Anterograde tracing of retinal axons in the avian embryo with low molecular weight derivatives of biotin

Several reactive biotin esters were injected into the eyes of chick and quail embryos at various stages of development. Four of the biotin esters reacted with molecules of the eye tissue and were detected with light and electron microscopy in fluorescein isothiocyanate and peroxidase-avidin incubated sections and whole mounts. Intra and extracellular components of the lens, the vitreous body, and the retina were labeled to different degrees. Three of the biotin esters (biotin-N-hydroxysuccinimidester, biotin-epsilon-aminocaproic acid-N-hydroxysuccinimidester, and desthiobiotin-N-hydroxysuccinimidester) prominently marked the optic fiber layer in the retina and the biotin labels were transported along the optic pathway. The tracers were detected up to the growth cone of axons 24 to 36 hr after injection. Explants from biotin marked retinas were cultured on collagen or basal laminae. During culturing axons grew out from these explants into the substratum showing that labeled tissue and nerve fibers were viable. The development of the optic pathway at the chiasma of quail embryos was studied using the biotin/avidin tracing. The bulk of fibers emerging from the retina crossed as shown by double labeling of both optic nerves in a complex pattern of segregated and interdigitizing axon bundles at the chiasma toward the contralateral side of the brain. From stage 25 onward a minor ipsilateral projection was found. At the same developmental stage a few fibers traveled into the contralateral optic nerve and grew retrogradely toward the contralateral eye. The percentage of specimens having this retino-retinal projection increased during development from 53% (stage 24 to 27; E3.5-E5.5) to 89% (stage 29 to 35; E6-E8) and declined to 40% at late embryogenesis (stage 37 to 41; E9-E12). The fact that all retinal axons were found within predictable pathways with some of them running in the wrong direction suggests that nerve fiber pathways provide accurate positional information, but at best weak directional information for growing nerve fibers.     

Optic nerve integrity is required for light to affect retina ganglion cell gangliosides

The labeling of retina ganglion cell and optic tectum gangliosides after an intraocular injection ofN-[³H]acetylmannosamine ([³H]ManNAc) is higher in chickens exposed to light than in those maintained in darkness (1,2). In the present work we studied whether the signal for the higher labeling of ganglion cells in light originates in the photoreceptor layer or comes from the nerve terminal. For this purpose the labeling of ganglion cell gangliosides was determined in light and dark in chickens with one optic nerve severed. The results showed that the effect of light occurred only in the eye normally connected to the optic tectum. In the eye with its optic nerve severed, no difference was observed between the labeling of gangliosides in animals in light and dark, having both groups the labeling values of the normal eyes exposed to light. The results indicate that the information that decreases labeling in darkness or accelerates it in light originates in the nerve terminal.Special Issue dedicated to Prof. Edwardo De Robertis.     

A developmental and ultrastructural study of the optic chiasma in Xenopus

The structure of the optic chiasma in Xenopus tadpoles has been investigated by light and electron microscopy. Where the optic nerve approaches the chiasma, a tongue of cells protrudes from the periventricular cell mass into the dorsal part of the nerve. Glial processes from this tongue of cells ensheath fascicles of optic axons as they enter the brain. Coincident with this partitioning, the annular arrangement of axons in the optic nerve changes to the laminar organization of the optic tract. Beyond the site of this rearrangement, all newly growing axons accumulate in the ventral-most part of the nerve and pass into the region between the periventricular cells and pia which we have called the 'bridge'. This region is characterized by a loose meshwork of glial cell processes, intercellular spaces and the presence of both optic and nonoptic axons. In the bridge, putative growth cones of retinal ganglion cell axons are found in the intercellular spaces in contact with both the glia and with other axons. The newly growing axons from each eye cross in the bridge at the midline and pass into the superficial layers of the contralateral optic tracts. As the system continues to grow, previous generations of axon, which initially crossed in the existing bridge, are displaced dorsally and caudally, forming the deeper layers of the chiasma. At their point of crossing in the deeper layers, these fascicles of axons from each eye interweave in an intimate fashion. There is no glial segregation of the older axons as they interweave within the chiasma.     

