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Biomedical subjects

L Tong

Publications and source records attributed to L Tong.

At least 145 records · Page 8Linked to original sources
PubMed1989

Structure of ras proteins.

In the Table of Contents of the 24 March 1989 issue, the title of the report "Histamine is an intracellular messenger mediating platelet aggregation" by S. P. Saxena et al. appearing on page 1596 was incorrectly printed.

Humans↗
PubMed1989

Three-dimensional reconstructions from incomplete data: interpretability of density maps at "atomic" resolution.

Three dimensional data collection in electron microscopy is normally limited to a range of tilt angles that is less than +/- 90 degrees. Thus, even under the best conditions, experimental values of the structure factors will be missing within a solid cone in reciprocal space. Previous work has already shown that the missing cone of data can produce serious artifacts in three-dimensional density maps at modest resolution, for example approximately 15A. We now report, however, that a missing cone as large as +/- 30 degrees appears to have no serious effect on the three-dimensional density map of a protein at 3.6 A resolution, and we attribute this result to the fact that the electron density features are quite well separated from one another at that resolution. The map calculated with a +/- 30 degree missing cone is, furthermore, no more sensitive to noise (error) than is the full (isotropic) Fourier map. This result does not seem to be unreasonable in view of the fact that less than 14% of the data (i.e., signal) is lost due to the missing cone. Our numerical simulations therefore indicate that there should be no difficulty in interpreting high-resolution Fourier maps that can be produced with data that fall within realistic estimates of achievable resolution, tilt angles, and experimental error.

Electronic Data Processing↗
PubMed1989

[Effects of dauricine on the metabolism of arachidonic acid in rat pleural neutrophils].

The effects of dauricine (Dau), an isoquinoline alkaloid and anti-arrhythmic agent used in China recently, on the biosynthesis of metabolites of arachidonic acid in rat pleural neutrophils, comparing with dazoxiben, indomethacin and BW-755 c, were studied. The major products of metabolism by 5-lipoxygenase (5-LPO), measured by HPLC, were LTB4 and 5-HETE, whereas the major cyclooxygenase products measured by HPLC and RIA, were HHT and TXB2. The formation of all products by neutrophils was significantly depressed by Dau in a dose-dependent manner. The concentration of Dau required to obtain 50% inhibition (IC50) of formation of HHT, TXB2, LTB4 and 5-HETE was 25.3, 59.3, 31.8 and 59.5 mumol/L, respectively. These results indicate that the two major metabolic pathways of arachidonic acid in rat pleural neutrophils are inhibited by Dau.

Alkaloids↗
PubMed1989

[Effect of dauricine on rat and human platelet aggregation and metabolism of arachidonic acid in washed rat platelets].

Dauricine (Dau), an isoquinoline alkaloid extracted from the roots of Menispermum dauricum D. C. and used as an antiarrhythmic agent in China recently, was shown to inhibit rat platelet aggregation induced by arachidonic acid (AA) and ADP, as well as human platelet aggregation induced by AA, ADP and adrenaline (Adr) in vitro in a dose-dependent manner. The concentration of Dau required for 50% inhibition (IC50) of rat platelet aggregation induced by AA and ADP was 26 and 37 mumol/L, respectively. For human platelet aggregation induced by AA, ADP and Adr the IC50 of Dau was found to be 39, 55 and 43 mumol/L, respectively. Dau inhibited the cyclooxygenase pathway metabolites of AA (TXB2 and HHT) in washed intact rat platelets. The production of TXB2 and HHT was reduced by 26% and 19%, respectively, when the Dau concentration was 50 mumol/L and by 46 and 45%, respectively, when the concentration of Dau was 100 mumol/L. The formation of 12-HETE was also inhibited at 100 mumol/L of Dau. The inhibitory effect of Dau on AA metabolism may be one of the mechanisms related to its inhibition of platelet aggregation.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1988

Development of neuronal responses in cat posteromedial lateral suprasylvian visual cortex.

