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G Seifert

Publications and source records attributed to G Seifert.

At least 37 records · Page 2Linked to original sources
PubMed2000

Structure and electronic properties of MoS2 nanotubes

Structural and electronic properties as well as the stability of MoS2 nanotubes are studied using the density-functional-based tight-binding method. It is found that MoS2 zigzag ( n,0) nanotubes exhibit a narrow direct band gap and MoS2 armchair ( n,n) possess a nonzero moderate direct gap. Interestingly, the ( n,n) tubes show a small indirect gap similar to the direct gap of ( n,0) nanotubes. Simulated electron diffraction patterns confirm the existence of armchair and zigzag disulphide nanotubes. The structure of the MoS2 nanotube tips is explained by introducing topological defects which produce positive and negative curvature.

Journal Article↗
PubMed2000

Developmental regulation of AMPA-receptor properties in CA1 pyramidal neurons of rat hippocampus.

AMPA-receptor (AMPA-R) currents were recorded from CA1 pyramidal neurons in situ and after acute isolation from the hippocampus of 3- to 45-day-old rats. Membrane currents were analyzed by combining the patch clamp method with fast application techniques. The complete block of receptor currents by GYKI 53655 and the absence of modulation by Concanavalin A indicated that the cells exclusively expressed non-NMDA glutamate receptors of the AMPA subtype while functional kainate receptors could not be detected. The lowest sensitivity to kainate and NBQX was observed at postnatal day (p) 18. These changes might reflect a lower abundance of GluR1 at that developmental stage. A decrease of potentiation of receptor currents by cyclothiazide (CTZ), an acceleration of the recovery from CTZ potentiation and a faster and more complete desensitization of glutamate-evoked currents suggest an up-regulation of flop splice variants with increasing age. These functional data indicate that AMPA-R expression in CA1 pyramidal neurons varies during postnatal development which can be expected to influence the kinetics of synaptic transmission and the excitotoxic vulnerability as well.

Alternative Splicing↗
PubMed2000

Astrocytes in the hippocampus of patients with temporal lobe epilepsy display changes in potassium conductances.

Functional properties of astrocytes were investigated with the patch-clamp technique in acute hippocampal brain slices obtained from surgical specimens of patients suffering from pharmaco-resistant temporal lobe epilepsy (TLE). In patients with significant neuronal cell loss, i.e. Ammon's horn sclerosis, the glial current patterns resembled properties characteristic of immature astrocytes in the murine or rat hippocampus. Depolarizing voltage steps activated delayed rectifier and transient K+ currents as well as tetrodotoxin-sensitive Na+ currents in all astrocytes analysed in the sclerotic human tissue. Hyperpolarizing voltages elicited inward rectifier currents that inactivated at membrane potentials negative to -130 mV. Comparative recordings were performed in astrocytes from patients with lesion-associated TLE that lacked significant histopathological hippocampal alterations. These cells displayed stronger inward rectification. To obtain a quantitative measure, current densities were calculated and the ratio of inward to outward K+ conductances was determined. Both values were significantly smaller in astrocytes from the sclerotic group compared with lesion-associated TLE. During normal development of rodent brain, astroglial inward rectification gradually increases. It thus appears reasonable to suggest that astrocytes in human sclerotic tissue return to an immature current pattern. Reduced astroglial inward rectification in conjunction with seizure-induced shrinkage of the extracellular space may lead to impaired spatial K+ buffering. This will result in stronger and prolonged depolarization of glial cells and neurons in response to activity-dependent K+ release, and may thus contribute to seizure generation in this particular condition of human TLE.

Adult↗
PubMed2000

Functional and molecular properties of human astrocytes in acute hippocampal slices obtained from patients with temporal lobe epilepsy.

