Retinal projections in a snake, Thamnophis sirtalis

The retinofugal projections of the snake Thamnophis sirtalis were studied by the method of experimentally induced Wallerian degeneration stained by the Fink-Heimer method. The retinal ganglion cells project to all parts of the contralateral lateral geniculate complex, nucleus lentiformis mesencephali, nucleus geniculatus pretectalis, nucleus posterodorsalis, basal optic nucleus and superficial layers of the optic tectum. In addition, the retinofugal projections were observed terminating in portions of the ipsilateral lateral geniculate complex and nucleus posterodorsalis. Examination of the morphology of the retinal terminal areas stained for Nissl substance with cresyl violet led to the conclusion that these regions are well differentiated and should not be considered poorly developed when compared with other reptilian forms such as turtles.     

Evolutionary evaluation of reciprocity of connections in the turtle tectofugal visual system

In two turtle species—Emys orbicularis and Testudo horsfieldi—by the method of anterograde and retrograde traicing at the light and electron microscopy level, the existence is proven of direct descending projections from the thalamic nucleus of the tectofugal visual system n. rotunds (Rot) to the optic tectum. After injection of tracers into Rot alone and into Rot with involvement of the tectothalamic tract (Trtth), occasional labeled fibers with varicosities and terminals are revealed predominantly in the deep sublayers of SGFS of the rostral optic tectum, while in the lower amount—in other tectal layers. After the tracer injections into the optic tectum, a few retrogradely labeled neurons were found mainly in the Rot ventral parts and within Trtth. Their localization coincides with that of GABA-immunoreactive cells. Electron microscopy showed the existence of many retrogradely labeled dendrites throughout the whole Rot; a few labeled cell bodies were also present there, some of them being also GABA-immunoreactive. These results allow us to conclude about the existence of reciprocal connections between the optic tectum and Rot in turtles, these connections being able to affect processing of visual information in tectum. We suggest that reciprocity of tectothalamic connections might be the ancestral feature of the vertebrate brain; in the course of amniote evolution the functional significance of this feature can be decreased and even lost in parallel with a rise of the role of direct corticotectal projections.     

Extrinsic cells, immunoreactive to Ca-binding protein, as sources of thalamic visual centres in tortoises

Extrinsic sources of calcium-binding proteins involved in immunoreactive innervation of the visual thalamic nuclei Rot and GLd in turtles (Testudo horsfieldi and Emys orbicularis) were studied using HRP tracing method and immunohistochemistry. In 1.5-4.5 months after monocular enucleation calbindin (Calb)-, parvalbumin (Parv)- and calretinin (Calr)-labeling was found in fragments of degenerated retinal fibers in the contralateral optic tract and in some retinorecipient structures (optic tectum, GLd and GLv). Changes in GLd were detected in its neuropil part. in 2.0-3.5 months after unilateral ablation of tectum and pretectum, the densities of Parv-, Calb- and Aclr-immunoreactivity terminals and fibers were diminisched in the ipsilateral n. Rot, with the maximum effect seen in Parv. Following HRP injection into the visual thalamus (Rot and GLd), retrogradely labeled cells with Parv label only, were revealed in the ventrothalamic nucleus Enta, pretectal nucleus Ptv, and in all types of Ca-binding proteins (CaBPr) in separately labeled cells of the optic tectum. Thus, it has been shown that thalamic visual centers in turtles have multiple extrinsic cells, which serve as sources of CaBPr projections. The present data suggest that organization of CaBPr inputs to visual thalamus in reptiles (turtle) and higher amniotes are fundamentally similar.     

Tangential cell migration during layer formation of chick optic tectum

The laminated structure of the optic tectum is formed by radial and tangential cell migration during development. Studies of developing chick optic tectum have revealed two streams of tangential cell migration in the middle and superficial layers, which have distinctive origins, migratory paths, modes of migration, and destinations. We will review the process of the two types of tangential migrations, in order to elucidate their roles in the formation of the optic tectum layers.     

