Quantitative solubilization and analysis of insoluble paired helical filaments from Alzheimer disease

In this study, we evaluate the ability of several solvents to solubilize insoluble paired helical filaments (PHF) of Alzheimer disease. Specifically, we use protein extraction and reduction in the volume of insoluble material as quantitative assays to establish solvents of PHF. Using sequential categories of protein solvent to analyze insoluble PHF, only alkali or exhaustive proteolysis are effective in completely solubilizing PHF, while a variety of denaturants are ineffective. Alkali does not affect the phosphorylation state of PHF and complete dephosphorylation of PHF with hydrofluoric acid does not affect PHF solubility. These findings suggest that the 'hyperphosphorylation' of PHF proteins is not responsible for PHF insolubility. However the in vitro glycation of tau generates PHF that are insoluble in SDS and soluble in alkali. These findings suggest that protein crosslinks, including advanced glycation endproduct-derived crosslinks which were recently described in Alzheimer disease, play a major role in effecting PHF insolubility in vivo.

The secondary leukemias: challenges and research directions

Acute myelogenous leukemia (AML) arising following exposure to genotoxic agents has been recognized as a distinctive entity for more than 40 years. Secondary, or therapy-related, AML accounts for 10%-20% of all AML cases. This review addresses four overarching areas of investigation focused on secondary AMLs: 1) dissection of the molecular structure of the induced genetic lesions and identification of the functional consequences of these changes, thereby providing clues to the pathogenesis of secondary AML and potentially serving as a basis for innovative therapeutic interventions; 2) identification and characterization of mechanisms of DNA damage and the orderly repair of such damage; 3) identification and application of accurate biomarkers of leukemogenesis for the purpose of risk prediction and quantification, potentially allowing recognition of patients especially susceptible to the leukemogenic effects of chemotherapy (for genetic or acquired reasons) and allowing their treatment for cancer to be modified on the basis of this susceptibility; and 4) design and implementation of longitudinal clinical and genetic monitoring of high-risk populations (i.e., individuals under-going cytotoxic therapies for primary cancers). This review of the literature relating to these areas builds upon these themes and attempts to synthesize these seemingly disparate areas of research so that they can be more effectively utilized together to address the problem of secondary AML. Ultimately, the evaluation of these areas will improve our understanding of de novo leukemia and will serve as a springboard for the development of new concepts of therapy and prevention.

Susceptibility testing of Propionibacterium acnes comparing agar dilution with E test

Propionibacterium acnes has been identified as a significant agent of nosocomial infections, including endophthalmitis. Data concerning susceptibility of P. acnes to newer beta-lactam antibiotics and fluoroquinolones are limited. Recent reports suggest that quinolones have activity against these organisms sufficient to warrant further study. We undertook a study to select appropriate antimicrobial agents for use in a rabbit model of P. acnes endophthalmitis. We compared the antibiotic susceptibilities of P. acnes by using the National Committee for Clinical Laboratory Standards method of agar dilution with the E test. Thirteen clinical isolates obtained from eye specimens and three American Type Culture Collection control strains were tested against 14 antibiotics. All the clinical isolates were susceptible by both methods to piperacillin, piperacillin-tazobactam, ampicillin-sulbactam, ticarcillin-clavulanate, cefotaxime, cefotetan, ceftriaxone, cefoxitin, and imipenem in addition to clindamycin but were resistant to metronidazole. The clinical P. acnes isolates also displayed high-level susceptibility to ciprofloxacin, sparfloxacin, and ofloxacin. Almost all the P. acnes strains demonstrated E-test MICs within 2 dilutions of the MICs observed by the agar dilution method. Those few strains for which discrepancies were noted exhibited E-test susceptibilities three- to fivefold dilutions lower than the agar dilution method susceptibilities but only with ampicillin-sulbactam, ticarcillin-clavulanate, and/or clindamycin. On the basis of our study, all of clinical eye isolates were susceptible to these newer antimicrobial agents and the two methods demonstrated similar susceptibility patterns.

