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Biomedical subjects

G E Wood

Publications and source records attributed to G E Wood.

At least 19 recordsLinked to original sources
PubMed2005

Immunocytochemical analysis of synaptic proteins provides new insights into diabetes-mediated plasticity in the rat hippocampus.

The hippocampus, an important integration center for learning and memory in the mammalian brain, undergoes neurological changes in response to a variety of stimuli that are suggestive of ongoing synaptic reorganization. Accordingly, the aim of this study was to identify markers of synaptic plasticity using rapid and reliable techniques such as radioimmunocytochemistry and confocal microscopy, thereby providing a "birds-eye view" of the whole hippocampus under hypercorticosteronemic conditions. The regulation of microtubule-associated protein 2, synaptophysin and postsynaptic density-95 was examined in two different animal models of hypercorticosteronemia: corticosterone administration and streptozotocin-induced diabetes using both a short-term (1 week) and long-term (5 weeks) treatment. Glucocorticoids and/or hyperglycemia increased synaptophysin expression in CA1, CA3 and the dentate gyrus, regions that exhibit synaptic plasticity in response to glucocorticoid exposure. In these models, postsynaptic density-95 expression increased in the CA3 region, particularly in the diabetic rats, while microtubule-associated protein 2 exhibited more selective changes. Fluoro-Jade histochemistry did not detect neuronal damage, suggesting that glucocorticoids and/or hyperglycemia induce plastic and not irreversible neuronal changes at these time points. Collectively, these results demonstrate that changes in the expression and distribution of synaptic proteins provide another measure of synaptic plasticity in the rat hippocampus in response to glucocorticoid exposure, changes that may accompany or contribute to neuroanatomical, neurochemical, and behavioral changes observed in experimental models of type 1 diabetes.

Animals↗
PubMed2001

The genome of the natural genetic engineer Agrobacterium tumefaciens C58.

The 5.67-megabase genome of the plant pathogen Agrobacterium tumefaciens C58 consists of a circular chromosome, a linear chromosome, and two plasmids. Extensive orthology and nucleotide colinearity between the genomes of A. tumefaciens and the plant symbiont Sinorhizobium meliloti suggest a recent evolutionary divergence. Their similarities include metabolic, transport, and regulatory systems that promote survival in the highly competitive rhizosphere; differences are apparent in their genome structure and virulence gene complement. Availability of the A. tumefaciens sequence will facilitate investigations into the molecular basis of pathogenesis and the evolutionary divergence of pathogenic and symbiotic lifestyles.

Agrobacterium tumefaciens↗
PubMed2001

The role of the hippocampus in trace conditioning: temporal discontinuity or task difficulty?

It is well established that the hippocampal formation is critically involved in the acquisition of trace memories, a paradigm in which the conditioned (CS) and unconditioned stimuli (US) are separated by a temporal gap (Solomon et al., 1986). The structure is reportedly not critical for the acquisition of delay memories, where the CS and the US overlap in time (Berger & Orr, 1983; Schmaltz & Theios, 1972). Based on these results, it is often stated that the hippocampus is involved in "filling the gap" or otherwise associating the two stimuli in time. However, in addition to the presence of a temporal gap, there are other differences between trace and delay conditioning. The most apparent difference is that animals require many more trials to learn the trace task, and thus it is inherently more difficult than the delay task. Here, we tested whether the hippocampus was critically involved in delay conditioning, if it was rendered more difficult such that the rate of acquisition was shifted to be analogous to trace conditioning. Groups of rats received excitotoxic lesions to the hippocampus, sham lesions or were left intact. Using the same interstimulus intervals (ISI), control animals required more trials to acquire the trace than the delay task. As predicted, animals with hippocampal lesions were impaired during trace conditioning but not delay conditioning. However, when the delay task was rendered more difficult by extending the ISI (a long delay task), animals with hippocampal lesions were impaired. In addition, once the lesioned animal learned the association between the CS and the US during delay conditioning, it could learn and perform the trace CR. Thus, the role of the hippocampus in classical conditioning is not limited to learning about discontiguous events in time and space; rather the structure can become engaged simply as a function of task difficulty.

Animals↗
PubMed2001

The contribution of adrenal and reproductive hormones to the opposing effects of stress on trace conditioning in males versus females.

