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Biomedical subjects

D S Weiss

Publications and source records attributed to D S Weiss.

At least 37 records · Page 2Linked to original sources
PubMed2000

Interpersonal and cultural issues involving crews and ground personnel during Shuttle/Mir space missions.

BACKGROUND: Anecdotal reports from space and results from simulation studies on Earth suggest that interpersonal and cultural issues will have an impact on the interactions of crewmembers and mission control personnel during future long-duration space missions. METHODS: To evaluate this impact we studied 5 astronauts, 8 cosmonauts, and 42 American and 16 Russian mission control personnel who participated in the Shuttle/Mir space program. Subjects completed questions from the Profile of Mood States, the Group Environment Scale, and the Work Environment Scale on a weekly basis during the missions. Subscale scores from these measures were analyzed using a two-way ANOVA to examine mean differences as a function of country (American vs. Russian), group (crewmember vs. ground personnel), and their interaction. RESULTS: Americans scored higher on measures of vigor and work pressure, and Russians scored higher on measures of managerial control, task orientation, physical comfort, self discovery, and leader support (which also showed a significant interaction effect). Mission control subjects scored higher than crewmembers on four measures of dysphoric emotions, but both groups scored significantly lower than published norms from other studies. There were significant interaction effects for subscales measuring leader support, expressiveness, and independence, with the American astronauts scoring the lowest of all comparison groups on all three subscales. CONCLUSIONS: In future long-duration space missions, countermeasures should focus on providing support for crewmembers from a culture in the minority, and crews should include more than one representative from this culture. Positive aspects of the interpersonal environment should be enhanced. The needs of mission control personnel should be addressed as well as those of crewmembers.

Adult↗
PubMed1999

Sensory gating in chronic posttraumatic stress disorder: reduced auditory P50 suppression in combat veterans.

BACKGROUND: Posttraumatic stress disorder (PTSD) may be associated with a general impairment of cognitive function that extends beyond the processing of trauma-specific stimuli. Suppression of the auditory P50 response to repeated stimuli occurs in normal subjects and reflects the central nervous system's ability to screen out repetitive stimuli, a phenomenon referred to as sensory gating. This study examines P50 sensory gating to nonstartle auditory stimuli in PTSD subjects and normal controls. METHODS: P50 generation and gating were studied using a conditioning/testing paradigm in 15 male subjects with PTSD and 12 male controls. P50 test/conditioning (T/C) ratios were estimated using the Singular Value Decomposition method. RESULTS: The amplitude of the P50 response to the conditioning stimulus did not differ in subjects with PTSD compared to normal controls. The P50 T/C ratio is increased in PTSD subjects (mean = .408, SD = .275) as compared to the controls (mean = .213, SD = .126, two tailed t, p = .024). CONCLUSIONS: This study provides evidence that PTSD is associated with impaired gating to nonstartle trauma-neutral auditory stimuli.

Auditory Threshold↗
PubMed1999

Permeability and single channel conductance of human homomeric rho1 GABAC receptors.

1. Homomeric human rho1 GABAC receptors were expressed in Xenopus oocytes and in human embryonic kidney cells (HEK293) in order to examine their conductance and permeability. 2. Reversal potentials of currents elicited by gamma-aminobutyric acid (GABA) were measured in extracellular solutions of various ionic composition to determine relative permeability of homomeric rho1 receptors. The rank order of anionic permeability was: SCN- > I- > NO3- > Br- > Cl- > formate (For-) > HCO3- > acetate (Ac-) approximately proprionate (Prop-) approximately isethionate (Ise-) approximately F- approximately PO4-. 3. In the oocyte expression system, relative permeabilities to SCN-, I-, NO3-, Br- and HCO3- were higher for rho1 GABAC receptors than alpha1beta2gamma2L GABAA receptors. 4. Expression of rho1 GABAC receptors in Xenopus oocytes and in HEK293 cells gave similar relative permeabilities for selected anions, suggesting that the expression system does not significantly alter permeation properties. 5. The pore diameter of the homomeric rho1 GABAC receptor expressed in oocytes was estimated to be 0.61 nm, which is somewhat larger than the 0.56 nm pore diameter estimated for alpha1beta2gamma2L GABAA receptors. 6. Homomeric rho1 GABA receptors expressed in oocytes had a single channel chord conductance of 0.65 +/- 0.04 pS (mean +/- s.e.m.) when the internal chloride concentration ([Cl-]i) was 20 mM. With a [Cl-]i of 100 mM, the single channel chord conductance was 1.59 +/- 0.24 pS. 7. The mean open time directly measured from 43 GABA-induced channel openings in six patches was 3. 2 +/- 0.8 s. The mean open time in the presence of 100 microM picrotoxin was 0.07 +/- 0.01 s (77 openings from 3 patches). 8. The differences observed in ionic permeabilities, pore size, single channel conductance and mean open time suggest that the rho1 homomeric receptor may not be the native retinal GABAC receptor reported previously.