Myxofibrosarcoma. Clinicopathologic analysis of 75 cases with emphasis on the low-grade variant

Myxofibrosarcoma is one of the most common sarcomas in the extremities of elderly patients. We analysed the clinicopathologic features in a series of 75 patients. All patients were adults (range, 22-91 years; median, 66 years) with an approximately equal incidence in men and women. Thirty-five tumors arose in the lower and 25 in the upper extremities, nine on the trunk, two each in the retroperitoneum and the head and neck region, and one each in the pelvis and penis. Forty-eight cases (69.5%) were located in dermal or subcutaneous tissues. Distinctive histologic features included the following: a commonly nodular growth pattern; a myxoid matrix containing elongated, curvilinear capillaries; and fusiform, round or stellate tumor cells with indistinct cell margins, slightly eosinophilic cytoplasm, and hyperchromatic atypical nuclei. These lesions varied from a hypocellular, mainly myxoid, and purely spindle-cell appearance (low-grade neoplasms) to high-grade, pleomorphic (malignant fibrous histiocytoma-like) lesions with multinucleated giant cells, high mitotic activity, and areas of necrosis. Immunohistochemistry in 44 cases revealed only vimentin and occasional actin positivity. Ultrastructurally, tumor cells had a fibroblastic phenotype. DNA flow cytometry and proliferation analysis showed an association between aneuploidy and histologic grade. An average follow-up of 45 months (range, 5-300 months) in 60 cases has revealed local recurrence in 33 cases (54%). Thirteen patients developed metastases, and 13 tumor-related deaths occurred. A short interval to first local recurrence was associated with poor clinical outcome. The rate of local recurrence was independent of histologic grade, but only intermediate and high-grade neoplasms metastasized. The depth of the primary lesion did not influence the incidence of local recurrence. However, in deep-seated neoplasms, the incidence of metastases was higher and the percentage of tumor-related deaths was twice as high as in superficially located lesions, reflecting the fact that deep-seated lesions tended to be higher-grade, larger tumors. Myxofibrosarcoma tends to become progressively higher grade in recurrences, as demonstrated in five cases in our series. The poorly recognized low-grade myxofibrosarcoma is emphasized, as proper diagnosis and treatment and scrupulous follow-up are mandatory to avoid local recurrence and gradual tumor progression to a higher-grade neoplasm that may then metastasize.

Agrin mRNA expression in the developing chick Edinger-Westphal nucleus

Agrin is a large extracellular matrix protein that directs the accumulation of acetylcholine receptors at the neuromuscular junction. Recent evidence suggests that agrin may be involved in organizing synapses in the visual system as well. Focussing on the pathway that controls accommodation and pupilloconstriction, this study examined the temporal pattern of agrin expression with reference to the organization of cholinergic synapses between embryonic chick Edinger-Westphal and ciliary ganglion neurons. In situ hybridization with an S35-labeled agrin cRNA probe was used to characterize agrin expression in the Edinger-Westphal nucleus during development. Agrin mRNA was detected in the Edinger-Westphal nucleus at all time points studied, from embryonic day 7 (E7, Hamburger and Hamilton stage 31) through newly hatched chicks. Throughout this period, agrin mRNA expression in Edinger-Westphal neurons was lower than in nearby oculomotor and trochlear neurons, suggesting that cells projecting to neuronal targets may require less agrin than those projecting to muscle. Agrin mRNA expression in the Edinger-Westphal nucleus at E7, E8, E9, and E10 was significantly higher than at E12. The early appearance of agrin mRNA coincides with the period during which acetylcholine receptors are being organized on ciliary ganglion neurons, consistent with the possibility that agrin contributes to neuron-neuron synapse formation in this pathway.

The asthma health outcome indicators study

Health outcomes have become an important public health policy focus in Australia. The New South Wales Health Department's Health Outcomes Program includes asthma as one of its priority areas. This study combined a survey of a non-random sample of 14 asthma researchers and clinicians and the results of a literature review to determine the current status and validity of outcome indicators used in relation to asthma. A written questionnaire was used to present individual patient, clinical trial, school intervention and public health scenarios, and respondents were asked to nominate asthma outcome indicators they would use in each scenario as well as their estimate of the indicators' validity. The results provide a critical appraisal of a variety of asthma outcome indicators with regard to their repeatability, and their concurrent and predictive validity.

