Neural development and regeneration in the visual system of teleosts

The structure of the developing optic tectum of the trout has been investigated using histological preparations and fresh material. The neuroblasts reached the pial surface and started to differentiate before separating from the ependymal processes. A new finding was the presence of inverted pear- shaped neurones in the plexiform external layer in Golgi sections of adult tectum. The organisation of the tectum was found to be similar to that described by Leghissa (1955).The first optokinetic responses occurred in trout embryos at a stage of development at which the thickness of the outer white zone was equal to that of the inner grey zone. The topographical representation of the visual field on the optic tectum of ten normal goldfish was mapped electro-physiologically using metal-filled micropipette electrodes.The topographical representation of the visual field on the optic tectum of ten normal goldfish was mapped electro- physiologically using metal -filled micropipette electrodes. Responses were evoked by visual stimulation with spots of light and with black discs of various sizes.Restoration of the visual projection over the right tectum following excision and reimplantation of the tectum in its normal orientation was studied in a series of goldfish at different times after the operation. There was a wide variation in the time taken for the restoration of the retinotectal projection map. From the third postoperative month some normal projections in the graft area were seen. It was concluded that optic nerve fibres can regenerate into the graft, and that the graft may retain its original specificities, viz. its specialization to represent a particular part of the retinaeCases where recovery occurred later than three months were those with larger areas of grafted tissue.When the graft was reimplanted 90° rotated it was predicted that the recovered projection would show a corresponding 90° rotation over the grafted area. Results tended to show the predicted distortion in the projection though not at the edges of the grafts.It was difficult to draw any useful conclusions from the retinotectal projection of 180° rotated tectum.In another series when the posterior half of the tectum was removed and the entire optic nerve allowed to regenerate, the resulting projection was compressed into the remaining half tectum.There was a gross abnormality in the histological structure of the grafted tectum even in those cases where the restoration of the visual map was more or less normal.An attempt has been made using various microscopic techniques to compare regeneration within tectal grafts with normal tectal development

How Do Whales See?

The eyes of two whales Balaenoptera physalus and Baleoptera borealis were studied by our group. In this chapter, we present the anatomical, histological, immunohistochemical and ultrastructural studies of the eyes of both types of whales. Based on the results, we can conclude that at least in these two species, the whales are rod monochromat; their resolution is very limited due to the reduced number of retinal ganglion cells, some of which were giant size (more than 100 micrometers in diameter). The excellent representation of melanopsinic positive retinal ganglion cells suggests an adaptation to the dim light as well as involvement in the circadian rhythms. The large cavernous body located in the back of the eye may provide a mechanism that allows them to move the eye forward and backwords; this may facilitate focusing and provide protection from cold deep-sea temperatures

Differential Distribution of RBPMS in Pig, Rat, and Human Retina after Damage

RNA binding protein with multiple splicing (RBPMS) is expressed exclusively in retinal ganglion cells (RGCs) in the retina and can label all RGCs in normal retinas of mice, rats, guinea pigs, rabbits, cats, and monkeys, but its function in these cells is not known. As a result of the limited knowledge regarding RBPMS, we analyzed the expression of RBPMS in the retina of different mammalian species (humans, pigs, and rats), in various stages of development (neonatal and adult) and with different levels of injury (control, hypoxia, and organotypic culture or explants). In control conditions, RBPMS was localized in the RGCs somas in the ganglion cell layer, whereas in hypoxic conditions, it was localized in the RGCs dendrites in the inner plexiform layer. Such differential distributions of RBPMS occurred in all analyzed species, and in adult and neonatal retinas. Furthermore, we demonstrate RBPMS localization in the degenerating RGCs axons in the nerve fiber layer of retinal explants. This is the first evidence regarding the possible transport of RBPMS in response to physiological damage in a mammalian retina. Therefore, RBPMS should be further investigated in relation to its role in axonal and dendritic degeneration.This research was funded by ELKARTEK KK-2019/00086, Research groups of the UPV/EHU (GIU 2018/50)and MINECO-Retos (PID2019-111139RB-I00) to E.V. Programa de perfeccionamiento de personal InvestigadorDoctor, Gobierno Vasco to X.P

Pathogenesis of Glaucoma

Glaucoma, a neurodegenerative disease, has a varied pathogenesis scenario, including elevated intraocular pressure (IOP), and hypoxic conditions in the retina. Consequently, degenerating optic axons at the optic nerve head are observed clinically when extensive damage has already occurred. Following elevated IOP, changes in retinal ganglion cells lead to apoptosis immediately followed by degeneration of their optic axons. Degradation of axons leads to cupping of the optic nerve head and visual field losses. Here we emphasize that it is the retinal ganglion cells that are initial targets of elevated IOP, and, together with hyperactivity of retinal astrocytes, create the ischemic conditions which represent the earliest sign in the pathogenesis of glaucoma

Pathogenesis of Glaucoma

Glaucoma, a neurodegenerative disease, has a varied pathogenesis scenario, including elevated intraocular pressure (IOP), and hypoxic conditions in the retina. Consequently, degenerating optic axons at the optic nerve head are observed clinically when extensive damage has already occurred. Following elevated IOP, changes in retinal ganglion cells lead to apoptosis immediately followed by degeneration of their optic axons. Degradation of axons leads to cupping of the optic nerve head and visual field losses. Here we emphasize that it is the retinal ganglion cells that are initial targets of elevated IOP, and, together with hyperactivity of retinal astrocytes, create the ischemic conditions which represent the earliest sign in the pathogenesis of glaucoma

Enkephalin-immunoreactive cells in the mesencephalic tegmentum project to the optic tectum of the teleosts Salmo gairdneri and Salmo salar

Immunocytochemistry using antibodies against Met-enkephalin and Leu-enkephalin has demonstrated a group of large enkephalin-immunoreactive neurons in the nucleus of the rostral mesencephalic tegmentum (mRMT) of two teleost fish, Salmo gairdneri and Salmo salar. Injections of cobalt-lysine in the medial optic tectum retrogradely labeled the above group of tegmental neurons. Tegmental neurons were labeled only ipsilaterally to the injection site. This indicates that enkephalinergic neurons in the nRMT project to the optic tectum, and that at least some of the enkephalinergic axons observed in the optic tectum belong to a tegmento-tectal pathway. Comparable enkephalinergic pathways have been described in reptiles and birds, where pretectal-mesencephalic nuclei contribute to the enkephalin-containing fibers that project to the optic tectum