PURPOSE: The specific role of glial cells in epilepsy is still elusive. In this study, functional properties of astrocytes were investigated in acute hippocampal brain slices obtained from surgical specimens of patients with drug-resistant temporal lobe epilepsy (TLE). METHODS: The patch-clamp technique together with a single-cell reverse transcription-polymerase chain reaction approach were used to combine functional and molecular analysis in the same individual cell in situ. RESULTS: In patients with Ammon's horn sclerosis, the glial current patterns resembled properties of immature astrocytes in rodent hippocampus. Depolarizing voltage steps activated delayed rectifier and transient K+ currents as well as tetrodotoxin-sensitive Na+ currents. Hyperpolarizing voltages elicited inward rectifier K+ currents. Comparative recordings were made in astrocytes from patients with lesion-associated TLE that lacked significant histopathological hippocampal alterations. The inward rectifier K+ current density was significantly smaller in astrocytes from the sclerotic group compared with lesion-associated TLE patients. CONCLUSIONS: During normal development of rodent brain, astroglial inward rectification gradually increases. It thus appears that astrocytes in human sclerotic tissue reexpress an immature current pattern. Reduced astroglial inward rectification in conjunction with seizure-induced shrinkage of the extracellular space may lead to impaired spatial K+ buffering. This will result in stronger and prolonged depolarization of glial cells and neurons in response to activity-dependent K+ release and may thus contribute to seizure generation and spread in this particular condition of human TLE.

Action Potentials↗
PubMed1999

Developmental changes in the expression of Shaker- and Shab-related K(+) channels in neurons of the rat trigeminal ganglion.

We have investigated properties of voltage-gated K(+) channels in neurons of the pre- and postnatal rat trigeminal ganglion (TG). To correlate functional data with information on gene expression of Shaker- and Shab-related channels in these pseudo-unipolar neurons, the patch-clamp technique was combined with the single-cell reverse transcription-polymerase chain reaction (RT-PCR). A majority (80%) of prenatal TG neurons possessed only sustained delayed rectifier currents with half-maximal current inactivation at -30 mV. In the postnatal cells, steady-state inactivation of sustained currents occurred at more negative voltages (half-maximal inactivation at -58 mV). About 65% of the postnatal cells displayed a transient outward component in addition to the sustained currents. With increasing age, the sensitivity of sustained currents to 4-aminopyridine (4-AP) decreased significantly. The Shaker channel toxins, alpha-dendrotoxin and agitoxin-2 (50 and 10 nM), were much less effective. Discrimination between both stages with tetraethylammonium chloride (5 mM) was not possible since the currents were reduced generally by about 50%. After recording, the cell content was harvested and single-cell RT-PCR was performed to compare K(+) current properties and mRNA expression within the same cell. Most cells simultaneously expressed several different Shaker- and Shab-like transcripts. At postnatal day 14, the frequency of cells carrying transcripts encoding Kv1.1 decreased. Detailed analysis revealed a higher 4-AP sensitivity of TG neurons expressing Kv1.1 transcripts.

4-Aminopyridine↗
PubMed1999

Unusual choristoma of the parotid gland in a girl. A possible trichoadenoma.

An 8-year-old girl had a painless circumscribed nodule in the right parotid gland for 4 weeks. A tumour (1.3 cm diameter) within the salivary gland parenchyma showed small cystic spaces with horn-like material macroscopically. The tumour tissue contained solid squamous cell formations and cystic spaces limited by multilayered squamous epithelium and covered by layers of ortho- and parakeratotic cells. The cystic spaces contained keratotic lamellae. In some areas pin-like epithelial proliferations were seen. All epithelial cells were characterized by uniform nuclei, and no atypical mitoses were seen. Keratinizated masses with partial calcification were occasionally located in the interstitial tissue and replaced by multinucleated giant cells. The tumour was classified as a choristoma and resembled a trichoadenoma. The ectodermally derived oral and salivary gland epithelium may be the source of skin-like or adnexal tumours.

Adenoma↗
PubMed1999

Lipomatous pleomorphic adenoma of the parotid gland. Classification of lipomatous tissue in salivary glands.

