Insect pupil mechanisms

Summary The spectral characteristics of the pupil mechanism in blowfly photoreceptors and their dependence on light intensity have been investigated together with the intensity dependence of the receptor potential. The threshold for the pupil response as measured by reflectance is found at an intensity at which the peak of the receptor potential is about half maximal and the plateau potential starts to saturate. The reflectance saturates at about 3 log-units above threshold. The reflectance spectrum peaks near 620 nm, and its shape is independent of adaptation intensity. The absorbance change, measured by transmission, is extreme in the blue, at about 470 nm. The shape of the absorbance spectrum is slightly intensity dependent, presumably due to optical waveguide effects. The dynamic ranges of the light-induced reflectance and absorbance changes do not coincide. The reflectance change shows saturation at least 1 to 1.5 log units before the absorbance change saturates.     

Localization of the pupil trigger in insect superposition eyes

Summary In the superposition eyes of the sphingid moth Deilephila and the neuropteran Ascalaphus, adjustment to different intensities is subserved by longitudinal migrations of screening pigment in specialized pigment cells. Using ophthalmoscopic techniques we have localized the light-sensitive trigger that controls pigment position.In both species, local illumination of a small spot anywhere within the eye glow of a dark-adapted eye evokes local light adaptation in the ommatidia whose facets receive the light. Details of the response pattern demonstrate that a distal light-sensitive trigger is located axially in the ommatidium, just beneath the crystalline cone, and extends with less sensitivity deep into the clear zone. The distal trigger in Deilephila was shown to be predominantly UV sensitive, and a UV-absorbing structure, presumably the distal trigger, was observed near the proximal tip of the crystalline cone.In Ascalaphus we also found another trigger located more proximally, which causes local pigment reaction in the ommatidia whose rhabdoms are illuminated (the centre of the eye glow). The light-sensitive trigger for this response appears to be the rhabdom itself.     

Properties of pupil mechanisms in owl-fly Ascalaphus macaronius (Neuroptera)

Regulation of light flux by pupil mechanisms in the UV-sensitive superposition eye of owl-fly Ascalaphus macaronius (Neuroptera) was studied with a fast reflection microspectrophotometric technique. The spectral sensitivity of pupil reaction, which was calculated on the basis of changes of transient amplitude reflection, was almost identical with the one of Deilephila eye. This indicates that in spite of different life styles and spectral sensitivities of photoreceptors, pupil closing is triggered by the same photosensitive structure in both eyes. By measuring the spectra of reflected light from the Ascalaphus eye between 400 and 700 nm after different dark periods following light stimulation, it was established that the restoration of reflection was much faster in the red than in the blue spectral range. Based on this, we propose that two different pupil mechanisms with different spectral absorption characteristics are involved in light-flux regulation. Fast-reacting pupil is probably represented by screening pigment migration in the secondary pigment cells and a slow blue-absorbing system by the activity in primary pigment cells. The importance of two different pupils for the photoregeneration of visual pigment is discussed. Accepted: 1 October 1998     

Relationships between pupil working range and habitat luminance in flies and butterflies

The luminance range over which the pupil mechanism operates was measured with pupil reflectometry in 11 species of butterflies and 13 species of dipteran flies. The different species were selected to be as different as possible regarding the range of ambient luminances in which they are active. Habitat luminance ranges were also measured and correlated to luminances in the experimental situation. The pupil mechanism in butterflies operates in the centre of the luminance range in which the different species are active. Three distinct groups of butterflies with pupil sensitivities matched to their specific types of activity pattern were identified: species active only in direct sunlight, species active also in shaded places and species extending their activity into dawn and dusk. Quite differently, the pupil mechanisms of dipteran flies operate in the upper end of the ambient luminances, and in some species well above the luminances normally encountered by the animal. All fly pupils start to close roughly at the same luminance, irrespective of the luminances in which the species are active. The results suggest that the most important role for the pupil mechanism in many of the butterfly species is to maximize acuity over a wide range of luminances, whereas in flies it is to avoid saturation of transduction units and thereby maximize the photoreceptor's signal-to-noise ratio at high light intensities. Accepted: 1 July 1997     

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     

Pupillary effects of leucine and methionine enkephalin in rats after intraperitoneal administration

