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Biomedical subjects

G Li

Publications and source records attributed to G Li.

At least 793 records · Page 44Linked to original sources
PubMed1995

Correlation of axon projections and peptide immunoreactivity in mesocerebral neurons of the snail Helix aspersa.

The purpose of this investigation was to elucidate the organization of efferent neurons in the mesocerebrum of a terrestrial snail. The mesocerebrum is one of three regions, or lobes, that can be identified by gross inspection. Previous studies have indicated a possible function for the mesocerebrum in the control of mating behavior. We used both anterograde and retrograde tracing methods to determine the axon projections of mesocerebral neurons. Virtually all the neurons (96%) send an axon into the cerebropedal connective nerve, and about 25% of these fibers continue into the nervus cutaneous pedalis primus dexter, which innervates the dart sac. Many neurons have additional axon branches in other nerves, especially the penial nerve, which receives projections from about 25% of mesocerebral cells. Neurons that are backfilled from the nervus cutaneus pedalis primus dexter are predominantly immunoreactive for FMRF amide, whereas neurons that are backfilled from the penial nerve are predominately immunoreactive for APGWamide. These results suggest a functional association between FMRFamide and dart shooting on the one hand, and between APGWamide and penial eversion on the other. Some cells contain both APGWamide and FMRFamide; these cells may have dual projections in both the penial nerve and the nervus cutaneous pedalis primus dexter.

Animals↗
PubMed1995

A regulatory role for ARF6 in receptor-mediated endocytosis.

Adenosine diphosphate-ribosylation factor 6 (ARF6), ARF6 mutants, and ARF1 were transiently expressed in Chinese hamster ovary cells, and the effects on receptor-mediated endocytosis were assessed. Overexpressed ARF6 localized to the cell periphery and led to a redistribution of transferrin receptors to the cell surface and a decrease in the rate of uptake of transferrin. Similar results were obtained when a mutant defective in guanosine triphosphate hydrolysis was expressed. Expression of a dominant negative mutant, ARF6(T27N), resulted in an intracellular distribution of transferrin receptors and an inhibition of transferrin recycling to the cell surface. In contrast, overexpression of ARF1 had little or no effect on these parameters of endocytosis.

ADP-Ribosylation Factor 1↗
PubMed1995

Myristoylation cannot functionally replace the isoprenylation of Rab5.

C-terminal isoprenylation is necessary for the small GTPase Rab5 to associate with early endosomes and to exert its regulatory function in endocytosis. In this study, we tested whether Rab5 could retain its membrane association and biological function if the isoprenylation were replaced by another type of lipid modification (myristoylation). Rab5 mutants were constructed that contained both isoprenylation and myristoylation (Gag-Rab5), myristoylation only (Gag-Rab5 delta C4), and neither of the modifications (Rab5 delta C4), respectively. These mutants and wild-type Rab5 were expressed, via a Sindbis virus vector, in cultured BHK-21 cells and their membrane association and biological activity (stimulation of endocytosis) were examined. Wild-type Rab5 was isoprenylated, membrane associated, and biologically active. With additional myristoylation, Gag-Rab5 showed increased affinity for membranes but decreased biological activity. Rab5 delta C4 contained no lipid modifications, failed to associate with membranes, and had no biological activity. With myristoylation (Gag-Rab5 delta C4), there was a significant increase in membrane association (approximately 30%). However, this increased membrane association did not result in any recovery of Rab5 activity. In light of these data, we conclude that N-terminal myristoylation cannot functionally replace the C-terminal isoprenylation of Rab5. Furthermore, myristoylation of Rab5 (Gag-Rab5) interferes with its normal function.

Animals↗
PubMed1995

Peripheral generators of the vestibular evoked potentials in the cat.

OBJECTIVES: The contributions of each of the vertical semicircular canals (SCCs) and otoliths to the short-latency vestibular evoked potentials in response to angular acceleration impulses were studied in the cat. DESIGN: The experiments were conducted on unilateral labyrinthectomized cats. Vestibular activation was achieved by delivering angular acceleration impulses to the animal's head, held in the position presumed to be optimal for maximal stimulation of either the anterior or the posterior SCCs before and after obliteration of the SCC studied, and before and after obliteration of the other SCCs and ablation of the maculae. INTERVENTIONS: Unilateral labyrinthectomy, obliteration of the SCCs, and ablation of the otoliths and section of the commissural vestibular fibers in the brain stem with histologic confirmation were carried out in the experiments. RESULTS: Following selective obliteration of either the anterior or the posterior SCC of the remaining ear and stimulation in the presumed optimal plane of the obliterated canal, the early prominent waves (P1 and P2) disappeared, leaving only much smaller-amplitude waves. These were severely depressed after ablation of the maculae. On the other hand, the vestibular evoked potentials in response to excitatory stimuli were not affected by obliteration of the other two SCCs and ablation of the maculae. CONCLUSION: These results indicate that when the head is stimulated in the optimal plane of each of the SCCs, the vestibular evoked potentials are generated mainly by the cristae ampullaris being stimulated, while the otoliths contribute smaller responses.

