PubMed Health⌕ Search

Biomedical subjects

G Schmahl

Publications and source records attributed to G Schmahl.

At least 19 recordsLinked to original sources
PubMed1996

Multiparameter microscopic analysis of nucleolar structure and ribosomal gene transcription.

A survey of novel microscopic approaches for structural and functional analysis of subnucleolar compartments will be presented. Research on nucleolar structure and function concentrates predominantly on two distinct types of nucleoli: (1) nucleoli present during the interphase of the cell cycle in somatic tissue culture cells and (2) nucleoli present in meiotic cells, e.g. oocytes of amphibians. These nucleoli are found during meiotic prophase of oogenesis and are functional during several months of the diplotene stage of oogenesis. A further characteristic is the fact that these nucleoli are extrachromosomal, since they originate by selective ribosomal DNA (rDNA) amplification during the early pachytene stage of oogenesis. Miller-type chromatin spread preparations using transcriptionally active nucleoli, to a major part, contributed to our understanding of the structural organization of polymerase I directed pre-rRNA transcription. Although the structural organization of the template-associated pre-rRNA transcript is known in some detail from chromatin spreads, relatively little is known about structural aspects of pre-rRNA processing. In order to investigate this intriguing question in more detail, we have developed a computer-based densitometry analysis of both template-associated and template-dissociated pre-rRNA transcripts in order to follow the structural modification of pre-rRNA transcripts during processing. Another line of experiments is devoted to the in situ structure of actively transcribing genes in the nucleolus. In order to bridge the gap between light microscopy and electron microscopy we started video-enhanced light microscopical analysis of actively transcribing genes. Although the dimensions of individual spread genes are critical for detection by optical microscopy, we succeeded in obtaining the first series of images of transcribing genes in their "native' hydrated state. An additional promising type of microscopy is transmission X-ray microscopy. Recent progress in instrumentation as well as in sample preparation has allowed us to obtain the first images of density distribution within intact, fully hydrated nucleoli using amplitude-contrast and/or phase-contrast X-ray microscopy of non-contrasted, fully hydrated nucleoli at different states of transcriptional activity. Whereas the above mentioned investigations using video microscopy and X-ray microscopy are predominantly applicable to the analysis of amplified nucleoli in amphibian oocytes, which are characterized by an extremely high transcription rate of 80-90% of rDNA genes per individual nucleolus, structural analysis of the in situ arrangement of actively transcribing genes in somatic nucleoli as present in the interphase nucleus is far more difficult to perform, mainly due to the much lower number of simultaneously transcribed active genes per individual nucleolus. Visualization of actively transcribed gene clusters is approached by an integrated experimental assay using video microscopy, confocal laser scan microscopy, and antibodies against specific nucleolar proteins.

Animals↗
PubMed1996

Effects of an asymmetric triazine derivative, HOE 092 V, on Glugea anomala, Moniez, 1887 (Microsporidia) parasitic in the three-spined stickleback Gasterosteus aculeatus.

An asymmetric triazine derivative, HOE 092 V,2-[3,5-alpha-dichloro-4-(4-methyl-sulfonylphenoxy)-phenyl]- 1-methyl-hexahydro-1,2,4-triazine-3,5-dion, was tested in vivo against Glugea anomala parasitizing the connective tissue of sticklebacks (Gasterosteus aculeatus). Naturally infected sticklebacks were incubated in 10-1 plastic aquaria in water containing 0, 2.5, 5, and 10 micrograms HOE 092 V/ml for 2, 3, and 4 h at 22 degrees C. As seen at the ultrastructural level, the drug caused severe damage to all developmental stages of G. anomala except the mature spores. Starting with a dose of 2.5 micrograms/ml, the drug caused significant damage on uni- and multinucleate meronts, sporogonial plasmodia, and sporoblasts. The damage mainly consisted in a decrease in the number of ribosomes, an enlargement of the smooth endoplasmic reticulum and a vacuolization of the cytoplasma. When treatment was done with 5 micrograms for 2 h, multinucleate meronts and sporogonial plasmodia were no longer detectable, and the sporoblasts and the prespore stages except the mature spores had shrunk. After incubation of the infected fish with 10 micrograms HOE 092 V/ml and 4 h exposure, uninucleate meronts were no longer detectable by means of transmission electron microscopy. In the sporoblast mother cells, vacuolization of the cytoplasma and lysis of the nuclei occurred. However, mature spores were not affected. It seems likely that HOE 092 V can be successfully applied in medicinal baths against Microsporidia in fish. The infected fish should be incubated in separate, aerated containers.