Trypsin interaction with the senile plaques of Alzheimer disease is mediated by beta-protein precursor

In this study we demonstrate by in situ binding that trypsin interacts with the senile plaques found in Alzheimer disease. Characterization of various potential trypsin binding proteins shows that trypsin binding is mediated by beta-protein precursor (beta PP)-the progenitor of amyloid-beta in senile plaques. Using specific antisera against various proteins to sterically block trypsin blocking, we found that only those antibodies raised against proteins or peptides containing the Kunitz protease inhibitor domain were able to abolish binding. By analogy with other protease/inhibitor interactions, we speculate that the binding of trypsin to beta PP could involve concomitant beta PP cleavage. Therefore, beta PP in protecting against potentially damaging proteolysis could simultaneously liberate beta PP fragments or intermediate precursors of amyloid-beta deposits.

Filament heterogeneity within the dystrophic neurites of senile plaques suggests blockage of fast axonal transport in Alzheimer's disease

In this study, the direct comparison of biopsy and autopsy tissue by morphological and immunocytochemical techniques, respectively, was used to document cytoskeletal changes of dystrophic neurites (DN) of senile plaques in Alzheimer's disease. This dual approach demonstrated several unreported abnormalities which, together with analogous findings in several experimental models, suggest that DN are associated with deficiencies in fast axonal transport and replacement of the cytoskeleton by an array of related abnormal filaments.

Contaminated stethoscopes revisited

BACKGROUND

Because of their universal use by medical professionals, stethoscopes can be a source of nosocomial infections.

OBJECTIVE

To determine the frequency of contamination of stethoscopes with bacteria and fungi.

METHODS

Cultures were obtained from 200 stethoscopes from four area hospitals and outpatient clinics in Houston, Tex. The frequency of stethoscope contamination in different groups of hospital personnel and medical settings was determined. We also measured the frequency of antimicrobial resistance of the staphylococcal strains that were isolated.

RESULTS

One hundred fifty-nine (80%) of the 200 stethoscopes surveyed were contaminated with microorganisms. The majority of organisms that were isolated were gram-positive bacteria, primarily Staphylococcus species. Fifty-eight percent of the Staphylococcus species that were isolated, including four (17%) of 24 Staphylococcus aureus isolates, were resistant to methicillin. Physicians' stethoscopes were contaminated more often than those of other medical personnel groups (P = .02). Stethoscopes used only in designated areas were contaminated less frequently than stethoscopes belonging to individual medical personnel (P = .01). Although stethoscopes were contaminated in all areas, stethoscopes from the pediatric medical setting were contaminated less frequently than those from other hospital areas (P = .009).

CONCLUSIONS

Stethoscope use may be important in the spread of infectious agents, including antimicrobial-resistant strains, and strategies to reduce the contamination of stethoscopes should be developed. We recommend disinfection of stethoscopes or regular use of disposable stethoscope covers.

Alzheimer disease: protein-protein interaction and oxidative stress

Alzheimer disease, the most prevalent dementia of the aged, is defined by the concurrence of two filamentous brain lesions: neurofibrillary tangles and senile plaques. The lesions are temporally and spatially correlated to each other and to cognitive impairment suggesting that is a interaction between neurofibrillary tangles and senile plaques that might play a role in disease pathogenesis. Here we present findings demonstrating specific interactions between the major protein components of the lesions. Such an interaction is likely important to lesion genesis and to the overall cognitive deficits seen clinically. Also important are forces that stabilize and cement abnormal interactions and protect them form removal. Oxidative post-translational modifications is probably one of the major mediators that by disrupting cellular homeostatic balance both promotes abnormal interactions and makes them resistant to proteolytic removal. Overall, these findings support the view that the lesions of Alzheimer disease are intimately involved in neuronal destructions.

beta PP and Tau interaction. A possible link between amyloid and neurofibrillary tangles in Alzheimer's disease