Changes in pupil size after peripheral administration of met-enkephalin, leu-enkephalin, or morphine were studied in the rat. With a simple pupillographic technique, the pupil diameter of male, S.D. rats (250–300 g) was measured by a series of photographs taken every 60 sec for at least 45 min after the last drug injection. Morphine (8 mg/kg, SC) caused mydriasis characterized by rapid and marked fluctuations of pupil size. Mydriasis also occurred after leu-enkephalin (5 and 10 mg/kg, IP) and met-enkephalin (20 mg/kg, IP). Both peptides induced morphine-like fluctuations. When given 15 min after morphine, leu-enkephalin (5 and 10 mg/kg) increased the mydriatic effect of morphine from 172 percent of control to 224 and 272 percent, respectively. Met-enkephalin (20 mg/kg, but not 10 mg/kg) also enhanced the mydriatic response of morphine, to 244 percent of control. These interactions appear to represent simple addition rather than potentiation. The effects of both peptides were reversed by naloxone (1 mg/kg, SC), suggesting an opiate receptor interaction for the pupillary effects of the enkephalins. The rat pupil thus provides one of the few in vivo models permitting quantification of enkephalin action after parenteral administration.     

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。     

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.     

术后早期散瞳对DR合并白内障患者眼部血流动力学的影响及散瞳后瞳孔直径达标的相关因素分析

摘要 目的：探讨术后早期散瞳对糖尿病视网膜病变（DR）合并白内障患者眼部血流动力学的影响,分析影响散瞳后瞳孔直径达标的相关因素。方法：选择2018年1月至2022年1月河北北方学院附属第一医院收治的150例行白内障手术治疗的DR合并白内障患者,将患者按随机数字表法分为对照组和观察组,两组术后均给予复方托吡卡胺滴眼液散瞳,对照组于术后7 d、14 d各散瞳1次,观察组给予早期散瞳治疗,即术后次日开始每日散瞳1次。比较两组术后眼部血流动力学变化。根据术后第14 d散瞳后瞳孔直径是否达标分为达标组（瞳孔直径≥5 mm）和未达标组（瞳孔直径<5 mm）,收集患者临床资料,采用多因素Logistic回归分析影响散瞳后瞳孔直径达标的因素。结果：观察组术后14 d视网膜中央动脉、睫状后短动脉舒张末期血流速度（EDV）、收缩期速度峰值（PSV）较术后7 d增加（P＜0.05）,阻力指数（RI）较术后7 d降低（P＜0.05）,且术后7 d、14 d视网膜中央动脉、睫状后短动脉EDV、PSV高于对照组（P＜0.05）,RI低于对照组（P＜0.05）。观察组术后14 d散瞳时间较术后7 d缩短（P＜0.05）,散瞳后瞳孔直径较术后7 d增大（P＜0.05）,且观察组术后7 d、14 d散瞳时间短于对照组（P＜0.05）,散瞳后瞳孔直径大于对照组（P＜0.05）。糖尿病病程＞10年、DR增殖期是影响散瞳后瞳孔直径达标的危险因素（P＜0.05）,术后早期散瞳治疗是其保护因素（P＜0.05）。结论：DR合并白内障患者经白内障术后早期散瞳治疗可缩短散瞳时间,改善眼部血流动力学,增加散瞳后瞳孔直径。糖尿病病程、DR严重程度、术后散瞳时机是散瞳后瞳孔直径达标的影响因素。     

The visual ecology of pupillary action in superposition eyes

The two most common mechanisms of pupillary screening-pigment migration in arthropod superposition eyes are the cone and longitudinal pigment migration mechanisms. The dynamics of each were investigated by optical modelling and by determining experimentally the relationship between eye glow brightness and screening pigment position within the eyes of two representative insect species: the noctuid moth Agrotis infusa and the dung beetle Copris elphenor. During dark adaptation, in both mechanisms, the screening pigment is contracted distally to expose the proximal half of each crystalline cone. During light adaptation the pigment migrates proximally and reduces light flux in the retina. In the longitudinal mechanism, pigment migrates into the clear zone of the eye. In the cone mechanism, pigment never enters the clear zone and is instead restricted to the proximal half of each crystalline cone: a migrating sleeve of pigment creates a small aperture at the end of the crystalline cone, the area of which depends on the degree of light adaptation. According to the model, the cone mechanism provides a limited range of light attenuation (ca. 0.6 log units) for which both good spatial resolution and accuracy of control are maintained, and within this range attenuation is controlled very finely. Beyond this range, whilst attenuation is still possible, diffraction at the pigment aperture and increasing coarseness of control worsen visual performance significantly. In contrast, the longitudinal mechanism provides a much larger useful range of light attenuation (up to several log units) and maintains reasonable fineness of attenuation control over the entire range (although not as fine as the cone mechanism). The experimental results support the model. An extensive survey of arthropods with superposition eyes reveals that the cone mechanism is almost exclusively possessed by those animals experiencing a narrow range of light intensities, and the longitudinal mechanism by those experiencing a wide range.Dedicated to Professor Rolf Elofsson on the occasion of his retirement from the Chair of Zoology in Lund