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A Singer

Publications and source records attributed to A Singer.

At least 73 records · Page 4Linked to original sources
PubMed1999

Hyperforin, a major antidepressant constituent of St. John's Wort, inhibits serotonin uptake by elevating free intracellular Na+1.

Extracts of Hypericum perforatum (St. John's Wort) are widely used for the treatment of depressive disorders and are unspecific inhibitors of the neuronal uptake of several neurotransmitters. Previous studies have shown that hyperforin represents the reuptake inhibiting constituent. To characterize the mechanism of serotonin reuptake inhibition, kinetic analyses in synaptosomes of mouse brain were performed. Michaelis-Menten kinetics revealed that hyperforin (2 microM) induces a decrease in V(max) by more than 50% while only slightly decreasing K(m), indicating mainly noncompetitive inhibition. By contrast, citalopram (1 nM) leads to an elevation of K(m) without changing V(max). Monensin, a Na(+)/H(+) exchanger, showed similar properties as hyperforin (decrease of V(max) without changing K(m)). Compared with classical antidepressants, such as selective serotonin reuptake inhibitors and tricyclic antidepressants, hyperforin is only a weak inhibitor of [(3)H]paroxetine binding relative to its effects on serotonin uptake. As monensin decreases serotonin uptake by increasing Na(+)/H(+) exchange, we compared the effects of hyperforin and monensin on the free intracellular sodium concentration ([Na(+)](i)) in platelets by measuring 1,3-benzenedicarboxylic acid, 4,4'-[1,4,10-trioxa-7, 13-diazacyclopentadecan-7,13-diylbis(5-methoxy-6, 2-benzofurandiyl)]bis-, tetraammonium salt (SBFI/AM) fluorescence. Both drugs elevated [Na(+)](i) over basal levels, with a maximal [Na(+)](i) of 69 +/- 16.1 mM (50 microM hyperforin) and 140 +/- 9.1 mM (10 microM monensin). Citalopram at concentrations relevant for [(3)H]serotonin uptake inhibition had no effect on [Na(+)](i). Although the mode of action of hyperforin seems to be associated with elevated [Na(+)](i) similar to those levels found with monensin, the molecular mechanism might be different, as even at high concentrations, hyperforin does not elevate free intracellular sodium concentration ([Na(+)](i)) up to the extracellular level, as monensin does. Hyperforin represents the first substance with a known preclinical antidepressant profile that inhibits serotonin uptake by elevating [Na(+)](i).

Animals↗
PubMed1999

Characterization of soluble factors from cultures of premalignant cervical epithelium.

PURPOSE: Immune responses within the cervical microenvironment are likely to play an important role in the natural history of premalignant lesions but the pattern of this response and how it is regulated has not been documented in detail. METHODS: Explants of premalignant cervical epithelium were cultured in vitro for 24 hours. The culture supernatants were assayed for the presence of IL-1alpha, IL-10, IL-12 and TNF-alpha by ELISA. Aliquots of each supernatant were also added to a CD3-dependent T cell proliferation assay. RESULTS: The pattern of cytokines found in different samples was heterogeneous and no significant correlation was observed between the various cytokines examined. The functional effects observed were also diverse, with some supernatants showing strong inhibitory T cell activity, while others were stimulatory. CONCLUSION: Our results document the heterogeneity of the local cytokine microenvironment of premalignant cervical lesions, which may play a role in regulating the immune response associated with such lesions and hence influence clinical outcome.

CD3 Complex↗
PubMed1998

The HPV-activating cellular transcription factor Brn-3a is overexpressed in CIN3 cervical lesions.

