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Biomedical subjects

D L Nelson

Publications and source records attributed to D L Nelson.

At least 235 records · Page 13Linked to original sources
PubMed1993

DOI and alpha-methylserotonin: comparative vascular and nonvascular smooth muscle effects and central 5-hydroxytryptamine2 receptor affinities.

Both alpha-methylserotonin and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) are agonists at 5-hydroxytryptamine2 (5-HT2) receptors. The present study compared these agonists for their binding affinities at the high- and low-affinity states of the 5-HT2 receptor and for their contractile activities in certain smooth muscle preparations. Both agonists contracted the rat aorta and rat jugular vein, tissues possessing 5-HT2 receptors, and contraction was blocked by ketanserin. However, alpha-methylserotonin produced greater maximal response (80-90% maximum response to serotonin) than DOI. In the rat jugular vein, the calculated dissociation constant of DOI (-log Kb = 7.7) corresponded well with its affinity for [3H]ketanserin- (pKi = 7.5) but not [125I]DOI- (pKi = 8.6) radiolabeled sites. This might suggest that binding to the agonist low-affinity state of the 5-HT2 receptor is more relevant to vascular agonist activity. alpha-Methylserotonin was slightly more potent than serotonin in contracting the rat aorta but not the jugular vein, whereas DOI was more potent in the jugular vein than in the aorta. In the jugular vein but not the aorta, the relative potency of these agents corresponded well with their relative affinities for either the [3H]ketanserin- or the [125I]DOI-labeled 5-HT2 receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Amphetamines↗
PubMed1993

Pharmacological characteristics of the newly cloned rat 5-hydroxytryptamine2F receptor.

The rat 5-hydroxytryptamine (5-HT)2F (serotonin2F) receptor is a newly cloned member of the 5-HT2/1C receptor family. The pharmacology of the 5-HT2F receptor was explored using a variety of structurally different compounds in a radioligand binding assay. In addition, the 5-HT2F receptor was shown to stimulate production of inositol 1,4,5-trisphosphate in the transformed cells. Based on the affinities of the compounds tested, their known affinities for certain of the other 5-HT receptors, and the fact that activation of the cloned 5-HT2F receptor stimulates inositol 1,4,5-trisphosphate production, the 5-HT2F receptor was determined to be a novel receptor and a member of the 5-HT2/1C receptor family. In addition, several agonists and partial agonists were evaluated for contractile activity in the rat stomach fundus, and these activities were correlated with their binding affinities at the 5-HT2F receptor. A highly significant correlation was found, providing additional evidence that is consistent with the 5-HT2F receptor being the stomach fundal contractile receptor. [3H]5-HT had high affinity for this receptor both at 37 degrees and at 0 degree (Kd = 7.87 +/- 0.55 and 0.12 +/- 0.02 nM, respectively). The difference in affinity for [3H]5-HT at the two temperatures prompted an investigation of potential temperature-dependent differences in the binding affinities of agonists versus antagonists. Agonists such as 5-HT, 5-methoxytryptamine, etc., showed higher affinity for the 5-HT2F receptor at 0 degree than at 37 degrees, whereas antagonists such as methysergide, 1-naphthylpiperazine, etc., showed no difference in affinity for this receptor at the two different temperatures. Therefore, the affinity of a compound for the 5-HT2F receptor at 37 degrees versus 0 degree was shown to be useful for predicting agonist or antagonist activity. Additionally, information is provided about some of the structural requirements for the affinity of certain tryptamines at the 5-HT2F receptor.

Animals↗
PubMed1993

Species differences in the pharmacology of the 5-hydroxytryptamine2 receptor: structurally specific differentiation by ergolines and tryptamines.