Extracellular deposition of amyloid fibrils and intraneuronal accumulation of paired helical filaments (PHFs) are the neuropathological hallmarks of Alzheimer's disease. The major constituent of amyloid fibrils is a 39- to 43-residue peptide (termed A beta), which is derived from a 695- to 770-amino-acid precursor protein (termed beta PP). The main component of PHFs identified so far is the microtubule-associated protein tau. Yet, there is no direct evidence of interconnection between these two pathological states. We report here that antibodies to an epitope located between residues 713 and 723 of beta PP770 (ie, the transmembrane region of beta PP distal to A beta) consistently labeled PHFs in the brain of Alzheimer patients. Solid phase immunoassay showed that a peptide homologous to residues 713 to 730 of beta PP770 bound tau proteins. This beta PP peptide spontaneously formed fibrils in vitro and, in the presence of tau, generated dense fibrillary assemblies containing both molecules. These data suggest that beta PP or beta PP fragments containing the tau binding site are involved in the pathogenesis of PHFs in Alzheimer's disease.

Changes in cholecystokinin mRNA expression after amygdala kindled seizures: an in situ hybridization study

Cholecystokinin (CCK) can be a potent anticonvulsant neuropeptide in certain seizure models. Therefore, we examined whether seizures produced by electrical kindling of the amygdala or electroconvulsive seizures (ECS) would affect the expression of CCK mRNA in rat brain. Following a single kindled seizure, CCK mRNA expression was decreased about 20-58% in the amygdala. In contrast, after multiple consecutive kindled seizures, CCK mRNA expression was increased in the amygdala, cerebral cortex, CA1 pyramidal cell layer of the hippocampus and dentate hilus. A single ECS produced no effect on CCK mRNA expression, but multiple ECS increased expression in the interneurons of the hippocampus 24 h after the last seizure. Since seizures produced by ECS can be anticonvulsant to further ECS or kindled seizures, the CCK increases in the hippocampus may represent a compensatory anticonvulsant adaptation observed in both models. Overall, the kindling-induced alterations in CCK expression appear to be more complex involving multiple brain regions and distinct temporal properties.

Effects of stress on neurotrophic factor expression in the rat brain

Changes in neurotrophic factor expression in the brain are part of the stress response. Decreased BDNF may contribute to hippocampal damage that occurs during chronic stress or aging. Stress-induced increases in NT-3 may be important for neural plasticity and adaptation or sensitization to repeated stress. Stress-induced changes in neurotrophic factors may be particularly relevant to the cognitive changes that occur in recurrent depression, aging, and posttraumatic stress disorder.

Localization of alpha 7 nicotinic receptor subunit mRNA and alpha-bungarotoxin binding sites in developing mouse somatosensory thalamocortical system

Previous studies in rat, showing a transient pattern of expression of the alpha 7 nicotinic acetylcholine receptor in the ventrobasal thalamus and barrel cortex during the first 2 postnatal weeks, suggest that these receptors may play a role in development of the thalamocortical system. In the present study, in situ hybridization and radiolabeled ligand binding were employed to examine the spatiotemporal distribution of alpha 7 mRNA and alpha-bungarotoxin binding sites in the thalamocortical pathway of mouse during early postnatal development. As in the rat, high levels of alpha 7 mRNA and alpha-bungarotoxin binding sites are present in the barrel cortex of mouse during the first postnatal week. Both alpha 7 mRNA and its receptor protein are observed in all cortical laminae, with the highest levels seen in the compact cortical plate, layer IV, and layer VI. When viewed in a tangential plane, alpha 7 mRNA and alpha-bungarotoxin binding sites delineate a whisker-related barrel pattern in layer IV by P3-5. Quantitative analysis reveals a dramatic decrease in the levels of expression of alpha 7 mRNA and alpha-bungarotoxin binding sites in the cortex by the end of the second postnatal week. Unlike in the rat, only low levels of alpha 7 mRNA or alpha-bungarotoxin binding sites are present in the ventrobasal complex of the mouse thalamus. The broad similarities between the thalamocortical development of rat and mouse taken together with the present results suggest that alpha 7 receptors located on cortical neurons, rather than on thalamic neurons, play a role in mediating aspects of thalamocortical development.