Lipomatous pleomorphic adenoma is an unusual subtype with a lipomatous stromal component of more than 90% of the tumour tissue. This special type of pleomorphic adenoma must be distinguished from other types of lipomatous tumours or non-tumourous lipomatosis of the salivary glands. Until now only two cases of lipomatous pleomorphic adenoma have been reported in the literature. We report of a 36-year old woman who developed a well circumscribed nodule measuring 3.5 x 2.5 x 2 cm in the right parotid gland. The cut surface was grey-yellowish. Histologically, more than 90% of the tumour tissue was fatty tissue with univacuolar adipocytes. The pleomorphic epithelial elements were duct-like cells forming small lumina and spindle-shaped myoepithelial cell with surrounding mucoid stroma. Components of pleomorphic adenoma were intermingled with mature adipose tissue which was more concentrated in the central portion of the adenoma. Some compressed epithelial cords in the adipose tissue formed a septa-like pattern. The differential diagnosis to other lipomatous tumours (lipoadenoma, lipoma) and to non-tumourous interstitial lipomatosis as well as the possible pathogenesis as metaplastic change or epithelial-mesenchymal transdifferentiation are discussed.

Adenoma, Pleomorphic↗
PubMed1999

Adenolymphoma (Warthin's tumor) with multiple sarcoid-like granulomas.

Five cases of adenolymphoma (Warthin's tumor) (AL) with numerous sarcoid-like granulomas within the lymphoid stroma are described. All patients were males, aged from 44 to 71 years (mean 57.3 years); all tumors were localized in the parotid gland. Fine needle aspiration cytology was performed in two cases 7.5 and 2 weeks before operation, respectively. Microscopic examination demonstrated the typical structure of AL. In addition, dispersed throughout the lymphoid stroma there were numerous granulomas formed by both epithelioid and multinucleated giant cells of Langhans type, strongly resembling sarcoidosis. The pathogenesis of the granulomatous change remains speculative. It could be caused by a toxic effect of the cysts' contents but probably not by its direct action; the spread of the fluid via sinuses into the lymphatic tissue seems to be more probable. We presume that the previous FNA may have some triggering effect. Granulomatous transformation of the lymphoid stroma resembling sarcoidosis is rare, but should be included in the spectrum of secondary changes in AL. It is not limited to metaplastic AL; it can be seen in an otherwise typical AL without any additional histologic changes. Knowledge of a previous FNA and awareness of the possibility of this peculiar histologic change are necessary to avoid incorrect diagnosis.

Adenolymphoma↗
PubMed1999

Lesion-induced changes of electrophysiological properties in astrocytes of the rat dentate gyrus.

Reorganization of the adult dentate gyrus following unilateral entorhinal cortex lesion (ECL) is a well-established model for studying mechanisms of trauma-induced neuronal plasticity. The lesion induces deafferentiation of the outer molecular layer, which is accompanied by a strong astroglial reaction. This glial response is thought to contribute to subsequent repair processes, but the underlying mechanisms are poorly understood. In this study we addressed the question whether denervation leads to modifications in the electrophysiological properties of astrocytes, assuming that such changes might be involved in the remodeling of neural circuitry. Patch-clamp recordings were obtained from astrocytes in the dentate gyrus of adult rats that underwent ECL and compared to corresponding data from control animals. We observed a significant reduction of inward rectifier K(+) current densities, a positive shift of resting potentials, and an increase in input resistance in astrocytes of the denervated molecular layer. Current densities were reduced between 6 and 19 days postlesion (dpl), reaching a minimum at 10 dpl. Voltage-gated outward K(+) currents were not affected by the lesion. Inward rectifier K(+) currents increase with maturation in astrocytes. Thus, our results provide evidence that, following ECL, mature astrocytes dedifferentiated and readapted an immature current pattern. Presumably, these changes lead to stronger and prolonged depolarization of glial cells and neurons in response to activity-dependent K(+) release, which in turn might enhance the synthesis of neurotrophic factors and contribute to a permissive environment for neuronal reorganization.

Animals↗
PubMed1998

[Differential diagnosis of squamous epithelial carcinoma of the salivary glands].

