Horstmar Holländer

Electroretinographic responses and retrograde changes of retinal morphology after intracranial optic nerve section. A quantitative analysis in the cat.

SummaryPrevious experiments have shown that the ERG response to alternating gratings vanishes gradually within 4 months after transection of the optic nerve, changes begin after 2–3 weeks. The response to gratings of low spatial frequencies deteriorates earlier than the response to gratings of high spatial frequencies (Maffei and Fiorentini 1981). Quantitative analysis of ganglion cell sizes in retinal wholemounts shows that ganglion cell shrinkage and ganglion cell loss begin at three weeks in the periphery of the retina, particularly in the temporal retina. The same morphological alteration subsequently becomes apparent also in the area centralis and the nasal retina, respectively. The main and early cell loss occurs among medium sized ganglion cells, supposedly the beta-cells. Among the alpha-cells only shrinkage is observed up to two months postoperatively. Light- and electron microscopic examination of cross sections through the retina show that pathological changes are restricted to the innermost layers.

The section embedding (SE) technique. A new method for the combined light microscopic and electron microscopic examination of central nervous tissue

Abstract A new method for the combined light microscopic and electron microscopic examination of central nervous tissue is described. After aldehyde perfusion, tissue blocks measuring up to 3mm× 20mm× 20mm are postfixed in osmium tetroxide and dehydrated in alcohol. Without embedding, 30 μm serial sections are cut from the blocks under alcohol on a sliding microtome. The sections are collected in isopropanol and embedded in Araldite between acetate foils. The embedded sections are durable preparations that can be studied light microscopically. For electron microscopic investigation the cover-foil is removed and a plain Araldite block is polymerized to the surface of the embedded section.

Fate of DNA from retinal cells dying during development: uptake by microglia and macroglia (Müller cells).

The tunel technique of labelling fragmenting dna was used to examine cell death in the developing retina of the rabbit, rat and cat. TUNEL-labelled structures included the still-intact nuclei of retinal cells and smaller, strongly labelled bodies interpreted as fragments of disintegrating nuclei (apoptotic or pyknotic bodies). With confocal microscopy, the cytoplasm around labelled nuclei was observed to be labelled, suggesting that DNA fragments spread into the cytoplasm of the dying cell. Also observed were cells whose nuclei were TUNEL-but whose cytoplasm was TUNEL+, so that their morphology could be discerned. Evidence is presented that these are phagocytes, their cytoplasmic labelling resulting from the ingestion of the fragmenting DNA of a dying neighbour. Results suggest that in developing retina fragmenting DNA is phagocytosed principally by microglia and Müller cells, with a few neurones and no astrocytes active as phagocytes. In the postnatal material studied, microglia are the predominant phagocytes for cells dying in the ganglion cell and inner nuclear layers. Müller cells appear able to phagocytose cells dying in any retinal layer and, since microglia do not normally enter the outer nuclear layer, may be important for the phagocytosis of dying photoreceptors.

Fluorescent compounds as retrograde tracers compared with horseradish peroxidase (HRP). I. A parametric study in the central visual system of the albino rat

Abstract Several fluorescent compounds which are currently used as retrograde tracers were tested in the rat geniculo-cortical system and compared with horseradish peroxidase (HRP). Small micropipette injections were made into the primary visual cortex and the extent of retrograde labeling in the thalamus was examined. Some compounds (DAPI, Fast blue, Granular blue, True blue) gave similar results as HRP. With others (Primuline, propidium iodide, Evans blue) the labeling was less than with HRP. Bisbenzimide and Nuclear yellow may produce false positive results due to anterogradely transported tracer. In some instances, bisbenzimide stained mainly the cytoplasm and Fast blue mainly the nuclei in retrogradely labeled nerve cells.

Fluorescent compounds as retrograde tracers compared with horseradish peroxidase (HRP). II. A parametric study in the peripheral motor system of the cat

Fluorescent compounds which are currently used as retrograde tracers were tested in the cat peripheral motor system and compared with horseradish peroxidase (HRP). The tracers were either injected into forelimb muscles or applied to the proximal end of transected forelimb nerves. The remaining muscles of the limb has been carefully denervated. Following intramuscular injection all fluorescent compounds labeled spinal cord motoneurons, the DAPI compounds labeled endothelial cells in addition. In the nerve application mode tracer positive motoneurons were only observed when propidium iodide (PI) and the DAPI compounds were used, whereas bisbenzimide (BB), nuclear yellow (NY) and primuline did not label any cells. The fluorescence of BB labeled motoneurons were predominantly located in the cytoplasma. NY positive motoneurons showed a different localization of the fluorescent label between the different neurons of the same motornucleus: in some neurons it was exclusively located in the nucleus, in others predominantly in the cytoplasma, in the majority in both compartments. The intracellular distribution of the BB and the NY label was independent of the pH of the fixation fluid. The fluorescent tracers labeled the motoneuronal cell columns in their complete rostrocaudal extent and in a position identical to the one obtained with HRP. However, some substances (PI, fast blue) labeled less motoneurons of a motornucleus than did HRP, none of the fluorescent tracers labeled more. The results are discussed under several aspects: use of the investigated fluorescent compounds as single tracers; use of several tracers in the same animal to map collateral projections of one and the same neuron; use of several tracers in the same animal to establish the topographical relation between several independent neuronal populations.

