Biomedical subjects

D A Baker

Publications and source records attributed to D A Baker.

At least 55 records · Page 3Linked to original sources

PubMed1996

Differential effects of intra-accumbens sulpiride on cocaine-induced locomotion and conditioned place preference.

The effects of intra-accumbens sulpiride on conditioned place preference and locomotion produced by i.v. cocaine were investigated. Every other day during conditioning, rats received infusions of sulpiride (0-0.4 microgram) into the nucleus accumbens (NAc) or caudate-putamen. Fifteen min later, they were placed into a distinct compartment and injected with saline or cocaine (4.2 mg/kg, i.v.). On the alternate days, rats received sham intracranial injections and were placed into a different compartment. Locomotion and stereotypies were assessed after the first and last injection, and conditioned place preference was assessed 24 hr after the last conditioning day. After behavioral testing, receptors occupied by sulpiride were quantified by injecting rats intracranially with their respective dose of sulpiride, followed by a systemic injection of the irreversible antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). Receptors protected from EEDQ induced inactivation by sulpiride were revealed on autoradiograms of sections labeled with 3H-sulpiride. Sulpiride did not alter cocaine-conditioned place preference or cocaine-induced stereotypies. However, the two lowest doses of intra-accumbens sulpiride attenuated cocaine-induced locomotion and occupied > 42% of the sulpiride binding sites in the NAc, and the highest dose completely reversed cocaine-induced locomotion and occupied > 96% of the sulpiride binding sites in the NAc. Intracaudate sulpiride also attenuated cocaine-induced locomotion without occupying a significant number of binding sites in the NAc. These findings suggest that D2-like receptors in the NAc and anterior medial caudate-putamen are involved in cocaine-induced locomotion, but not cocaine-conditioned place preference.

Animals↗

PubMed1995

Evidence for cell-specific differences in transformation by N-, H- and K-ras.

Although Ras plays a fundamental role in cellular proliferation, differentiation and transformation, clear functional differences between the three major Ras proteins (N-, H- and K-Ras) have not as yet been demonstrated. In this study, chimeric constructs were used to compare directly transformation by N-, H- and K-ras oncogenes. In Rat-2 and NIH3T3 fibroblasts, transformation assays (anchorage independence, focus-formation and growth in 1% FCS) showed that H12-Ras was more transforming than N12-Ras or K12-Ras. By contrast, in the human multipotent haemopoietic cell line, TF-1, N12-Ras exhibited greater biological activity. Northern blotting and protein analyses indicated that these findings were not the result of differences in expression or stability of p21Ras. Using further H-ras/N-ras chimeric constructs, we found that the greater transforming activity of H12-Ras in fibroblasts was not due to the hypervariable-CAAX region, but rather to unique sequences between amino acids 84 and 143. These data demonstrate cell specific differences in the intrinsic transforming potential of N-ras, H-ras and K-ras oncogenes.

Animals↗

PubMed1995

Selection of activating mutations of c-fms in FDC-P1 cells.

FDC-P1 haemopoietic cells were used to select mutations of c-fms that constitutively activate the receptor for macrophage-colony stimulating factor (M-CSF or CSF-1). One mutation changed Ser 929 to Gly within a Ser/Gly rich region of the C-terminal tail and a second changed a nearby, highly conserved Leu 926 for Pro. A third mutation (D802V) changed Asp 802 to Val within the alpha L12/beta 9 region of the tyrosine kinase domain, so supporting the crystallographic evidence that this region triggers kinase activation. A c-kit mutation exactly equivalent to D802V was previously identified in a leukamic cell line and was demonstrated here to be transforming. Surprisingly, although D802V potently transformed FDC-P1 cells, it could not induce Rat-2 fibroblast foci, even in the presence of M-CSF. It is suggested that the accelerated receptor degradation induced by D802V may account for its cell specific effect.

Amino Acid Sequence↗

PubMed1995

GM-CSF rapidly primes mice for enhanced cytokine production in response to LPS and TNF.