The cervical cellular transcription factors Brn-3a and Brn-3b have antagonistic effects on transcription of the human papilloma virus types 16 and 18 E6 and E7 oncogenes, with Brn-3a activating expression and Brn-3b repressing it. We therefore measured expression of Brn-3a and Brn-3b mRNAs in biopsies from 16 women with no detectable cervical abnormality, and in 14 women with cervical intraepithelial neoplasia grade 3 (CIN3) lesions. Although the mean level of Brn-3b expression was similar in both groups, the mean level of Brn-3a expression was over 300-fold higher in the CIN3 samples when compared with normals. Elevated expression of Brn-3a was also detected in 16 histologically normal regions of the cervix adjacent to the CIN3 lesions, indicating that elevation of Brn-3a levels is not confined to the lesion in women with CIN3, and is thus not a consequence of the oncogenic process. The elevated levels of Brn-3a in the CIN3 patient samples, together with the activating effect of Brn-3a on HPV-16 and -18 oncogene expression, suggest that induction of this factor is involved in activating HPV-16 and -18 oncogene expression in the cervix, and hence in the production of cervical cancers induced by HPV.

Base Sequence↗
PubMed1998

Positive selection of CD4+ T cells by TCR-specific antibodies requires low valency TCR cross-linking: implications for repertoire selection in the thymus.

The developmental fate of immature CD4+ 8+ thymocytes is determined by intrathymic signals transduced by surface TCR complexes. In particular, TCR signals are required for immature CD4+ 8+ thymocytes to further differentiate into CD4+ 8- or CD4- 8+ T cells, a process referred to as positive selection. It is generally thought that positive selection results from low affinity TCR interactions with self antigens which engage the relatively few surface TCR complexes that are on immature CD4+ 8+ thymocytes. However, we now demonstrate with TCR-specific antibodies that positive selection of CD4+ T cells requires low valency cross-linking of surface TCR complexes on immature thymocytes. That is, positive selection signals are only generated within a narrow range of TCR cross-linking: cross-linking either too few or too many surface TCR complexes fails to signal positive selection. We interpret these results as indicating that positive selection of CD4+ T cells is not signaled by low affinity TCR interactions per se, but rather can be signaled by any combination of TCR affinity and ligand density that induces low valency TCR cross-linking on immature thymocytes.

Animals↗
PubMed1998

Hyperforin as a possible antidepressant component of hypericum extracts.

We demonstrate that the phloroglucinol derivative hyperforin is not only the major lipophilic chemical constituent of the medicinal plant Hypericum perforatum (St. John's wort) but also a potent uptake inhibitor of serotonin (5-HT), dopamine (DA), noradrenaline (NA), GABA and L-Glutamate with IC50 values of about 0.05-0.10 microg/ml (5-HT, NA, DA, GABA) and about 0.5 microg/ml (L-glutamate) in synaptosomal preparations. Furthermore, potencies of two different hypericum extracts in two conventional pharmacological paradigms useful for the detection of antidepressants (behavioral despair, learned helplessness), closely correlate with their hyperforin contents. In addition, most till now known neuropharmacological properties of the clinically used hypericum extracts can also be demonstrated with pure hyperforin. It appears, therefore, that this non-nitrogenous constituent is a possible major active principle responsible for the observed clinical efficacies of the extract as an antidepressant and that it could also be a starting point for drug discovery projects engaged in the search of psychoactive drugs with novel mode of action.

Animals↗
PubMed1998

Vertebrate genome evolution and the zebrafish gene map.

In chordate phylogeny, changes in the nervous system, jaws, and appendages transformed meek filter feeders into fearsome predators. Gene duplication is thought to promote such innovation. Vertebrate ancestors probably had single copies of genes now found in multiple copies in vertebrates and gene maps suggest that this occurred by polyploidization. It has been suggested that one genome duplication event occurred before, and one after the divergence of ray-finned and lobe-finned fishes. Holland et al., however, have argued that because various vertebrates have several HOX clusters, two rounds of duplication occurred before the origin of jawed fishes. Such gene-number data, however, do not distinguish between tandem duplications and polyploidization events, nor whether independent duplications occurred in different lineages. To investigate these matters, we mapped 144 zebrafish genes and compared the resulting map with mammalian maps. Comparison revealed large conserved chromosome segments. Because duplicated chromosome segments in zebrafish often correspond with specific chromosome segments in mammals, it is likely that two polyploidization events occurred prior to the divergence of fish and mammal lineages. This zebrafish gene map will facilitate molecular identification of mutated zebrafish genes, which can suggest functions for human genes known only by sequence.