Free radical damage, iron, and Alzheimer's disease

We present evidence to support the premise that many of the pathological correlates of Alzheimer's disease are precipitated by free radical- and oxidative stress-induced mechanisms. We propose that amyloid-beta deposition in senile plaques, intracellular accumulation of protein in neurofibrillary tangles, and the degeneration of specific neuronal populations can be attributed to specific oxidative stress-type mechanisms. Free radicals in disease pathogenesis, generated in part as a result of Fenton-type reactions, suggest that lowering the level of available iron, intervention with antioxidants, or the administration of free radical scavengers could provide a therapeutic inroad in the fight against Alzheimer's disease.

Plasma membrane fragility in dystrophic neurites in senile plaques of Alzheimer's disease: an index of oxidative stress

This study presents evidence for plasma membrane abnormalities of the dystrophic neurites in senile plaques of Alzheimer's disease. We found that the plasma membranes of dystrophic neurites are more labile to fixation than those membranes of other cells of the senile plaque or of normal neurites distant from senile plaques. Further, we found vesicles in the extracellular space adjacent to dystrophic neurites and similar to those within them, suggesting that the increased lability seen in our preparations may, in vivo, be associated with release of neuritic contents. Plasma membrane alterations may be critical to deposition of amyloid-beta in senile plaques from the abundant beta-protein precursor of dystrophic neurites. The consequences of altered membrane integrity, such as calcium influx, lipid peroxidation and free radical damage, could also be responsible for many of the pathological correlates of the disease.

Editing for an AMPA receptor subunit RNA in prefrontal cortex and striatum in Alzheimer's disease, Huntington's disease and schizophrenia

Animal studies and cell culture experiments demonstrated that posttranscriptional editing of the transcript of the GluR-2 gene, resulting in substitution of an arginine for glutamine in the second transmembrane region (TM II) of the expressed protein, is associated with a reduction in Ca2+ permeability of the receptor channel. Thus, disturbances in GluR-2 RNA editing with alteration of intracellular Ca2+ homeostasis could lead to neuronal dysfunction and even neuronal degeneration. The present study determined the proportions of edited and unedited GluR-2 RNA in the prefrontal cortex of brains from patients with Alzheimer's disease, in the striatum of brains from patients with Huntington's disease, and in the same areas of brains from age-matched schizophrenics and controls, by using reverse transcriptase-polymerase chain reaction, restriction endonuclease digestion, gel electrophoresis and scintillation radiometry. In the prefrontal cortex of controls, < 0.1% of all GluR-2 RNA molecules were unedited and > 99.9% were edited; in the prefrontal cortex both of schizophrenics and of Alzheimer's patients approximately 1.0% of all GluR-2 RNA molecules were unedited and 99% were edited. In the striatum of controls and of schizophrenics, approximately 0.5% of GluR-2 RNA molecules were unedited and 99.5% were edited; in the striatum of Huntington's patients nearly 5.0% of GluR-2 RNA was unedited. In the prefrontal white matter of controls, approximately 7.0% of GluR-2 RNA was unedited. In the normal human prefrontal cortex and striatum, the large majority of GluR-2 RNA molecules contains a CGG codon for arginine in the TMII coding region; this implies that the corresponding AMPA receptors have a low Ca2+ permeability, as previously demonstrated for the rat brain. The process of GluR-2 RNA editing is compromised in a region-specific manner in schizophrenia, in Alzheimer's disease and Huntington's Chorea although in each of these disorders there is still a large excess of edited GluR-2 RNA molecules. Disturbances of GluR-2 RNA editing leading to excessive Ca2+ permeability, may contribute to neuronal dysfunction in schizophrenia and to neuronal death in Alzheimer's disease and Huntington's disease.