Pigment-dispersing hormone-immunoreactive fibers persist in crickets which remain rhythmic after bilateral transection of the optic stalks

Lesion studies combined with immunocytochemical experiments were used to examine whether pigment-dispersing hormone-immunoreactive processes in the midbrain of crickets correlate with the presence of circadian activity. After interruption of both optic stalks in the crickets Teleogryllus commodus and Gryllus bimaculatus animals retained circadian rhythms in their activity patterns. This suggests that there is another circadian oscillator in the midbrain. The pigment-dispersing hormone-immunoreactive fibers in the midbrain of both operated species appeared not to degenerate although they were separated from their somata in the optic lobes. These data could suggest that surviving fibers, separated from the somata of the circadian pacemaker in the optic lobes, contribute to the persistance of circadian activity in operated crickets.Abbreviations DD constant darkness - LD light dark cycles - PDH pigment-dispersing hormone - PDHLI pigment-dispersing hormone-like immunoreactivity - PDH Me pigment-dispersing hormone-immunoreactive cells of the accessory medulla - QV Quantification value     

Comparative study of the lamina cribrosa and the pial septa in the vertebrate optic nerve and their relationship to the myelinated axons

The optic nerve contains the connective tissues, i.e. the lamina cribrosa and pial septa. This report presents a histological comparison of the lamina cribrosa and pial septa in the five classes (mammals, birds, reptiles, amphibians and teleosts) of vertebrates. Furthermore, the distribution of myelinated fibers was observed from the optic nerve through the retina in the same animals. The lamina cribrosa is found in mammals except for mice, and in birds. Structural complexity of the lamina was different in animals but generally dependent of the optic nerve thickness. The pial septa were present in the optic nerve proper of the mammals except for the mice, in birds and in a part of teleosts. Fasciculation of the optic nerve by the pial septa tended to be more prominent as the optic nerve become thicker. The optic nerve consisted of largely myelinated fibers in vertebrates. The retina contained some myelinated fibers in submammals but was thoroughly devoid of myelinated fibers in mammals. The borderline between myelinated and unmyelinated portions in the optic nerve of different species did not related to the lamina cribrosa. Amphibians had exceptionally only a few myelinated fibers in the optic nerve and no myelinated fibers in the retina.     

Mechanisms controlling the sensitivity of the Limulus lateral eye in natural lighting

Electroretinograms were recorded from the horseshoe crab compound eye using a high-intensity light-emitting diode and a whole-eye seawater electrode. Recordings were made from both lateral eyes in natural daylight or in continuous darkness with the optic nerve intact or cut. Recordings from two eyes of the same animal in different conditions facilitated direct comparisons of the effects of diurnal lighting and circadian efferent activity on the daily patterns of sensitivity of the eye. Structural changes appear to account for about half of the total electroretinogram excursion. Circadian input begins about 45 min in advance of sunset and the nighttime sensitivity returns to the daytime values 20 min after sunrise. When the optic nerve is cut, the nighttime sensitivity shows exponential decay over the next 5 or 6 days, consistent with a light-triggered structural light adaptation process unopposed by efferent input. Our results suggest that two mechanisms mediate the increase in lateral eye sensitivity at night—physiological dark adaptation and circadian efferent input. Three mechanisms appear to be involved in mediating the decrease in lateral eye sensitivity during daylight—physiological light adaptation, a continuous structural light adaptation process, and a separate light-triggered, efferent-primed structural light adaptation process.     

Distribution of dopamine-beta-hydroxylase-like immunoreactivity in the rat pineal organ

The aim of the present investigation was to study the distribution in the rat pineal gland of dopamine-beta-hydroxylase (DBH) which is essential for the formation of the melatonin synthesis-regulating substance noradrenaline (NA). In 5- and 8-month-old male Sprague-Dawley rats DBH-like immunoreactivity (DBH-LI) was studied using polyclonal antibodies against DBH and the indirect immunofluorescent technique. DBH-LI was mainly located in pineal nerve fibres coming from the superior cervical ganglia. The intensity of the staining reaction was considerably lower than in non-pineal noradrenergic nerve fibres and the impression was gained by comparison of DBH-LI specimens with glyoxylic acid-treated sections that only approximately one third of the NA-containing intrapineal nerve fibres exhibited DBH-LI. There were no detectable differences in DBH-LI with regard to time of day and age of the animals. These results suggest that NA synthesis may be relatively low in intrapineal sympathetic nerve fibers and that the NA required for the regulation of pineal melatonin synthesis may, to a large degree, stem from the circulation. In addition to nerve fibres, some rare intrapineal cell bodies exhibited DBH-LI; in 5-month-old rats their numbers did not reveal significant differences between day and night. These cells do not appear to represent pinealocytes. They may be a special population of noradrenergic nerve cells perhaps belonging to an as yet unknown intrapineal regulatory system.     