Distribution of an endogenous lectin in the developing chick optic tectum

We determined the cellular localization of an endogenous lectin at various times during the development of a well-characterized region of chick brain, the optic tectum. This lectin is a carbohydrate-binding protein that interacts with lactose and other saccharides, undergoes striking changes in specific activity with development, and has previously been purified by affinity chromatography from extracts of embryonic chick brain and muscle. Cellular localization in the tectum was done by indirect immunofluoresecent staining, using immunoglobulin G derived from an antiserum raised against pure lectin. No lectin was detectable in the optic tectum examined at 5 days of embryonic development. From approximately 7 days of development, neuronal cell bodies and fibers were labeled by the antibody; and extracts of tectum contained hemagglutination activity that could be inhibited by lactose or by the antiserum. Lectin remained present in many tectal neuronal layers after hatching; but in 2-month-old chicks it was sparse or absent in most of the tectum except for prominent labeling of fibers in the stratum album centrale. The initial appearance of lectin in the optic tectum was not dependent on innervation by optic nerve fibers since bilateral enucleation during embryogenesis did not affect it. Lectin was detectable on the surface of embryonic optic tectal neurons dissociated with a buffer containing EDTA.     

Specific cell surface labels in the visual centers of Xenopus laevis tadpole identified using monoclonal antibodies

Monoclonal antibodies (MAbs) against the optic tectum of Xenopus tadpoles were generated and screened by the immunofluorescent staining of frozen sections of tadpole brains. MAb-A5 stains the 8th and 9th plexiform layers of the optic tectum, whereas MAb-B2 stains all but the eighth and ninth plexiform layers of the optic tectum. MAb-A5 antigen is also detectable in the nucleus of Belonci, the corpus geniculatum thalamicum, the pretectal area, and the basal optic nucleus, all targets of the optic nerve, but is not detectable in the optic nerve or the optic tract. On the other hand, MAb-B2 does not stain any of these visual centers, though many fibers surrounding them are stained. Eye-enucleation experiments showed that MAb-A5 antigen is expressed in the optic tectum even when it is not innervated by optic nerves. Staining of viable brains with these MAbs indicates that these antigens are cell surface molecules. Immunoadsorption followed by SDS-PAGE suggests that proteins are constituents of these antigens. The MAb-A5 antigen in the diencephalon and the mesencephalon is not detectable at stage 35/36, but is detectable at stage 39 when the optic nerves begin to innervate the optic tectum. The spatial as well as the temporal patterns of the expression of the MAb-A5 antigen suggest that this molecule may be involved in the target recognition of optic nerve fibers.     

Axoplasmic transport of RNA

The transport of RNA from the ganglion cell bodies within the retina to the contralateral optic tectum has been studied in the chick following intraocular injection of radioactive uridine. By tracing the appearance of labeled RNA at the proximal end of the optic nerve as it leaves the eyeball and comparing this to the time of arrival of RNA within the optic tectum, the migratory velocity of axonal RNA has been calculated to be around 12 mm per day. The continuation of RNA migration to the optic tectum in the presence of intracerebrally injected actinomycin-D but not in the presence of the intraocularly injected drug, suggests a retinal site of synthesis of the excess RNA found in the tectum innervated by the injected eye. A study of the rate of disppearance of radioactivity of the transported RNA in the optic lobes, suggested that this RNA turns over more rapidly than the bulk of tectal RNA. The destination of migrating RNA within the optic tectum has been autoradiographically examined. Most radioactive RNA is found in the outer tectal layers in which are found the afferent fibers of the optic tract and most of their synaptic terminations. Label is not confined to these areas however but is also present in the deeper layers of the optic tectum which are not known to contain any primary synapses of the axons from retinal ganglion cells.     