Animals↗
PubMed1996

The control of ichthyophthiriasis by a medicated food containing quinine: efficacy tests and ultrastructure investigations.

The present report demonstrates that a medicated food containing quinine kills the skin-inhabiting trophozoite stage of Ichthyophthirius multifiliis in ornamental fish. Artificially infected swordtails. (Xiphophorus helleri), black mollies (Poecilia sphenops), and black neons (Hyphessobrycon herbertaxelrodi) were used in the trials. The fish were maintained in groups of 10 or 20 inside aquaria (20 or 60 l) at 25 degrees C. Ultrastructure investigations by means of transmission electron microscopy revealed clear deleterious effects of quinine on the trophozoite stages. Following the initial application the outer limiting membrane of the trophozoite was broken at places. Within the nephridial plasma the plasma bridges were broken in part. After 2 days of treatment the lumen of the alveolar sac became enlarged. The food vacuoles in treated trophozoites were more electron-dense than those in the untreated controls. Numerous lipid droplets were found close to the vacuoles. The degree of damage in the nephridial plasma was intensified. When feeding was prolonged for 3 or more days, all kinds of damage became more extensive as seen in the trophozoites after 1 or 2 days of treatment. In addition food vacuoles in the final stages of digestion were no longer detectable. In long-term feeding tests, when typical ornamental fish species were fed three times daily ad libitum with the medicated food over a 12-week period, the animals showed no adverse clinical symptom. From the toxicological as well as the ecological and economical point of view the feeding of flakes containing quinine has considerable advantages as compared with conventional bath treatment.

Administration, Oral↗
PubMed1996

[X-ray microscopy].

Owing to the short wavelengths of X-radiation X-ray microscopes allow higher resolution than optical microscopes. In contrast to electron microscopes, X-radiation can be used to study relatively thick aqueous specimens in their natural environment. X-ray microscopes require intense X-radiation, which is best provided by electron storage rings, as well as efficient X-ray optics. X-ray microscopes with zone plate optics are installed at the storage ring BESSY in Berlin for studies in the fields of biology, medicine, biophysics, colloid chemistry, and soil sciences.

Animals↗
PubMed1993

Treatment of fish parasites. 10. Effects of a new triazine derivative, HOE 092 V, on Monogenea: a light and transmission electron microscopy study.

For chemotherapy of fish parasitized by monogeneans, a novel triazine derivative, 2-[3,5-alpha-dichloro-4-(4-methyl-sulfonylphenoxy)-phenyl]-1-methy l- hexahydro-1,2,4-triazine-3,5-dion (HOE 092 V), was tested in vivo against the gill- and skin-parasitizing species Dactylogyrus extensus, D. vastator, and Gyrodactylus arcuatus. Naturally infected fish were incubated in aerated, separate tanks at 22 degrees C for 1, 2, 3, and 4 h in water containing 0, 1, 5, 10, or 15 micrograms HOE 092 V/ml, whereas Pseudodactylogyrus bini was tested in vitro at 10 micrograms HOE 092 V/ml for 2.25 h. As seen by means of transmission electron microscopy, in vivo treatment against D. extensus caused vacuolization and lysis of the parasite's tegument at a dose as low as 1 micrograms/ml over a 3-h exposure period. Higher doses, such as 5 and 10 micrograms/ml over the same exposure period, produced lesions in the circular and longitudinal musculature of D. extensus and differing degrees of damage to the ciliary cells of protonephridia and immature vitelline cells. There was 100% mortality in D. vastator when incubation was done with 10 micrograms HOE 092 V/ml for 4 h (G. arcuatus; 5 micrograms/ml for 4 h; 10 micrograms/ml for 1 h) and in P. bini after 2.25 h in vitro exposure. In all species tested, the anterior portion and the opisthaptor region were most sensitive to the drug action.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Treatment of fish parasites. 11. Morphogenesis of Henneguya laterocapsulata Landsberg, 1987 (Myxosporea, Myxozoa), and the effects of a new triazine derivative, HOE 092 V, on its developmental stages: a light and electron microscopy study.

