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Biomedical subjects

D R Cross

Publications and source records attributed to D R Cross.

8 recordsLinked to original sources
PubMed1998

Antisocial tendency among drug-addicted adults: potential long-term effects of parental absence, support, and conflict during childhood.

This study examined the relationship between perceptions of parent-child relations in the family of origin and antisocial tendency in a sample of drug-addicted adults. Data included retrospective accounts of childhood family factors, adolescent antisocial tendency, and self-reported hostility and risk-taking prior to treatment entry. A developmental model was tested that included adolescent antisocial tendency as a mediator of the relationship between childhood parenting factors and adulthood antisocial tendency. The effects of parental support and conflict were found to operate primarily through adolescent measures. Specifically, lower levels of parental support and higher levels of conflict with parents predicted greater adolescent antisocial tendency, which in turn predicted more hostility and risk-taking in adulthood. Thus, parental support appears to serve as a buffer against deviant behavior and drug use.

Adolescent↗
PubMed1995

Psychosocial functioning among adult drug users: the role of parental absence, support, and conflict.

The relationship between perceptions of parental absence, support, and conflict during childhood and psychosocial functioning in adulthood was examined for 411 drug user clients in methadone treatment. History of parental support was related to adult psychosocial functioning and parent-child conflict was related to psychosocial functioning only when parental support was low. Findings indicate parental absence is related to the quality of parental support, which in turn predicts psychosocial functioning in adulthood. Implications for treatment intervention are discussed.

Adolescent↗
PubMed1993

A simplified HPLC method for simultaneously quantifying ribonucleotides and deoxyribonucleotides in cell extracts or frozen tissues.

Agents and conditions that induce alterations in deoxyribonucleotide pools can have important regulatory effects on the rate of DNA synthesis as well as cell cycle progression. A simplified procedure for the separation of both ribonucleoside triphosphates (NTP) and deoxyribonucleoside triphosphates (dNTP) is presented which utilizes reversed phase high-performance liquid chromatography coupled with diode array detection. The simultaneous resolution of NTP and dNTP peaks within the same cell extract effectively eliminates the need for post-extraction steps such as periodate oxidation and/or boronate affinity chromatography previously used to degrade or isolate co-eluting NTP from dNTP. The resolution of two nucleotides, dGTP and ADP, was found empirically to vary with the efficiency of the C18 column. High efficiency columns (> 90,000 plates/m) provided good separation; however, less efficient columns resulted in co-elution of dGTP and ADP. These co-eluting nucleotides can be accurately quantified, if necessary, using diode array technology and a mathematical expression which incorporates molar peak coefficients and peak areas obtained by monitoring at dual wave-lengths. Tissue samples or single cell suspensions were extracted with trichloroacetic acid and the neutralized extract was injected directly into the column without prior lyophilization. The per cent recovery of standards was > or = 99% and replicate extractions within or between samples were highly reproducible (SD < 5%). The single step method described minimizes potential losses associated with post-extraction manipulation and provides the capability to examine alterations in nucleotide precursor-product metabolism under various physiological and pharmacological conditions.

Adenosine Diphosphate↗
PubMed1993

The essentiality of folate for the maintenance of deoxynucleotide precursor pools, DNA synthesis, and cell cycle progression in PHA-stimulated lymphocytes.

The fidelity and progression of DNA synthesis is critically dependent on the correct balance and availability of the deoxynucleoside triphosphate (dNTP) precursors for the polymerases involved in DNA replication and repair. Because folate-derived one-carbon groups are essential for the de novo synthesis of both purines and pyrimidines, the purpose of this study was to determine the effect of folate deprivation on deoxynucleotide pool levels and cell cycle progression. Primary cultures of phytohemagglutin (PHA)-stimulated splenocytes were used as the cellular model. T-cells and macrophages were purified from spleen cell suspensions obtained from F344 rats and recombined in culture. The cells were harvested after a 66-hr incubation with PHA and analyzed for nucleotide levels by reverse-phase HPLC with diode array detection. The proportion of cells in the different phases of the cell cycle was determined by bivariate flow cytometric measurement of bromodeoxyuridine (BrdU) incorporation and DNA content (propidium iodide staining). PHA-stimulated T-cells cultured in medium lacking folate and methionine manifested significant decreases in the deoxynucleotides dCTP, dTMP, dGTP, and dATP relative to cells cultured in complete medium. The reduction in dNTP pools was associated with a decrease in the corresponding ribonucleotide pools. Flow cytometric analysis revealed a 2-fold increase in S and G2/mitosis (G2/M) DNA content in PHA-stimulated cells cultured in the medium lacking folate and methionine, which suggests a delay in cell cycle progression. These alterations in DNA content were accompanied by a 5-fold decrease in BrdU incorporation relative to PHA-stimulated cells cultured in complete medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Alterations in nucleotide pools in rats fed diets deficient in choline, methionine and/or folic acid.

