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Biomedical subjects

C A Ross

Publications and source records attributed to C A Ross.

At least 181 records · Page 10Linked to original sources
PubMed1994

Localization of inositol trisphosphate receptor subtype 3 to insulin and somatostatin secretory granules and regulation of expression in islets and insulinoma cells.

Calcium ions play a central role in stimulus-secretion coupling in pancreatic beta cells, and an elevation of cytosolic Ca2+ levels is necessary for insulin secretion. Inositol 1,4,5-trisphosphate mobilizes intracellular Ca2+ stores in the beta cell by binding to specific receptors that are ligand-activated Ca2+ channels. The inositol trisphosphate receptors comprise a family of structurally related proteins with distinct but overlapping tissue distributions. Previous studies indicated that the predominant inositol trisphosphate receptor subtype expressed in rat pancreatic islets was the protein designated IP3R-3. We have confirmed the expression of IP3R-3 in pancreatic islets by immunohistocytochemistry and localized this protein to the secretory granules of insulin-secreting beta cells and somatostatin-secreting delta cells by immunogold electron microscopy. Secretory granules contain high levels of Ca2+, and the presence of IP3R-3 in the granule provides a mechanism for mobilizing granule Ca2+ stores in response to glucose and/or hormones. The release of Ca2+ from granule stores would increase the Ca2+ concentration in the surrounding cytoplasm and promote rapid exocytosis of granules, especially those granules in close proximity to the plasma membrane. The levels of IP3R-3 were increased in pancreatic islets of diabetic rats and rats that had been refed after a period of fasting. They were also increased in rat insulinoma RINm5F cells cultured in 25 mM glucose compared with cells cultured in 5 mM glucose. The localization of IP3R-3 to secretory granules of insulin-secreting beta cells and somatostatin-secreting delta cells suggests that granule Ca2+ stores actively participate in the secretory process and that their release is regulated by inositol 1,4,5-trisphosphate. The regulation of IP3R-3 levels by glucose, diabetes, and refeeding may allow the beta cell to adjust the insulin secretory response to changing physiological conditions.

Amino Acid Sequence↗
PubMed1994

Selective loss of [3H]kainic acid and [3H]AMPA binding in layer VI of frontal cortex in Huntington's disease.

Excitatory amino acid neurotoxicity has been proposed to cause the neostriatal neuronal degeneration of Huntington's disease (HD); N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), and kainate receptors have been hypothesized to play important roles in this process. We have recently reported a loss of neurons in layer VI of the cerebral cortex in HD. Using quantitative autoradiographic methods, we have now measured NMDA, AMPA, and kainate receptor binding in the frontal cerebral cortex of the brains of controls and individuals with HD. We find no change in NMDA receptor binding but a selective decrease in kainate and AMPA receptor binding in layer VI. These data suggest that cerebral cortical neurons possessing kainate or AMPA receptors may be selectively vulnerable in individuals with HD.

Autoradiography↗
PubMed1994

Human GluR6 kainate receptor (GRIK2): molecular cloning, expression, polymorphism, and chromosomal assignment.

Glutamate receptors mediate the majority of excitatory neurotransmission in the brain, and molecular cloning studies have revealed several distinct families. Because neuropathological states and possibly human disorders may involve kainate-preferring glutamate receptors, we have isolated a cDNA clone for the human GluR6 kainate-preferring receptor. This clone shows a very high sequence similarity with that of the rat, except for a part of the 3' untranslated region in which there is a TAA triplet repeat. When the protein was overexpressed in human embryonic kidney 293 cells, it had a molecular weight, an antibody recognition, and a glutamate ligand-binding profile similar to those of the rat GluR6 receptor. Northern analysis showed expression in both human cerebral and cerebellar cortices. By PCR analysis of rodent-human monochromosomal cell lines, the human GluR6 could be assigned to chromosome 6. The length of the TAA triplet repeat was polymorphic in the normal population, with at least four alleles and an observed heterozygosity of about 45%. These studies should provide the basis for expression or linkage studies of the GluR6 kainate receptor in human disease or neuropathologic states.

Amino Acid Sequence↗
PubMed1994

Trypanocidal activity of a myristic acid analog in axenic cultures of Trypanosoma evansi.