Animals↗
PubMed1999

Evidence for phosphorylation-dependent internalization of recombinant human rho1 GABAC receptors.

1. Recombinant wild-type or mutant human rho1 GABA receptors were expressed in human embryonic kidney (HEK) 293 or monkey COS-7 cells and studied using the patch clamp technique. 2. Standard whole-cell recordings with 4 mM Mg-ATP in the patch pipette induced a time-dependent decrease in the GABA-activated current (IGABA) amplitude that was not the result of a decrease in GABA sensitivity. In contrast, IGABA remained stable when recordings were obtained using the perforated patch configuration or with standard whole-cell recording and no Mg-ATP in the patch pipette. 3. The inhibitors of serine/threonine protein kinases KN-62 (20 microM) or staurosporine (20 nM) prevented the time-dependent decrease in the amplitude of IGABA seen in the presence of ATP. Alkaline phosphatase (220 U ml-1), when added to the patch pipette in the absence of ATP, induced a transient potentiation of IGABA. Although the protein kinase C (PKC) activator 4beta-phorbol 12-myristate, 13-acetate (PMA) did not reduce the amplitude of IGABA, inclusion of the catalytic domain of PKC in the recording pipette accelerated the time-dependent decrease in current amplitude. These data suggest that phosphorylation is involved in the regulation of the amplitude of IGABA. 4. Mutation of the three PKC consensus sequences of the rho1 receptor had no significant effect on the decline in IGABA, indicating that direct phosphorylation of these putative sites on the rho1 receptor does not underlie the time-dependent decrease in amplitude. 5. In COS-7 cells transfected with wild-type rho1 receptors, the amplitude of IGABA had completely recovered to the original value when the same cells were repatched after 30-40 min, indicating that the decline in IGABA was a reversible process. 6. The inhibitor of actin filament formation cytochalasin B, when added to the patch pipette in the absence of ATP, induced a time-dependent inactivation suggesting that the actin cytoskeleton may play a role in the regulation of the amplitude. 7. Coincident with the decrease in the amplitude of IGABA, the cell capacitance significantly decreased in the presence of ATP in the patch pipette. This decrease in capacitance was not observed in the absence of Mg-ATP. The decrease in the membrane surface area suggests that receptor internalization could be a potential mechanism for the observed inactivation. 8. At 32 C, compared with 22 C, the rate and magnitude of the decline was increased dramatically. In contrast, at 16 C, no significant change in IGABA was observed over the 20 min recording time. This marked temperature sensitivity is consistent with receptor internalization as a mechanism for the time-dependent decline in IGABA. 9. The specificity of the decrease in IGABA was assessed by coexpressing the voltage-dependent potassium channel Kv1.4 along with the rho1 receptor in HEK293 cells. The amplitude of the potassium current (IKv1.4) exhibited very little decrement in comparison to IGABA suggesting that the putative GABA receptor internalization was not the consequence of a non-specific membrane retrieval.

Adenosine Triphosphate↗
PubMed1999

Benzodiazepines do not modulate desensitization of recombinant alpha1beta2gamma2 GABA(A) receptors.