Species differences in the recognition of a series of ergolines by the 5-hydroxytryptamine2 (5-HT2, serotonin2) receptor were investigated in four species, the rat, pig, squirrel monkey and human. In pig frontal cortical membranes the initial studies showed that the ergolines gave shallow displacement curves against [3H]ketanserin binding. The component of [3H]ketanserin binding having low affinity for the ergolines was determined to be the result of [3H]ketanserin binding to alpha-1 adrenergic receptors. Thus, in all subsequent assays prazosin was used to mask [3H]ketanserin binding to alpha-1 adrenergic receptors. Examination of a series of ergolines revealed a distinct pattern in the species selectivity. Compounds that were unsubstituted at the N1 position of the ergoline nucleus showed higher affinity for the pig, squirrel monkey and human 5-HT2 receptors than for the rat. Conversely, compounds that had an N1-isopropyl substituent showed higher affinity for the rat receptor compared to the pig, squirrel monkey and human 5-HT2 receptors. For example, LY53857, a widely used 5-HT2 antagonist, has an isopropyl substituent at position N1 of the ergoline nucleus and exhibited a 4- to 5-fold higher affinity for the rat 5-HT2 receptor, whereas its N1-unsubstituted homologue, LY86057, had more than 10-fold higher affinity for the pig, squirrel monkey and human 5-HT2 receptors. Similar results were seen with three additional ergoline pairs, each having different substituents at the C8 position compared to LY53857. Even an N1-substitution on LY53857 as small as a methyl group, LY108742, resulted in the compound having higher affinity for the rat 5-HT2 receptor compared to the other species.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Genome analysis and the human X chromosome.

A unified genetic, physical, and functional map of the human X chromosome is being built through a concerted, international effort. About 40 percent of the 160 million base pairs of the X chromosome DNA have been cloned in overlapping, ordered contigs derived from yeast artificial chromosomes. This rapid progress toward a physical map is accelerating the identification of inherited disease genes, 26 of which are already cloned and more than 50 others regionally localized by linkage analysis. This article summarizes the mapping strategies now used and the impact of genome research on the understanding of X chromosome inactivation and X-linked diseases.

Animals↗
PubMed1992

Cloning of human and bovine homologs of SNF2/SWI2: a global activator of transcription in yeast S. cerevisiae.

We performed positional cloning of genes carried on yeast artificial chromosomes that span a human translocation breakpoint associated with a human disease and isolated by chance human and bovine genes with strong homology to the S. cerevisiae genes, SNF2/SWI2 and STH1, and the D. melanogaster gene brahma. We report here sequence analysis, expression data, and functional studies for this human SNF2-like gene (hSNF2L) and its bovine homolog (bovSNF2L). Despite strong homology at the amino acid level, hSNF2L is not capable of complementing the yeast mutations snf2 or sth1 in S. cerevisiae. Furthermore, in contrast to SNF2 itself, a fusion protein consisting of the DNA binding domain of LexA and hSNF2L did not transactivate a reporter gene downstream of LexA binding sites in a yeast expression system. The strong similarity between hSNF2L and these yeast and drosophila genes suggest that the mammalian genes are part of an evolutionarily conserved family that has been implicated as global activators of transcription in yeast and fruitflies but whose function in mammals remains unknown.

Adenosine Triphosphatases↗
PubMed1992

The Lowe's oculocerebrorenal syndrome gene encodes a protein highly homologous to inositol polyphosphate-5-phosphatase.

Lowe's oculocerebrorenal syndrome (OCRL) is a human X-linked developmental disorder of unknown pathogenesis and has a pleiotropic phenotype affecting the lens, brain and kidneys. The OCRL locus has been mapped to Xq25-q26 by linkage and by finding de novo X; autosome translocations at Xq25-q26 in two unrelated females with OCRL. Here we use yeast artificial chromosomes with inserts that span the X chromosomal breakpoint from a female OCRL patient in order to isolate complementary DNAs for a gene that is interrupted by the translocation. We show that the transcript is absent in both female OCRL patients with X; autosome translocations and that it is absent or abnormally sized in 9 of 13 unrelated male OCRL patients with no detectable genomic rearrangement. The open reading frame encodes a new protein with 71% similarity to human inositol polyphosphate-5-phosphatase. Our results suggest that OCRL may be an inborn error of inositol phosphate metabolism.

Amino Acid Sequence↗
PubMed1992

Triplet repeat mutations in human disease.