The growth of bloodstream forms of Trypanosoma evansi in axenic culture was inhibited by incubation with 11-oxatetradecanoic acid (O-11), an analog of myristic acid. Parasites isolated from Asia, Africa and South America were affected to a similar extent in measurements using three different assay systems concerned with different aspects of trypanosome growth and metabolism. The concentration of O-11 that inhibited trypanosome growth by 50% (LD50) was 3.7 +/- 0.2 microM as measured by direct counting of survivors using a haemocytometer, 5.1 +/- 2.0 microM in a colorimetric test based on the formation of a formazan product, and 8.8 +/- 3.7 microM by estimation of pyruvate. The activity of the drug was enhanced by the addition of fatty-acid-free bovine serum albumin as a carrier protein to the culture medium at an optimal concentration of 5 mg/ml. Increasing amounts of the donor horse serum used for routine maintenance of these cultures, which is normally the only source of myristic acid for these trypanosomes, also affected the toxicity of the drug, in this case increasing the LD50.

Animals↗
PubMed1994

Triplet repeats in clinical subtypes of schizophrenia: variation at the DRPLA (B 37 CAG repeat) locus is not associated with periodic catatonia.

Clinical evidence for a dominant mode of inheritance and anticipation in periodic catatonia, a distinct subtype of schizophrenia, indicates that genes with triplet repeat expansions or other unstable repetitive elements affecting gene expression may be involved in the etiology of this disorder. Because patients affected with dentatorubral-pallidoluysian atrophy (DRPLA) may present with "schizophrenic" symptoms, we have investigated the DRPLA (B 37 CAG repeat) locus on chromosome 12 in 41 patients with periodic catatonia. The B 37 CAG repeat locus was highly polymorphic but all alleles in both the patient and control group had repeat sizes within the normal range. We conclude that variation at the DRPLA locus is unlikely to be associated with periodic catatonia. The evidence for dominant inheritance and anticipation as well as the high prevalence of human brain genes containing trinucleotide repeats justifies further screening for triplet repeat expansions in periodic catatonia.

Adult↗
PubMed1994

The inositol trisphosphate receptor gene family: implications for normal and abnormal brain function.

1. The phosphatidyl inositol (PI) second messenger system has been extensively investigated in the past decade. This complex pathway results in the production of two second messengers, one of which, inositol 1,4,5-trisphosphate, will be the focus of this review. 2. The intracellular receptor for this second messenger (IP3R) has been purified, reconstituted and extensively characterized in both brain and peripheral tissues. 3. Localization and functional studies show that IP3 binding causes the receptor to release portions of the intracellular calcium stores. 4. Multiple modulators of the receptor have been identified, including pH, calcium concentration, adenine nucleotide concentration and phosphorylation. 5. The cDNA for this molecule has been cloned from a number of sources. Studies of the molecular structure of the receptor have revealed additional levels of complexity including multiple alternative splicing events in the initially cloned cerebellar (Type I) receptor, as well as the existence of highly related but distinct cDNAs which likely reflect a gene family. 6. There is suggestive evidence linking the PI system, and thus the IP3R, to bipolar disorder and the actions of lithium.

Animals↗
PubMed1994

The interaction of Trypanosoma congolense with endothelial cells.

Factors which affect adhesion of cultured Trypanosoma congolense bloodstream forms to mammalian feeder cells have been examined. Using an in vitro binding assay, the initial events following interaction of trypanosomes with bovine aorta endothelial (BAE) cells were monitored by both light- and electron microscopy. Metabolic inhibitors and other biochemicals were incubated with either cells or parasites, to test whether any inhibited the process. Our findings suggest that adhesion of the parasites is an active process requiring metabolic energy from the trypanosomes, but not from endothelial cells. We also provide data suggesting that T. congolense bloodstream forms possess a lectin-like domain, localized at distinct sites on their flagellar surface, which interacts with specific carbohydrate receptors, most likely sialic acid residues, on the endothelial cell plasma membrane. We also suggest that the cytoskeletal protein actin is probably involved in this interaction.