Subcutaneous administration of Granulocyte-macrophage-colony stimulating factor (GM-CSF) to mice enhanced LPS-induced cytokine production in the circulation (TNF, IL-6) and peritoneal cavity (IL-1 beta, IL-6). This effect was induced rapidly (within 1 h) and persisted for 4 h. Mice made leukopenic with cyclophosphamide retained the ability to respond to GM-CSF. In addition, TNF induced IL-6 production was also enhanced. These results demonstrate that GM-CSF has a pronounced priming effect on cytokine producing cells in vivo and raises the possibility that this cytokine may contribute to the pathogenesis of septic shock.

Animals↗

PubMed1995

Dose-dependent effects of the D3-preferring agonist 7-OH-DPAT on motor behaviors and place conditioning.

Dose-dependent effects of 7-OH-DPAT on several behaviors, including place preference, were assessed. Three 2-day conditioning trials were conducted. On 1 day, animals received an injection of one of eight doses of 7-OH-DPAT (0-5 mg/kg) and were placed into a distinct compartment for 40 min. On the other day, animals received an injection of saline and were placed into a different compartment for 40 min. Locomotion, sniffing, and yawning were measured following the first and last injection of 7-OH-DPAT. Place conditioning was assessed on the day following the last trial. 7-OH-DPAT produced a U-shaped dose-dependent change in locomotion and sniffing, and an inverted U-shaped dose-dependent change in yawning. Additionally, repeated administration of 0.1 mg/kg sensitized yawning, whereas 5 mg/kg sensitized locomotion. None of the doses of 7-OH-DPAT produced conditioned place preference, however, there was a trend for conditioned place aversion at 0.03 mg/kg. By contrast, LiCl (127 mg/kg) produced conditioned place aversion and amphetamine (1 mg/kg) produced conditioned place preference using the same conditioning parameters. A subsequent experiment in which the number of animals and conditioning trials were increased demonstrated that the 0.03 mg/kg dose of 7-OH-DPAT produced conditioned place aversion. 7-OH-DPAT has a higher affinity for D3 receptors relative to D2 receptors. Therefore, it is suggested that intermediate doses (0.01-0.1 mg/kg) that increase yawning, and decrease locomotion and sniffing, may preferentially occupy D3 receptors. Furthermore, the results suggest that these putative D3-preferring doses have weak aversive effects.

Amphetamine↗

PubMed1995

Sexual-stage-specific RNA expression of a new Plasmodium falciparum gene detected by in situ hybridisation.

A gene, Pf77, transcribed in the sexual stages of Plasmodium falciparum was isolated from a genomic expression library with a polyclonal antibody raised to gametocyte proteins. The entire coding region was obtained from a series of overlapping genomic and cDNA clones (from gametocyte RNA). A single open reading frame is present with no introns and no tandem repeat sequences. A Pf77 probe hybridised to a single transcript present in RNA prepared from purified gametocytes and could not be detected in RNA prepared from asexual blood stages. In situ hybridisation studies confirmed that the expression of Pf77 mRNA is sexual-stage-specific and in addition, showed that Pf77 mRNA is present only in female gametocytes during the vertebrate stages of the parasite's development.

Amino Acid Sequence↗

PubMed1995

Application of modelling in HACCP plan development.

Incorporating Hazard Analysis Critical Control Points (HACCP) in the initial stages of food product development allows for an assessment of the risk and severity of hazards, which may be associated with the raw materials used, their processing, the system of distribution, and the intended use. Implementation of a HACCP plan provides a mechanism to ensure that product safety is continuously achieved. Models developed to predict microbial survival and growth may become an integral tool to evaluate, control, document, and even defend the safety designed into a food product. This paper will examine some current uses of modelling to design critical control parameters and aid in regulatory decisions.

Consumer Product Safety↗

PubMed1995

An automatic technique for micro-drilling a stapedotomy in the flexible stapes footplate.