The ultrastructure of sporogenesis was studied in Henneguya laterocapsulata parasitizing the skin of hybrid catfish (Clarias gariepinus x Heterobranchus bidorsalis) in Nigeria. Sporogenesis started when a generative cell was surrounded by a second nondividing cell (i.e., envelope cell). By subsequent divisions of the generative cell, ten cells were produced, which finally became arranged into two spore-producing units. Each unit consisted of a binucleate sporoplasm, two capsulogenic cells, and two valvogenic cells. Apparently capsulogenesis, valvogenesis, and sporoplasm differentiation occurred concomitantly. In research for chemotherapy of fish parasitized by myxosporeans a new triazine derivative, 2-[3,5-alpha-dichloro-4-(4-methyl-sulfonylphenoxy)-phenyl]-1-me thy l- hexahydro-1,2,4-triazine-3,5-dion (HOE 092 V), was tested in vivo against the uni- and multicellular developmental stages of H. laterocapsulata. Naturally infected catfish were incubated in water containing 0, 2.5, 5, and 10 micrograms HOE 092 V/ml or the pure solvent for 3 h. After the fish had been returned into fresh water, they were killed 1 day after the treatment and the plasmodia were studied by means of light and transmission electron microscopy. Starting with a dose of 2.5 micrograms HOE 092 V/ml, the pericyte's outer membrane was broken in the bi- and multicellular stages. The number of ribosomes in the bi- and multicellular stages decreased. In the multicellular stages the rough endoplasmic reticula of the capsulogenic cells were enlarged. Treatment with 5 micrograms HOE 092 V/ml led to breaks in the limiting outer membranes of the capsulogenic cells and to vacuolization of their peripheral cytoplasm. In early prespore stages a decrease in the number of spherical inclusions was recognized.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Light and scanning electron microscopy studies on the effects of the enantiomers of praziquantel and its main metabolite on Schistosoma mansoni in vitro.

In the present study, the effects of the enantiomers of the anthelmintic drug praziquantel (PZQ) and its main metabolite trans-4-hydroxy-praziquantel (TRANS) on pairs of Schistosoma mansoni worms were examined in vitro. Highly purified enantiomers (optical purity, greater than 99.9% for PZQ and 99.0% for TRANS) were used. Paired worms were incubated for 4 h in RPMI medium containing 0.01, 0.02, 0.075, 0.1, 2.5, 10, and 100 micrograms PZQ or TRANS enantiomers/ml, respectively, before being transferred to drug-free medium for another 20 h. PZQ is used as a racemate in the therapy, and its effect is attributed to the R(-)-enantiomer. R(-)-PZQ and R(-)-TRANS proved to be at least 10(5) times more effective than the respective S(+)enantiomers, causing tegumental damage and surface blebbing on S. mansoni. As judged from the effective doses in 50% of the worms (ED50 values); R(-)-PZQ and R(-)-TRANS showed nearly the same efficacy against adult S. mansoni. Male worms reacted more sensitively than did females. As determined by scanning electron microscopy, alterations in lethally damaged worms depended on the drug used, even following incubation at the lowest concentration tested (0.01 microgram/ml). Worms exposed to R(-)-TRANS were elongated, whereas treatment with R(-)-PZQ led to contractions and twisted parasites. Both compounds caused excessive surface blebbing along the dorsal side of the worms' tegument.

Animals↗
PubMed1992

Treatment of fish parasites. 9. Effects of a medicated food containing malachite green on Ichthyophthirius multifiliis Fouquet, 1876 (Hymenostomatida, Ciliophora) in ornamental fish.

For systemic therapy against trophozoites of the skin-inhabiting stage of Ichthyophthirius multifiliis in ornamental fish, the latter were fed medicated food flakes containing malachite green once daily for 1-11 days ad libitum. Naturally or artificially infected cardinal tetras (Paracheirodon axelrodi), blue gouramis (Trichogaster trichopterus), or clown loach (Botia macracantha) were used in the trials. The fish were maintained in aerated 12.5- or 60-1 aquaria at 23 degrees C. Ultrastructural investigations (scanning and transmission electron microscopy) revealed clear deleterious effects of malachite green on the parasitic stages. Following the initial application, the inner membrane of the mitochondria was destroyed. In fish fed for 2 days, aggregation of the mucocysts and polymerization the microtubules within the macronucleus occurred. Finally, the trophozoite's membrane was completely destroyed. In fish fed for 4 days, the medicated food killed all trophozoites of I. multifiliis. Sensitive ornamental fish (e.g., P. axelrodi) showed no adverse effects after they had been fed with only the medicated food flakes for 2 months. Therefore, the oral administration of malachite green using this newly developed medicated food considerably reduces the risk of toxic effects on the fish hosts, which are sometimes caused by malachite green following its application by immersion therapy. The feeding of flakes medicated with malachite green provides and easy-to-handle and highly effective treatment of I. multifiliis in ornamental fish.