Previous studies suggest that diazepam (DZP) increases the desensitization rate of GABA(A) receptors, although this effect could simply be a consequence of the DZP-induced increase in GABA sensitivity rather than a direct modulation of desensitization kinetics. To distinguish these two possibilities, voltage clamp recordings were performed on rat alpha1beta2gamma2 GABA(A) receptors expressed in Xenopus laevis oocytes. Complete GABA concentration-response relationships were obtained in the absence and presence of 1 microM DZP and the observed shift in GABA sensitivity (approximately 2.5-fold) was used to adjust GABA and GABA plus DZP to the same level of activation. In this case, DZP had no significant effect on either the rate of onset or recovery from desensitization. This suggests that the apparent effect of DZP on the rate of desensitization is secondary to the increase in GABA sensitivity and not due to a direct effect on the process of desensitization.

Animals↗
PubMed1999

Allosteric activation mechanism of the alpha 1 beta 2 gamma 2 gamma-aminobutyric acid type A receptor revealed by mutation of the conserved M2 leucine.

A conserved leucine residue in the midpoint of the second transmembrane domain (M2) of the ligand-activated ion channel family has been proposed to play an important role in receptor activation. In this study, we assessed the importance of this leucine in the activation of rat alpha 1 beta 2 gamma 2 GABA receptors expressed in Xenopus laevis oocytes by site-directed mutagenesis and two-electrode voltage clamp. The hydrophobic conserved M2 leucines in alpha1(L263), beta2(L259), and gamma 2(L274) subunits were mutated to the hydrophilic amino acid residue serine and coexpressed in all possible combinations with their wild-type and/or mutant counterparts. The mutation in any one subunit decreased the EC(50) and created spontaneous openings that were blocked by picrotoxin and, surprisingly, by the competitive antagonist bicuculline. The magnitudes of the shifts in GABA EC(50) and picrotoxin IC(50) as well as the degree of spontaneous openings were all correlated with the number of subunits carrying the leucine mutation. Simultaneous mutation of the GABA binding site (beta 2Y157S; increased the EC(50)) and the conserved M2 leucine (beta 2L259S; decreased the EC(50)) produced receptors with the predicted intermediate agonist sensitivity, indicating the two mutations affect binding and gating independently. The results are discussed in light of a proposed allosteric activation mechanism.

Allosteric Regulation↗
PubMed1999

Channel opening locks agonist onto the GABAC receptor.

Determination of the activation mechanism of neurotransmitter-operated ion channels has been hindered by a limited understanding of the relationship between agonist binding and the gating of the integral ion pore. Here we describe a [3H]ligand binding assay that enables us to make repeated binding measurements from the same intact oocyte expressing recombinant human rho 1 GABAC receptors and directly correlate the binding kinetics with electrophysiological measurements. We have determined an association rate for GABA of about 10(5) M-1s-1; this is four orders of magnitude slower than diffusion, indicating GABA has restricted access to its binding site. We also demonstrate that GABA dissociates at two rates. Our data are consistent with the faster rate being the true microscopic dissociation rate of GABA, with the slower rate occurring because the opening of the pore detains agonist release.

Diffusion↗
PubMed1999

Localization of FtsL to the Escherichia coli septal ring.

In Escherichia coli, nine gene products are known to be essential for assembly of the division septum. One of these, FtsL, is a bitopic membrane protein whose precise function is not understood. Here we use fluorescence microscopy to study the subcellular localization of FtsL, both in a wild-type strain and in a merodiploid strain that expresses a GFP-FtsL fusion protein. We show that FtsL localizes to the cell septum where it forms a ring analogous to the cytoplasmic FtsZ ring. FtsL localization is dependent upon the function of FtsZ, FtsA and FtsQ, but not FtsI. In a reverse approach, we use fusions of green fluorescent protein (GFP) to FtsZ, FtsA and ZipA to show that these proteins localize to the division site in an FtsL-independent fashion. We propose that FtsL is a relatively late recruit to the ring structure that mediates septation.

Bacterial Proteins↗
PubMed1999

Longitudinal course and predictors of continuing distress following critical incident exposure in emergency services personnel.