Proliferative response of the mesencephalic matrix areas in the reparation of the optic tectum of Triturus cristatus carnifex

The localization and proliferative response of optic tectum matrix cells has been studied in adult newt following an experimental lesion on an optic lobe. The results show that 15 days after the lesion the cells in division, autoradiographically labelled, are located in the periventricular layer. Thirty days after the lesion the labelled cells are also found in the innermost grey layers; at 90 days the injured optic tectum regains the cytoarchitecture characteristic of this centre, with labelled cells, whether in the external or in the internal pyriform layers. In all the stages the labelled cells are also found in the periventricular layers of the controlateral optic tectum, in the dorsal pallium and in the striatum. The quantitative data exhibit the existence of a direct relationship between the number of proliferating cells in the injured optic lobe and the extent of the lesion. These data show the possibility of active cellular proliferation for the reconstruction of the lesioned nervous area and for restoration of the characteristic histological structure.     

Corticalization of two divisions of the visual system during vertebrate evolution

Data on the evolution of the visual system in vertebrate phylogeny are described. Visual projections are demonstrated in the telencephalon of cyclostomata (lampreys). The existence of a retino-thalamo-telencephalic pathway is demonstrated in elasmobranchs (skates). Two visual pathways are present in amphibians (frogs) and reptiles (turtles): retino-thalamo-telencephalic and retino-tecto-thalamo-telencephalic, and these overlap partly at the thalamic level in the lateral geniculate nucleus and completely in the telencephalon. In turtles the earliest visual and tectal impulses relay on their way to the telencephalon in the lateral geniculate body, and later impulses relay in the nucleus rotundus. In mammals (rats) visual tecto-cortical connections are seen; judging from the latent period of potentials arising in the visual cortex in response to stimulation of the superior colliculi these connections have one synaptic relay in the thalamus. The much shorter latent periods of visual evoked potentials recorded in the tectum of the monkey than in turtles (under identical chronic experimental conditions) confirm the views of morphologists on the progressive development of the tectal division of the visual system in vertebrate phylogeny. It is concluded that corticalization of both divisions of the visual system, i.e., the existence of telencephalic representation, appears in the early stages of vertebrate evolution.     

Calcium-binding proteins and cytochrome oxidase activity in the turtle optic tectum with special reference to the tectofugal visual pathway

Using immunohistochemistry and a tracer technique we investigated the distribution in the optic tectum of turtles (Emys orbicularis and Testudo horsfieldi) of the calcium-binding proteins (CaBPr) parvalbumin (PV), calbindin (CB) and calretinin (CR) before and after labeling of the nucleus rotundus (Rot) with horseradish peroxidase. The optic tectum activity of the cytochrome oxidase (CO) was studied in parallel. In the principal link of the tectofugal visual pathway (central gray layer, SGC) in both chelonian species, the sparse PV-ir as well as CB- and CR-ir neurons were found significantly varying both in number and the intensity of immunoreactivity of their bodies and dendrites. In contrast, the superficial (SGFS) and deeper periventricular (SGP) tectal layers comprised numerous cells immunoreactive to all three CaBPr in different proportions. Only few retrogradely labeled tectorotundal SGC neurons expressed PV, CB or CR. The very large PV-ir neurons in SGC and SAC were not retrogradely labeled; morphologically they matched the efferent neurons with descending projections. SGC neurons of two chelonian species differed in the level of CO activity. Intense immunoreactivity to all three CaBPr and high CO activity were detected in both species in SGFS neuropil with some differences in sublaminar distribution patterns. The peculiarities of the CaBPr and CO activity distribution patterns in different segments of SGC neurons are discussed as related to the laminar organization of the turtle tectum and its retinal innervation. It is suggested that in the projection tectorotundal SGC neurons the CaBPr are concentrated mainly in their distal dendrites that contact retinal afferents in the superficial retinorecipient tectal layer.     