Animals↗
PubMed1998

Hyperforin represents the neurotransmitter reuptake inhibiting constituent of hypericum extract.

Hydroalcoholic hypericum extract inhibits the synaptosomal uptake of serotonin, norepinephrine, and dopamine with about similar affinities and leads to a significant down-regulation of cortical beta-adrenoceptors and 5-HT2-receptors after subchronic treatment of rats. While neither hypericine nor kaempferol did show any reuptake inhibiting properties, hyperforin was identified as the unspecific reuptake inhibitor of hypericum extracts with half-maximal inhibitory concentrations for the three synaptosomal uptake systems mentioned above between 80 and 200 nmol/l. Moreover, a hyperforin-enriched (38%) CO2 extract also leads to a significant beta-receptor down-regulation after subchronic treatment. The data suggest hyperforin as the active principle of hypericum extracts in biochemical models of antidepressant activity.

Animals↗
PubMed1998

[Screening for amblyopia, strabismus and refractive abnormalities in 1,030 kindergarten children].

BACKGROUND: There are controversies concerning the necessity of pre-school vision screening. AIM OF THE STUDY: evaluation of the prevalence of pathologic ophthalmologic findings in kindergarten children. MATERIALS AND METHODS: 1030 families were offered a vision screening. Of these, a total of 948 children, aged 3 to 6 years, voluntarily underwent a screening for strabismus, amblyopia and refractive anomalies. The examination was performed in the kindergarten in the absence of the parents. METHODS OF EXAMINATION: A questionnaire concerning general and ophthalmologic history of the child and of the family was evaluated. Visual acuity, cover-uncover-test, Lang-stereotest, retinoscopy, ophthalmoscopy (undilated pupils) were performed and the glasses were evaluated. RESULTS: The screening was highly accepted by the parents and 92% of the families (n = 948) took part. The compliance of the children was very good. A total of 38.7% (n = 381) of the children showed one or more abnormal parameters. 21.4% (n = 229) showed a reduced visual acuity. Strabismus was found in 3.7%. Half of the children with abnormal findings already had had a vision screening, but only 25% had received ophthalmologic treatment. Of those who possessed glasses, 25% came without them, and another 25% had a reduced visual acuity even with their glasses. The main problems were many false-positive results and high costs. CONCLUSIONS: Ophthalmologic and orthoptic screening in kindergarten is technically easy and conclusive in experienced hands. Ideas to reduce costs and to avoid overreferrals are an age-related lowering of the visual acuity limit and a rescreening of suspected children in a screening-setting a second time before sending them to an ophthalmologist. Another possibility to reduce costs would be to perform examinations not by ophthalmologists but by "screening-orthoptists" who should be trained in retinoscopy and ophthalmoscopy.

Amblyopia↗
PubMed1998

Differential regulation of HLA-DQ expression by keratinocytes and Langerhans cells in normal and premalignant cervical epithelium.

Keratinocytes in normal ectocervix did not express major histocompatibility complex class II molecules. In low-grade intraepithelial lesions expression was confined to HLA-DR, while in high-grade disease there was expression of HLA-DR and occasional expression of HLA-DQ. HLA-DR was expressed constitutively on the majority of Langerhans cells. In contrast, few Langerhans cells expressed HLA-DQ in normal cervix, but there was a steady upregulation of the proportion expressing HLA-DQ which paralleled the severity of disease. There was no direct correlation between human papillomavirus 16 and the expression of major histocompatibility complex class II by keratinocytes and Langerhans cells. Significant upregulation of HLA-DQ by Langerhans cells is observed in high-grade intraepithelial cervical lesions, suggesting antigen-presenting cell activation in papillomavirus-related premalignant disease.

Female↗
PubMed1998

The social process of undocumented border crossing among Mexican migrants.

