Publication: Photoreceptor fine structure in the southern fiddler ray (Trygonorhina fasciata)
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Date
1992
Authors
Braekevelt, Charlie R.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The fine structure of the retinal lntroduction
photorecéptors has been studied by light and electron
microscopy in the southern fiddler ray or guitarfish
(Trygonorhina fasciata). The duplex retina of this
species contains only rods and single cones in a ratio
of about 40:l. No multiple receptors (double cones),
no repeating pattern or mosaic of photoreceptors and
no retinomotor movements of these photoreceptors
were noted. The rods are cylindrical cells with inner
and outer segments of the same diameter. Cones are
shorter, stouter cells with a conical outer segment and
a wider inner segment. Rod outer segment discs
display severa1 irregular incisures to give a scalloped
outline to the discs while cone outer segment discs
have only a single incisure. In al1 photoreceptors a
non-motile cilium joins the inner and outer segments.
The inner segment is the synthetic centre of
photoreceptors and in this compartment is located an accumulation of mitochondria (the ellipsoid), profiles
of both rough and smooth endoplasmic reticulum,
prominent Golgi zones and frequent autophagic
vacuoles. The nuclei of rods and cones have much the
same chromatin pattern but cone nuclei are invariably
located against or particularly through the externa1
limiting membrane (ELM). Numerous Landolt's clubs
which are ciliated dendrites of bipolar cells as well as
Müller cell processes project through the ELM, which
is composed of a series of zonulae adherentes between
these cells and the photoreceptors. The synaptic
region of both rods (spherules) and cones (pedicles)
display both invaginated (ribbon) synapses and
superficial (conventional) synapses with cones showing
more sites than the rods.
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