Animal Feed↗
PubMed1991

Fine structure of spermatogenesis in polyopisthocotylid monogeneans (Protomicrocotyle ivoriensis, Gastrocotyle sp.).

The development of spermatozoa in the polyopisthocotylean fish-gill flukes Protomicrocotyle ivoriensis and Gastrocotyle sp. was investigated by light and transmission electron microscopy. In both species the spermatogonia were undifferentiated cells, the cytoplasm of which contained numerous free ribosomes, and successive mitoses gave rise to primary spermatocytes, which are clearly identified by the presence of synaptonemal complexes in their nuclei. As compared with that of the spermatogonia, the cytoplasm of the primary spermatocytes contained an increased number of ribosomes. Golgi complexes were frequently seen in the spermatocytes of P. ivoriensis but not in Gastrocotyle sp. In P. ivoriensis the secondary spermatocytes were separated by interspaces between the irregularly shaped cell surfaces. In both species a syncytial mass of spermatids developed, which gave rise to 64 spermatozoa. Cross sections of the mature spermatozoa of both species revealed the presence of numerous submembranous microtubules and two axonemes showing a pattern of 9 doublet peripheral microtubules plus a central one. In contrast to microtubules plus a central one. In contrast to P. ivoriensis, in Gastrocotyle sp. the axonemes originated from different places at the axis of the spermatozoon. With respect to the other results obtained, the spermiogenesis and the fine structure of spermatozoa of both species studied were similar to previous findings in other polyopisthocotyleans.

Animals↗
PubMed1991

The chemotherapy of monogeneans which parasitize fish: a review.

Monogeneans which parasitize fish are still treated by bathing the fish in solutions of simple chemicals or staining dyes. In the early 1960s an insecticide, trichlorphon, replaced to a large extent the formerly used simple chemicals. Its success was greater specificity against monogeneans and other ectoparasites, and to its great tolerance by the fish. The fact that the number of important monogenean species (i.e. Pseudodactylogyrus anguillae, P. bini, Gyrodactylus salaris) which cannot be treated sufficiently with simple chemicals or even trichlorphon is increasing, led to the need for systemically acting, novel chemotherapeutics. In laboratory and small scale trials praziquantel, levamisole, mebendazole and toltrazuril have been tested for efficacy against a broad spectrum of monogenean species.

Animals↗
PubMed1990

Transmission electron microscopic studies on the effects of toltrazuril on Glugea anomala, Moniez, 1887 (Microsporidia) infecting the three-spined stickleback Gasterosteus aculeatus.

A symmetric triazinone, toltrazuril, was tested in vivo against Glugea anomala parasitizing the connective tissue of sticklebacks (Gasterosteus aculeatus). Naturally infected sticklebacks were incubated in toltrazuril-containing water as intermittent therapy (3 x 2 micrograms/ml for 6 h at 3-day intervals or 3 x 2 micrograms/ml for 24 h at 2-day intervals). As seen at the ultrastructural level, the drug caused severe damage to all developmental stages of G. anomala. When treatment was carried out for 6 h, the xenoma wall exhibited a network appearance. The multinucleate meronts showed tapering at one end and were lysed at places; disintegration of the nuclei was also observed. The sporogonial plasmodia were partially fragmented, and the dumbbell-shaped nuclei of the sporoblast mother cells showed damaged spindle fibres and lysis of the chromosomal material and nuclear membranes. The shape of the mature spores was altered as well. When treatment was done for 24 h, the xenoma wall was completely destroyed. The uni- and multinucleate meronts were completely destroyed and lacked their nuclei, and the sporogonial plasmodia were frequently totally fragmented. The development of the sporophorous vesicle stopped in many cases. In the sporoblasts and their mother cells, vacuolization of the cytoplasma and lysis of the nuclei were observed. Destroyed spores with damaged polar tubes and polaroblasts were frequently detected. It seems likely that toltrazuril could be successfully applied against Microsporidia in fish when used as intermittent therapy at low doses and with prolonged exposure.

Animals↗
PubMed1989

Chemotherapy of fish parasites.

There are few agents on the market that control fish parasites. These are substances that are mainly used in other hosts; due to the different metabolism of fish, they often have only moderate effects on fish parasites. Therefore, the research and development of fish-specific antiparasitic compounds is needed to avoid the high losses suffered by commercial fish hatcheries. Drugs similar to toltrazuril would perhaps be promising, due to their broad spectrum of efficacy.

