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Biomedical subjects

M D Baker

Publications and source records attributed to M D Baker.

At least 55 records · Page 3Linked to original sources
PubMed1998

High efficiency site-specific modification of the chromosomal immunoglobulin locus by gene targeting.

Site-specific modification of the chromosomal immunoglobulin locus by gene targeting is a powerful tool in studying the molecular requirements for immunoglobulin gene structure and function and in the production of engineered antibodies. Here, we describe a two step- integration then excision-gene targeting procedure for introducing planned genetic alterations into the chromosomal immunoglobulin locus. The efficiency of gene targeting with an enhancer-trap vector in which an enhancerless neo and HSV-tk gene were inserted into the vector backbone was compared to that of the corresponding enhancer-positive vector. Both insertion vectors also contained homology to the chromosomal immunoglobulin target locus along with the desired genetic alteration. The first step involved insertion of the transferred vector into the target locus by homologous recombination. An approximately 15-fold enrichment in the frequency of vector insertion was obtained with the enhancer-trap compared to the enhancer-positive vector. The majority of targeted cells (75%) contained a single copy of the vector integrated into the chromosomal immunoglobulin locus. The second step involved excision of the integrated vector by intrachromosomal homologous recombination between the duplicated region of homology that removed the integrated vector, neo and tk genes along with one copy of homologous DNA. Vector excision was very efficient generating G418S, FIAU(R) secondary recombinants at the high rate of approximately 10(-3)/cell generation. In the secondary recombinants, the overall structure of the chromosomal immunoglobulin locus was restored with the desired genetic alteration being present in an expected proportion of the cells.

Animals↗
PubMed1998

Phylogeny of amblyospora (Microsporida: amblyosporidae) and related genera based on small subunit ribosomal DNA data: A possible example of host parasite cospeciation.

Small subunit ribosomal RNA (SSU rRNA) gene sequences were analyzed for six species and four genera of microsporidia from mosquito hosts; Amblyospora stimuli (Aedes stimulans), Amblyospora californica (Culex tarsalis), Amblyospora sp. (Culex salinarius), Edhazardia aedis (Aedes aegypti), Culicosporella lunata (Culex pilosus), and Parathelohania anophelis (Anopheles quadrimaculatus). Comparison of these sequences to those of other microsporidia show that these sequences are longer with the SSU rRNA gene of E. aedis being the longest microsporidia sequenced to date (1447 base pairs). Parsimony, maximum likelihood, and distance methods produced identical trees, suggesting that the above microsporidian taxa, contrary to current classification schemes, form a monophyletic group. Relationships within this group are further supported by high bootstrap and decay analysis values. Based on the molecular analysis, P. anophelis is the most divergent species in this group of mosquito parasites. Amblyospora is paraphyletic with A. californica and Amblyospora sp., forming a sister taxon to a clade composed of E. aedis and A. stimuli. Culicosporella lunata comprises a sister taxon to the Amblyospora/Edhazardia clade. The pattern of host relationships on the tree provides preliminary evidence that the branching pattern seen here may indicate that host-parasite cospeciation is an important mechanism of evolution in this group.

Aedes↗
PubMed1998

Adapalene 0.1% gel for the treatment of acne vulgaris: its superiority compared to tretinoin 0.025% cream in skin tolerance and patient preference.

One hundred patients with acne vulgaris applied adapalene (Differin) 0.1% gel to one side of their face and tretinoin 0.025% cream to the other once a day for 4 weeks; the side of application was determined by randomization code. Patient tolerance (assessed as the side of the face least irritated by drug application) was recorded weekly and patient preference (assessed as the preparation more easily spread, absorbed more quickly, smelled better, felt best on the skin and least greasy to the feel) at completion of the study. The investigator measured skin irritation weekly, scoring erythema, skin dryness, desquamation and burning/stinging on a 10-point scale. After each week of treatment, 64-68% of patients found adapalene 0.1% gel more tolerable than tretinoin 0.025% cream (P < 0.05). At study completion, 65% of patients preferred adapalene 0.1% gel over tretinoin 0.025% cream (P = 0.003). An overall assessment showed adapalene 0.1% gel was significantly less irritating to the skin in terms of producing erythema, dryness, desquamation and burning/stinging, at Visits 2, 3 and 4 (P < 0.02). Thirty-two patients experienced mild to moderately severe adverse events; three had adverse events considered to be drug related (two with skin discomfort; one with skin dryness). One patient stopped using the study drugs because of dry skin. This study showed that a majority of patients preferred adapalene 0.1% gel over tretinoin 0.025% cream and that it caused significantly less skin irritation.