Correlation between conduction velocities in optic nerve and optic radiation fibers in the cat

Responses of relay neurons of the dorsal lateral geniculate body to stimulation of area 17 of the visual cortex and the optic chiasma were studied in curarized cats. A high degree of correlation was found between the latent periods of antidromic responses of these neurons to stimulation of the visual cortex and orthodromic responses of the same neurons to stimulation of the optic chiasma (r=0.895; P=0.01). In 9% of cases antidromic unit responses were recorded to stimulation of the optic chiasma, evidence that the optic nerve contains centrifugal fibers. The functional role of the temporal dispersion of the afferent flow in the visual system is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 606–612, November–December, 1978.     

Dolphin peripheral visual pathway in chronic unilateral ocular atrophy: Complete decussation apparent

Components of the peripheral visual pathway were examined in two bottlenose dolphins, Tursiops truncatus, each with unilateral ocular degeneration and scarring of 3 or more years' duration. In both animals, the optic nerve associated with the blind eye right eye in Tg419 and left eye in Tt038 had a translucent, gel-like appearance upon gross examination. This translucency was also evident in the optic tract contralateral to the affected eye. In Tg419, myelinated axons of varying diameters were apparent in the left optic nerve, whereas the right optic nerve, serving the blind eye, appeared to be devoid of axons. In Tt038, myelinated axons were associated with the right optic nerve (serving the functional eye) and left optic tract but were essentially absent in the left optic nerve and right optic tract. Examined by light microscopy in serial horizontal sections, the optic chiasm of Tt038 was arranged along its central plane in segregated, alternating pathways for the decussation of right and left optic nerve fibers. Ventral to this plane, the chiasm was comprised of fibers from the left optic nerve, whereas dorsal to the central plane, fibers derived from the right optic nerve. Because of this architectural arrangement, the right and left optic nerves grossly appeared to overlap as they crossed the optic chiasm with the right optic nerve coursing dorsally to the left optic nerve. At the light and electron microscopic levels, the optic nerves and tracts lacking axons were well vascularized and dominated by glial cell bodies and glial processes, an expression of the marked glial scarring associated with postinjury axonal degeneration. The apparent absence of axons in one of the optic tract pairs (right in Tt038 and left in Tg419) supports the concept of complete decussation of right and left optic nerve fibers at the optic chiasm in the bottlenose dolphin. © 1994 Wiley-Liss, Inc.     

Effect of transection at different levels of hypothalamus on the hypothalamo-hypophysial system of the toad,Bufo bufo,with particular reference to the ultrastructure of the zona externa of the median eminence

Summary The ultrastructural changes taking place in the median eminence of Bufo bufo 3 hours to 4 months after transection of the brain at different levels, are described.5 types of neurons in the zona externa of the median eminence of normal toads are described. All types of neurons degenerate, and profound changes of the ultrastructure of the capillaries are observed after transection just behind, or immediately in front of the optic chiasma. A few neurons containing dense granules with a diameter of about 1,000–1,300 Å remain intact, however. The degeneration following denervation in front of the optic chiasma was considerably delayed compared to degeneration after denervation behind the optic chiasma.After transection more rostral to the optic chiasma, no significant degeneration of the median eminence was observed.The results are discussed with regard to degenerative dynamics and origin of the different nerve types. It is concluded, that all types of neurons terminating in the median eminence, originate at a level between the caudal and rostral parts of the preoptic nucleus, some fibres, however, containing dense, 1,000–1,300 Å granules, originate caudally to the optic chiasma, in the posterior hypothalamus.Part of this study was presented at the Vth International Symposium on Neurosecretion, Kiel, Germany, August 1969.     

Demonstration of centrifugal fibers in the optic chiasma and optic nerves in the rat after lesions of the suprachiasmatic nucleus

After an unilateral destruction of the suprachiasmatic nucleus and with the use of several silver impregnation techniques, degenerating centrifugal fibers were found in both optic nerves. Centrifugal fibers to the retina originate from three different regions of the nucleus and their position in the chiasma are different. In large majority the degenerating fibers were located at the periphery of the optic nerve and were more frequent on the contralateral than on the ipsilateral side to the destroyed suprachiasmatic nucleus. The possibility that our experimental procedure demonstrates the existence of fibers originating not only in the suprachiasmatic nucleus but also in other structures whose efferent fibers pass at this level, is discussed.     

