Roles of Eph receptors and ephrins in neural crest pathfinding |
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Authors: | Vicky Robinson Alexa Smith Ann M Flenniken David G Wilkinson |
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Institution: | (1) Department of Zoology, Technical University of Darmstadt, Schnittspahnstr.3, D-64287 Darmstadt, Germany, DE |
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Abstract: | Ichthyophis kohtaoensis, a member of the limbless Gymnophiona, has a specialized subterranean burrowing mode of life and a predominantly olfactory-guided
orientation. The only visually guided behavior seems to be negative phototaxis. As these animals possess extremely small eyes
(only 540 μm in diameter in adults), functional investigations of single retinal cells by electrophysiological methods have
so far failed. Therefore, the content and distribution of retinal transmitters have been investigated as indications for a
functioning sense organ in an animal that is supposed to be blind. In this study, the organization and development of the
dopaminergic system have been examined in the retinae of embryonic, larval, and adult I. kohtaoensis, by using an antiserum against tyrosine hydroxylase, the rate-limiting enzyme in the catecholamine synthetic pathway, and
an antiserum against dopamine itself. Labeled somata are situated in the inner nuclear layer and in the ganglion cell layer.
Dopamine-positive fibers form a dense diffuse plexus, that covers the whole inner plexiform layer, whereas tyrosine hydroxylase-immunoreactive
processes show a tendency to arborize in a stratified manner. Tyrosine-hydroxylase-immunolabeled fibers can occasionally be
observed in the optic nerve head of larval stages. During ontogenesis and larval development, the distribution of transmitter-expressing
cells changes and their number decreases, but no general degeneration of the visual system is detectable. Adult Ichthyophis still have retinal transmitters, indicating that the eyes, although obviously playing a minor role in a subterranean ecological
niche, retain all the elements of functioning sense organs.
Received: 20 November 1996 / Accepted: 23 February 1997 |
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Keywords: | : Retina Amacrine cells Neurotransmitters Immunocytochemistry Tyrosine hydroxylase Dopamine Ichthyophis kohtaoensis (Gymnophiona) |
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