Acne Vulgaris↗
PubMed1998

Adapalene 0.1% gel has low skin irritation potential even when applied immediately after washing.

The purpose of this study was to evaluate the difference, if any, in facial skin tolerance of adapalene 0.1% gel applied immediately after washing, compared to delayed application as recommended for the other topical retinoids: tretinoin and isotretinoin. Twenty-five acne patients with mild to moderate acne vulgaris were included in this intra individual randomized comparison study where adapalene 0.1% gel was applied immediately after washing on one half of the face and 20-30 min after washing on the contralateral half-face, for 22 consecutive days. No difference between the two regimens was detected by the investigator or by 21 of the 22 patients who completed the study. It was concluded that application of adapalene gel 0.1% is well tolerated even when applied immediately after washing.

Acne Vulgaris↗
PubMed1998

Inactivation of macroscopic late Na+ current and characteristics of unitary late Na+ currents in sensory neurons.

Na+ currents in adult rat large dorsal root ganglion neurons were recorded during long duration voltage-clamp steps by patch clamping whole cells and outside-out membrane patches. Na+ current present >60 ms after the onset of a depolarizing pulse (late Na+ current) underwent partial inactivation; it behaved as the sum of three kinetically distinct components, each of which was blocked by nanomolar concentrations of tetrodotoxin. Inactivation of one component (late-1) of the whole cell current reached equilibrium during the first 60 ms; repolarizing to -40 or -50 mV from potentials of -30 mV or more positive gave rise to a characteristic increase in current (tau >/= 5 ms), attributed to removal of inactivation. A second component (late-2) underwent slower inactivation (tau > 80 ms) at potentials more positive than -80 mV, and steady-state inactivation appeared complete at -30 mV. In small membrane patches, bursts of brief openings (gamma = 13-18 pS) were usually recorded. The distribution of burst durations indicated that two populations of channel were present with inactivation rates corresponding to late-1 and late-2 macroscopic currents. The persistent Na+ current in the whole cell that extended to potentials more positive than -30 mV appeared to correspond to sporadic, brief openings that were recorded in patches (mean open time approximately 0.1 ms) over a wide potential range. None of the three types of gating described corresponded to activation/inactivation gating overlap of fast transient currents.

Animals↗
PubMed1997

Effect of fever on capillary refill time.

OBJECTIVE: To assess the effect of fever on capillary refill time in children. DESIGN: Prospective cohort study. SETTING: Tertiary care children's hospital emergency department (ED). PARTICIPANTS: Convenience sample of 234 children age one month to five years presenting to the ED with a complaint of vomiting, diarrhea, or poor oral fluid intake. INTERVENTION: None. MEASUREMENTS: Before any therapy, capillary refill was measured according to a standard protocol. Rectal temperature was measured in children less than three years old, oral temperature in older children. Fluid deficit was calculated as the percentage difference between initial weight and stable weight following treatment. MAIN RESULTS: Among the 80 children with dehydration, defined as a deficit of > or = 5% of body weight, mean capillary refill was 2.0 +/- 1.0 seconds, versus 1.3 +/- 0.5 seconds in the well hydrated group (P < 0.001). Within each group, mean capillary refill time for febrile patients (temperature > or = 38.3 degrees C) was essentially the same as in those without fever. Using a two-second upper limit of normal, prolonged capillary refill had a sensitivity of 0.44 and specificity of 0.94 for diagnosing dehydration; the diagnostic performance did not differ when stratified by presence or absence of fever. CONCLUSIONS: Presence of fever does not have a clinically important effect on capillary refill time in children.

Capillaries↗
PubMed1997

Factors influencing termination of resuscitative efforts in children: a comparison of pediatric emergency medicine and adult emergency medicine physicians.