Exposure to an acute stressful experience facilitates classical conditioning in male rats but impairs conditioning in female rats (T. J. Shors, C. Lewczyk, M. Paczynski, P. R. Mathew, & J. Pickett, 1998; G. E. Wood & T. J. Shors, 1998). The authors report that these effects extend to performance on the hippocampal-dependent task of trace conditioning. The stress-induced impairment of conditioning in females was evident immediately, 24 hr and 48 hr after stress, depending on the stage of estrus. Moreover, the effect could be reactivated days later by reexposure to the stressful context. Corticosterone levels correlated with overall performance in males but not in females. Unlike the effect seen in males, adrenalectomy did not prevent the stress-induced effect on conditioning in females. These data indicate that exposure to the same experience can have opposite effects on learning in males versus females and that these opposing effects are mediated by differing hormonal systems.

Adrenalectomy↗
PubMed2001

Haemophilus ducreyi inhibits phagocytosis by U-937 cells, a human macrophage-like cell line.

Haemophilus ducreyi is a gram-negative obligate human pathogen that causes the genital ulcer disease chancroid. Chancroid lesions are deep necrotic ulcers with an immune cell infiltrate that includes macrophages. Despite the presence of these phagocytic cells, chancroid ulcers can persist for months and live H. ducreyi can be isolated from these lesions. To analyze the interaction of H. ducreyi with macrophages, we investigated the ability of H. ducreyi strain 35000 to adhere to, invade, and survive within U-937 cells, a human macrophage-like cell line. We found that although H. ducreyi strain 35000 adhered efficiently to U-937 cells, few bacteria were internalized, suggesting that H. ducreyi avoids phagocytosis by human macrophages. The few bacteria that were phagocytosed in these experiments were rapidly killed. We also found that H. ducreyi inhibits the phagocytosis of a secondary target (opsonized sheep red blood cells). Antiphagocytic activity was found in logarithmic, stationary-phase, and plate-grown cultures and was associated with whole, live bacteria but not with heat-killed cultures, sonicates, or culture supernatants. Phagocytosis was significantly inhibited after a 15-min exposure to H. ducreyi, and a multiplicity of infection of approximately 1 CFU per macrophage was sufficient to cause a significant reduction in phagocytosis by U-937 cells. Finally, all of nine H. ducreyi strains tested were antiphagocytic, suggesting that this is a common virulence mechanism for this organism. This finding suggests a mechanism by which H. ducreyi avoids killing and clearance by macrophages in chancroid lesions and inguinal lymph nodes.

Animals↗
PubMed2000

The Bvg accessory factor (Baf) enhances pertussis toxin expression in Escherichia coli and is essential for Bordetella pertussis viability.

Pertussis toxin expression in the Gram-negative respiratory pathogen, Bordetella pertussis, is regulated by the BvgAS two-component system. Previous studies suggested that an additional gene encoding a Bvg accessory factor (Baf) was required, along with BvgAS, for expression of a ptx-lacZ fusion in Escherichia coli grown in rich medium. However, other studies showed that BvgAS is sufficient for ptx-lacZ expression in minimal medium. Here we show that Baf acts with BvgAS to further increase ptx-lacZ expression in E. coli grown in minimal media and this is concomitant with a two-fold increase in BvgA protein levels. Gene replacement experiments show that baf is essential for viability of B. pertussis, suggesting that Baf affects the expression of other genes in addition to ptx.

Bacterial Proteins↗
PubMed2000

The modulation of Pavlovian memory.

Exposure to stressful experiences as well as sex differences in the brain are known to influence the acquisition of new memories. This review focuses on acquisition of two types of Pavlovian learning paradigms: hippocampal-independent delay conditioning and hippocampal-dependent trace conditioning and their modulation by exposure to stressful experience and sex differences in the brain. We concentrate on two sets of findings: the first is that exposure to an acute stressful experience enhances Pavlovian conditioning in the male rat, while exposure to the very same experience dramatically impairs conditioning in female rat. The sexually-opposed effects of stress on conditioning are mediated by differing hormonal substrates (adrenal versus ovarian steroids) and possibly by differing anatomical and biochemical pathways. The second set of findings is that training with hippocampal-dependent trace conditioning enhances the survival of newly generated neurons in the adult hippocampal formation. The same amount of training with hippocampal-independent delay conditioning does not affect their survival. In addition, females acquire the trace task faster than males and generate more new neurons. As with the stress effects on learning, these sex effects are influenced by hormonal status. It is our contention that identifying the hormonal and neuronal processes that modulate associative memory formation will provide insight into the processes of memory formation itself.