This paper describes a technique for controlling the drill bit breakthrough during low-speed micro-drilling of a flexible bone element. The research reported focuses on the penetration of the stapes footplate at the boundary of the middle and inner ear where there is a need to minimize the penetration of the drill bit through the medial surface. The bone is of unknown thickness and compliance, and the efficiency of cutting is variable between specimens. An automated system is presented that is able to determine these unknowns, to detect the onset of breakthrough and to control drill protrusion beyond the medial surface. The methods used to determine and control the level of protrusion on breakthrough are described. It is reported that the drill bit protrusion beyond the medial surface is achieved to within 0.02 mm of the ideal position.

Evaluation Studies as Topic↗

PubMed1994

Subcellular localization of Pfs16, a Plasmodium falciparum gametocyte antigen.

We have used immunoelectron microscopy to investigate the subcellular location of Pfs16 in Plasmodium falciparum. It was detected in the outer membrane region of gametocytes and more specifically on the parasitophorous vacuole membrane (pvm), since, during gametogenesis when the pvm disintegrates, the majority of the antigen was detected on the remains of this membrane in multilaminated whorls and not on the gamete plasma membrane. The antigen was also present on other gametocyte cellular structures, including those which we believe to be Garnham bodies, present in the host cell cytoplasm of some gametocytes. The antigen was present too on the membrane surrounding cytosomes and the resulting food vacuoles in the parasite cytoplasm.

Animals↗

PubMed1994

Management of the female HIV-infected patient.

Management of women with HIV infection or AIDS should follow the established guidelines for antiretroviral therapy and prevention and treatment of opportunistic complications of HIV infection. Gynecological manifestations of HIV are primarily cervical dysplasia and cancer associated with human papillomavirus (HPV) infection and vaginal and mucocutaneous candidiasis. Human papillomavirus-associated cervical dysplasia/neoplasia is more common in women with advanced rather than early HIV disease, and monitoring with Pap smears should probably increase to every 6 months in patients with CD4+ cell counts < 500 cells/microliter (and certainly when this value falls below 200), with positive Pap smears confirmed by colposcopy and biopsy. For patients with CD4+ cell counts > 350 cells/microliter, cryotherapy is probably adequate, but therapy should be increasingly aggressive at lower CD4+ cell counts. Results of ongoing studies should be available soon to guide therapy. Optimal treatment of candidiasis in HIV-infected women includes prevention of recurrence with a combination of topical and systemic antifungal agents. Women with child-bearing potential should be treated as medically indicated for other HIV-infected patients, including during pregnancy. In fact, preliminary results of ACTG 076 indicated that zidovudine therapy during pregnancy reduces vertical transmission of HIV about threefold.

AIDS-Related Opportunistic Infections↗

PubMed1994

Synergy between SCF or M-CSF with IL-3 or GM-CSF in FDC-P1 cells: a sensitive assay of transforming mutations of c-fms.

Stem cell factor (SCF) was found to stimulate the growth of the haemopoietic cell line FDC-P1 in synergy with either interleukin 3 (IL-3) or granulocyte-macrophage-colony stimulating factor (GM-CSF). Similarly, macrophage colony-stimulating factor (M-CSF) was shown to synergize with IL-3 or GM-CSF, following the infection of FDC-P1 cells with a recombinant retrovirus which encoded the receptor for M-CSF (M-CSFr). These results raise the possibility that signal transduction pathways which are controlled by SCF in FDC-P1 cells, can be activated by M-CSF if its receptor is illicitly expressed. FDC-P1 cells that expressed the M-CSFr were responsive to as little as 100 U/ml of M-CSF when added in combination with IL-3 or GM-CSF. This sensitive assay was used to demonstrate that transforming deletions of the C-terminal tail of the M-CSFr and two-point mutations within the same region that converted tyrosine 969 to either phenylalanine or to cysteine, allowed the mutant M-CSF receptors to synergize with IL-3 or GM-CSF in the absence of M-CSF. These mutations were found to be more evidently transforming in FDC-P1 cells than in Rat-2 fibroblasts. The possible relevance of these results to leukaemia and to gynaecological malignancies is discussed.