Primary squamous cell carcinomas (SCC) of the salivary glands are localized predominantly in the major salivary glands and must be distinguished from metastases of extraglandular SCC of the skin, especially the head and neck area. Squamous cell metaplasia in non-tumourous diseases of the salivary gland (e.g. necrotizing sialometaplasia) as well as in benign or malignant salivary gland tumours (e.g. metaplastic Warthin tumour) can simulate SCC. Other differential diagnostic problems are the structural variants of SCC which develop predominantly in the minor salivary glands, but not in the major salivary glands. Special types include the very rare adenoid SCC with pseudoglandular structures as the result of acantholysis, the biphasic adenosquamous carcinoma with differentiation as SCC and adenocarcinoma, the biphasic basaloid squamous carcinoma with a structure as SCC and solid basaloid carcinoma (analogous to the solid type of adenoid-cystic carcinoma) and the poorly differentiated mucoepidermoid carcinoma (grade III) with biphasic structure of undifferentiated epidermoid and intermediate cells as well as inclusion of small groups of mucous-producing goblet cells. The differential diagnostic criteria are analysed concerning prognosis and treatment.

Carcinoma, Squamous Cell↗
PubMed1998

[Juvenile pleomorphic parotid adenoma of embryonal structure].

Juvenile pleomorphic adenoma of the parotid gland represents an extremely rare tumour entity and is comparable to congenital tumours of the salivary glands concerning its embryonal structure. The clinical detection of the tumour in a 7-year-old girl does not exclude that the tumour had developed either earlier or immediately after the birth. The high cellularity and the evidence of primitive epithelial and myoepithelial cellular structures do not justify its classification as a malignant tumour. However the presence of embryonal tissue structures associated with the end of the third month of embryogenesis is characterized by more solid cell formations in partly verticulate arrangement. The absence of further differentiation into lobular structures and differentiated duct or acinic cell formations may be due to cell arrest. Differential diagnosis of juvenile pleomorphic adenoma must distinguished it from other congenital salivary gland tumours (e.g. congenital basal cell adenoma, hybrid basal cell adenoma-adenoid cystic carcinoma, sialoblastoma, salivary gland anlage tumour.

Adenoma, Pleomorphic↗
PubMed1998

[Diagnostic pitfalls in benign and malignant salivary gland diseases. Their significance for prognosis and therapy].

Diagnostic pitfalls exist when benign salivary gland diseases are mistakenly classified as malignant, with consequences for treatment and prognosis. Examples are necrotizing sialometaplasia, metaplastic Warthin tumour and sclerosing polycystic sialadenopathy. The proper diagnosis is of eminent importance to distinguish cases of primary tumours that have developed in salivary glands or their lymph nodes from cases of extraglandular tumours with metastases in these glands or their nodes. In these cases clinical data and additional immunocytochemical methods are necessary to clarify the exact diagnosis, especially when the primary salivary gland tumours have a structure largely identical to the metastases (e.g. squamous cell carcinoma). Nasopharyngeal or cervical chordomas can be mistaken for pleomorphic adenoma or mucinous adenocarcinoma. The initial stage of malignant MALT lymphomas in association with Sjögren's syndrome demands identification of clonal rearrangement for therapeutic implication. The diagnostic criteria for proper classification are analysed in detail.

Diagnosis, Differential↗
PubMed1998

[Cranial and cervical chordomas. A differential diagnostic problem].

Cranial and cervical chordomas can spread by para- or retropharyngeal extension up to the region of the salivary glands or the jaw and may simulate a tumor of the salivary glands or jaw. In occasional cases, because the tumors often expand slowly, months or years may pass between the first clinical symptoms and diagnosis. Diagnostic problems exist in differentiating these chordomas from pleomorphic adenoma, mucinous carcinoma, or chondrosarcoma. Ten relevant observations of typical cranial and cervical chordomas (Salivary Gland Register Hamburg 1965-1996) were analyzed more closely by pathohistological and immunohistochemical means. The exact diagnosis is based upon the evidence of blown-up, bubble-like ("physaliform") cells which contain mucus drops in a vacuolized cytoplasm and are surrounded by extensive areas of mucoid mucus. The pattern of immunohistochemistry is characterized by the multifold expression of cytokeratin, vimentin, and EMA. The differential diagnosis is discussed with reference to further types of chordoma (chondroid chordoma, dedifferentiated chordoma with spindle cell sarcomatous transformation), chondrosarcoma, pleomorphic adenoma, and mucus-producing carcinoma.