OBJECTIVES: To examine factors that influence termination of resuscitative efforts (TORE) and compare pediatric emergency medicine (PEM) and general emergency medicine (GEM) physicians regarding TORE in children. DESIGN: Cross-sectional survey. PARTICIPANTS: All physicians board-certified in PEM as of November 1993 and a random sample of board-certified GEM physicians listed in the 1993 American College of Emergency Physicians directory. INTERVENTIONS: Self-administered questionnaires were mailed to participants who were asked about experience providing pediatric cardiopulmonary resuscitation (CPR) and demographic information. We posed a series of management questions eliciting factors that influence TORE decision-making in single context and case scenario format. Specific emphasis was placed on the influence of time and epinephrine dosing. RESULTS: One hundred and sixty (70%) PEM and 127 (62%) GEM responded. These groups differed significantly in years of experience (PEM 8.2, GEM 11.8), urban practice setting (PEM 84%, GEM 32%) and number of pediatric cardiopulmonary resuscitations per year (PEM 10.6, GEM 4.8), P < 0.001 for all. There were no significant differences between groups regarding features pathognomonic of death. PEM were more likely to consider low blood pH and iatrogenic causes of arrest as factors influencing TORE; GEM were more likely to consider co-morbid conditions (P < 0.05 for all). Medians for time estimates of minimum minutes of pulselessness that influence TORE were: PEM 26 to 30 minutes, GEM 31 to 35 minutes for both prehospital and emergency department settings (P < 0.05 for each). Approximately 20% of all respondents did not place a strict limit on time of pulselessness when determining TORE. No difference was observed between groups regarding maximum doses of epinephrine used prior to TORE. However, fewer GEM (50%) than PEM (75%) utilize "high dose" epinephrine according to current Pediatric Advanced Life Support (PALS) guidelines (P < 0.05). PEM physicians were more than two times more likely to terminate resuscitative efforts if return of spontaneous circulation was not achieved by 25 minutes compared to GEM physicians for both prehospital time of pulselessness [odds ratio 2.1, 95% confidence interval (1.01, 4.5)] and emergency department time of pulselessness [odds ratio 2.2, confidence interval (1.1, 4.6)]. CONCLUSIONS: 1) Several laboratory and clinical factors significantly influence physician's decisions regarding TORE; 2) regardless of setting, time of pulselessness does appear to be an influential factor in determining when to terminate resuscitation in children for most physicians; 3) PEM physicians are more likely to terminate resuscitative efforts than are GEM physicians if return of spontaneous circulation is not achieved by 25 minutes; 4) a significant number of PEM and GEM physicians do not use high dose epinephrine in accordance with current PALS recommendations.

Adolescent↗
PubMed1997

Low-threshold, persistent sodium current in rat large dorsal root ganglion neurons in culture.

Dorsal root ganglion neurons from adult rats (> or = 200 g) were maintained in culture for between 1 and 3 days. Membrane currents generated by large neurons (50-75 microns apparent diameter) were recorded with the whole cell patch-clamp technique. Large neurons generated transient Na+ currents and at least two types of inward current that persisted throughout 200-ms voltage-clamp steps to +20 mV. One persistent current activated close to -35 mV (high threshold), whereas in about half of the cells another persistent current began to activate negative to -70 mV (low threshold). The high-threshold persistent current was identified as a Ca2+ current, as previously described in these neurons. The low-threshold current was reversibly suppressed either by replacing external Na+ with tetramethylammonium ions or by reducing external Na+ concentration ([Na+]) and simultaneously raising external [Ca2+]. It was blocked by tetrodotoxin (TTX) with an apparent equilibrium dissociation constant in the single nanomolar range. We conclude that the low-threshold current is a TTX-sensitive, persistent Na+ current. The persistent TTX-sensitive current contributed to steady-state membrane current from at least -70 mV to 0 mV, a wider potential range than predicted by activation-inactivation gating overlap for transient Na+ current. Because of its low threshold and fast activation kinetics, the persistent Na+ current is expected to play an important role in determining membrane excitability.

Animals↗
PubMed1997

Anaphylaxis in children: a 5-year experience.

OBJECTIVES: To identify the causative agents, presenting signs and symptoms, and course of disease in children diagnosed with anaphylaxis. Design. Five-year retrospective chart review. SETTING: Urban children's hospital pediatric emergency department, operating suite, and inpatient units. PARTICIPANTS: Fifty-five cases of anaphylaxis in 50 patients 1 to 19 years of age. INTERVENTIONS: None. RESULTS: The most common inciting agents in this population were latex (27%), food (25%), drugs (16%), and venoms (15%). Thirty-two cases (58%) occurred outside of the hospital, including 3 of 11 severe cases. Nineteen (35%) had histories of prior allergy to the causative agent. Most agent exposures were intravenous (38%), oral (27%), or dermal (20%). The most common systems involved were respiratory (93%), skin (93%), cardiovascular (26%), and neurologic (26%). Features distinguishing the 11 patients requiring intensive care included latex agents (45%), nonenteral route of exposure (91%), and presence of cardiovascular symptoms (45%). Of the 17 patients with known past anaphylaxis, only 5 had epinephrine self-administration devices available, and 3 had used them. CONCLUSIONS: (1) Most patients with anaphylaxis present with skin or respiratory symptoms. (2) Severely ill children more commonly have nonenteral and/or latex exposures that occur in the hospital. (3) Most children with anaphylaxis have no stated histories of prior reaction to the causative agent. (4) Those patients who have had past episodes of anaphylaxis infrequently have epinephrine self-administration devices available for use.

