ,缺少感光色素—— cryptochrome的小鼠也没有正常的瞳孔收缩反应。两篇近期的论文详细叙述了这些发现 (《科学》,2 0 0 2年 11月 13日 ) …     

光点位移运动激发的瞬态瞳孔反应

用等高度的光点位移运动作为刺激来测量瞳孔反应,实验记录表明,即使输入到视网膜的总光通量不变,仅仅是刺激点的位置改变就能激发起瞳孔反应,且其反应的位置分辨率可达１０’,这一实检结果揭示了瞳孔对光反射通路不仅传递了进入瞳孔的总光通量的信息,而且还检测了刺激光点位置变化的信息。     

瞳孔光反应系统的空间分布式神经网络模型

为模拟刺激光空间分布变化引起瞳孔反应的实验现象,本文建立了空间分布式神经网络瞳孔模型。它是在瞳孔双通道模型基础上,借鉴Ｃａｎｎｏｎ－Ｒｏｂｉｎｓｏｎ的Ｏｃｕｌｏｍｏｔｏｒ模型的双层网络结构和视网膜的镶嵌式特点,经空间延括而成。空间各部位信号经第一层神经元处理得到对应各部位的线性ＤＣ和非线性ＡＣ输出,在第二层神经元进行空间综合,再经第三层神经元复合去控制效应器官虹膜肌的反应。该分布式部位机制模型能解释多种瞳孔实验现象。     

中华鳖眼睛发育的形态及组织学观察

在孵化基质沙粒径为0.3～0.6mm、孵化温度为(33.0±0.5)℃、孵化基质的湿度为7%～10%、相对湿度为70%～85%的条件下孵化中华鳖(Trionyx sinensis)卵,孵化周期35～36 d.破壳取不同发育时期的胚胎并制作切片,观察眼睛发育的形态学和组织学特征.孵化第4 d头部两侧出现眼泡的突起;第6d眼睛开始出现色素,第14 d色素由褐色变为黑色;第7 d瞳孔出现,透过瞳孔可见晶状体;虹膜于第14d出现,第18、19 d瞳孔周围呈放射状;巩膜突自第19 d出现,第21 d增至最多,第23 d消失;上、下眼睑分别在第19 d和22 d出现,第32 d眼睑可覆盖瞳孔,眼睛形态与成体眼睛相似.表皮外胚层于第3 d形成角膜原基和晶体泡,第32 d角膜发育完成;第34 d晶状体发育完成;神经外胚层于44～48 h由前脑的两侧分化形成视泡,第3 d由视泡分化形成视杯,并逐步分化形成视网膜;第23 d视网膜的八层结构基本形成;第34 d视网膜发育完成.     

ACROSS‐ENVIRONMENT GENETIC CORRELATIONS AND THE FREQUENCY OF SELECTIVE ENVIRONMENTS SHAPE THE EVOLUTIONARY DYNAMICS OF GROWTH RATE IN IMPATIENS CAPENSIS

Trade‐offs can exist within and across environments, and constrain evolutionary trajectories. To examine the effects of competition and resource availability on trade‐offs, we grew individuals of recombinant inbred lines of Impatiens capensis in a factorial combination of five densities with two light environments (full light and neutral shade) and used a Bayesian logistic growth analysis to estimate intrinsic growth rates. To estimate across‐environment constraints, we developed a variance decomposition approach to principal components analysis, which accounted for sample size, model‐fitting, and within‐RIL variation prior to eigenanalysis. We detected negative across‐environment genetic covariances in intrinsic growth rates, although only under full‐light. To evaluate the potential importance of these covariances, we surveyed natural populations of I. capensis to measure the frequency of different density environments across space and time. We combined our empirical estimates of across‐environment genetic variance–covariance matrices and frequency of selective environments with hypothetical (yet realistic) selection gradients to project evolutionary responses in multiple density environments. Selection in common environments can lead to correlated responses to selection in rare environments that oppose and counteract direct selection in those rare environments. Our results highlight the importance of considering both the frequency of selective environments and the across‐environment genetic covariances in traits simultaneously.     