This study examines the longitudinal course and predictors of stress-specific and general symptomatic distress in emergency services personnel. A three-group quasi-experimental design was used to determine the responses of 322 rescue workers to the Loma Prieta earthquake Interstate 880 Freeway collapse and to unrelated control critical incidents. Self-report questionnaires, including measures of incident exposure, peritraumatic dissociation and emotional distress, and current symptoms, were administered 1.9 years (initial) and 3.5 years (follow-up) after the freeway collapse. Despite modest symptom improvement at follow-up, rescue workers were at risk for chronic symptomatic distress after critical incident exposure. Peritraumatic dissociation accounted for significant increments in current posttraumatic stress disorder symptoms, over and above exposure, adjustment, years of experience, locus of control, social support, and general dissociative tendencies. The results suggest that rescue workers, particularly those with more catastrophic exposure and those prone to dissociate at the time of the critical incident, are at risk for chronic symptomatic distress.

Adaptation, Psychological↗
PubMed1999

Localization of FtsI (PBP3) to the septal ring requires its membrane anchor, the Z ring, FtsA, FtsQ, and FtsL.

Assembly of the division septum in bacteria is mediated by several proteins that localize to the division site. One of these, FtsI (also called penicillin-binding protein 3) of Escherichia coli, consists of a short cytoplasmic domain, a single membrane-spanning segment, and a large periplasmic domain that encodes a transpeptidase activity involved in synthesis of septal peptidoglycan. We have constructed a merodiploid strain with a wild-type copy of ftsI at the normal chromosomal locus and a genetic fusion of ftsI to the green fluorescent protein (gfp) at the lambda attachment site. gfp-ftsI was expressed at physiologically appropriate levels under control of a regulatable promoter. Consistent with previous results based on immunofluorescence microscopy GFP-FtsI localized to the division site during the later stages of cell growth and throughout septation. Localization of GFP-FtsI to the cell pole(s) was not observed unless the protein was overproduced about 10-fold. Membrane anchor alterations shown previously to impair division but not membrane insertion or transpeptidase activity were found to interfere with localization of GFP-FtsI to the division site. In contrast, GFP-FtsI localized well in the presence of beta-lactam antibiotics that inhibit the transpeptidase activity of FtsI. Septal localization depended upon every other division protein tested (FtsZ, FtsA, FtsQ, and FtsL). We conclude that FtsI is a late recruit to the division site, and that its localization depends on an intact membrane anchor.

Bacterial Proteins↗
PubMed1999

Septal localization of FtsQ, an essential cell division protein in Escherichia coli.

Septation in Escherichia coli requires several gene products. One of these, FtsQ, is a simple bitopic membrane protein with a short cytoplasmic N terminus, a membrane-spanning segment, and a periplasmic domain. We have constructed a merodiploid strain that expresses both FtsQ and the fusion protein green fluorescent protein (GFP)-FtsQ from single-copy chromosomal genes. The gfp-ftsQ gene complements a null mutation in ftsQ. Fluorescence microscopy revealed that GFP-FtsQ localizes to the division site. Replacing the cytoplasmic and transmembrane domains of FtsQ with alternative membrane anchors did not prevent the localization of the GFP fusion protein, while replacing the periplasmic domain did, suggesting that the periplasmic domain is necessary and sufficient for septal targeting. GFP-FtsQ localization to the septum depended on the cell division proteins FtsZ and FtsA, which are cytoplasmic, but not on FtsL and FtsI, which are bitopic membrane proteins with comparatively large periplasmic domains. In addition, the septal localization of ZipA apparently did not require functional FtsQ. Our results indicate that FtsQ is an intermediate recruit to the division site.

Bacterial Proteins↗
PubMed1998

Substitutions of the highly conserved M2 leucine create spontaneously opening rho1 gamma-aminobutyric acid receptors.