Animals↗
PubMed1994

Heligmosomoides polygyrus and Trypanosoma congolense infections in mice: a laboratory model for concurrent gastrointestinal nematode and trypanosome infections.

A murine model using Heligmosomoides polygyrus and Trypanosoma congolense has been developed for studying the effects of concurrent chronic gastrointestinal nematode and trypanosome infections. Female outbred mice were infected either with 500 infective larvae (L3) of H. polygyrus or with 10(4) bloodstream forms of T. congolense or both. In concurrent infections, animals were dosed with both parasites simultaneously or the trypanosomes were injected 5 or 10 days after the mice were infected with the nematode. The course of infection was monitored by routine parasitological and immunological techniques for 30 days after the H. polygyrus infection. Concurrently infected mice were severely compromised, except when T. congolense was superimposed on a 10-day-old (adult) H. polygyrus infection. In H. polygyrus-infected mice, simultaneous or subsequent infection with trypanosomes did not markedly influence worm establishment or fecundity, but the female worms were slightly stunted. Surviving mice displayed a markedly reduced antibody response to H. polygyrus antigens and a slightly reduced antibody response to T. congolense antigens.

Animals↗
PubMed1994

RNA editing of the glutamate receptor subunits GluR2 and GluR6 in human brain tissue.

Editing of mRNA in the coding region of the second transmembrane domain of glutamate receptor subunits GluR2, GluR5, and GluR6 involves a change of the base A in genomic DNA to the base G in mRNA as described in rat brain. To determine whether this reaction occurs in humans as well as rats, we studied RNA editing of GluR2 and GluR6 in human brain. We compared the extent of editing in controls and cases with Huntington's disease. To assay the extent of editing in brain RNA, first strand cDNA was amplified using the polymerase chain reaction yielding a product across the region of the second transmembrane spanning segment in which editing takes place in rats. The PCR product was incubated with the restriction enzyme BbvI, which recognizes the sequence GCAGC present in the nonedited sequence of the mRNA in subunits GluR2 and GluR6. Thus, BbvI cuts the nonedited version but leaves the edited version intact. As in the rat, the GluR2 subunit mRNA was completely edited in human brain. The GluR6 subunit was nearly completely edited in all gray matter structures investigated including cortex, striatum, thalamus, hippocampus, amygdala, and cerebellum with extent of editing ranging from 89% in the cerebellum to 95% in the cortex and striatum. No significant differences in the extent of RNA editing were apparent in control versus Huntington's disease brains. To compare the extent of editing in neurons and glia in the brain, editing in cerebral cortex (predominantly gray matter and thus neurons) was compared with editing in corpus callosum (white matter and thus nearly completely glial cells).(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1994

The Valsalva DCR bubble test: a new method of assessing lacrimal patency after DCR surgery.

Objective confirmation of nasolacrimal patency following dacryocystorhinostomy is a desirable postoperative goal for both the surgeon and the patient. The authors describe a simple method to demonstrate dacryocystorhinostomy patency and present a study comparing the effectiveness of this novel test with Jones fluorescein testing in 32 cases seen consecutively at postoperative follow-up. The test consists of demonstrating reflux of air through the dacryocystorhinostomy as the patient performs the Valsalva maneuver. This reflux is most easily seen as bubbles rising through a drop of saline placed in the medial canthus. A high correlation was found between this test and Jones testing. The Valsalva dacryocystorhinostomy bubble test (VBT) appears to be a fast, safe, and accurate method of confirming dacryocystorhinostomy patency.

Dacryocystorhinostomy↗
PubMed1994

Reversal of desipramine toxicity in rats with polyclonal drug-specific antibody Fab fragments.

