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Biomedical subjects

J R Thomas

Publications and source records attributed to J R Thomas.

At least 127 records · Page 7Linked to original sources
PubMed1991

Structural characterization of a novel glycosyl-phosphatidylinositol from the protozoan Tetrahymena mimbres.

A glycolipid metabolically labelled with [14C]GlcN was isolated from the free-living protozoan Tetrahymena mimbres. The glycolipid was sensitive to a bacterial phosphatidylinositol-specific phospholipase C, and the headgroup was shown to contain a phosphorylated Man alpha 1-2Man alpha 1-4Man alpha 1-4GlcN glycan. The Tetrahymena glycolipid is structurally unique among the glycosylphosphatidylinositols that have so far been characterized, including those from several protozoan parasites of humans.

Animals↗
PubMed1991

Rapid intraoperative tissue expansion for closure of facial defects.

Rapid intraoperative tissue expansion (RITE) has been shown to have definite applicability to reconstruction in the head and neck. However, widespread use of this modality has yet to be adopted by the otolaryngologic community. Believing that RITE might offer some advantages in the reconstruction of soft-tissue facial defects following Mohs micrographic surgery for cutaneous malignant neoplasms, we evaluated 30 consecutive patients referred for cosmetic reconstruction after Mohs micrographic surgery for the use of RITE. Eight patients were selected and underwent reconstruction using a total of 10 tissue expanders. Herein, we describe our experience with this initial series as well as some background and future applications of RITE.

Adult↗
PubMed1991

Thermal stress modulates temporal patterns of responding on a multiple DRL-FR schedule.

To investigate temporal changes in behavior induced by moderate cold temperatures, rats performing on a multiple differential-reinforcement-of-low-rate (DRL) fixed-ratio (FR) schedule were exposed to ambient temperatures of 2, 8, 16, and 24 degrees C. DRL response rates markedly increased with decreasing cold temperatures, while FR response rates remained unchanged. In addition, as ambient temperatures decreased, the interresponse time (IRT) distribution of DRL responses shifted toward shorter times and short IRT bursts increased. Compared with cold effects, exposure to 38 degrees C heat induced decreases in both DRL and FR response rates which were associated with increases in long IRTs. Decreases in reinforcement frequency was associated only with the DRL schedule in cold, and with both DRL and FR schedules during heat exposures. The distinct effects of cold and heat on both DRL and FR responding suggest that the increases in DRL response rates and shifts in IRT distribution are unique to cold, and are not due to general effects of nonspecific thermal change in the ambient environment.

Animals↗
PubMed1991

Hippocampal and body temperature changes in rats during delayed matching-to-sample performance in a cold environment.

In order to study the effects of temperature changes induced by cold stress on working memory, telemetry thermistor probes were implanted into the hippocampal region of the brain and into the peritoneal cavity of rats. Temperatures in these regions were monitored while rats performed on a delayed matching-to-sample (DMTS) task at ambient temperatures of 23 degrees C and 2 degrees C. Matching accuracy was significantly decreased during exposure to 2 degrees C, indicating a marked impairment of short-term or working memory. Temperature in the hippocampus increased 2 degrees C during exposure to 23 degrees C, but only 1 degrees C when the environmental temperature was 2 degrees C. Body temperature showed a similar but less pronounced pattern in that cold exposure attenuated the increase in temperature observed when animals performed the DMTS task. These results suggest that cold-induced impairment of working memory may be associated with subtle temperature changes in the brain.

Animals↗
PubMed1991

Neuropeptide-Y both improves and impairs delayed matching-to-sample performance in rats.

Neuropeptide-Y (NPY) was administered intracerebroventricularly to rats performing on delayed matching-to-sample (DMTS) to determine if NPY modulates short-term (working) memory. Rats administered saline demonstrated a characteristic DMTS delay gradient in which accuracy decreased as the delay interval between sample and comparison stimuli increased from 2 to 8 to 16 seconds. At 8- and 16-second delays, low doses of NPY (0.25 and 0.5 nmol/kg) increased matching accuracy. As doses increased from 1 to 16 nmol/kg, accuracy decreased in a dose- and delay-dependent manner. NPY effects were specific to working memory, since NPY did not affect accuracy of responses to the sample stimulus (reference memory). At higher doses, a greater decline in accuracy occurred when the correct stimulus was on the opposite side from the response on the previous trial compared to accuracy when the previous response was on the same side. These data show NPY may both improve and impair accuracy on DMTS and that some portion of impairment is due to proactive interference resulting from previous trials.

Animals↗
PubMed1991

Cold-induced impairment of delayed matching in rats.