Level dependent signal flow in the light pupil reflex

Latency of pupillary responses to light stimuli are smaller for larger steps of light, and larger for smaller steps of light (Alpern 1954; Lowenstein et al. 1964; Lee et al. 1969; Terdiman et al. 1969; Cibis et al. 1977; and many others). Miller and Thompson (1978), however, reported negligible change in pupil cycle time (period of high gain instability oscillations) with increased mean brightness. Sandberg and Stark (1968) reportd a negligible reduction in phase lag of pupillary responses to sinusoidal light stimuli as the modulation coefficient (m) increased. To resolve the inconsistency between the well-documented dependence of latency upon brightness, and the apparent absence of level dependence in the phase characteristics (as reflected directly in the responses to sinusoidal stimuli and indirectly in pupil cycle time experiments) we measured: 1. Latency to step stimuli of light, 2. Phase of responses to sinusoidal light stimuli and 3. Period (pupil cycle time) of high gain instability oscillations. The dependence of pupillary latency upon stimulus level (both light and accommodation) and the interaction between accommodation and light responses were investigated. We show that most of the level dependence of light-pupil latency resides in the afferent path. In the companion papers, we demonstrate that: 1. Phase of pupillary response to sinusoidal light stimuli is reduced by increased mean light level, but is independent of pupil size and accommodative stimulus level; and 2. The period of high gain oscillations is shown to decrease with increased mean light level. Taken together, these results imply the existence of a Level Dependent Signal Flow (LDSF) operator that resides in the light-pupil pathway, but not in the accommodation-pupil pathway. We propose a systems model of this operator in which the neural signals controlling pupil size are treated as waves whose phase velocity increases in response to brighter stimuli, and decreases in response to dimmer stimuli. When parameters of the model are adjusted to fit measured pupillary latency over a range of light levels, the model exhibits reduced phase lag in response to increased mean light level in the sinusoidal paradigm, and it exhibits reduced pupil cycle time in the high-gain oscillation paradigm. The model exhibits saturation of the LDSF effect in all paradigms at high light levels, as do experimental results. It simulates directional asymmetry of pupillary response to positive and negative steps of light, with constriction more rapid than dilatation. Finally, it simulates tonic pupillary constriction in response to modulation of a light simulus without changing average light level (Varju 1964; Troelstra 1968). All of these stimulated results are in accord with experimental observation.     

Binocular alternating pulse stimuli: Experimental and modeling studies of the pupil reflex to light

In our experiment, alternating pulse stimuli of both low and high intensity are used to study the pupil reflex to light. When applied monocularly, high intensity stimulation normally results in a sustained contraction; when alternated between the two eyes, it is found to produce small transient responses similar to those obtained with low intensity monocular stimulation. In order to study the mechanisms regulating these binocular responses, a model of the pupillary light reflex is constructed. It includes parallel AC and DC pathways for processing the light stimulus to produce motor signals to the iris muscles, nonlinear parameter control of pathway gains dependent upon internal operating level, binocular summation of DC pathway signals to produce that operating level, equal motor responses of both pupils, and iris neuromuscular delays and lags. The model is found to simulate the experimental data. It shows the binocular transient responses to be due to the canceling by summation of the symmetric DC pathway responses to alternating stimuli, thus allowing the AC pathway signals to become manifest. Therefore the dilatory portion of the transient responses is shown to be due to the lead-lag operator in the AC pathway and not to the off-dilatation elicited by removal of the light stimulus from the eye. Finally the results of our study are used to discuss the Marcus Gunn pupillary sign, a clinical test utilizing this binocular alternating pulse stimulation for detecting unilateral afferent defects.     

A systems model for the pupil size effect

The human pupillary control system is a paradigm for linearized biological control systems. It also exhibits a series of interesting nonlinear behaviors, particularly asymmetry, “pupillary escape”, and “pupillary capture.” We present a nonlinear model in which a signal dependent upon pupil size is fed back internally to cause a change in system parameters related to gains and rates of light adaptation. The model was simulated on a digital computer, a variety of experimental data was well matched, and improvements over previous pupil models demonstrated. A candidate physiological mechanism for adaptive components of the model might have the form of an inverse “Henneman coded” neuronal pool.     

Visual pigment processes and prolonged pupillary responses in insect photoreceptor cells

The visual pigment in the peripheral retinular cells of the hoverfly Syrphus balteatus was investigated by absorbance difference measurements. Different visual pigments were found in the dorsal versus the ventral part of the eye in the male, but not in the female. In the male in the dorsal part of the eye the visual pigment has an isosbestic point at 513 nm; in the ventral part this value is 490 nm. The latter value is found in the female in both parts of the eye.Prolonged pupillary responses were studied in the male Syrphus and appeared to be most marked in the ventral part of the eye. In both hoverfly and blowfly prolonged pupillary responses are induced by short wavelength light only; i.e., by light which excessively can convert rhodopsin into metarhodopsin. By contrast, in butterflies red light (and a long dark adaptation time) is necessary to evoke a prolonged pupillary response. It was demonstrated in both hoverfly and blowfly that long wavelength light, which reconverts metarhodopsin into rhodopsin, inhibits a prolonged pupillary response; or, accelerates pupil opening.Based on material presented at the European Neurosciences Meeting, Florence, September 1978