Adolescent↗
PubMed1997

Effect of desonide ointment, 0.05%, on the hypothalamic-pituitary-adrenal axis of children with atopic dermatitis.

Desonide ointment has demonstrated a good safety and efficacy profile during the many years it has been used in treating dermatoses. However, there have been no controlled clinical trials to evaluate its systemic safety when used in treating children. Suppression of the hypothalamic-pituitary-adrenal (HPA) axis can occur after repeated application of topical corticosteroids. In general, the degree of suppression of the HPA axis function is related to the daily dosage of steroid given, the duration of its administration, the extent of body surface covered, and the potency of the corticosteroid. This study sought to determine the comparative effects of 0.05 percent desonide and 2.5 percent hydrocortisone ointments on the HPA axis of children with atopic dermatitis. There was no suppression of early morning cortisol in either treatment group. The ACTH-stimulated mean cortisol values after four weeks of treatment were not significantly different from the baseline values for either treatment group. We conclude that neither 0.05 percent desonide ointment nor 2.5 percent hydrocortisone ointment compromised the HPA axis of children with atopic dermatitis treated topically for four weeks.

Administration, Topical↗
PubMed1996

Characteristics of type I and type II K+ channels in rabbit cultured Schwann cells.

1. Voltage-dependent K+ currents were studied in rabbit Schwann cells cultured from neonatal sciatic nerve and from the lumbar or sacral spinal roots of 10-day-old animals. 2. Whole-cell K+ currents, evoked in response to depolarizing voltage-clamp steps, were categorized as type I or type II on the basis of their apparent threshold and activation kinetics. In the presence of a quasi-physiological [K+] gradient, the magnitude of the fully activated type I current varied linearly with membrane potential, whereas type II current always gave rise to a curved and outwardly rectifying current-membrane potential (I-E) relation. 3. Type II whole-cell currents, obtained with long duration voltage-clamp steps (> or = 1 s), have an apparent threshold for activation close to -40 mV. Type II current inactivated slowly, and apparently to completion. The current is more than 90% inactivated over 5 s at 0 mV (time consant of inactivation, tau h, approximately 2 s, 20-22 degrees C). Type I current, which activates at close to -60 mV, inactivated at about half this rate at the same potential, assuming that inactivation also proceeds to completion. 4. Type I whole-cell currents were reversibly blocked by superfused beta-bungarotoxin (beta-BuTX; apparent KD = 46 nM). beta-BuTX did not appear to reduce type II whole-cell currents at concentrations up to 500 nM. 5. In outside-out patches, the type I channel had an almost linear I-E relation over the potential range -60 to +60 mV with a quasi-physiological [K+] gradient. A best linear fit gave a single-channel conductance of 12 pS under these conditions. In symmetrical 170 mM K+, type I channels had a single-channel conductance of 30 pS over the same potential range. 6. More slowly activating type II single-channel currents were also recorded in inside-out patches. With symmetrical 170 mM K+, the major conductance level was close to 9.0 pS. With a quasi-physiological [K+] gradient, type II single channels exhibit outward rectification that is reasonably well described by the Goldman-Hodgkin-Katz current equation. 7. In the presence of 2 nM externally superfused alpha-dendrotoxin (alpha-DTX), or 50 nM superfused beta-BuTX, unitary currents were recorded (outside-out patches, -60 or -50 mV) that were smaller than control type I currents. Virtually all transitions in the presence of 50 nM beta-BuTX were at one-third of the control current level. The currents did not conform to the characteristics of type II. 8. The electrophysiological and pharmacological characteristics of the type I channel strongly suggest that it is a member of the mammalian K+ channel subfamily of Shaker homologues, most similar to the homomultimeric Kv1.1 translation product. The type II channel may be a member of the mammalian Shab subfamily. 9. Possible roles for Na+ channels and type I K+ channels in the Schwann cell are discussed.

Animals↗
PubMed1996

Use of racemic epinephrine, dexamethasone, and mist in the outpatient management of croup.