Expression of agrin mRNA is altered following seizures in adult rat brain

Agrin mRNA is broadly distributed throughout the adult rat brain, consistent with its proposed role in synaptogenesis and the organization of synaptic proteins in the central nervous system. The present study examined the effect of neuronal activity on agrin mRNA expression in adult rat forebrain using the hilus lesion paradigm for seizure induction and in situ hybridization and polymerase chain reaction techniques for quantification and characterization of agrin mRNA content. Seizures induced rapid, prolonged, and region-specific changes in agrin mRNA expression with the most prominent alterations occurring in hippocampal and cortical neurons. However, there were no detectable perturbations in the relative abundance of alternatively spliced agrin transcripts in affected brain regions. Activity-dependent changes in agrin expression suggest a role for this protein in modifications of synaptic structure associated with functional synaptic plasticity.

Evidence for oxidative stress in Pick disease and corticobasal degeneration

Oxidative stress is increasingly implicated in a number of neurodegenerative disorders characterized by abnormal filament accumulation in affected neurons, including Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis. To further evaluate the role of oxidative stress in the neurodegenerative process and the accumulation of abnormal filaments, we examined the pathologic lesions in Pick disease and of corticobasal degeneration with immunocytochemistry by using antisera to heme oxygenase-1 (HO-1) - a putative marker of oxidative injury. Immunoreactivity to HO-1 was demonstrated in ballooned neurons, Pick bodies, neuropil threads, and glial inclusions (the latter two in a case of corticobasal degeneration). By immunoelectron microscopy, HO-1 immunolabelling of Pick bodies was closely associated with the abnormal filaments comprising the inclusion. Apparently unaffected neurons in all cases showed only background levels of HO-1 immunoreactivity. These data suggest that oxidative stress is important in the formation of the lesions characteristic of Pick disease and corticobasal degeneration. Moreover, taken together with our previous demonstration that HO-1 immunoreactivity is associated with the neurofibrillary pathology of Alzheimer disease, progressive supranuclear palsy, and subacute sclerosing panencephalitis, it appears that oxidative stress specifically targets the cytoskeleton in a variety of neurodegenerative disorders characterized by abnormal filament accumulation.

Regulation of corticotropin-releasing hormone receptor messenger ribonucleic acid in the rat brain and pituitary by glucocorticoids and stress

Glucocorticoids and stress are known to influence the synthesis of corticotropin-releasing hormone (CRH) at a variety of sites in brain, including the hypothalamus and amygdala. The recent cloning of the CRH receptor (CRH-R) enabled us to determine whether glucocorticoids or stress influenced CRH action via regulation of CRH-R. We, therefore, used in situ hybridization to measure CRH-R messenger RNA (mRNA) levels in the hypothalamic paraventricular nucleus (PVN), anterior pituitary (AP), amygdala, and bed nucleus of the stria terminalis (BNST) under several conditions. Systemic corticosterone (CORT) treatment, both daily injection (5 mg/rat.day) up to 14 days and pellet implant (200 mg) for 14 days, decreased CRH-R mRNA in the PVN and lateral and basolateral nucleus of the amygdala (BLA). Corticosterone injection (10 mg/rat.day, for 7 days) decreased CRH-R mRNA in the AP. Adrenalectomy also decreased CRH-R mRNA in the PVN and AP, but did not alter it in the BLA. In both sham and adrenalectomized rats with CORT pellet replacement (39 mg; ADX+CORT rats), acute (2-h) and repeated (2 h daily for 14 days) immobilization stress (which produced a large increase in plasma CORT in sham rats) increased CRH-R mRNA in the PVN and decreased it in the AP, but did not affect CRH-R mRNA in the BLA. However, ADX+CORT rats consistently had higher levels of CRH-R mRNA in both the PVN and AP than sham rats after stress. Brain stem hemisection, which damaged all ascending catecholaminergic fibers with the exception of the locus ceruleus, attenuated immobilization stress-induced up-regulation of CRH-R mRNA ipsilaterally in the PVN. None of the treatments affected CRH-R mRNA levels in the central and medial nucleus of the amygdala or the BNST. These results suggest that high concentrations of CORT or CRH synergistically decrease CRH-R mRNA levels in the AP, and that at least high CORT has an inhibitory effect on PVN CRH-R mRNA levels. However, stress input can override such inhibitory effects and thus up-regulate CRH-R mRNA in the PVN. The extrahypothalamic regions, such as amygdala and BNST may have different sensitivities to CORT or CRH for the regulation of CRH-R mRNA.