Animals↗
PubMed1988

Treatment of fish parasites. 4. Effects of sym. triazinone (toltrazuril) on Monogenea.

For chemotherapy in fish parasitized by monogeneans, toltrazuril was tested in vivo and in vitro against gill-parasitizing species (Dactylogyrus vastator, D. extensus, D. cornu, Pseudodactylogyrus anguillae, Diplozoon paradoxum, Dip. homoion) as well as the skin-parasitizing species Gyrodactylus arcuatus. Naturally infected fish were incubated at 20 degrees C for 0.3, 1, 2, 3, 4, and 6h in water containing 0.5, 10, 20, 30, and 50 microgram toltrazuril/ml. In general, the damage observed resulted in the vacuolization and lysis of the parasitic tegument. Toltrazuril caused irreversible lesions in the tegument of Dactylogyrus species and Pseudodactylogyrus bini, beginning at a dose of 5 microgram/ml (4-h exposure). In vitro treatment with 10 microgram/ml toltrazuril caused death in Dip. paradoxum and Dip. homoion after 4-80 min, depending on the age of the parasites. Subadult worms were more susceptible to the drug than adults. Specimens of G. arcuatus were severely affected after 1-h exposure to 20 microgram/ml. In all species, the prohaptor and peduncle regions of the specimens were most sensitive to the drug. Treatment of infections of Gyrodactylus species, D. vastator, D. extensus, C. cornu, and P. bini using a water bath with 10 micrograms toltrazuril/ml for 4 h (D. cornu, 15 degrees C; other species, 20 degrees C) is recommended, since then species diagnosis is not needed. Fish with extensive skin lesions caused by net catching or infection by Saprolegnia spp. should be carefully observed during treatment, as these factors decrease their drug tolerance.

Animals↗
PubMed1987

Treatment of fish parasites. 2. Effects of praziquantel, niclosamide, levamisole-HCl, and metrifonate on monogenea (Gyrodactylus aculeati, Diplozoon paradoxum).

In research for successful treatment of fish parasitized by monogeneans, four substances (Praziquantel, Niclosamide, Levamisole-HCl, and Metrifonate) were tested in vivo against Gyrodactylus aculeati parasitizing the skin of sticklebacks (Gasterosteus aculeatus). Fish were incubated in water containing different solutions of the drugs. Praziquantel, Niclosamide and Levamisole-HCl were effective against Gyrodactylus aculeati. Praziquantel caused irreversible lesions in the parasite tegument (beginning with 1 microgram/ml and 90 min exposure). Niclosamide was effective in a narrow concentration range of 0.075-0.1 microgram/ml (90 min). Levamisole-HCl was effective in a concentration range of 20-50 micrograms/ml for 120 min. Like Praziquantel, Niclosamide and Levamisole-HCl led to damage of the parasite tegument. The opisthaptor region and the openings of the cephalic glands were most severely affected. Furthermore, the effects of Niclosamide, Levamisole-HCl and Metrifonate on Diplozoon paradoxum parasitizing the gills of chubs (Squalius cephalus) and breams (Abramis brama) were investigated. Levamisole-HCl (10 micrograms/ml) and Niclosamide (0.2 microgram/ml) were effective against Diplozoon paradoxum after an exposure of 90 min and 45 min in vitro. The parasites were severely affected along the midbody. Metrifonate caused a lysis of the tegument and a strong secretion of slime. It is suggested that chemotherapy against Gyrodactylus sp. may be accomplished with 10 mg Praziquantel/l for 3 h during storage in smaller tanks. Niclosamide (0.1 mg/l for 90 min), or Levamisole-HCl (50 mg/l for 120 min) may be used alternatively. Concentrations of Niclosamide and Levamisole-HCl have to be calculated with accuracy, since fish only tolerate a very narrow range of these drugs (Niclosamide: 0.1 mg/l for 120 min; Levamisole-HCl: 50 mg/l for 120 min).

Animals↗
PubMed1986

X ray microscopy--state of the art and expected developments.

The Göttingen X ray microscope at the electron storage ring BESSY in Berlin and X ray microscopy experiments with biological specimens are described. A look ahead to future developments--optics for higher resolution and with better efficiency, detector devices with higher detective quantum efficiency, and the development of a laboratory X ray microscope with a plasma X ray source--is taken.

Electron Probe Microanalysis↗