"In this article a theoretical model is developed that views undocumented border crossing as a well-defined social process influenced by the quantity and quality of human and social capital that migrants bring with them to the border, and constrained by the intensity and nature of U.S. enforcement efforts. Detailed histories of border crossing from undocumented migrants originating in 34 Mexican communities are employed to estimate equations corresponding to this model.... As people gain experience in border crossing, they rely less on the assistance of others and more on abilities honed on earlier trips, thus substituting migration-specific human capital for general social capital.... On all trips, the intensity of the U.S. enforcement effort has little effect on the likelihood of arrest, but INS involvement in drug enforcement sharply lowers the odds of apprehension."

Americas↗
PubMed1998

The Polarprobe--emerging technology for cervical cancer screening.

The Polarprobe is a portable non invasive electronic device designed for the detection of cervical precancer and cancer. It measures both electrical and optical properties of cervical tissue to allow a real time comparison with a databank of previously determined cervical tissue types. The need for additional tests to augment or even replace the Papanicolaou smear has partly prompted its development. Indeed it has been shown to be associated with less pain and anxiety than the smear and has the capability of encouraging women to attend for screening. Some of the preliminary clinical trials on the Polarprobe are reported as well as the ongoing developments and modifications to the device.

Electrodiagnosis↗
PubMed1997

T cell receptor (TCR)-induced death of immature CD4+CD8+ thymocytes by two distinct mechanisms differing in their requirement for CD28 costimulation: implications for negative selection in the thymus.

Negative selection is the process by which the developing lymphocyte receptor repertoire rids itself of autoreactive specificities. One mechanism of negative selection in developing T cells is the induction of apoptosis in immature CD4+CD8+ (DP) thymocytes, referred to as clonal deletion. Clonal deletion is necessarily T cell receptor (TCR) specific, but TCR signals alone are not lethal to purified DP thymocytes. Here, we identify two distinct mechanisms by which TCR-specific death of DP thymocytes can be induced. One mechanism requires simultaneous TCR and costimulatory signals initiated by CD28. The other mechanism is initiated by TCR signals in the absence of simultaneous costimulatory signals and is mediated by subsequent interaction with antigen-presenting cells. We propose that these mechanisms represent two distinct clonal deletion strategies that are differentially implemented during development depending on whether immature thymocytes encounter antigen in the thymic cortex or thymic medulla.

Animals↗
PubMed1997

Limiting dilution analysis of primary cytotoxic T-cell precursors.

An efficient colorimetric assay has been adapted for limiting dilution analysis of cytotoxic T-cell precursors. Application of this assay in a suitable experimental model of thymic education could be especially useful in identifying factors that shape the CD8 T-cell repertoire. The essential elements of such a model are described here and elsewhere.

Animals↗
PubMed1997

Commitment of immature CD4+8+ thymocytes to the CD4 lineage requires CD3 signaling but does not require expression of clonotypic T cell receptor (TCR) chains.

As a consequence of positive selection in the thymus, immature CD4(+)8(+) double-positive, [DP] thymocytes selectively terminate synthesis of one coreceptor molecule and, as a result, differentiate into either CD4(+) or CD8(+) T cells. The decision by individual DP thymocytes to terminate synthesis of one or the other coreceptor molecule is referred to as lineage commitment. Previously, we reported that the intrathymic signals that induced commitment to the CD4 versus CD8 T cell lineages were markedly asymmetric. Notably, CD8 commitment appeared to require lineage-specific signals, whereas CD4 commitment appeared to occur in the absence of lineage-specific signals by default. Consequently, it was unclear whether CD4 commitment, as revealed by selective termination of CD8 coreceptor synthesis, occurred in all DP thymocytes, or whether CD4 commitment occurred only in T cell receptor (TCR)-CD3-signaled DP thymocytes. Here, we report that selective termination of CD8 coreceptor synthesis does not occur in DP thymocytes spontaneously. Rather, CD4 commitment in DP thymocytes requires signals transduced by either CD3 or zeta chains, which can signal CD4 commitment even in the absence of clonotypic TCR chains.

Animals↗