Neuronal and synaptic organization in the gravity receptor system of the statocyst of Octopus vulgaris

Summary The optic tectum of Calamoichthys calabaricus (Polypteriformes) shows a relatively complex vertical stratification, with six main layers and a varied neuronal typology. In particular, pyriform neurons in the well developed stratum griseum periventriculare and some multipolar neurons in the stratum griseum profundum represent the efferent elements of the tectum, while the optic and lemniscal inputs to the tectum converge in the plexiform sublayers of the stratum fibrosum et griseum superficiale. In the circuitry of the tectum some modulation is achieved by some of the polymorphic cells of the stratum griseum internum and by the horizontal cells of the outer layers. Notwithstanding some differences with respect to the teleost optic lobe (i.e., the absence of a torus longitudinalis; the lack of a stratum fibrosum marginale; the modest size of the stratum fibrosum profundum; the paucity of neurons in the stratum fibrosum et griseum superficiale; and the ill-defined separation of the layers of the afferent and efferent fibers), the optic tectum of Calamoichthys resembles the mesotectal type characteristic of teleosts, anurans and reptiles. It exhibits higher degree of organization than the optic tectum of the Chondrostei.     

Effect of retinal ablation on the expression of calbindin D28k and GABA in the chick optic tectum

The effect of retinal ablation on qualitative and quantitative changes of calbindin D28k and GABA expression in the contralateral optic tectum was studied in young chicks. Fifteen days old chicks had unilateral retinal ablation and after 7 or 15 days, calbindin expression was analyzed by Western blot and immunocytochemistry. Neuronal degeneration was followed by the amino-cupric silver technique. After 15 days, retinal lesions produced a significant decrease in calbindin immunostaining in the neuropil of layers 5-6 and in the somata of neurons from the layers 8 and 10 of the contralateral tectum, being this effect less marked at 7 days post-lesion. Double staining revealed that 50-60% of cells in the layers 8 and 10 were calbindin and GABA positive, 30-45% were only calbindin positive and 5-10% were only GABAergic neurons. Retinal ablation also produced a decrease in the GABA expression at either 7 or 15 days after surgery. At 7 days, dense silver staining was observed in the layers 5-6 from the optic tectum contralateral to the retinal ablation, which mainly represented neuropil that would come from processes of retinal ganglion cells. Tectal neuronal bodies were not stained with silver, although some neurons were surrounded by coarse granular silver deposits. In conclusion, most of calbindin molecules are present in neurons of the tectal GABAergic inhibitory circuitry, whose functioning apparently depends on the integrity of the visual input. A possible role of calbindin in the control of intracellular Ca2+ in neurons of this circuit when the visual transmission arrives to the optic tectum remains to be studied.     

Rotational optokinesis in reptiles and its bearing on pupillary shape

Summary Members of all orders of reptiles rotate the optic bulb to compensate for changes in pitch of the head. The eye rotates through 20–30° in snakes and turtles, 50° in crocodiles and 60° in rhynochocephalians. The eye fully compensates for changes in pitch of the head over about 1/2 the range of its response. This response is largley mediated by vestibular position reflexes. It is relatively independent of the visual horizon, body proprioceptors and temperature.Rotation of the eye bulb can be related to pupillary shape and to the reported organization of the visual projections to the optic tectum. Regardless of head position, reptiles orient their eyes to keep the horizon under close inspection.This work was supported by NSF grants GB-3702 and GB-6303.     

Distribution of calbindinlike immunoreactive structures in the optic tectum of normal and eye-enucleated cyprinid fish

Summary Using the ABC immunohistochemical method, we investigated the distribution of calbindinlike immunoreactive structures in the optic tectum of normal fish, Tinca tinca, and from normal and unilaterally eye-enucleated fish, Cyprinus carpio. In nonoperated individuals of both species the optic tectum contained numerous immunoreactive neurons with strongly positive somata located in the stratum periventriculare and a thick immunolabeled dendritic shaft ascending radially toward the stratum fibrosum et griseum superficiale. The retinorecipient layers contained many fibrous immunoreactive structures. Some varicose fibers, isolated or in small bundles, were localized to the stratum album centrale, especially in the dorsal tectal half. Unilateral eye removal produced the disappearance of the immunoreactive fibrous structures located in the retinorecipient layers of the tectum contralateral to the enucleation. The present work shows that calbindinlike immunoreactive substances are localized in specific neural circuits of the fish optic tectum and suggests that the calbindin-like immunoreactive fibers in the retinorecipient strata are of retinal origin.     