We studied the normal development of responses to visual stimulation among neurons in the posteromedial lateral suprasylvian (PMLS) visual cortex, an extrastriate visual cortical area in cats. Recordings were made from 495 single neurons in 19 kittens that were 2, 3, 4, 8, or 12 weeks of age, and the results were compared with those from normal adult cats. The percentage of neurons that respond to light increased from 57% in 2-week-old kittens to approximately adult values in 8-week-old kittens (81%). The strength and consistency of neuronal responses also increased with age. Nearly all of the responsive cells had well-defined excitatory receptive-field centers, and the receptive-field center sizes were similar to adults at all ages studied. However, few cells (5%) had inhibitory receptive-field surrounds in 2-week-old kittens. The incidence of surround inhibition increased to adult levels (about 40% of the cells) by 8 weeks of age, and the strength of surround inhibition also increased with age. Most cells responded best to moving stimuli in 2-week-old kittens, just as in adults. However, only about 20% of the responsive cells were direction sensitive at 2 weeks of age. The percentage of direction-sensitive cells increased gradually with age and reached approximately adult values by 8 weeks of age (74%). Once cells developed complete direction selectivity, with no response in the null direction, directional tuning width was similar to that in adults. When tested with slits of light flashed at various orientations or with spots and slits moving in various directions, few cells (8% or less) showed orientation selectivity at any age, just as in adults. Most of the cells were binocularly driven, and the ocular dominance distribution was similar to adults at all ages studied. These results indicate that many response properties of PMLS neurons are similar to those of adults as early as 2 weeks of age, soon after the time of eye opening. However, some properties show marked developmental changes. The mechanisms and sources of these changes are considered. In addition, the relevance of these results to mechanisms of compensation following early damage to visual cortical areas 17, 18 and 19 is discussed.

Aging↗
PubMed1988

Functional influence of areas 17, 18, and 19 on lateral suprasylvian cortex in kittens and adult cats: implications for compensation following early visual cortex damage.

The aim of the present study was to investigate the mechanisms of physiological compensation that is seen in the posteromedial lateral suprasylvian (PMLS) cortex of cats that received visual cortex (areas 17, 18, and 19) damage early in life. The strategy was to compare the response properties of PMLS neurons just after visual cortex damage (before any compensation has occurred) with the properties of PMLS neurons in normal cats and cats with long-standing visual cortex damage. Fourteen animals (aged 8 weeks, 18 weeks, 26 weeks, or adult) received a unilateral visual cortex lesion and recordings were made from ipsilateral PMLS cortex within about 24 h. An additional 4 adult cats were studied within either 24 or 3 h of a bilateral visual cortex lesion. Results from these animals were compared with results from normal cats and cats with long-standing visual cortex damage studied previously in this laboratory. At all ages studied, an acute visual cortex lesion reduced the percentage of direction-sensitive cells in PMLS cortex from nearly 80% in normal cats to about 20% after the lesion. In 8- and 18-week-old kittens, nearly all of the remaining PMLS cells responded best to stimulus movement but were not direction sensitive. In 26-week-old and adult cats, the remaining cells were divided between those that responded to movement without a directional preference and those that responded as well to stationary flashed stimuli as to moving stimuli. The presence of receptive-field surround inhibition was not affected significantly by an acute lesion at any age. In addition, few PMLS cells were orientation selective to elongated slits of light in cats with an acute lesion, just as in normal cats. The ocular dominance distributions of PMLS neurons also were normal following an acute visual cortex lesion at all ages studied. These results suggest that the influences of areas 17, 18, and 19 on the response properties of PMLS neurons are the same when the properties first reach maturity as in adult cats. The results also suggest that the mechanisms of physiological compensation for an early visual cortex lesion differ for different response properties. Compensation of direction sensitivity and orientation selectivity (an anomalous property) develops de novo after the early lesion. In contrast, compensation of ocular dominance appears to be due to the maintenance of a preexisting property that is present immediately after the lesion. Thus, plasticity after early visual cortex damage represents multiple developmental changes in the remaining visual pathways.

Aging↗
PubMed1988

Three-dimensional structure of an oncogene protein: catalytic domain of human c-H-ras p21.

The crystal structure at 2.7 A resolution of the normal human c-H-ras oncogene protein lacking a flexible carboxyl-terminal 18 residue reveals that the protein consists of a six-stranded beta sheet, four alpha helices, and nine connecting loops. Four loops are involved in interactions with bound guanosine diphosphate: one with the phosphates, another with the ribose, and two with the guanine base. Most of the transforming proteins (in vivo and in vitro) have single amino acid substitutions at one of a few key positions in three of these four loops plus one additional loop. The biological functions of the remaining five loops and other exposed regions are at present unknown. However, one loop corresponds to the binding site for a neutralizing monoclonal antibody and another to a putative "effector region"; mutations in the latter region do not alter guanine nucleotide binding or guanosine triphosphatase activity but they do reduce the transforming activity of activated proteins. The data provide a structural basis for understanding the known biochemical properties of normal as well as activated ras oncogene proteins and indicate additional regions in the molecule that may possibly participate in other cellular functions.