On the origin of the corticotectal projections in the cat

SummaryStereotaxic injection of horseradish peroxidase into the superior colliculus produced retrograde labelling of layer V pyramides in the Clare Bishop area and the lateral bank of the suprasylvian sulcus, in area 17,18 and 19. Single labelled cells were also found scattered in the splenial, the suprasplenial, the lateral and the suprasylvian gyri. In the cruciate sulcus no labelled cells were observed. Autoradiographically, the lateral bank of the suprasylvian sulcus was also shown to give rise to fibres to the superior colliculus.

Evidence of Constriction of Optic Nerve Axons at the Lamina cribrosa in the Normotensive Eye in Humans and Other Mammals

The ultrastructure of optic nerve axons was examined in several mammals (human, cat, rat, sheep, ox, pig, guinea pig, rabbit). Human material was obtained from normotensive, glaucoma-free eyes and from eyes with a history of glaucoma and raised intra-ocular pressure (IOP). We describe accumulations of organelles (principally mitochondria) in optic nerve axons where they traverse the lamina cribrosa. Accumulations were most prominent in unmyelinated lengths of axons close to lamellae of the lamina cribrosa. Comparable accumulations were not apparent in axons in the retina or optic nerve, suggesting that axoplasmic flow is constricted at the lamina cribrosa. Accumulations were observed both centrally and peripherally to the lamellae, suggesting that flow is constricted in both ortho- and anterograde directions. Accumulations of organelles were more marked in unmyelinated axons than in adjacent, myelinated axons. In the rabbit, in which most axons are myelinated as they traverse the optic nerve head, organelle accumulations were observed only in a sparse population of unmyelinated axons. In human eyes with a history of raised IOP and glaucoma, the accumulations were abnormally large and frequent and in many axons showed dense-body and fibrillar changes not seen in normotensive eyes. It is suggested that chronic, partial constriction of axoplasmic flow is present at the lamina cribrosa of normotensive eyes in a wide range of mammals, including humans, that the constriction results from the pressure gradient across the lamina cribrosa and that the constriction may be a factor in the many cases of primary glaucoma in which IOP is not raised.

Optic nerve axon diameters measured in the cat retina: Some functional considerations

SummaryBecause of the arrangement of axon bundles in the fibre layer of the cats retina, it is possible to obtain electronmicroscopic sections of axon bundles which contain exclusively either axons arising from the area centralis, or axons arising from peripheral retina. From electronmicrographs of such sections we have constructed axon diameter spectra for central and peripheral axon samples. The centrally originating axons are markedly smaller than peripheral axons, in good agreement with their slower conduction velocity (described in an accompanying paper). The diameter spectra of both peripheral and area centralis axon samples are unimodal, in contrast to the two conduction velocity groups known to exist within each axon population. Alternative explanations of this discrepancy between diameter and conduction velocity spectra are discussed.

The projection from the visual cortex to the lateral geniculate body (LGB) an experimental study with silver impregnation methods in the Cat

SummarySmall lesions were made in the visual cortex of 15 adult cats both uni-and bilaterally. Using thermocoagulation it was possible to make lesions restricted to particular cortical cytoarchitectonic areas. The degeneration in the lateral geniculate body (LGB) was studied with silver impregnation methods of Nauta and Laidlaw and Pink and Heimer. The distribution of terminal degeneration was mapped by means of a new 3-dimensional reconstruction technique. The man results are as follows:1.Most of the fibres projecting from the visual cortex to the LGB come from area 18. They terminate in laminae A and A1 and in the central interlaminar nucleus. Rostral portions of area 18 project to rostral parts of the LGB and caudal portions to caudal parts. The medial portion of area 18 projects more medially in the LGB and the lateral portion projects more laterally.2.Area 17 does not project to any part of the LGB. A projection from the most caudal part of area 17 to the tail of the LGB cannot, however, be entirely excluded.3.Area 19 and possibly also the suprasylvian gyrus project to the medial interlaminar nucleus and to the ventral nucleus. One of these cortical areas or both send fibres to laminae A and A1, and to the central interlaminar nucleus.4.The nucleus lateralis posterior of the thalamus receives fibres from area 17, area 18, and possibly also from area 19 and the suprasylvian gyrus.

A small population of retinal ganglion cells projecting to the retina of the other eye

SummaryWe traced the retino-retinal projection with Rhodamine B isothiocyanate (RITC), Rhodamin labelled latex microspheres (RLM), horseradish peroxidase (HRP) and choleratoxin conjugated horseradish peroxidase (BHRP). The number and distribution of ganglion cells projecting to the contralateral eye were recorded. Newborn and young rats have up to about 130 ganglion cells projecting to the other retina; this confirms previous findings. We extended these findings in two ways. First, we describe a similar projection in rabbits consisting of fewer cells; second, we describe the persistence of a small component of this projection into adulthood. In addition we show with RITC and Nuclear Yellow double tracing that some of the retino-retinal ganglion cells have an axon collateral which projects to the superior colliculus. We performed control experiments in order to exclude spillover of tracer which might produce false positive labelling.