The fidelity of DNA synthesis is critically dependent on the correct balance and availability of the deoxynucleoside triphosphate (dNTP) precursors for the polymerases involved in replication and repair. Since folate-derived one-carbon groups are essential for the de novo synthesis of both purines and pyrimidines, the purpose of the present investigation was to determine whether diet-induced depletion of folates would alter intracellular dNTP pools. Fischer 344 rats were fed one of four semi-purified diets for a period of 8 weeks: (i) supplemented control; (ii) deficient in folic acid; (iii) deficient in methionine and choline; and (iv) deficient in methionine, choline and folic acid. In contrast to natural diets, semi-purified diets are nucleotide-free and consequently lack substrates for salvage pathway synthesis. This omission may place unusual stress on folate-dependent de novo nucleotide synthesis especially under conditions of dietary methyl-donor deficiency. Reversed-phase HPLC analysis of dNTP in spleen cell extracts indicated that both the thymidylate monophosphate and thymidylate triphosphate pools were decreased in spleen cells from the deficient rats consistent with a decrease in folate-dependent de novo synthesis. In addition, purine biosynthesis appeared to be negatively affect by methyl-donor deficiency as evidenced by a reduction in dGTP and dATP pools. These data indicate that deoxynucleotide pool imbalance, well known to produce cytogenetic and mutagenic events in vitro, can also be induced in this in vivo model of diet-induced carcinogenesis.

Animals↗
PubMed1990

Using informed strategies for learning to enhance the reading and thinking skills of children with learning disabilities.

The purpose of this study was to improve the reading performance of children with learning disabilities using a classroom-based metacognitive reading program. The participants were third- and fourth-level 8- and 9-year-olds (13 boys and 5 girls) at a school for children with learning disabilities. A cross-sectional time series design was used. During pre- and posttesting participants were assessed on two measures of strategy awareness and a measure of perceived self-competence. During the instructional phase the metacognitive reading program was introduced. Participants were assessed on measures of reading performance throughout the study. In general, the findings were positive: Students increased in performance and awareness of strategies from pre- to posttesting. In addition, participants were placed in subgroups based on pretesting assessments. The subgroups differed on their improvements over time. This study provides preliminary evidence that a metacognitive reading program can be used with children with learning disabilities to improve their awareness about reading and their comprehension skills.

Awareness↗
PubMed1989

Another look at amphetamine-induced stereotyped locomotor activity in rats using a new statistic to measure locomotor stereotypy.

Rat open field behavior is often used as a tool to study the behavioral effects of drugs. In this report, drug-induced patterns of locomotion in an open field were studied with the aid of a simple new statistic. Briefly, the animal's path through the open field is converted into a series of trips. Gamma (gamma) estimates the probability that the animal will repeat the trip that it has just exhibited; thus gamma quantifies "locomotor stereotypy". Trip lengths can also be compared across drug groups. Thus caffeine has no effect on gamma even though it produces a dose-related increase in locomotions. Caffeine does not produce amphetamine-like stereotypy. On the other hand, amphetamine produces a dose-related increase in gamma. Although gamma was designed to detect any pattern of locomotor behavior, rats treated with high doses of amphetamine almost always exhibited the same pattern of locomotor behavior - repetitive trips around the perimeter of the open field. Although further characterization of the statistic is necessary, these findings suggest that gamma has potential for quantifying "locomotor stereotypy" and for providing a more subtle description of locomotor behavior in general.

Amphetamine↗