All members of the receptor-operated ion channel family that includes gamma-aminobutyric acid (GABA), glycine, nicotinic acetylcholine, and serotonin type 3 receptors have a conserved leucine near the center of the presumed second membrane-spanning domain. This leucine has been postulated to play a role in the gating of the pore. In this study, we examined the effects of mutating this leucine (L301) on the function of human homomeric rho1 GABA receptors. Oocytes expressing rho1 GABA receptors in which this leucine was substituted with alanine (A), glycine (G), serine (S), threonine (T), valine, or tyrosine, but not isoleucine or phenylalanine, demonstrated larger-than-normal resting conductances in the absence of GABA. This resting conductance had a reversal potential (and shifted reversal potential with chloride substitution) indistinguishable from that of the wild-type rho1 GABA-activated current. This resting conductance was antagonized by picrotoxin and, in the case of the A, G, S, and T substitutions, by GABA itself. Although the rho1 competitive antagonist 3-aminopropyl(methyl)-phosphinic acid did not block the resting conductance, this compound did competitively inhibit the GABA-mediated antagonism of the resting conductance. At higher concentrations, both 3-aminopropyl(methyl)-phosphinic acid and GABA directly activated the A, G, S, and T mutant receptors. Taken together, these data suggest that substitution of this highly conserved leucine with either small or polar residues produced rho1 GABA receptors that can open in the absence of GABA and support the hypothesis that this leucine may play a key role in the gating of the pore.

Animals↗
PubMed1998

Sleep disturbances in the Vietnam generation: findings from a nationally representative sample of male Vietnam veterans.

OBJECTIVE: This study analyzed questionnaire items that address complaints about sleep from the National Vietnam Veterans Readjustment Study, a nationally representative sample of the 3.1 million men and women who served in Vietnam. This study compared the frequency of nightmares and difficulties with sleep onset and sleep maintenance in male Vietnam theater veterans with male Vietnam era veteran and male civilian comparison subjects. It focused on the role of combat exposure, nonsleep posttraumatic stress disorder (PTSD) symptoms, comorbid psychiatric and medical disorder, and substance abuse in accounting for different domains of sleep disturbance. METHOD: The authors undertook an archival analysis of the National Vietnam Veterans Readjustment Study database using correlations and linear statistical models. RESULTS: Frequent nightmares were found exclusively in subjects diagnosed with current PTSD at the time of the survey (15.0%). In the sample of veterans who served in Vietnam (N = 1,167), combat exposure was strongly correlated with frequency of nightmares, moderately correlated with sleep onset insomnia, and weakly correlated with disrupted sleep maintenance. A hierarchical multiple regression analysis showed that in Vietnam theater veterans, 57% of the variance in the frequency of nightmares was accounted for by war zone exposure and non-sleep-related PTSD symptoms. Alcohol abuse, chronic medical illnesses, panic disorder, major depression, and mania did not predict the frequency of nightmares after control for nonsleep PTSD symptoms. CONCLUSIONS: Frequent nightmares appear to be virtually specific for PTSD. The nightmare is the domain of sleep disturbance most related to exposure to war zone traumatic stress.

Combat Disorders↗
PubMed1998

Debriefing of American Red Cross personnel: pilot study on participants' evaluations and case examples from the 1994 Los Angeles earthquake relief operation.

The Multiple Stressor Debriefing (MSD) model was used to debrief 112 American Red Cross workers individually or in groups after their participation in the 1994 Los Angeles earthquake relief effort. Two composite case examples are presented that illustrate individual and group debriefings using the MSD model. A questionnaire which evaluated workers' experience of debriefing, was completed by 95 workers. Results indicated that workers evaluated the debriefings in which they participated positively. In addition, as participant to facilitator ratio increased, workers shared less of their feelings and reactions about the disaster relief operation. These findings, as well as more specific issues about debriefing, are discussed.

Adult↗
PubMed1997

Inactivation of FtsI inhibits constriction of the FtsZ cytokinetic ring and delays the assembly of FtsZ rings at potential division sites.