Triplet repeats are the sites of mutation in three human heritable disorders, spinal and bulbar muscular atrophy (SBMA), fragile X syndrome, and myotonic dystrophy (DM). These repeats are GC-rich and highly polymorphic in the normal population. Fragile X syndrome and DM are examples of diseases in which premutation alleles cause little or no disease in the individual, but give rise to significantly amplified repeats in affected progeny. This newly identified mechanism of mutation has, so far, been identified in two of the most common heritable disorders, fragile X syndrome and DM, and one rare disease, SBMA.

Female↗
PubMed1992

Isolation of cDNA sequences around the chromosomal breakpoint in a female with Lowe syndrome by direct screening of cDNA libraries with yeast artificial chromosomes.

The Lowe oculocerebrorenal syndrome (OCRL; McKusick 309000) is an X-linked disorder characterized by congenital cataracts, muscular hypotonia, mental retardation, and Fanconi syndrome of the renal tubules. A pair of yeast artificial chromosomes (YACs) that span the Xq25-q26 translocation breakpoint in a female with OCRL were used as probes to screen cDNA libraries made from bovine lens and human kidney. The methods used to prepare the YACs as probes and to screen the libraries are presented in detail. Two different transcripts were found that map to the region around the Xq25-q26 breakpoint. These transcripts are now being studied to determine whether one or the other is a candidate gene for OCRL.

Blotting, Southern↗
PubMed1992

PCR amplification and analysis of yeast artificial chromosomes.

A strategy for the analysis of yeast artificial chromosome (YAC) clones that relies on polymerase chain reaction (PCR) amplification of small restriction fragments from isolated YACs following adapter ligation was developed. Using this method, termed YACadapt, we have amplified several YACs from a human Xq24-qter library and have used the PCR products for physical mapping by somatic cell hybrid deletion analysis and fluorescent in situ hybridization. One YAC, RS46, was mapped to band Xq27.3, near the fragile X mutation. The PCR product is an excellent renewable source of YAC DNA for analyses involving hybridization of YAC inserts to a variety of DNA/RNA sources.

Animals↗
PubMed1992

Implicit processing in the cued recall of young and old adults.

Two cued recall experiments were reported in which younger and older subjects studied target words varying in number of preexperimental associates. In Experiment 1, targets were studied in either the absence or presence of meaning-related context cues, with recall always prompted by the cues. In the absence of context, words with smaller sets of associates were easier to recall than those with larger sets, but this effect was reduced for older subjects. The presence of a study context cue facilitated recall and eliminated the effect of associative set size for both ages. In Experiment 2, targets were studied and tested in the presence of unrelated words. In this situation, words with smaller sets of associates were less likely to be recalled than words with larger sets; again the effect was reduced for older subjects. The results are interpreted as an age decrement in processing implicitly activated information.

Adult↗
PubMed1992

Processing implicit and explicit representations.

This article summarizes the results of a 15-year research program dedicated to understanding how implicitly activated memories affect remembering and proposes a model for describing such influences. Implicit memories are manipulated by varying the number of associates preexperimentally linked to test cues or to studied words. Assumptions of the model specify when implicit memories of various types are likely to contribute to performance in various tasks. The main assumptions are that encoding involves both explicit and implicit processing components and that these components provide mutually exclusive sources of information during testing. Experiments designed to evaluate the exclusivity assumption are reported, and implications of the findings for several theoretical frameworks are discussed.

Attention↗
PubMed1992

DNA methylation represses FMR-1 transcription in fragile X syndrome.

Fragile X syndrome is the most frequent form of inherited mental retardation and segregates as an X-linked dominant with reduced penetrance. Recently, we have identified the FMR-1 gene at the fragile X locus. Two molecular differences of the FMR-1 gene have been found in fragile X patients: a size increase of an FMR-1 exon containing a CGG repeat and abnormal methylation of a CpG island 250 bp proximal to this repeat. Penetrant fragile X males who exhibit these changes typically show repression of FMR-1 transcription and the presumptive absence of FMR-1 protein is believed to contribute to the fragile X phenotype. It is unclear, however, if either or both molecular differences in FMR-1 gene is responsible for transcriptional silencing. We report here the prenatal diagnosis of a male fetus with fragile X syndrome by utilizing these molecular differences and show that while the expanded CGG-repeat mutation is observed in both the chorionic villi and fetus, the methylation of the CpG island is limited to the fetal DNA (as assessed by BssHII digestion). We further demonstrate that FMR-1 gene expression is repressed in the fetal tissue, as is characteristic of penetrant males, while the undermethylated chorionic villi expressed FMR-1. Since the genetic background of the tissues studied is identical, including the fragile X chromosome, these data indicate that the abnormal methylation of the FMR-1 CpG-island is responsible for the absence of FMR-1 transcription and suggests that the methylation may be acquired early in embryogenesis.