Adult↗
PubMed1997

The congenital basal cell adenoma of salivary glands. Contribution to the differential diagnosis of congenital salivary gland tumours.

Congenital epithelial tumours of the salivary glands are very rare. The Salivary Gland Registry maintained in the Department of Pathology. University of Hamburg, contains only three cases among a total of 6,646 salivary gland tumours from the years 1965-1994. The three cases were classified as congenital basal cell adenoma, two of the parotid gland and one of the submandibular gland. Histologically, the three adenomas were similar in structure to the adult counterpart of basal cell adenoma with solid, trabecular or tubular (duct-like) patterns. In some cystic spaces of the duct-like structures PAS- and Astra blue-positive substances were secreted. On immunocytochemistry, the luminal duct-like cells showed membranous expression of cytokeratins 3, 5, 6, 7, 13 and 19. In the isomorphic basaloid cells of the solid and trabecular cell nests few cells expressed cytokeratin. On the outside of the solid cell nests there were smaller elongated myoepithelial-like cells, which expressed cytokeratin 14 and vimentin. Cytokeratins 1, 2, 4 and 18 were not expressed. The pattern of expression reflects the different stages of maturity of the tumour cells and is related to the development of the salivary glands until the end of the 3rd embryonal month with an arrest of further cell differentiation. No acinic cells, invasive growth, recurrence or metastases were observed. The differential diagnosis includes other congenital salivary gland tumours, such as hybrid basal cell adenoma-adenoid cystic carcinoma, sialoblastoma or embryoma, carcinoma, hamartoma and teratoma.

Adenoma↗
PubMed1997

[Diagnosis and prognosis of salivary gland tumors. An interpretation of new revised WHO classification].

An exact morphological classification of salivary gland tumours is necessary for international comparison of clinical tumour studies. The basis is formed by the TNM system for determining tumour stage ("staging") and the WHO classification as the underlying principle of identifying the pathohistological tumour state and cellular tumour differentiation ("grading"). The second, revised edition of the WHO classification of salivary gland tumours differs from the first in that the exact definition of a considerably greater number of tumour entities is given and in the consideration of additional factors concerning prognosis and therapy. In the present interpretation of salivary gland tumours, not only are solitary tumour entities defined, but new findings are also considered concerning immunohistochemical tumour markers, proliferation markers (Ki-67 resp. MIB 1, AgNORs, PC-NA), oncogenes and cell receptors as well as cytogenetic alterations as prognostic factors. In particular the new tumour entities of adenomas (myoepithelial adenoma, basal cell adenoma, canalicular adenoma) and carcinomas (acinic cell carcinoma, mucoepidermoid carcinoma, polymorphous low-grade adenocarcinoma, salivary duct carcinoma, myoepithelial carcinoma) are characterized. In addition, the tumour-like lesions and differential diagnostic aspects are mentioned and a general review about new prognostic factors is presented.

Biomarkers, Tumor↗
PubMed1997

[Primary salivary gland tumors in lymph nodes of the parotid gland. Report of 3 cases and review of the literature].

Multiple intra- and paraglandular lymph nodes develop in the parotid gland, including salivary gland tissue with acinar and ductal formations. In the same way heterotopic salivary gland tissue can be localized in cervical lymph nodes. Except for the frequently occurring Warthin tumours, primary salivary gland tumours, which develop in the lymph nodes of the parotid gland or the cervical lymph nodes, are rare. Examples of these are adenomas (pleomorphic adenoma, basal cell adenoma) and carcinomas (acinic cell carcinoma, mucoepidermoid carcinoma, sebaceous gland carcinoma). Three of our own observations (sebaceous lymphadenoma, acinic cell carcinoma, mucoepidermoid carcinoma) are analysed. The condition for the diagnosis of primary salivary gland tumour within a lymph node is reliable evidence that the salivary gland tissue is tumour-free and that no other occult carcinoma is present.

Adenoma↗