A specific area of the compound eye in the cricket Gryllus bimaculatus sends photic information to the circadian pacemaker in the contralateral optic lobe

The circadian locomotor rhythm of the cricket Gryllus bimaculatus is primarily regulated by a pair of interacting optic lobe circadian pacemaker systems. The interaction involves phase-dependent modulation of the free-running period and phase-dependent suppression of activity. Since photic information has been shown to be involved in the interaction, we examined the regional difference in photoreception for the interaction within cricket compound eyes. The activity rhythm of animals receiving partial reduction of one compound eye combined with severance of the contralateral optic nerve split into entrained and free-running components under a 13-h light to 13-h dark cycle. All the animals operated on showed a phase-dependent suppression of activity, and most animals showed a phase-dependent modulation of the period of the free-running component. However, removal of the dorsocaudal area of the compound eye resulted in a severe reduction of the amplitude of the phase-dependent-period modulation. These results suggest that the dorsocaudal portion of the compound eye is a specific region receiving photic signals that are transmitted to the circadian pacemaker in the contralateral optic lobe and that the phase-dependent suppression of activity is caused by a mechanism separate from that for the period modulation.     

Fine structure of the sight organs in the tickHyalomma (Hyalomma) dromedarii (ixodoidea: Ixodidae)

The paired eyes in adultsHyalomma (Hyalomma) dromedarii consists of a cuticular, transparent, convex lens extending downward as an inner, hemispherical, semitransparent projection, and underlying group of photoreceptor cells. The lateral cell cytoplasm consists mainly of interrupted cisternae of rough and smooth endoplasmic reticulum, while the cell middle side is packed with rhabdomeric microvilli. The cell basal regions become function axons forming the optic nerve. These cells are adapted to distinguish between light and darkness.     

Demonstration of the tuberoinfundibular tract of the cat

Summary The distribution of dopaminergic nerve cells in the cat hypothalamus, particularly in the arcuate and periventricular nuclei, and the projections of their axons were studied by fluorescence and electron microscopy after electrothermic coagulation. The majority of these perikarya were located in the arcuate nucleus and the periventricular nucleus dorsocaudal to the optic chiasma. Large lesions caused a wide and diffuse depletion of dopamine fluorescence within the external layer; small lesions caused ipsilateral partial depletion of the dopamine fluorescence. Electron microscopic observations in animals with a lesioned arcuate nucleus revealed that in the external layer degenerating nerve terminals are engulfed by glial processes. In some cases nerve fibers had entirely disappeared and a heavy reactive proliferation of glial processes was observed. Persistence of the form of the median eminence in spite of the extensive degeneration of its nervous elements is considered to depend upon this glial proliferation.Dedicated to Professor W. Bargmann in honour of his 70th birthday     

Light alters activity but does not disturb tandem coordination of termite mating pairs

Group-living animals coordinate their movements via local interactions, which can be mediated by visual, tactile, and chemical communication channels. Termite mating pairs form tandems with one male imago following one female imago in a synchronised way to explore the environment and search for a nesting site. Imagoes are the only developmental stage with compound eyes in termites, but the role of vision during tandem runs remains unknown. Here, we investigate the movements during tandem runs of two termite species, Coptotermes formosanus, which swarms during the night, and Reticulitermes speratus, which swarms during the day. We performed the experiments with light and in complete darkness. We found that females and males of both species adjust their speed to each other to form a stable tandem and reunite efficiently upon separation, with or without light. However, the activity was dependent on light conditions in the diurnal R. speratus, in which termites were more active with light. On the other hand, the nocturnal C. formosanus was mostly insensitive to light environments, with termites being slightly more active in darkness. Our results suggest that termites can use light as an environmental cue to start forming mating pairs but not as means to locate mates or coordinate their movements.     

