Biomedical subjects
Publications and source records attributed to B Ehinger.
3H-serine does not label retinal neurons selectively when injected intraocularly in rabbits, as would have been expected if it had been converted to neutrotransmitter glycine. The reason is unknown, but one possibility is that the conversion was blocked during the conditions of the experiment.
The light-evoked release of [3H]glycine from retina in cat (in vivo) after pre-retinal perfusion and in rabbit (in vitro) after intravitreal injection was studied. The site of uptake of [3H]glycine into retina was checked by autoradiography and was found to be almost exclusively in a type of amacrine cells. If the retina loaded with [3H]glycine was stimulated by light flashes the release increased significantly in both in vivo and in vitro experiments. When the flashing light was exchanged for continuous light there was not change in the spontaneous efflux of radioactivity. Chromatographic experiments showed that the main part of the radioactivity released by light was glycine. The light-evoked release of glycine from retina was dependent on temperature and Ca2+. Low temperature (+2 to +4 degrees C) abolished the increased release. If Ca2+ was ommitted from the perfusion medium and EDTA was added there was no light-inducable change in the efflux of radioactivity in retinas loaded with [3H]valine. The present results, that light stimulation will release glycine from the retina both in vivo and in vitro, are further criterion for it as neurotransmitter.
The uptakes of radioactive glycine, beta-alanine, GABA, delta-aminovaleric acid and epsilon-aminocaproic acid were studied in the rabbit retina in vivo and in vitro. Autoradiography demonstrated that the amino acids were mainly taken up and retained by certain cells of amacrine type. In the neurons, the omega-amino acids seem to be stored in a protected fashion. The uptake of delta-aminovaleric acid and epsilon-aminocaproic acid was temperature dependent, saturable, and of high-affinity type (with Km for delta-aminovaleric acid = 3.02 X 10(-5) M and for epsilon-aminocaproic acid 9.38 X 10(-5) M). The uptake of both delta-aminovaleric acid and epsilon-aminocaproic acid was competitively inhibited by GABA, but not by glycine or a number of other amino acids regarded as possible neurotransmitters. The uptakes of delta-aminolevulinic acid, taurine and alpha-amino-isobutyric acid were studied for comparison, but no selective neuronal uptake was observed. It is concluded that there are certain amacrine cells which selectively accumulate delta-amino acids such as beta-alanine, GABA, delta-aminovaleric acid and epsilon-aminocaproic acid. It seems possible that the mechanism accumulating GABA may also work with the other omega-amino acids. This opens the possibility that the omega-amino acids may serve as 'false neurotransmitters'.
Dopaminergic retinal neurons become weakly radioactive after the injection of tritiated octopamine into the vitreous, but no other neurons do so. This indicates the absence of any effective mechanism for the accumulation of octopamine in rabbit retina.
The lateral eye of the horseshoe crab, Limulus polyphemus, was studied by fluorescence microscopy according to Falck and Hillarp and microspectrofluorometry for identifying neuronal monoamines. After the formaldehyde treatment, the eccentric cells and their axons have a yellowish, rapidly fading fluorescence, such as is seen with 5-hydroxytryptamine. The microspectrofluorometric analysis was compatible with the fluorescence being caused by an indole, which could not be definitely identified, however. The eccentric cells have the ability to accumulate indoleamines such as 5-hydroxytryptamine, 6-hydroxytryptamine and 5,6-dihydroxytryptamine. Their axons were best demonstrated after being loaded with 6-hydroxytryptamine. Characteristic varicose terminals were seen in the neuropil, often arranged in clusters. Other terminals, possibly originating from the eccentric cells, were also seen among the pigment cells in the basal part of the ommatidia.
Fluorescence microscopy has revealed a new type of amine-containing retinal neuron, the interplexiform cell, that extends processes in both plexiform layers. After intravitreal injection of 5,6-dihydroxytryptamine in goldfish and Cebus monkey, the processes of these cells can be identified by electron microscopy. In goldfish, the processes are pre- and postsynaptic to amacrine cells in the inner plexiform layer and presynaptic to bipolar and horizontal cells in the outer plexiform layer. Interplexiform cells thus provide an intraretinal centrifugal pathway from inner to outer plexiform layers.
A series of 131 successive hospitalized cases of traumatic hyphaema after blunt injury of the eye were treated with complete bed-rest for 6 days and double eye-patching but without any topical medication. Seven patients (5.3%) had a secondary bleeding. The visual acuities of 115 patients were tested, and 105 regained their normal vision, i.e. 1.0 or over. These results are no better than those reported in series treated with moderate bed-rest for 3-4 days combined with topical administration of corticosteroids and mydriatics. The results indicate that our present treatment may be unnecessarily severe.
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