This study aims to determine whether a subpopulation of children with croup, given mist and dexamethasone, can be treated with nebulized racemic epinephrine and safely discharged after observation in the emergency department. A prospective study was designed, enrolling children aged three months to six years with a clinical diagnosis of croup. Croup scores were assigned on arrival, after 30 minutes of saline mist, and 30, 120, and 240 minutes after nebulized racemic epinephrine. All children received mist; those with a croup score > 3 after mist were given nebulized racemic epinephrine. All patients received intramuscular dexamethasone. Patients were discharged if they were significantly improved after four hours of observation. Phone follow-up occurred 24 to 48 hours after discharge. Sixty children received racemic epinephrine for croup. The median croup score on arrival was 5, and there was no difference in arrival croup score by disposition. The two-hour croup score was significantly higher for admitted patients (P < 0.05 by the Mann-Whitney U test). Forty children (66%) were discharged after nebulized racemic epinephrine and four hours of observation. No patients returned to the emergency department within 24 hours for further treatment. Two patients could not be contacted. The 95% confidence interval for 0/38 patients with a negative outcome is (0-9.3%). We conclude that children with croup treated with dexamethasone and mist, receiving one nebulized racemic epinephrine treatment, can be discharged after a four-hour period of observation if they appear clinically well to an experienced physician, and if close follow-up can be established.

Ambulatory Care↗
PubMed1996

A microsporidian isolated from an AIDS patient corresponds to Encephalitozoon cuniculi III, originally isolated from domestic dogs.

The ribosomal DNA internal transcribed spacer (ITS) region of a recently cultured human Encephalitozoon cuniculi isolate was analyzed by gene amplification and DNA sequencing. Restriction endonuclease digestion (FokI) and double-stranded DNA heteroduplex mobility shift analysis were performed to determine their utility for strain differentiation. The human E. cuniculi isolate was identical to E. cuniculi III, which had been isolated only from domestic dogs until now. The patient providing the isolate owned a pet dog, but no microsporidia were detected in the pet's urine.

AIDS-Related Opportunistic Infections↗
PubMed1996

Requirements for ectopic homologous recombination in mammalian somatic cells.

Ectopic recombination occurs between DNA sequences that are not in equivalent positions on homologous chromosomes and has beneficial as well as potentially deleterious consequences for the eukaryotic genome. In the present study, we have examined ectopic recombination in mammalian somatic (murine hybridoma) cells in which a deletion in the mu gene constant (Cmu) region of the endogenous chromosomal immunoglobulin mu gene is corrected by using as a donor an ectopic wild-type Cmu region. Ectopic recombination restores normal immunoglobulin M production in hybridomas. We show that (i) chromosomal mu gene deletions of 600 bp and 4 kb are corrected less efficiently than a deletion of only 2 bp, (ii) the minimum amount of homology required to mediate ectopic recombination is between 1.9 and 4.3 kb, (iii) the frequency of ectopic recombination does not depend on donor copy number, and (iv) the frequency of ectopic recombination in hybridoma lines in which the donor and recipient Cmu regions are physically connected to each other on the same chromosome can be as much as 4 orders of magnitude higher than it is for the same sequences located on homologous or nonhomologous chromosomes. The results are discussed in terms of a model for ectopic recombination in mammalian somatic cells in which the scanning mechanism that is used to locate a homologous partner operates preferentially in cis.

Animals↗
PubMed1996

Pneumothorax ex vacuo.

Pneumothorax ex vacuo is a little-known complication of lobar collapse. In this condition, acute bronchial obstruction from mucous plugs, aspirated foreign bodies, or malpositioned endotracheal tubes causes acute lobar collapse and a marked increase in negative intrapleural pressure around the collapsed lobe. As a result, gas is drawn into the pleural space around the collapsed lobe while the seal between the visceral and parietal pleura of the adjacent lobe or lobes remains intact. The pneumothorax spontaneously resolves when the bronchial obstruction is relieved and the lobe reexpands. Recognition of pneumothorax ex vacuo is crucial in directing treatment to relieve the bronchial obstruction rather than inserting a chest tube into the pleural space.

Adolescent↗
PubMed1995

Interchromosomal recombination is suppressed in mammalian somatic cells.

Homologous recombination occurs intrachromosomally as well as interchromosomally, both in mitotic (somatic) cells as well as meiotically in the germline. These different processes can serve very different purposes in maintaining the integrity of the organism and in enhancing diversity in the species. As shown here, comparison of the frequencies of intra- and interchromosomal recombination in meiotic and mitotic cells of both mouse and yeast argues that interchromosomal recombination is particularly low in mitotic cells of metazoan organisms. This result in turn suggests that the recombination machinery of metazoa might be organized to avoid the deleterious effects of homozygotization in somatic cells while still deriving the benefits of species diversification and of DNA repair.

Animals↗