Drug-specific antibodies, or fragments containing their binding site(s), are a potential means of treating drug overdose. Affinity purified polyclonal ovine Fab (TFab) with a high average affinity constant (Ka = 1.4 x 10(10) M-1) for the common tricyclic antidepressants was evaluated as a possible treatment for tricyclic antidepressant toxicity. Groups of eight anesthetized rats received 30 mg/kg body weight of desipramine (DMI) intraperitoneally, followed after 15 minutes by a 10-minute intravenous injection of 3 ml normal saline solution, 2 gm/kg nonspecific Fab as a control (CFab), or 1 or 2 gm/kg TFab (representing a molar ratio of TFab to DMI of 0.11 and 0.22, respectively). The animals were observed for 3 hours. During the initial 15 minutes, serum DMI levels in the four groups reached 2.3 to 2.9 micrograms/ml, the QRS duration increased by 67.5% to 77.9%, and the systolic pressure fell to between 65% and 85% of its initial value. The group given saline solution showed a gradual return of all these parameters toward normal, whereas CFab caused a transient further QRS prolongation. CFab also caused an initial rise in blood pressure, which then fell progressively, and two of the rats died 2 to 3 hours later with hypotension and bradycardia. Serum DMI concentration did not change significantly in either the saline or CFab groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Novel triplet repeat containing genes in human brain: cloning, expression, and length polymorphisms.

Human genes containing triplet repeats may markedly expand in length and cause neuropsychiatric disease, explaining the phenomenon of anticipation (increasing severity or earlier age of onset in successive generations in a pedigree). To identify novel genes with triplet repeats, we screened a human brain cDNA library with oligonucleotide probes containing CTG or CCG triplet repeats. Fourteen of 40 clones encoded novel human genes, and 8 of these inserts have been sequenced on both strands. All contain repeats, and 5 of the 8 have 9 or more consecutive perfect repeats. All are expressed in brain. Chromosomal assignments reveal a distribution of these genes on multiple autosomes and the X-chromosome. Further, the repeat length in two of the genes is highly polymorphic, making them valuable index linkage markers. We predict that many triplet repeat-containing genes exist; screening with the CTG probe suggests approximately 50-100 genes containing this type of repeat are expressed in the human brain. Since additional disorders, such as Huntington's disease, bipolar affective disorder, and possibly others, show features of anticipation, we suggest that these novel human genes with triplet repeats are candidates for causing neuropsychiatric diseases.

Base Sequence↗
PubMed1993

Genes with triplet repeats: candidate mediators of neuropsychiatric disorders.

Recently a new form of human mutation-expansion of trinucleotide repeats-has been found to cause the diseases of fragile X syndrome, spinal and bulbar muscular atrophy, myotonic dystrophy and, most recently, Huntington's disease. We review the emerging data on the genetics and neurobiology of these disorders. Three are characterized by unusual patterns of inheritance, in particular, genetic 'anticipation', in which the severity of the disorder increases and the age of onset decreases in successive generations of a pedigree. Several idiopathic neuropsychiatric disorders have features of inheritance consistent with anticipation. In bipolar affective disorder, there is evidence for both earlier age of onset and more severe illness in the second generation of a subset of unilineal pedigrees. There is also the suggestion of anticipation in some forms of schizophrenia, spinocerebellar atrophy and autism. Triplet repeats are present in additional known genes, both in coding regions and untranslated regions. Furthermore, many novel genes with triplet repeats are expressed in the human brain, and these are candidates to cause some forms of these neuropsychiatric disorders.

Humans↗
PubMed1993

Inositol (1,4,5)-trisphosphate receptor: characterization of neuron-specific alternative splicing in rat brain and peripheral tissues.

One source of diversity in the inositol (1,4,5)-trisphosphate receptors (IP3Rs) is generated at the level of alternative splicing. Our previous studies of splice isoforms of the receptor in various tissues suggested that some tissues, specifically those containing neurons, selectively express a 40 amino acid insert located between 2 sites for phosphorylation by cyclic AMP-dependent protein kinase (PKA), and that the presence of this insert changes the preferred site of phosphorylation of the receptor. Studies of the mouse receptor have also suggested the existence of intermediately spliced forms containing partial versions of the splice and exhibiting different brain distributions. In this study, we have investigated the alternative splicing of the rat receptor in greater detail using RNase protection and PCR analysis. We find little evidence for the existence of intermediately spliced forms in rat, raising the possibility that the degree of alternative splicing at this site differs in the brains of two very similar species. Our screen of tissue distribution supports the selectively neuronal expression of the long spliced form, and suggests that regulation of this receptor in neurons may be different than in other tissues.

Alternative Splicing↗