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G. R. Queiroz, A. García-Alcázar, V. Pinilla, J. De Juan; Ultrastructural Substrates of the Emergence of Visual Activity in the Sea Bass (Dicentrarchus labrax) Larvae Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5887.
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© ARVO (1962-2015); The Authors (2016-present)
In the teleosts retina, synapses between cone pedicles and horizontal cells undergo dramatic morphological re-arrangement. In light adaptation, cone pedicles are invaginated by spinules from the lateral processes of horizontal cells. These spinules disappear almost completely during dark-adaptation. Quantitative data from synaptic ribbons in cone pedicles are controversial. The aim of this work is to study ultrastructural retina changes during larval development and to correlate them with the awakening of visual experience in the sea bass.
Larvae of Dicentrarchus labrax were supplied by the Spanish Institute of Oceanography (Murcia). Larvae were dark- or light-adapted for at least 2 hours prior to sacrifice. Specimens at 1, 3, 5, 7, 9, 11, 13, 15, 26, 33 and 38 days post-hatching (dph) were sacrificed (six per stage, three per luminous condition). After the experiment, larvae were immediately immersed in fixative and processed for electron microscopy study. ANOVAs are performed for comparative analysis.
At 1 dph, the larvae have no visual function and the retina are immature and without layer organization. At 5 dph, when larvae open their mouth and their bowel is able to absorb, the retina shows the first evidence of photoreceptor outer segments and signs of disc shedding. Cone pedicles are immature and lacking synaptic vesicles, spinules and synaptic ribbons. Between 7 and 9 dph, larvae can detect prey and have synaptic vesicles in cone pedicles. At 9 dph cone pedicles show the first synaptic ribbons. Spinules and defined triads appear at 11. Between 11 and 15 dph the number of synaptic ribbons is greater in light-adapted retinas than in dark-adapted ones but present no significant differences in length. At this time, larvae increase their ability to detect prey. Apoptosis is very scarce during this period.
There is a close relationship between the ultrastructure of cone photoreceptors and synaptic connections in the outer plexiform layer. The appearance of membranous sacs, synaptic vesicles and synaptic ribbons marks the beginning of visual experience. However, the appearance of spinules marks the beginning of predatory activity.
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