Animals↗
PubMed1999

Prevalence of, antibody response to, and immunity induced by Haemophilus ducreyi hemolysin.

Haemophilus ducreyi, the etiologic agent of chancroid, a genital ulcer disease, produces a cell-associated hemolysin whose role in virulence is not well defined. Hemolysin is encoded by two genes, hhdA and hhdB, which, based on their homology to Serratia marcescens shlA and shlB genes, are believed to encode the hemolysin structural protein and a protein required for secretion and modification of this protein, respectively. In this study, we determined the prevalence and expression of the hemolysin genes in 90 H. ducreyi isolates obtained from diverse geographic locations from 1952 to 1996 and found that all strains contained DNA homologous to the hhdB and hhdA genes. In addition, all strains expressed a hemolytic activity. We also determined that hemolysin is expressed in vivo and is immunogenic, as indicated by the induction of antibodies to hemolysin in both the primate and rabbit disease models as well as in human patients with naturally acquired chancroid. Wild-type strain 35000 and isogenic hemolysin-negative mutants showed no difference in lesion development in the temperature-dependent rabbit model. However, immunization of rabbits with the purified hemolysin protein reduced the recovery of wild-type H. ducreyi, but not hemolysin-negative mutants, from lesions. Our study indicates that hemolysin is a possible candidate for vaccine development due to its immunogenicity, expression in vitro and in vivo by most, if not all, strains, and the effect of immunization on reducing the recovery of viable H. ducreyi in experimental disease in rabbits.

Animals↗
PubMed1999

Target cell range of Haemophilus ducreyi hemolysin and its involvement in invasion of human epithelial cells.

Haemophilus ducreyi, the causative agent of chancroid, produces a hemolysin, whose role in virulence is not well defined. To assess the possible role of hemolysin in pathogenesis, we evaluated its target cell range by using wild-type H. ducreyi 35000, nonhemolytic mutants with the hemolysin structural gene deleted, and isogenic strains expressing different amounts of hemolytic activity. The cytotoxicity of the various cell types was assessed by quantitating the release of lactate dehydrogenase into culture supernatants as a measure of cell lysis. In these experiments, human foreskin fibroblasts, human foreskin epithelial cells, and, to a lesser extent, HEp-2 cells were lysed by H. ducreyi hemolysin. Hemolysin also lysed human blood mononuclear cells and immune system cell lines including U937 macrophage-like cells, T lymphocytes, and B lymphocytes. In contrast, human polymorphonuclear leukocytes were not sensitive to hemolysin under the conditions tested. We also analyzed the effect of hemolysin on invasion of human epithelial cells and found that H. ducreyi strains expressing cloned hemolysin genes showed a 10-fold increase in invasion compared to the control strain. These data support the hypothesis that the H. ducreyi hemolysin is important in the pathogenesis of chancroid and may contribute to ulcer formation, invasion of epithelial cells, and evasion of the immune response.

Cell Line↗
PubMed1998

Stress facilitates classical conditioning in males, but impairs classical conditioning in females through activational effects of ovarian hormones.

Exposure to restraint and brief intermittent tailshocks facilitates associative learning of the classical conditioned eyeblink response in male rats. Based on evidence of sex differences in learning and responses to stressful events, we investigated sexually dimorphic effects of a stressor of restraint and intermittent tailshock on classical eyeblink conditioning 24 h after stressor cessation. Our results indicate that exposure to the acute stressor had diametrically opposed effects on the rate of acquisition of the conditioned response in male vs. female rats. Exposure to the stressor facilitated acquisition of the conditioned response in males, whereas exposure to the same stressful event dramatically impaired acquisition in females. We further demonstrate that the stress-induced impairment in female conditioning is dependent on the presence of ovarian hormones. Conditioning of stressed sham-ovariectomized females was significantly impaired relative to the unstressed controls, whereas conditioning in stressed ovariectomized females was not impaired. We present additional evidence that estrogen mediates the stress-induced impairment in female acquisition. Females administered sesame oil vehicle and then stressed were significantly impaired relative to their unstressed controls, whereas females administered the estrogen antagonist tamoxifen prior to stress were not impaired. In summary, these results indicate that exposure to the same aversive event can induce opposite behavioral responses in males vs. females. These effects underscore sex differences in associative learning and emotional responding, and implicate estrogen in the underlying neuronal mechanism.