Animals↗
PubMed1995

The phenylalanine ammonia-lyase gene family in Arabidopsis thaliana.

Phenylpropanoid derivatives are a complex class of secondary metabolites that have many important roles in plants during normal growth and in responses to environmental stress. Phenylalanine ammonialyase (PAL) catalyzes the first step in the biosynthesis of phenylpropanoids, and is usually encoded by a multi-gene family. Genomic clones for three Arabidopsis thaliana PAL genes containing the entire protein-coding region and upstream and downstream sequences have been obtained and completely sequenced. Two A. thaliana PAL genes (PAL1 and PAL2) are structurally similar to PAL genes that have been cloned from other plant species, with a single intron at a conserved position, and a long highly conserved second exon. Previously identified promoter motifs plus several additional sequence motifs were found in the promoter regions of PAL1 and PAL2. Expression of PAL1 and PAL2 is both qualitatively and quantitatively similar in different plant organs and under various inductive conditions. A third A. thaliana PAL gene, PAL3, differs significantly from PAL1 and PAL2 and other sequenced plant PAL genes. PAL3 contains an additional intron, and its deduced amino acid sequence is less homologous to other PAL proteins. The PAL3 promoter region lacks several sequence motifs conserved between A. thaliana PAL1 and PAL2, as well as motifs described in other genes involved in phenylpropanoid metabolism. A. thaliana PAL3 was expressed at very low levels under the conditions examined.

Arabidopsis↗
PubMed1995

Factors affecting posture for machine sewing tasks: the need for changes in sewing machine design.

Sewing machinists suffer from musculoskeletal problems, which have been attributed to poor working postures as well as to the repetitive hand and arm movements. Their posture is constrained by both the visual and the manual aspects of the task, and the design of the sewing machine and table have a considerable influence on the posture adopted. The potential for improvement of industrial sewing machines was investigated in a study of the effects of two design parameters (table inclination and view of the needle). It was shown that both trunk posture and head/neck flexion could be improved significantly by altering these design parameters. Trunk posture was found to be strongly related to the manual aspects of the task, and could be improved by altering the working positions for the arm. Head posture was most influenced by the view of the task/needle and could be improved by improving the visual condition for the task.

Journal Article↗
PubMed1995

Agmatine, the bacterial amine, is widely distributed in mammalian tissues.

We sought to determine whether agmatine (decarboxylated arginine), a bacterial product recently discovered for the first time in mammalian brain, was contained in other organs. A method was developed for isolation of agmatine from tissue and detection by RP-HPLC following solid-liquid extraction and derivatization with o-phthalaldehyde and mercaptoethanol. Recovery was about 80% and the limit of fluorometric detection was about 10 pg on column. In male Sprague-Dawley rats agmatine was unevenly and widely distributed in many tissues confirming its presence in mammals. The highest concentration (approximately 71 ng/mg net weight) was found in stomach, with aorta and small intestine next, followed by smaller levels in spleen, adrenal, aorta, and skeletal muscle and brain. Serum concentrations were high. Agmatine in male Long Evans rats of 3, 12, and 24 months of age demonstrated similar but not identical tissue distribution without any effect of aging. Since agmatine binds to alpha 2-adrenergic and imidazoline receptors, is bioactive in a number of tissues, is contained in neurons and is found in serum and tissues, the findings are consistent with a potential role for agmatine as a neurotransmitter and/or hormone. It also raises the possibility that agmatine may, as in bacteria, serve as a polyamine precursor along metabolic pathways previously not detected in mammals.

Agmatine↗
PubMed1995

The interaction effect of bereavement and sex on the risk of suicide in the elderly: an historical cohort study.