中华蟾蜍中脑组织学研究

采用HE染色和Holmes银染法对蟾蜍中脑的显微结构进行了研究.中脑背侧,视叶可分为顶盖和被盖,顶盖从外侧到内侧依次分为:带状层、外灰质层、浅白质层、中灰质层、中白质层、深灰质层、深白质层和中央灰质.被盖前端分层与顶盖相同,后端分层不明显.中脑腹侧包括被盖和大脑脚,HE染色和Holmes银染法显示,大脑脚从外向内颜色由浅变深,存在大量纵向神经纤维束,两脚底分界处有横向交错的神经纤维.被盖外侧细胞不分层,聚集形成核团.被盖内侧,细胞和纤维以中脑水管为中心,呈同心圆环分8层.通过比较蟾蜍中脑背腹差异程度,了解背腹功能不同.同时对中华蟾蜍中脑同其他脊椎动物的进行了比较.     

Glutamate-like immunoreactivity in chick cerebellum and optic tectum

Glutamate was coupled via glutaraldehyde to bovine serum albumin. The conjugate was used for raising specific anti-glutamate antibodies. The purified antibody was used for immunostaining of chick cerebellum and optic tectum. Staining was intense in the molecular layer and in cell bodies of the granule cell layer. In the optic tectum a diffuse staining was detected in the superficial layers of stratum griseum fibrosum superficiale and in cell bodies especially in the layers a and e. Large cell bodies located in the stratum griseum centrale were also stained.     

Retinal projections in European Salamandridae

Summary The retinal projections to the brain were studied in three species of European Salamandridae using anterograde transport of horseradish peroxidase and autoradiography. The results obtained were basically identical for all species and confirmed earlier findings on the fiber supply to the preoptic nucleus and the basal optic neuropil. In the anterior thalamus projections to three distinct terminal fields are clearly visible: (i) the diffusely stained corpus geniculatum thalamicum, (ii) the neuropil of Bellonci, pars lateralis, and (iii) a dorsomedial terminal field, the neuropil of Bellonci, pars medialis. Caudal to these terminal fields is an almost terminal-free region, the lateral neuropil. In the posterior thalamus a medial terminal field, the uncinate field, and a laterally located terminal field, the posterior thalamic neuropil, are distinguishable. The tectum opticum displays as many as four dense layers of retinofugal fibers and terminals in the rostral part and, in addition, a more densely stained strip of neuropil running from rostral to caudal over the tectum. The extent of ipsilateral fibers is greater than previously reported in other urodele species. They supply the medial and the lateral parts of the neuropil of Bellonci, the uncinate field, and reach the tectum opticum via the medial optic tract. Further, they form terminals in the innermost optic fiber layer throughout the rostral half of the ipsilateral tectum. A small proportion of ipsilateral fibers contributes very sparsely to all other thalamic terminal fields, leaving only the caudal part of the tectum and several layers of the rostral tectum completely free of a direct retinofugal fiber supply.     

Histochemical localization of acetylcholinesterase in the cerebellum and optic tectum of four freshwater teleosts.

A histochemical study has been carried out on the localization of acetylcholinesterase (AChE) in the cerebellum and optic tectum of four species of freshwater teleosts. AChE distribution in the cerebellar cortex of teleosts shows differences among the species examined and, in the trout, also differences between different cerebellar areas. This uneven kind of enzyme distribution corresponds to a similar variety of AChE patterns noticed in other vertebrates, especially mammals. AChE distribution in the optic tectum shows a prevalent pattern characterized by precise laminar distribution of enzymatic activity which is alternatively strong, weak or absent in the different tectal layers. The results suggest that most of sensitive imput and many systems of stimuli propagation may be mediated by cholinergic mechanisms in the optic tectum of telecosts.