Inhibition in the eye of Limulus

In the compound lateral eye of Limulus each ommatidium functions as a single receptor unit in the discharge of impulses in the optic nerve. Impulses originate in the eccentric cell of each ommatidium and are conducted in its axon, which runs without interruption through an extensive plexus of nerve fibers to become a fiber of the optic nerve. The plexus makes interconnections among the ommatidia, but its exact organization is not understood. The ability of an ommatidium to discharge impulses in the axon of its eccentric cell is reduced by illumination of other ommatidia in its neighborhood: the threshold to light is raised, the number of impulses discharged in response to a suprathreshold flash of light is diminished, and the frequency with which impulses are discharged during steady illumination is decreased. Also, the activity that can be elicited under certain conditions when an ommatidium is in darkness can be inhibited similarly. There is no evidence for the spread of excitatory influences in the eye of Limulus. The inhibitory influence exerted upon an ommatidium that is discharging impulses at a steady rate begins, shortly after the onset of the illumination on neighboring ommatidia, with a sudden deep minimum in the frequency of discharge. After partial recovery, the frequency is maintained at a depressed level until the illumination on the neighboring receptors is turned off, following which there is prompt, though not instantaneous recovery to the original frequency. The inhibition is exerted directly upon the sensitive structure within the ommatidium: it has been observed when the impulses were recorded by a microelectrode thrust into an ommatidium, as well as when they were recorded more proximally in single fibers dissected from the optic nerve. Receptor units of the eye often inhibit one another mutually. This has been observed by recording the activity of two optic nerve fibers simultaneously. The mediation of the inhibitory influence appears to depend upon the integrity of nervous interconnections in the plexus: cutting the lateral connections to an ommatidium abolishes the inhibition exerted upon it. The nature of the influence that is mediated by the plexus and the mechanism whereby it exerts its inhibitory action on the receptor units are not known. The depression of the frequency of the discharge of nerve impulses from an ommatidium increases approximately linearly with the logarithm of the intensity of illumination on receptors in its vicinity. Inhibition of the discharge from an ommatidium is greater the larger the area of the eye illuminated in its vicinity. However, equal increments of area become less effective as the total area is increased. The response of an ommatidium is most effectively inhibited by the illumination of ommatidia that are close to it; the effectiveness diminishes with increasing distance, but may extend for several millimeters. Illumination of a fixed region of the eye at constant intensity produces a depression of the frequency of discharge of impulses from a nearby ommatidium that is approximately constant, irrespective of the level of excitation of the ommatidium. The inhibitory interaction in the eye of Limulus is an integrative process that is important in determining the patterns of nervous activity in the visual system. It is analogous to the inhibitory component of the interaction that takes place in the vertebrate retina. Inhibitory interaction results in the exaggeration of differences in sensory activity from different regions of the eye illuminated at different intensities, thus enhancing visual contrast.     

Effects of continuous light and darkness on the eyes of the troglobitic salamander Typhlotriton spelaeus

Larval Typhlotriton spelaeus collected from five caves in Pulaski Co., Missouri, were kept as larvae or induced to transform in darkness or continuous fluorescent illumination. Larvae maintained in darkness for 215 and 279 days had smaller eyes, smaller rod inner and outer segments, and fewer metaphase figures in the genninative zone of the neural retina than comparable larvae maintained in light (258 lux). Except for visual cell size, differences were small and for each characteristic exceptions were observed. One larva kept in light showed early retinal degeneration comparable to that in transformed adults of T. spelaeus. All larvae exhibited optomotor behavior both before and after the experiment. Among animals induced to transform by L-thyroxin and maintained in darkness 111 to 366 days, visual cell and pigment epithelium degeneration was more extensive and more frequent than in animals kept for the same length of time in light (237-298 lux). In darkness the frequency of animals with retinal degeneration increased between 111 and 366 days. In light some animals exhibited pigment epithelium reduction with normal visual cells, and others had free, pigmented cells in the subretinal space. These effects were not comparable to degeneration in darkness. Eyelids covered the eyes of only a few animals in both light and dark treatments. The extent of eyelid encroachment over the eye was greater in darkness than in light. Most animals exhibited optomotor responses after experiments, but responses of animals kept in darkness were impaired in comparison to those of animals kept in light.     

Optic lobe circadian pacemaker sends its information to the contralateral optic lobe in the cricket Gryllus bimaculatus

The bilaterally paired optic lobe pacemakers of the cricket Gryllus bimaculatus are mutually coupled. In the present study we recorded the neural activity conveyed from the brain toward the optic lobe with a suction electrode to examine the coupling signals. The results demonstrated that the brain efferents to the optic lobe encode the circadian information: Both in constant light (LL) and constant darkness (DD), the neural activity of brain efferents showed a clear circadian rhythm with a nocturnal peak. Since the rhythm survived the severance of the contralateral optic nerve but disappeared when the contralateral optic lobe was removed, it is apparent that the rhythm originates from the contralateral optic lobe. The amplitude of the rhythm was greater in LL than in DD, suggesting that light affects the amplitude of the rhythm. This was confirmed by the fact that the light-induced response was under circadian control, being greater during the subjective night. These data suggest that the bilaterally paired optic lobe pacemakers exchange circadian information as well as light information. The data are also consistent with the results of previous behavioral experiment.Abbreviations DD constant darkness - LD light dark cycle - LL constant light     

Neurosecretory cells in the circadian-clock system of the scorpion,Androctonus australis

Summary The somata of the efferent neurosecretory fibers that control the circadian sensitivity rhythm in the median eyes of the scorpion, Androctonus australis, were detected in the brain by retrograde labeling with Lucifer Yellow CH. A total of 20–40 neurons are arranged in two groups displaying a bilaterally symmetrical, marginal position near the circumesophageal connectives. Half the cells in each group send fibers into the ipsilateral optic nerve; the fibers from the other half enter the contralateral optic nerve.