To examine the hypothesis that the increased risk of suicide for the widowed elderly is dependent of sex, suicide mortality in a cohort of 6266 white married and 3486 white widowed persons aged 60 yr or older in 1963 was evaluated based on a 12-yr follow-up survey in Washington County, MD. Death rates from suicide were 28.7 per 100,000 person-yr for the married, and 40.4 for the widowed. An interaction effect was found between bereavement and sex: the risk of suicide for widowed men was 3.3 times as high as for married men (95% confidence interval, 1.3-8.3), but the risk of suicide for widowed women did not increase compared with that for married women (relative risk 1.0, 95% CI 0.3-3.1). Adjustment for social and behavioral factors did not change the interaction effect to any meaningful extent. The results suggest that widowed men should be one of the prior targets of suicide prevention and intervention programs for the elderly.

Aged↗
PubMed1995

Detection of putative periodontal pathogens in subgingival specimens by 16S ribosomal DNA amplification with the polymerase chain reaction.

The utility of the 16S ribosomal RNA-based polymerase chain reaction (PCR) for detection of Actinobacillus actinomycetemcomitans, Bacteroides forsythus, Campylobacter rectus, Eikenella corrodens, Porphyromonas gingivalis, Prevotella intermedia, and Treponema denticola was examined and compared with that of anaerobic culture. Primer pairs consisting of 20-27 nucleotides amplified 404- to 688-bp regions of 16S ribosomal RNA genes of these organisms. This method had a lower detection limit of 50 target cells in a background of 10(7) cells. Its specificity for B. forsythus, P. gingivalis, and T. denticola seemed high. The primers for A. actinomycetemcomitans, C. rectus, and P. intermedia cross-reacted with some closely related species but did not reveal amplification products in tests with more distantly related organisms. The primers for E. corrodens did not seem to cross-react with oral organisms. This PCR technique was sensitive, reproducible, and easy to perform. PCR-based amplification may prove valuable for the detection of some periodontal pathogens in crude subgingival specimens.

Adult↗
PubMed1995

Experimental study of early diagnosis and treatment of fat embolism syndrome.

An experimental animal model has been established using i.v. fat injection to mimic fat embolism syndrome (FES). Fourteen healthy mongrel dogs who were administered 0.7 ml/kg of fluid marrow fat obtained from the long bone marrow cavity of mongrel dogs were divided into control and therapeutic groups. The therapeutic group (n = 7) was given dexamethasone (1.0 mg/kg) and repeated every 6 h i.v. During 48 h of observation, blood gas analysis and frozen sections were performed on blood samples collected from the pulmonary vessels by a floating catheter and from a peripheral vein at different time intervals. The frozen sections were stained with Oil Red O. Positive results were seen 2 h after fat injection in both pulmonary and peripheral blood samples of both control and therapeutic groups. By computer image analysis, the average median number of fat droplets per section and the average median diameter of fat droplets in pulmonary blood of the control group were found to be significantly higher and larger than were those of the therapeutic group. The average median number and diameter of fat droplets in pulmonary blood were significantly higher and larger than were those of peripheral blood in both control and therapeutic groups. These findings correlated well with blood gas changes and the clinical appearance of the experimental animals. The fat droplets from pulmonary or peripheral blood as demonstrated by Oil Red O staining in combination with blood gases changes [PaO2 < 7.99 KPa, difference between the alveolar and arterial oxygen tension (P(A - a)O2) > 6.09 KPa] may be a rapid method for screening of an earlier diagnosis of FES.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Factors related to the presence of head injury in bicycle-related pediatric trauma patients.

Using data from the National Pediatric Trauma Registry, this study examined the characteristics of bicycle-related head injury, factors related to the presence of head injury, and different outcomes of head injury up to the time of discharge. Of the 2,333 patients ages 0 to 14 years who were admitted to trauma centers because of bicycle-related injury during 1989 through 1992, more than one-half (54%) sustained head injury, predominantly concussions and skull fractures. With adjustment for age, sex, and motor vehicle involvement, children who had pre-existing mental disorders, who did not wear a helmet at the time of injury, or who were injured on roads had a significantly increased likelihood of sustaining head injuries. Patients with a head injury were four times as likely as patients with no head injury to be treated in intensive care units, and were almost twice as likely to develop complications. Head injury was associated with an increased risk of inhospital fatality and high prevalence rates of communication and behavior impairments at discharge. Although it is urgent to increase helmet use substantially by child bicyclists, special attention should be paid to high-risk groups, such as children with mental disorders and children who are likely to ride in traffic.

Adolescent↗