Base Sequence↗
PubMed1992

Frequent small amplifications in the FMR-1 gene in fra(X) families: limits to the diagnosis of 'premutations'.

In five of 40 fra(X) families reinvestigated using the new intragenic probe StB12.3, small amplifications of the DNA fragment appeared unexpectedly in addition to the mutations found in the probands. This suggests that enlargements of the FMR-1 gene detectable by Southern blotting using this probe must be present at an appreciable frequency in the general population. A proportion of these may be classifiable as 'premutations', or precursors of the much amplified, hypermethylated, and somatically unstable fragment associated with the fragile X syndrome, while others will merely represent stable polymorphisms in fragment length. Hence, accurate diagnosis of some fra(X) carriers will depend upon a more precise measurement of insert size than is currently provided by the newly available molecular probes.

DNA↗
PubMed1992

Proteolytic processing of secretory proteins in Paramecium: immunological and biochemical characterization of the precursors of trichocyst matrix proteins.

We used polyclonal serum raised against mature trichocyst matrix proteins to detect their unprocessed precursors, a group of proteins (45-55 kDa) present in the whole-cell extract. These precursor proteins were partially purified from the soluble fraction of wild-type cells by ammonium sulfate precipitation and anion-exchange chromatography. Using monoclonal antibodies against each of four families of mature (processed) matrix proteins, we showed that each family was derived from a separate group of precursors. Our results also suggest that in three of four precursors, those in which the mature proteins consist of disulfide-linked heterodimers, intrachain disulfide bonds form before proteolytic processing. Purified precursors eluted from preparative SDS-gels were used to raise rabbit antiserum, which after preadsorption with mature processed proteins specifically recognized precursors, as judged by ELISA and immunoblots. In cross-sections of developing trichocysts, the anti-precursor serum after preadsorption no longer stained the central, paracrystalline region, but still stained the peripheral as well as the structureless region of the secretory granule. In trichocyst-developing mutants tl (trichless) and ftA (football A), the precursors for all four groups of mature proteins were present but their processing was affected: severely blocked in tl (which has no recognizable crystalline trichocyst matrix), and partially blocked in ftA (which has some abnormal trichocyst matrices with crystalline centers). These observations constitute further evidence that proteolytic processing of precursors occurs in parallel with crystallization.

Animals↗
PubMed1992

The effects of perfluorodecanoic acid (PFDA) on humoral, cellular, and innate immunity in Fischer 344 rats.

The in vivo effects of perfluorodecanoic acid (PFDA) exposure on antibody production, delayed type hypersensitivity (DTH), and natural killer (NK) cell activity were determined. Fischer 344 rats were injected with PFDA (20 mg/kg or 50 mg/kg, 8 days or 30 days prior to sacrifice) and were immunized with keyhole limpet hemocyanin (KLH). Pair-fed and ad libitum-fed control rats were included to evaluate effects of PFDA-induced anorexia. KLH-specific IgG2a production was significantly decreased (p < 0.05) in PFDA-treated rats when compared to ad libitum-fed and pair-fed controls at 8 days but not at 30 days following PFDA treatment. The DTH response of PFDA-treated rats was decreased 8 days and 30 days after PFDA treatment when compared to ad libitum-fed and pair-fed controls, however, the decrease was not statistically significant. NK activity 30 days after PFDA treatment was significantly elevated (p < 0.05) when compared to ad libitum-fed controls, but pair-fed controls had similarly elevated NK activity. NK activity at 8 days after PFDA treatment was not significantly altered. In conclusion, PFDA has been demonstrated to have immunomodulatory effects, some of which may be associated with drug-induced anorexia.

Animals↗