Amino Acid Sequence↗

PubMed1994

Evidence that ras and myc mediate the synergy between SCF or M-CSF and other haemopoietic growth factors.

We previously reported that M-CSF could mimic the synergistic effect of SCF upon myeloid FDC-P1 cells that were first infected with a c-fms retrovirus, which encodes the human M-CSFr. We now report that an M-CSFr with a mutation of its autophosphorylation site at position 809 was, in response to M-CSF, unable both to synergize with IL-3 or GM-CSF and to induce c-myc; whereas a mutant receptor with a deletion of its kinase insert was unaffected for these processes. The expression of an exogenous c-myc proto-oncogene or a 12H-ras oncogene lowered the requirement of FDC-P1 cells for IL-3 or GM-CSF, in a similar manner to M-CSF or SCF addition. Furthermore, the expression of either of these genes complemented the defective M-CSFr F809. These results strongly support a role for ras and myc in the synergistic action of M-CSF and, by implication, of SCF, which implies that these signalling intermediates are rate-limiting for the action of IL-3 and GM-CSF and possibly other haemopoietic growth factors.

Animals↗

PubMed1994

Re-emergence of tuberculosis.

Tuberculosis (TB) has remained a major infectious disease in the world. With the AIDS epidemic, the emergence of TB as a cause of severe and life-threatening infection has become a common-place occurrence in many countries. In the USA, the increase of new cases of TB average at the rate of 20% each year. Of great alarm is the findings of multidrug-resistant TB (MDR-TB) with outbreaks in hospitals throughout the world, as well as in other institutions. No health care worker is immune from exposure to TB. TB control requires education of health care workers, a program of ongoing screening, isolation of patients early in the course of their disease, and administration of multiple anti-TB drug to cover and treat MDR-TB. Newer diagnostic methods are needed as well as more active and less toxic drug therapies. Controlled clinical trials are required to determine optimum therapy.

AIDS-Related Opportunistic Infections↗

PubMed1994

A clinical evaluation of genetic stability.

Mutation in a genetically engineered cell line has not been shown to have been responsible for adverse clinical reactions in a currently licensed biotechnology product. There exists, however, the theoretical possibility that mutations in the production cell line could ultimately lead to patient exposure to aberrant proteins which could result in unanticipated or deleterious effects. The clinical trials of recombinant antihaemophilic factor, a large complex glycoprotein, which is administered chronically, offered a unique opportunity to explore this theoretical concern. In this retrospective analysis of patient data, evidence for unanticipated or adverse events which could possibly be attributed to mutations in the genetically engineered cell line was sought. Extensive analysis of a variety of patient data such as the efficacy, alterations in pharmacokinetic parameters, and inhibitor formation, gave no support for concern over host cell mutation. While this retrospective analysis cannot absolutely exclude the possibility of mutational events, those clinical data in combination with the product characterization information indicate that for this recombinant product, mutation is a highly improbable event.

Biotechnology↗

PubMed1994

Long-term suppressive therapy with acyclovir for recurrent genital herpes.

To review the long-term safety and efficacy profile of daily oral acyclovir for the treatment of recurrent genital herpes, this report describes the results from an ongoing clinical trial of more than 1100 immunocompetent individuals with a history of frequently recurring genital herpes. During the first year patients were randomized to receive either 400 mg acyclovir twice daily or placebo. Thereafter, patients received open-label acyclovir suppressive therapy. Complete data are available for 389 of the 430 patients who began the fifth year of study. The percentage of patients who were free of recurrence for any quarter of the fifth year ranged from 85 to 90%. The mean annual number of recurrences per patient declined from 12.9 to 1.7 during the first year of suppressive therapy to 0.8 during the fifth year. More than 20% of the patients receiving suppressive therapy for the entire 5-year period have been recurrence-free. The 50% effective dose (ED50) values for a population of herpes simplex virus clinical isolates before acyclovir treatment were compared with the values determined for isolates recovered at the first episode of recurrent disease after cessation of therapy, from patients in this study who had received up to 6 years of suppressive acyclovir therapy. Resistance of herpes simplex virus to acyclovir was not observed. This study extends the safety and efficacy profile of oral acyclovir in the suppression of genital herpes to 5 years.

