The neural basis of the psychomotor vigilance task

STUDY OBJECTIVE: To identify brain regions underlying the fastest and slowest reaction times on the Psychomotor Vigilance task (PVT) under well-rested conditions, as well as brain regions related to particularly poor performance after sleep deprivation. DESIGN: Subjects took the PVT twice while undergoing functional magnetic resonance imaging: once 12 hours after waking from a normal night of sleep and once after 36 hours of total sleep deprivation (TSD). Session order was counterbalanced. SETTING: UCSD J. Christian Gillin Laboratory for Sleep and Chronobiology (the sleep core of the General Clinical Research Center) and UCSD Magnetic Resonance Institute. PATIENTS OR PARTICIPANTS: Twenty right-handed healthy adults (8 women; age = 27.4 +/- 6.7 years; education = 15.6 +/- 1.5 years). MEASUREMENTS AND RESULTS: After a normal night of sleep, optimal performance was related to greater cerebral responses within a cortical sustained attention network and the cortical and subcortical motor systems. Slow reaction times, particularly after TSD, were associated with greater activity in the "default mode network" consisting of frontal and posterior midline regions. CONCLUSIONS: Optimal performance on the PVT appears to rely on activation both within the sustained attention system and within the motor system. Poor performance following TSD may result from a disengagement from the task and related inattention, and brain regions responsible for this localize within midline structures shown to be involved in the brain's "default mode." Finally, particularly poor performance after TSD may elicit a subsequent attentional recovery that manifests as greater activation within the same regions normally responsible for fast reaction times.     

Murine model of pulmonary anthrax: kinetics of dissemination, histopathology, and mouse strain susceptibility

Bioweapons are most often designed for delivery to the lung, although this route is not the usual portal of entry for many of the pathogens in the natural environment. Vaccines and therapeutics that are efficacious for natural routes of infection may not be effective against the pulmonary route. Pulmonary models are needed to investigate the importance of specific bacterial genes in virulence, to identify components of the host immune system that are important in providing innate and acquired protection, and for testing diagnostic and therapeutic strategies. This report describes the characteristics of host and Bacillus anthracis interactions in a murine pulmonary-infection model. The infective dose varied depending on the route and method of inoculation. The germination process in the lung began within 1 h of inoculation into the lung, although growth within the lung was limited. B. anthracis was found in the lung-associated lymph nodes approximately 5 h after infection. Minimal pneumonitis was associated with the lung infection, but significant systemic pathology was noted after dissemination. Infected mice typically succumbed to infection approximately 3 to 4 days after inoculation. The 50% lethal doses differed among inbred strains of mice, but within a given mouse strain, neither the age nor the sex of the mice influenced susceptibility to B. anthracis.     

Candidate vaccine antigens identified by antibodies from mice vaccinated with 15- or 50-kilorad-irradiated cercariae of Schistosoma mansoni.

In murine schistosomiasis, the highest levels of resistance to cercarial challenge are obtained by vaccination with radiation-attenuated cercariae. To identify candidate vaccine antigens relevant to the vaccine model, we examined parasite antigens recognized by antibodies from mice vaccinated with irradiated cercariae of Schistosoma mansoni. To optimize recognition of a wide spectrum of antigens, several factors that influence the level of protection in this model were varied; specifically, we examined the effect of (i) single versus multiple vaccinations with irradiated cercariae, (ii) the dose of irradiation (15 or 50 kilorads) administered to the cercariae, and (iii) the genetic background of mouse strains, high-responder (C57BL/6J) versus moderate-responder (CBA/J) mice. We found that the number of vaccinations did not alter antibody specificity but modified the relative antibody titers against particular antigens. The dose of irradiation used to attenuate the immunizing cercariae had a similar effect on antibody titers but in addition influenced antibody specificity. Only mice that had been vaccinated with moderately irradiated cercariae recognized cathepsin B (Sm31) and Sm32. Interestingly, when vaccinated mice of the two strains, C57BL/6J and CBA/J, were compared, differences in antibody responses to particular antigens were observed. Both strains recognized the integral membrane protein Sm23, glutathione S-transferase, and cathepsin B, whereas Sm32 and paramyosin were recognized only by CBA/J mice, and heat shock protein 70 was recognized exclusively by C57BL/6J mice. In this study, we conclusively identified six distinct antigens that are specifically recognized by the humoral immune response of vaccinated mice.     

