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A study on the fine structure of Clonorchis sinensis, a liver fluke 1. The body wall and the nervous system
Kye-Heon Jeong,Han-Jong Rim and Chang-Whan Kim
Department of Biology, Soon Chun Hyang Medical College, Korea.
Department of Parasitology and Institute for Tropical Endemic Diseases, College of Medicine, Korea University, Korea.
Department of Biology, College of Science, Korea University, Korea.
Abstract
A morphological study on the ultrastructures of body wall and the nervous system of Clonorchis sinensis was conducted.
For this study, liver flukes were collected from the liver of rabbit six months after the infection with metacercariae obtained from the fresh water fish, Pseudorasbora parva.
The collected materials were washed with 0.85% saline solution and then immediately moved to cold 2.5% glutaraldehyde buffered with 0.1 M Millonig's phosphate buffer (pH 7.4). The materials were dissected into appropriate pieces in the fixative about 30 minutes after beginning of the fixation. Two hours later the materials were rinsed several times with the buffer and were fixed with cold, buffered 1% osmium tetroxide(OsO4) for 2 hours. The fully fixed tissue blocks were dehydrated in a series of graded concentrations of acetone and were embedded in Epon 812 mixture. Thin sections obtained from Sorvall MT-2 ultramicrotome were stained with uranyl acetate and Reynold's lead citrate. Observations of the sections were carried out with Hitachi HS-7S electron microscope.
The following structures are newly identifed in a series of observations
1 . The mid-abdominal integument of the fluke is more thicker(~6 µm) than the dorsal side(about 3 µm).
2. Although it is so far known that only surface and epithelia of the suckers, pharynx, and the oesophagus are composed of integumental, anuclear layer, it is newly found that epithelium of the excretory pore also consists of integumental, anuclear layer.
3. There are lot of microvilli in the dorsal outer surface of the oral sucker.
4. A kind of ducts accumulated with unknown secretory granules are present within the parenchyrna around both of the oral suckers and the pharynx.
5.The nerve endings are distributed to the integument of the body where sensory hairs are projected outward.
The sensory hairs are rarely distributed throughout the whole integument, but a little more in the surroundings of both suckers. The sensory hairs are attached to the base of the sheath by a circular septate desmosome. No rootlet structure is observed but the upper part of the basal body is attached to the peripheral desmosome by transverse fibres. The mitochondria and the vesicles are present within the hair cavity. The nerve fibres are also found to be myelinated at least in main axons.
Figures
Figs. 1-4 Fig. 1. A lot of microvilli(MV) 60 nm in diameter are persent in the dorsal outer surface of the oral sucker. ×8,300.
Fig. 2. In the integumental layer around the oral sucker, some myelinated structures(MB) 1~1.5µm in sizes are rarely observed. ×16,200.
Fig. 3. Certain secretory vesicles(S) are packed in ducts surrounding the oral sucker(OS) and the pharynx. ×6,000.
Fig. 4. Enlarged view of the secretory vesicles(S) and the duct-like structure with microtubules(MT). ×19,000.
Figs. 5-8 Fig. 5. The nerve axons(AX) with many vesicles(V) and inclusions. ×18,200.
Fig. 6. The myelinated nerve fibers(MNF) very rarely observed in the liver fluke. ×11,300.
Fig. 7. The sensory hair(SH) connected with neuropile in parenchyma(Pa). The surrounding region of the sensory ending shows a protuberance. ×4,000.
Fig. 8. Fine structure of the nervous system of Clonorchis sinensis longitudinally sectioned through a sensory ending(SH) in the integument. The nerve ending(SH) is attached to the base of the sheath by a circular septate desmosome(SD). Rootlet structure is not seen but the upper part of the basal body(B) is attached to the peripheral desmosome by transverse fibres(TF). ×19,300.
Abbreviations
AX
Axon
B
Basal body
BM
Basement membrane
M
Mitochondria
MB
Myelinated body
MNF
Myelinated nerve fibre
MT
Microtubule
MV
Microvilli
NF
Nerve fibre
OS
Oral sucker
Pa
Parenchyma
S
Secretory vesicle
SD
Septate desmosome
SH
Sensory hair
T
Integumental layer
TF
Transverse fiber
V
Vesicles
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