Stress and antidepressants differentially regulate neurotrophin 3 mRNA expression in the locus coeruleus

The mechanisms by which stress and anti-depressants exert opposite effects on the course of clinical depression are not known. However, potential candidates might include neurotrophic factors that regulate the development, plasticity, and survival of neurons. To explore this hypothesis, we examined the effects of stress and antidepressants on neurotrophin expression in the locus coeruleus (LC), which modulates many of the behavioral and physiological responses to stress and has been implicated in mood disorders. Using in situ hybridization, we demonstrate that neurotrophin 3 (NT-3) is expressed in noradrenergic neurons of the LC. Recurrent, but not acute, immobilization stress increased NT-3 mRNA levels in the LC. In contrast, chronic treatment with antidepressants decreased NT-3 mRNA levels. The effect occurred in response to antidepressants that blocked norepinephrine uptake, whereas serotonin-specific reuptake inhibitors did not alter NT-3 levels. Electroconvulsive seizures also decreased NT-3 expression in the LC as well as the hippocampus. Ntrk3 (neurotrophic tyrosine kinase receptor type 3; formerly TrkC), the receptor for NT-3, is expressed in the LC, but its mRNA levels did not change with stress or antidepressant treatments. Because, NT-3 is known to be trophic for LC neurons, our results raise the possibility that some of the effects of stress and antidepressants on LC function and plasticity could be mediated through NT-3. Moreover, the coexpression of NT-3 and its receptor in the LC suggests the potential for autocrine mechanisms of action.

Induction of heme oxygenase-1 mRNA and protein in neocortex and cerebral vessels in Alzheimer's disease

Previous studies demonstrated the specific association of heme oxygenase (HO)-1 protein to the neurofibrillary pathology of Alzheimer's disease (AD). In this study, we used reverse transcription-polymerase chain reaction methods to show the increased expression of HO-1 but not HO-2 mRNA transcripts in cerebral cortex and cerebral vessels from subjects with AD compared with age-matched non-AD controls. Neither the HO-1 nor the HO-2 mRNA levels was altered in the cerebellum, a brain region usually spared from the pathological alterations of AD. There was no clear evidence that the expression of HO-1 in these tissues was related to postmortem interval, cause of death, or the age of the subjects studied. Using immunoblotting methods, we further showed that HO-1 protein content was increased in neocortical and vascular samples from AD subjects compared with controls. Our findings suggest the specific induction of HO-1 mRNA and protein in the cerebral cortex and cerebral vessels but not HO-2 mRNA or protein in association with the pathological lesions of the disease.

The influence of microaerophilia and anaerobiosis on metronidazole uptake in Helicobacter pylori

Resistance of Helicobacter pylori to metronidazole during therapy for gastroduodenal ulcers is claimed to be responsible for failure to eradicate the pathogen and thus the disease. Resistance to metronidazole and other nitroimidazoles is rare and documented only for anaerobes; the mechanism of resistance in typical microaerophiles, like Helicobacter, is not known. We have studied metronidazole uptake using high performance liquid chromatography in metronidazole sensitive and resistant strains of H. pylori under conditions of microaerophilia and in anaerobiosis. The uptake of metronidazole was faster in sensitive strains than resistant ones and was also increased in anaerobiosis. Drug uptake and the rate of cell kill was found to be dependent upon the relative oxygen tension of the environment and the cell density, both of which determine the redox conditions of the media. We suggest that resistance displayed in microaerophilia, but which disappears in anaerobiosis, may not involve futile cycling nor the induction of superoxide dismutase and catalase. We further propose that resistant organisms may have alterations in the pattern of pyruvate metabolism as documented for anaerobic bacteria and protozoa and that resistance in microaerophilia may involve the relative efficiencies of detoxifying oxygen in susceptible and resistant strains of H. pylori.