Amino Acid Sequence↗
PubMed1988

Infant feeding in Sydney: a survey of mothers who bottle feed.

Two hundred and seventy-four mothers who were bottle feeding their infants aged from 1 to 9 months, were interviewed. Particular attention was paid to mixing technique, storage of reconstituted formulae, the reasons for deciding to bottle feed and what influenced the choosing of a particular milk. Following the interview, a sample of milk from a previously prepared bottle was taken to measure osmolality and bacterial colony count. Eighty-two per cent of the mothers had initially attempted breast feeding. The commonest reason for changing to a bottle was that the mother felt she was not able to produce enough milk to satisfy the baby. Thirty per cent chose the milk they were using on the recommendation of the maternity hospital. Errors in reconstituting the formulae, compared with the manufacturer's instructions were made by 100 (30%) mothers. In 52 cases these were potentially serious errors, usually erring on the side of preparing an over-concentrated formula. This finding from the interviews was confirmed by osmolality analysis of milk samples. Twenty-two per cent of samples collected grew potential pathogens. There was no correlation between the presence of bacterial growth and the use of prewarmed formulae stored in insulated carriers. No correlation was found between triceps skinfold thickness, age of introduction of solids or method of reconstitution of formula.

Australia↗
PubMed1987

Effects of corpus callosum section on functional compensation in the posteromedial lateral suprasylvian visual area after early visual cortex damage in cats.

A visual cortex lesion made in adult cats leads to a loss of direction selectivity and a loss of response to the ipsilateral eye among cells in posteromedial lateral suprasylvian (PMLS) cortex of cats. However, a visual cortex lesion made in young cats results in normal direction selectivity and normal ocular dominance in PMLS cortex. Thus cats with an early lesion demonstrate functional compensation in PMLS cortex. The present experiment determined whether the functional compensation depends upon an intact corpus callosum. Cats received a unilateral visual cortex lesion on the day of birth (day 1) or at 8 weeks of age. When the cats were adult, the corpus callosum was sectioned and 24 hours later recordings were made in PMLS cortex ipsilateral to the visual cortex lesion. Results were compared to cats with a similar lesion and an intact corpus callosum. In cats with a lesion made on day 1, a corpus callosum section did not affect receptive-field properties or ocular dominance in PMLS cortex. Therefore, functional compensation is not dependent on input via the corpus callosum in these animals. However, in cats with a lesion made at 8 weeks. a corpus callosum section resulted in a decrease in the percentage of direction-selective cells and in the percentage of cells driven by the ipsilateral eye. Despite the decrease, the percentage of direction-selective cells still was greater than in cats with an adult unilateral visual cortex lesion. Thus, while partly dependent on callosal inputs, some functional compensation for direction selectivity remains on the basis of ipsilateral inputs.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

Personality development following sexual abuse.

Thirty-seven girls and twelve boys who had been sexually abused at an average of 2.6 years previously were traced and reviewed. The nonoffending parents participated in a structured interview and the children were assessed using the Piers-Harris Self-Concept Scale and the Achenbach Child Behavior Checklist. Each child was matched with a child not known to have been sexually abused and these control children underwent a similar psychological assessment. Interviews with the nonoffending parents found that 76% of the children were thought to be less confident than before, 30% had fewer friends, and 20% were more aggressive. Increased sexual awareness was noted in 24%. School teachers reported that 28% still had behavior problems, 17% had repeated a year at school, and a further 17% had deteriorated in their school work. The sexually abused girls had significantly lower self-esteem than the control girls. There was no difference in self-esteem between the control and the sexually abused boys. There was a higher incidence of stranger assault in the boys compared with the girls. The Child Behavior Checklist completed by the parents, the Teacher Report Form, and the Youth Self-Report of the Child Behavior Checklist showed that a highly significant proportion of sexually abused children fell into the clinical range. Sexual abuse appears to have long-term adverse consequences for many of the victims. This may have implications for their ability to relate to others, for the adult friendships they will make, and eventually for the way they will relate to their own children.

Adolescent↗
PubMed1986

Single thalamic neurons project to both lateral suprasylvian visual cortex and area 17: a retrograde fluorescent double-labeling study.