Animals↗
PubMed1998

Identification of Btr-regulated genes using a titration assay. Search for a role for this transcriptional regulator in the growth and virulence of Bordetella pertussis.

Bordetella pertussis is the causative agent of the respiratory disease pertussis or whopoping cough. Btr, an oxygen-responsive transcriptional regulator of B. pertussis, is homologous to the FNR protein of E. coli. Using a murine respiratory model, we observed in the present study that Btr is important in growth and survival of B. pertussis in vivo. A titration assay was developed that identified genes containing Btr binding sites including B. pertussis sodB and btr, E. coli aspA and a new B. pertussis gene, brg1. The brg1 gene encodes a protein similar to the LysR family of transcriptional regulators and its expression is activated threefold by Btr under anaerobic growth conditions but unaffected by Btr aerobically. The nucleotide sequence flanking brg1 encodes proteins with similarity to various metabolic enzymes. Putative overlapping promoters and a Btr binding site (FNR box) were identified in the DNA sequence between brg1 and the adjacent genes. These intervening sequences may represent sites for regulation by Btr and Brg1.

Amino Acid Sequence↗
PubMed1995

Contribution of stress and gender to exploratory preferences for familiar versus unfamiliar conspecifics.

An apparatus for measuring the exploratory preferences of rats for familiar and unfamiliar conspecifics in a novel environment was designed. The exploratory behavior of males and females was compared and contrasted to that elicited in response to an acute aversive event. Sprague-Dawley male and female rats were exposed to restraint and 60, 1 s, 1 mA tailshocks and returned to their home cage. Either 2 or 24 h later, they were placed in a novel environment with a familiar cage-mate and an unfamiliar conspecific of the same sex. Relative to unstressed controls and females, males stressed 2 h previously decreased the exploration of the unfamiliar conspecific, exhibiting a rapid decrease over the course of the trial. In response to the stressor, however both sexes, however, decreased the exploration of the familiar conspecific, decreased their overall activity, and returned preferentially to their starting quadrant. None of these stress-induced effects were evident 24 h later upon the first or second exposure to the apparatus. Thus, exposure to the stressor transiently increased perseveration and decreased activity in males and females, but only decreased the exploration of novel conspecifics in males. These results indicate that a number of behavioral responses to stressors are conserved across gender, but those relating to novelty are more pronounced in males.

Animals↗
PubMed1995

Identification of a Bordetella pertussis regulatory factor required for transcription of the pertussis toxin operon in Escherichia coli.

Transcription of the pertussis toxin operon (ptx) is positively regulated in Bordetella pertussis by the bvgAS locus. However, a ptx-lacZ transcriptional fusion in Escherichia coli cannot be activated by bvgAS in trans. This suggests that an additional factor(s) is required for transcription of ptx. A gene encoding a Bvg accessory factor (Baf) was identified by its ability to activate an E. coli ptx-lacZ fusion in the presence of bvgAS. The expression of ptx-lacZ was decreased by the addition of 40 mM MgSO4, a compound that also modulates ptx expression in B. pertussis. Baf alone did not activate expression of an E. coli fhaB-lacZ fusion, nor did it increase expression of fhaB-lacZ in trans with bvgAS. The gene encoding Baf was localized, sequenced, and found to produce a novel 28-kDa protein. Sequences homologous to B. pertussis baf were identified in Bordetella bronchiseptica and Bordetella parapertussis but not in Bordetella avium. When an additional copy of baf was integrated into the chromosome of BC75, a B. pertussis mutant that produces a low level of pertussis toxin, pertussis toxin production was partially complemented in the cointegrate strain.

Amino Acid Sequence↗
PubMed1994

Partial suppression of an Escherichia coli TonB transmembrane domain mutation (delta V17) by a missense mutation in ExbB.