A universally conserved event in cell division is the formation of a cytokinetic ring at the future site of division. In the bacterium Escherichia coli, this ring is formed by the essential cell division protein FtsZ. We have used immunofluorescence microscopy to show that FtsZ assembles early in the division cycle, suggesting that constriction of the FtsZ ring is regulated and supporting the view that FtsZ serves as a bacterial cytoskeleton. Assembly of FtsZ rings was heterogeneously affected in an ftsI temperature-sensitive mutant grown at the nonpermissive temperature, some filaments displaying a striking defect in FtsZ assembly and others displaying little or no defect. By using low concentrations of the beta-lactams cephalexin and piperacillin to specifically inhibit FtsI (PBP3), an enzyme that synthesizes peptidoglycan at the division septum, we show that FtsZ ring constriction requires the transpeptidase activity of FtsI. Unconstricted FtsZ rings are stably trapped at the midpoint of the cell for several generations after inactivation of FtsI, whereas partially constricted FtsZ rings are less effectively trapped. In addition, FtsZ rings are able to assemble in newborn cells in the presence of cephalexin, suggesting that newborn cells contain a site at which FtsZ can assemble (the nascent division site) and that the transpeptidase activity of FtsI is not required for assembly of FtsZ at these sites. However, aside from this first round of FtsZ ring assembly, very few additional FtsZ rings assemble in the presence of cephalexin, even after several generations of growth. One interpretation of these results is that the transpeptidase activity of FtsI is required, directly or indirectly, for the assembly of nascent division sites and thereby for future assembly of FtsZ rings.

Bacterial Proteins↗
PubMed1997

Bicuculline and gabazine are allosteric inhibitors of channel opening of the GABAA receptor.

Anesthetic drugs are known to interact with GABAA receptors, both to potentiate the effects of low concentrations of GABA and to directly gate open the ion channel in the absence of GABA; however, the site(s) involved in direct gating by these drugs is not known. We have studied the ability of alphaxalone (an anesthetic steroid) and pentobarbital (an anesthetic barbiturate) to directly activate recombinant GABAA receptors containing the alpha 1, beta 2, and gamma 2L subunits. Steroid gating was not affected when either of two mutated beta 2 subunits [beta 2 (Y157S) and beta 2 (Y205S)] are incorporated into the receptors, although these subunits greatly reduce the affinity of GABA binding. These observations indicate that steroid binding and subsequent channel gating do not require these particular residues, as already shown for barbiturates. Bicuculline or gabazine (two competitive antagonists of GABA binding) reduced the currents elicited by alphaxalone and pentobarbital from wild-type GABAA receptors; however, gabazine produced only a partial block of response pentobarbital or alphaxalone, and bicuculline only partially blocked responses to pentobarbital. These observations indicate that the blockers do not compete with alphaxalone or pentobarbital for a single class of sites on the GABAA receptor. Finally, at receptors containing alpha 1 beta 2 (Y157S) gamma 2L subunits, both bicuculline and gabazine showed weak agonist activity and actually potentiated responses to alphaxalone. These observations indicate that the blocking drugs can produce allosteric changes in GABAA receptors, at least those containing this mutated beta 2 subunit. We conclude that the sites for binding steroids and barbiturates do not overlap with the GABA-binding site. Furthermore, neither gabazine nor bicuculline competes for binding at the steroid or barbiturate sites. The data are consistent with a model in which both gabazine and bicuculline act as allosteric inhibitors of channel opening for the GABAA receptor after binding to the GABA-binding site.

Allosteric Regulation↗
PubMed1997

Localization of the Escherichia coli cell division protein Ftsl (PBP3) to the division site and cell pole.

FtsI, also known as penicillin-binding protein 3, is a transpeptidase required for the synthesis of peptidoglycan in the division septum of the bacterium, Escherichia coli. FtsI has been estimated to be present at about 100 molecules per cell, well below the detection limit of immunoelectron microscopy. Here, we confirm the low abundance of FtsI and use immunofluorescence microscopy, a highly sensitive technique, to show that FtsI is localized to the division site during the later stages of cell growth. FtsI was also sometimes observed at the cell pole; polar localization was not anticipated and its significance is not known. We conclude (i) that immunofluorescence microscopy can be used to localize proteins whose abundance is as low as approximately 100 molecules per cell; and (ii) that spatial and temporal regulation of FtsI activity in septum formation is achieved, at least in part, by timed localization of the protein to the division site.

Alkaline Phosphatase↗