Area 17 and the posteromedial lateral suprasylvian (PMLS) visual cortex receive inputs from three thalamic nuclei in common: the lateral division of the lateral posterior nucleus (LPl), the C-laminae of the lateral geniculate nucleus (LGNd), and the medial interlaminar nucleus (MIN). The present study determined whether these projections originate from the same cells via bifurcating axons or from separate populations of cells. Double-label retrograde transport techniques were used to label cells projecting to area 17 with one fluorescent dye and to label cells projecting to PMLS cortex with a different dye. The two dyes used were fast blue and Evans blue. Following injections into the two cortical areas, some cells were double labeled and some were single labeled in all three thalamic nuclei studied. However, the relative number of double- and single-labeled cells, as well as the relative number of cells single-labeled following injections into each cortical area, differed among the three thalamic nuclei. In both MIN and the C-laminae of the LGNd, the number of double-labeled cells was small. Similarly, the number of cells single labeled with the dye placed in PMLS cortex was small in these two nuclei. In contrast, a relatively large number of cells were single labeled with the dye placed in area 17, especially in the C-laminae of the LGNd. These results suggest that in both MIN and the C-laminae of the LGNd, few cells project to both area 17 and the PMLS cortex, few cells project only to PMLS cortex, and a relatively greater number of cells project only to area 17. In LPl, many cells were labeled after the cortical injections. In fact, when the areas of densest labeling for both dyes overlapped, almost every labeled cell in LPl was double labeled. This indicates that almost all LPl cells that project to one cortical area also project to the other via a bifurcating axon.

Animals↗
PubMed1986

Dose-response analysis of effects of antibodies to large ganglion cells on the cat's retinogeniculate pathways.

Previous studies have shown that antibodies against large retinal ganglion cells (alpha-/Y-cells) reduce the Y-cell retinogeniculate pathway while having little or no effect on the X- or W-cell pathways. The present study investigated the dose-response relationship of these effects. We began by studying effects on the T1 (largely Y-cell-mediated) and T2 (largely X-cell-mediated) waves of the retinal field-potential. Different concentrations of the antibodies were injected intraocularly in adult cats and retinal field-potentials evoked by optic chiasm stimulation were examined. The lowest concentration of immune serum tested (330 micrograms/100 microliter volume) reduced both the T1 and T2 amplitudes. With increasing concentrations, the ratio of T1:T2 amplitudes progressively decreased from 0.71 to only 0.05. The highest concentration of immune serum tested (1000 micrograms/100 microliter volume) virtually eliminated the T1 wave while the T2 wave remained (albeit reduced). Next, we carried out single-cell physiological and morphological studies to verify the effects of the highest antibody concentration and compare them with previous results on effects of the lowest antibody concentration (Kornguth et al., 1982; Spear et al., 1982). In single-cell recordings from the retina, the encounter rates of Y- and X-cells were reduced by 85 and 53%, respectively, after injection of the highest antibody concentration. There was no effect on the encounter rate of retinal W-cells. After injection of the lowest antibody concentration, there was no change in the encounter rates of any of the retinal cell types. Morphological studies revealed an 88-99% loss of alpha-cells in retinae treated with the highest antibody concentration. There also was a substantial (24-57%) loss of medium-size ganglion cells but no loss of small ganglion cells. The loss of alpha-cells was much greater after high-concentration injections than after low-concentration injections. In recordings from the LGN, the proportion of Y-cells was reduced by 87% in laminae receiving input from an eye injected with the highest antibody concentration. Laminae receiving input from an eye injected with the lowest concentration had a 77% reduction in Y-cells. The encounter rate of LGN X-cells was not affected by either concentration. Morphological analysis indicated that the loss of Y-cells in the LGN was not due to changes in cell size. These findings indicate that antibody-mediated effects on retinogeniculate pathways are dose-dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1985

Developmentally induced loss of direction-selective neurons in the cat's lateral suprasylvian visual cortex.

Single-cell recordings were carried out in the posteromedial lateral suprasylvian (PMLS) visual cortex of cats reared in an environment illuminated by 8-Hz stroboscopic flashes. These cats had a reduced proportion of direction-selective cells (8%) compared to PMLS cortex of normal cats (79%). Other receptive-field properties and ocular dominance of the neurons appeared normal. These results have implications for understanding the mechanisms of PMLS-cortex development and for interpreting behavioral studies of strobe-reared cats.

Animals↗