Acyclovir↗

PubMed1993

Locomotor activity in the ischemic gerbil.

Previous studies have shown that within 24 h after ischemic insult, gerbils exhibit an increase in locomotor activity. Because activity gradually diminishes to normal levels with repeated testing, it has been argued that this behavior represents a reversible or transient effect of ischemia. The present study challenged this notion by testing ischemic gerbils at a time when increased activity is not observed with repeated testing. Ischemic (5-min bilateral carotid occlusion) and sham gerbils were tested for 14 consecutive days after reperfusion in an open-field apparatus (n = 6/condition). As previously reported, ischemic gerbils exhibited a significant increase in activity (days 1 and 2) which returned to control levels with repeated testing (days 13 and 14). A second group of ischemic and sham gerbils (n = 6/condition) were tested only on days 13 and 14 after reperfusion. In contrast to those tested repeatedly, these ischemic gerbils displayed increased locomotor activity as compared with sham controls. In addition, gerbils in the repeated testing conditions were evaluated in a semi-novel testing environment on days 15 and 16 after surgery. The locomotor activity of ischemic gerbils significantly increased in response to the semi-novel environment. These results suggest that the effects of ischemia on locomotor activity are not limited to a brief period after occlusion and may represent a permanent deficit. In addition, as previously suggested, this behavior may represent a deficit in habituation or spatial mapping rather than motor hyperactivity.

Animals↗

PubMed1993

Neurotensin-induced hypothermia prevents hippocampal neuronal damage and increased locomotor activity in ischemic gerbils.

Hypothermia induced by surface cooling has shown to protect vulnerable regions of the brain during an ischemic insult. This study evaluated the neuroprotective efficacy of neurotensin, a potent hypothermic agent, using a 5-min carotid occlusion procedure in the gerbil. In Experiment 1, the dose-response and time course of neurotensin-induced hypothermia were evaluated (n = 5/dose). Central infusion of 10, 20, and 30 micrograms neurotensin were found to significantly decrease core body temperature of conscious gerbils within 30 min of administration. In Experiment 2, gerbils pretreated with 30 micrograms neurotensin were permitted to become hypothermic or were maintained at 37 degrees-38 degrees C (rectal) during ischemic insult. Other gerbils were pretreated with peptide vehicle prior to ischemic insult (at 37 degrees -38 degrees C) or underwent a sham procedure (n = 6/condition). At 24 h after surgery, gerbils were tested for increased locomotor activity in an open-field apparatus. Gerbils pretreated with peptide vehicle or neurotensin and maintained at 37 degrees-38 degrees C during ischemia had significantly higher activity levels compared to the other treated groups. In contrast, gerbils made hypothermic with neurotensin exhibited activity levels similar to sham gerbils. Histological assessment revealed that neurotensin-induced hypothermia protected the CA1 region from ischemic damage.

Analysis of Variance↗

PubMed1993

Dynamic concentration challenges for biosensor characterization.

A method and apparatus are described for characterization of the steady state and dynamic response of biosensors. The apparatus produces a steady stream of homogeneously mixed analyte whose concentration can be fixed at discrete values or varied continuously. The device is ideally suited for continuously operated biosensors, but is also effective for biosensors that operate in discrete sampling modes. The system permits simultaneous testing of several sensors and determination of the accuracy, precision and repeatability of sensor response. The characteristics of this testing apparatus were validated with ferrocyanide and glucose as indicators. As an example of use of the apparatus, concentration ramps were created and used to complement conventional step changes for characterizing an implantable glucose sensor. The ramp rate can be adjusted easily by scaling the apparatus to simulate the rate of concentration change anticipated during actual monitoring situations.

Animals↗