Exposure to moderate, nonhypothermic cold temperature has been reported to affect a variety of behavioral and neural functions. To elucidate the effects of mild cold stress on short-term (working) memory, Long-Evans rats were exposed to an ambient temperature of either 2 degrees or 23 degrees C while performing a delayed matching task. At the beginning of each trial, rats were required to respond on one of two levers cued by a light. Following a delay of 2, 8, or 16 s, a response on the lever previously cued produced food reinforcement. Relative to performance at 23 degrees C, exposure to 2 degrees C occasioned no change in matching accuracy at the 2-s delay, a modest decrement at the 8-s delay, and a larger decrement at the 16-s delay. The cold exposure did not decrease colonic temperature. In addition to accuracy decrements, matching response times were consistently shorter during cold exposures. Cold-induced impairments were absent during removal of the memory component from the task, indicating the observed cold effects on memory were not due to impaired attentional, sensory, or motor processes. These data suggest that mild cold stress may impair active maintenance of information in working memory but not processes related to reference memory.

Animals↗
PubMed1991

Does self-efficacy predict performance in experienced weightlifters?

Previous studies that have examined self-efficacy-performance relationships have used novice performers. It is unclear if these findings would generalize to "experienced" performers. Based on Bandura's self-efficacy theory, this study was designed to investigate (a) the effects of false information feedback on self-efficacy beliefs and subsequent weightlifting performance, and (b) whether self-efficacy or past performance is most related to subsequent weightlifting performance. Experienced weightlifters engaged in six performance sessions, each consisting of a one-repetition-maximum bench press. Male subjects (N = 36) were randomly assigned to one of three treatment groups: accurate performance information, false information that they lifted more than their actual lift, or false information that they lifted less than their actual lift. Before each session, subjects indicated the amount of weight they were 100%, 75%, and 50% confident they could lift. Results replicated existing research findings regarding deception and performance; false positive feedback increased future bench press performance. In addition, results indicated that past weightlifting performance accounted for nearly all of the variance in subsequent performance. This finding is discussed in light of the difficulty in extending the predictions of self-efficacy theory to sport settings where athletes have gained experience by undergoing repeated training trials.

Adult↗
PubMed1991

Single dose pharmacokinetics of perindopril and its metabolites in hypertensive patients with various degrees of renal insufficiency.

1 Perindopril is a prodrug which is hydrolysed in vivo to the active metabolite perindoprilat, an angiotensin-converting enzyme inhibitor. Perindoprilat glucuronide is also found in plasma. 2 The pharmacokinetics of perindopril and its metabolites were studied after administration of a single 4 mg dose to hypertensive patients with various degrees of renal failure. 3 The absorption and elimination of perindopril were not influenced by the degree of renal failure. 4 The mean area under the serum concentration-time curve of the active metabolite perindoprilat increased from 93 ng ml-1 h in subjects with normal renal function to 1106 ng ml-1 in patients with severe renal failure, whereas its half-life varied from 5.0 to 27.4 h. 5 In the same subjects, the mean area under the curve of perindoprilat glucuronide increased from 78 to 513 ng ml-1 h, while its half-life varied from 1.8 h to 7.7 h. 6 Perindopril, perindoprilat, and perindoprilat glucuronide were dialysable. 7 The extent and duration of serum angiotensin-converting enzyme inhibition was augmented in renal failure. The mean area under the inhibition time curve (extrapolated to infinity) increased from 2490%.h in subjects with normal renal function to 42241 %.h in patients with severe renal impairment. The half-life of inhibition varied from 12.1 h to 100.4 h. This effect of renal failure on the pharmacodynamics of perindoprilat was more pronounced than its influence on perindoprilat kinetics. 8 In view of the important influence of renal impairment on the elimination and action of the active substance perindoprilat, a dosage reduction of perindopril is proposed in in patients with renal failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Human choice on concurrent variable-interval variable-ratio schedules.

Each of 5 adult male humans sat in a 4 degrees C room where they could warm themselves by illuminating six heat lamps for 10-second periods according to a concurrent variable-interval variable-ratio schedule. Left-button presses on a response panel switched between the schedules and started a 2-second changeover delay. Right-button presses illuminated the heat lamps if assigned by the associated schedule and if the changeover delay had timed out. Panel lights identified the schedule in effect and each effective right-button press. A discrimination procedure--either a multiple variable-interval variable-ratio schedule or the presentation of each schedule individually on alternate days--preceded exposure to the choice procedure for some subjects. For subjects not exposed to a discrimination procedure prior to exposure to choice, or if such exposure failed to result in higher rates to the ratio than to the interval schedule, relative response rates matched relative reinforcement rates. However, if subjects responded at higher rates to the ratio schedule than to the interval schedule during a prior discrimination procedure, relative rates on a subsequent choice procedure deviated from matching in the direction of reinforcement-rate maximizing. In eight of 11 conditions, choice appeared to be governed by maximizing processes. In all cases, human concurrent ratio-interval performances differed from those of nonhumans in that matching was never obtained with local ratio-interval rate differences.