Active transport of vitamin B12 and Fe(III)-siderophore complexes across the outer membrane of Escherichia coli appears to be dependent upon the ability of the TonB protein to couple cytoplasmic membrane-generated protonmotive force to outer membrane receptors. TonB is supported in this role by an auxiliary protein, ExbB, which, in addition to stabilizing TonB against the activities of endogenous envelope proteases, directly contributes to the energy transduction process. The topological partitioning of TonB and ExbB to either side of the cytoplasmic membrane restricts the sites of interaction between these proteins primarily to their transmembrane domains. In this study, deletion of valine 17 within the aminoterminal transmembrane anchor of TonB resulted in complete loss of TonB activity, as well as loss of detectable in vivo crosslinking into a 59 kDa complex believed to contain ExbB. The delta V17 mutation had no effect on TonB export. The loss of crosslinking appeared to reflect conformational changes in the TonB/ExbB pair rather than loss of interaction since ExbB was still required for some stabilization of TonB delta V17. Molecular modeling suggested that the delta V17 mutation caused a significant change in the predicted conserved face of the TonB amino-terminal membrane anchor. TonB delta V17 was unable to achieve the 23 kDa proteinase K-resistant form in lysed sphaeroplasts that is characteristic of active TonB. Wild-type TonB also failed to achieve the proteinase K-resistant configuration when ExbB was absent. Taken together these results suggested that the delta V17 mutation interrupted productive TonB-ExbB interactions. The apparent ability to crosslink to ExbB as well as a limited ability to transduce energy were restored by a second mutation (A39E) in or near the first predicted transmembrane domain of the ExbB protein. Consistent with the weak suppression, a 23 kDa proteinase K-resistant form of TonB delta V17 was not observed in the presence of ExbBA39E. Neither the ExbBA39E allele nor the absence of ExbB affected TonB or TonB delta V17 export. Unlike the tonB delta V17 mutation, the exbBA39E mutation did not greatly alter a modelled ExbB transmembrane domain structure. Furthermore, the suppressor ExbBA39E functioned normally with wild-type TonB, suggesting that the suppressor was not allele specific. Contrary to expectations, the TonB delta V17, ExbBA39E pair resulted in a TonB with a greatly reduced half-life (approximately 10 min). These results together with protease susceptibility studies suggest that ExbB functions by modulating the conformation of TonB.

Amino Acid Sequence↗
PubMed1994

Molecular characterization of catalase from Bordetella pertussis: identification of the katA promoter in an upstream insertion sequence.

In this report we evaluate the role of catalase in the survival of Bordetella pertussis within human polymorphonuclear leukocytes (PMNs). Crude extracts of B. pertussis exhibited a single catalase activity when subjected to non-denaturing polyacrylamide gel electrophoresis and assayed for catalase activity. A plasmid containing B. pertussis katA was identified by complementation of UM255, a catalase-deficient strain of Escherichia coli. The nucleotide sequence of katA predicts a 55 kDa protein that shares homology with a class of haem-containing catalases found in both eubacteria and eukaryotes. Analysis of the nucleotide sequence upstream of katA revealed the presence of a copy of IS481, a B. pertussis-specific insertion sequence. The start site of transcription of katA was mapped to a T residue in IS481 by primer extension analysis performed with B. pertussis RNA and a katA-specific primer. A catalase-deficient strain of B. pertussis, DD900, was constructed by gene replacement. DD900 was more sensitive to killing by 1 and 5 mM H2O2 than the parental strain, BP339. However, there was no difference in the ability of DD900 and BP339 to survive for 2 h in human PMNs. This suggests that catalase plays no significant role in the survival of B. pertussis within PMNs.

Base Sequence↗
PubMed1993

The conserved proline-rich motif is not essential for energy transduction by Escherichia coli TonB protein.

TonB protein functions as an energy transducer, coupling cytoplasmic membrane electrochemical potential to the active transport of vitamin B12 and Fe(III)-siderophore complexes across the outer membrane of Escherichia coli and other Gram-negative bacteria. Accumulated evidence indicates that TonB is anchored in the cytoplasm, but spans the periplasmic space to interact physically with outer membrane receptors. It has been presumed that this ability is caused by a conserved (Glu-Pro)n-(Lys-Pro)m repeat motif, predicted to assume a rigid, linear conformation of sufficient length to reach the outer membrane. Based on in vitro studies with synthetic peptides and purified FhuA outer membrane receptor, it has been suggested that this region contains a site that directly binds outer membrane receptors and is essential for energy transduction. We have found a TonB lacking the (Glu-Pro)n-(Lys-Pro)m repeat motif (TonB delta(66-100)). TonB delta(66-100) is fully capable of irreversible phi 80 adsorption, except under physiological circumstances where the periplasmic space is expanded. Based on the ability of TonB delta(66-100) to interact with outer membrane receptors and components of the energy transduction apparatus under normal physiological conditions, it is evident that the TonB proline-rich region has no role in energy transduction other than to provide a physical extension sufficient to reach the outer membrane.

Amino Acid Sequence↗