Anoxic disturbance of the isolated respiratory network of neonatal rats

Tissue oxygen (PO₂), K⁺ (aK_e), pH (pH_e) and Ca²⁺ ([Ca²⁺]_e) were measured in the region of the ventral respiratory group (VRG) in the in vitro brainstem-spinal cord preparation of neonatal rats. During tissue anoxia, elicited by superfusion of N₂-gassed solutions, an initial increase in the frequency of respiratory activity, lasting between 2 and 12 min, turned into a frequency depression. During anoxia periods of up to 60 min, respiratory activity persisted in solutions containing CO₂/bicarbonate, whereas a complete blockade was observed after 15–25 min in N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid- (Hepes)-buffered salines. After such anoxic apnea, respiratory rhythmicity could be reactivated by superfusion of hypoxic, CO₂/bicarbonate-buffered solutions. In both types of hypoxic solutions, aK_e increased by maximally 1.5mM, whereas an initial increase of pH_e by up to 0.05 pH units turned, after 2–4 min, into an acidification which could exceed 0.5 pH units. In contrast, [Ca²⁺]_e remained unaffected by anoxia. Addition of 2–5 mM cyanide (CN^-) to oxygenated Hepes-buffered saline evoked an increase in PO₂ in the VRG from 100 to more than 300 mmHg. The effects of CN^- on respiratory activity, aK_e and pH_e were almost identical to those during anoxia. In oxygenated, CO₂/bicarbonatefree solutions of different pH, however, an increase in pH_e in the VRG led to a decrease in respiratory frequency, whereas a fall of pH_e produced a frequency acceleration. A rise of aK_e in the VRG by more than 2 mM as induced by superfusion of a 7 mM K⁺ solution led to a sustained increase of respiratory frequency. The results indicate that blockade of aerobic metabolism does not severely perturb K⁺ and Ca²⁺ homeostasis and that the biphasic response to anoxia is not directly related to the observed changes in PO₂, aK_e, pH_e, or [Ca²⁺]_e. In the respiratory network of neonatal mammals, CO₂ might provide a stimulus for long-term maintenance of respiratory activity under oxygen depletion.     

Genetic requirements for salmonella-induced cytopathology in human monocyte-derived macrophages

Infection of human macrophages with Salmonella enterica serovar Typhimurium or Salmonella enterica serovar Dublin produces delayed cytotoxicity characterized by cell detachment and associated apoptosis. Using a site-specific mutant in the SpvB active site, we verify that the ADP-ribosylation activity of SpvB is required for delayed cytotoxicity in human macrophages infected with Salmonella: SipB and the type III protein secretion system (TTSS) encoded by Salmonella pathogenicity island 1 (SPI1) are not involved, whereas the SPI2 TTSS is absolutely required for SpvB-dependent cytotoxicity. Furthermore, we show that infection of macrophage cultures with wild-type or sipB mutant bacteria led to a complete loss of polymerized actin in over half of the cells after 24 h. In contrast, macrophages infected with the spvB or SPI2 (ssaV or ssaJ) mutant strain retained normal F-actin filaments, despite similar numbers of intracellular bacteria. We conclude that SpvB and a functional SPI2 TTSS are essential for Salmonella-induced delayed cytotoxicity of human macrophages.     

Incidence of delirium and associated mortality in hematopoietic stem cell transplantation patients.

Delirium has been associated with a high risk of mortality in medical patients. Despite the high incidence of delirium in patients who undergo hemapoietic stem cell transplantation (HSCT), delirium as a risk factor for death has not been examined in this population. Thirty adult patients undergoing HSCT who were admitted to the University of Iowa Blood and Marrow Transplantation Program inpatient unit were assessed prospectively from 1 to 2 weeks before transplantation, throughout their inpatient stay, and at 100 days after transplantation. The Delirium Rating Scale and Memorial Delirium Assessment Scale were used twice weekly during the inpatient period to assess delirium severity and occurence. Patients' self-reports of medical history, computerized medical records, and neuropsychological and psychiatric assessments were used to identify pretransplantation risk factors. The incidence of delirium (Delirium Rating Scale score >12 or Memorial Delirium Assessment Scale score >or=8) was 43% and occurred with highest frequency in the first 2 weeks after transplantion. The presence of delirium at any point during hospitalization after transplantation and transplant type (allogeneic) were highly predictive of mortality (p < .0005; odds ratios, 14.0 and 14.4). In conclusion, this study highlights the importance of monitoring for delirium during the acute recovery period after transplantation and suggests that early or even prophylactic treatment for delirium should be studied. Studies to determine the factors that connect delerium soon after transplantation to mortality are highly warranted.     

Molecular genetics of pseudoxanthoma elasticum: type and frequency of mutations in ABCC6

Pseudoxanthoma elasticum (PXE) is a systemic heritable disorder that affects the elastic tissue in the skin, eye, and cardiovascular system. Mutations in the ABCC6 gene cause PXE. We performed a mutation screen in ABCC6 using haplotype analysis in conjunction with direct sequencing to achieve a mutation detection rate of 97%. This screen consisted of 170 PXE chromosomes in 81 families, and detected 59 distinct mutations (32 missense, eight nonsense, and six likely splice-site point mutations; one small insertion; and seven small and five large deletions). Forty-three of these mutations are novel variants, which increases the total number of PXE mutations to 121. While most mutations are rare, three nonsense mutations, a splice donor site mutation, and the large deletion comprising exons 23-29 (c.2996_4208del) were identified as relatively frequent PXE mutations at 26%, 5%, 3.5%, 3%, and 11%, respectively. Chromosomal haplotyping with two proximal and two distal polymorphic markers flanking ABCC6 demonstrated that most chromosomes that carry these relatively frequent PXE mutations have related haplotypes specific for these mutations, which suggests that these chromosomes originate from single founder mutations. The types of mutations found support loss-of-function as the molecular mechanism for the PXE phenotype. In 76 of the 81 families, the affected individuals were either homozygous for the same mutation or compound heterozygous for two mutations. In the remaining five families with one uncovered mutation, affected showed allelic compound heterozygosity for the cosegregating PXE haplotype. This demonstrates pseudo-dominance as the relevant inheritance mechanism, since disease transmission to the next generation always requires one mutant allelic variant from each parent. In contrast to other previous clinical and molecular claims, our results show evidence only for recessive PXE. This has profound consequences for the genetic counseling of families with PXE.