Adult↗
PubMed1990

Structures of the N-linked oligosaccharides of Gp63, the major surface glycoprotein, from Leishmania mexicana amazonensis.

The extent of protein N-glycosylation in Leishmania mexicana amazonensis has been proposed to be a factor in the virulence of the parasite. The N-linked oligosaccharides of gp63, the major surface glycoprotein of L. mexicana amazonensis, were characterized after their release by hydrazinolysis, re-N-acetylation, and reduction with NaB3H4. High voltage paper electrophoresis of the reduced oligosaccharides revealed only neutral species. Gel-permeation chromatography on Bio-Gel P-4 yielded four fractions, and the oligosaccharides present were structurally characterized by sequential exoglycosidase digestion, fragmentation by acetolysis, and methylation analysis. Four major structures were found and were biantennary oligomannose type with compositions of Glc1Man6GlcNAc2 (La), Man6GlcNAc2 (Lb), Man5GlcNAc2 (Lc), and Man4GlcNAc2 (Ld). The largest oligosaccharide (La) was shown to contain a terminal glucopyranosyl residue on the alpha (1----3) arm. The biantennary oligomannose structures (Lb and Lc) and the glucosylated structure Glc1Man6GlcNAc2 (La) have not previously been reported as a component of a mature glycoprotein from any source.

Animals↗
PubMed1990

Structure, biosynthesis, and function of glycosylphosphatidylinositols.

The last few years have witnessed an explosion in our knowledge of GPI membrane anchors and related glycolipids and molecules where structure details are available, as illustrated in Figure 2. There is now sufficient information on a handful of these molecules to allow a detailed comparison of their chemical structures. Despite a common structural theme, i.e., the presence of mannoglucosaminyl-PI, a great deal of diversity exists in both the glycan structures and the glycerol-linked aliphatic substituents. The complexities of the structures clearly show that a multitechnique approach is required in the elucidation of their structures. The anticipated publication of more structures from a wider range of organisms may reveal even greater diversity, as well as suggesting possible biosynthetic pathways. The details of a potential biosynthetic pathway in T. brucei are becoming apparent, but confirmation of its importance awaits the isolation and characterization of the enzymes involved. Leishmania, in which LPG, GPIs, GIPLs, and GPI membrane anchors are produced, may also provide an interesting system for biosynthetic studies. The recent description of a GPI biosynthetic system in yeast may provide the crucial breakthroughs necessary in unraveling the enzymes and sugar donors involved in the biosynthetic pathway and possibly the role of the GPI membrane anchor in the function of proteins containing these moieties. Knowledge of the solution structure (conformation), in addition to the complete chemical structure, of the T. brucei VSG anchor has led to speculation that the glycan fulfills a space-filling role in the VSG coat. Many other possible roles of GPI membrane anchors have been suggested, including the shedding and turnover of membrane proteins, signal transduction, and intracellular targeting. Nevertheless, the only function of GPIs that we can so far be certain of is that they anchor proteins or polysaccharide to a membrane. Regardless of the roles GPIs may or may not ultimately be shown to play, the fact that such a widely occurring structure has only recently been characterized serves as a reminder of the incompleteness of our knowledge of biological phenomena and the constant possibility of finding novel molecules in obvious places.

Animals↗
PubMed1990

Submental W-plasty for correction of 'turkey gobbler' deformities.

There are many causes and types of submental contour deformities. One such deformity called a turkey gobbler, is caused by an excess of flaccid submental skin and as an isolated defect is seen more commonly in men. We have found that skin excision and a running submental W-plasty for correction of this deformity yields a superior cosmetic result with excellent camouflage of the submental scar. Two cases are illustrated.

Chin↗
PubMed1990

Feruloylated xyloglucan and p-coumaroyl arabinoxylan oligosaccharides from bamboo shoot cell-walls.

A novel feruloylated xyloglucan disaccharide and p-coumaroylated arabinoxylan trisaccharide were isolated from cell walls of growing bamboo (Phyllostachys edulis) shoots. On the basis of chemical and spectral data, their structures were determined to be O-(4-O-trans-feruloyl-alpha-D- xylopyranosyl)-(1----6)-D-glucopyranose and O-[5-O-(trans-p-coumaroyl)- alpha-L-arabinofuranosyl]-(1----3)-O-beta-D-xylopyranosyl-(1----4)-D- xylopyranose, respectively. This is the first reported evidence of a phenolic acid covalently associated with the cell wall hemicellulose, xyloglucan.

Carbohydrate Conformation↗