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H S Chang

Publications and source records attributed to H S Chang.

At least 19 recordsLinked to original sources
PubMed1992

Chlorination of cellulose with N-chlorosuccinimide-triphenylphosphine under homogeneous conditions in lithium chloride-N,N-dimethylacetamide.

Microcrystalline cellulose was chlorinated with N-chlorosuccinimide-triphenylphosphine under homogeneous conditions in LiCl-N,N-dimethylacetamide. At the early stage of the reaction only replacement of the 6-hydroxyl groups with chlorine was observed, and 3-hydroxyl groups were replaced at a lower rate with Walden inversion. The effects of reaction conditions on the extent of chlorination were studied in detail. More than two equivalents of chlorination reagents per glucose residue were necessary to attain a high degree of substitution (ds) by chlorine, and the maximum ds attained was 1.86. Chlorinated disaccharides were found in the hydrolyzates of chlorodeoxycelluloses hydrolyzed under mild conditions, and their structures were studied by mass spectrometry.

Acetamides↗
PubMed1992

Differential effects of 3,4,5,3',4',5'-hexachlorobiphenyl (HCB) on interrenal steroidogenesis in male and female rainbow trout Oncorhynchus mykiss.

1. The conversion of progesterone to 17 alpha-hydroxyprogesterone (17 alpha-OHP), 11-deoxycortisol (11-DOCR) and deoxycorticosterone (DOC) was significantly higher in female rainbow trout than in male trout; in contrast, the interrenal production of cortisol (CR) plus cortisone (CN) was higher in males than in females. 2. Following treatment with 1 mg/kg of HCB, the interrenal conversion of progesterone to 17 alpha-OHP and 11-DOCR was significantly increased in male and female trout but at 20 mg/kg of HCB, the production of these metabolites was increased in males and decreased in females; CR+CN production was unchanged after HCB treatment in both sexes.

17-alpha-Hydroxyprogesterone↗
PubMed1992

Long-term cultured mouse mast cells: ultrastructure, histamine and leukotriene levels.

Interleukin 3 (IL3), dependent cells were obtained from bone marrow (9/10 experiments) and spleen cells (4/5 experiments), but not from the thymus. These cells were similar to mucosal mast cell toluidine blue staining and electron microscopy. They had heterogenous metachromatic granules, and some had large scroll-like structures. They also contained histamine (200-800 ng/10(6) cells) for the first 2-5 weeks, whose level diminished to less than 30 ng/10(6) cells by 10 weeks of culture. They also generated leukotriene (LT) C4/D4 (10-40 ng/10(6) cells) and LTB4 (2-5 ng/10(6) cells) for over 100 days of culture. In one experiment, bone marrow-derived mast cells after 150 days of culture began to produce an IL3-like substance and proliferated exponentially without exogenous IL3.

Animals↗
PubMed1990

Effect of monovalent measles and trivalent measles-mumps-rubella vaccines at various ages and concurrent administration with hepatitis B vaccine.

To determine the most suitable vaccination schedule in developing countries, a study was conducted to reevaluate the immunogenicity of monovalent measles vaccine and trivalent measles-mumps-rubella vaccine at different ages. The success rate of measles vaccination was 84% at 9 months, 88% at 12 months and 100% at 15 months of age. Vaccination with measles vaccines at 9 and 15 months of age was also 96% immunogenic. Most vaccinees (16 of 17) not responding to the first measles vaccine before 1 year of age developed measles antibody with another shot of vaccine after 15 months of age. Trivalent measles-mumps-rubella vaccine worked well in children ages 14 to 18 months. Administering trivalent vaccine and hepatitis B vaccine concurrently at 1 year of age, rubella and mumps antibodies developed in more than 95% of vaccinees, while measles antibody was detected in 88%. Responses to hepatitis B vaccine in this situation were good; 89% of vaccinees developed antibody against hepatitis B surface antigen (greater than or equal to 10 mIU/ml) and the geometric mean titer was 362.49 mIU/ml. In summary vaccination twice at 9 and 15 months is effective and is a useful regimen in developing countries where measles is still endemic. Trivalent vaccine and hepatitis B vaccine will not interfere with each other when given together at 1 year of age.

Age Factors↗
PubMed1989

Decreases in excitatory synaptic transmission and increases in recurrent inhibition in the rat dentate gyrus after transient cerebral ischemia.

Excitatory transmission along the perforant path from the entorhinal cortex to the granule cells of the dentate gyrus was evaluated two days after 10 min of transient cerebral ischemia in the rat. The amplitude of the population spike, and the amplitude and the initial slope of the population excitatory postsynaptic potential (EPSP) evoked by the perforant path stimulation were measured across a range of stimulus intensities, and were compared with control values. Inhibitory interactions were evaluated using the paradigm of paired pulse stimulation, comparing the amplitude of the population spike evoked by the second pulse of a pair to the initial spike. The maximal values of the initial slope of the population EPSP and the population spike were reduced in the ischemic group. Also, the extent of paired pulse inhibition was greater in the ischemic group. These results suggest that: (1) excitatory synaptic transmission along the perforant path is impaired in the postischemic period, (2) inhibition of the dentate granule cells is enhanced in this period. These results are not consistent with the hypothesis that there is a hyperactivation of the tri-synaptic circuit in the chronic postischemic period that accounts for the excitotoxic death of CA1 neurons.

Action Potentials↗
PubMed1989

Hippocampal unit activity after transient cerebral ischemia in rats.

Single unit activity of CA1 and CA3 neurons in the hippocampus was recorded in rats 1, 2, or 3 days after 10 minutes of transient cerebral ischemia induced by the clamping of both carotid arteries combined with hypotension. In addition, paired pulse inhibition/facilitation of the CA1 population spike was examined on Day 2 using two successive stimuli of the contralateral CA3 region delivered at various intervals. On Day 1, the mean +/- SEM firing rate in the CA1 region was 0.91 +/- 0.42/sec (n = 5), which was not significantly different from the control value of 0.98 +/- 0.26/sec (n = 5). Firing rate increased on Days 2 and 3 to 3.96 +/- 0.69/sec (n = 5), and 6.49 +/- 0.89/sec (n = 5), respectively. In the CA3 region, the mean +/- SEM firing rate of 1.18 +/- 0.27/sec in the five control rats sharply dropped to 0.14 +/- 0.11/sec in the five Day 1 rats and gradually increased to 0.45 +/- 0.11/sec in the five Day 3 rats. Histologic examination of these rats revealed ischemic changes restricted to CA1 neurons on Days 2 and 3. The paired-pulse experiment showed no significant difference between six control and six Day 2 rats in the inhibition of the second population spike with interstimulus intervals of less than 400 msec. At interstimulus intervals of greater than 500 msec there was facilitation of the second spike, which lasted 5 seconds in Day 2 rats. This facilitation was not observed in control rats. Because CA3 neurons constitute the main input to CA1 pyramidal cells, decreased activity of CA3 neurons indicates less excitatory input to CA1 neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Neuronal correlate of pictorial short-term memory in the primate temporal cortex.

It has been proposed that visual-memory traces are located in the temporal lobes of the cerebral cortex, as electric stimulation of this area in humans results in recall of imagery. Lesions in this area also affect recognition of an object after a delay in both humans and monkeys, indicating a role in short-term memory of images. Single-unit recordings from the temporal cortex have shown that some neurons continue to fire when one of two or four colours are to be remembered temporarily. But neuronal responses selective to specific complex objects, including hands and faces, cease soon after the offset of stimulus presentation. These results led to the question of whether any of these neurons could serve the memory of complex objects. We report here a group of shape-selective neurons in an anterior ventral part of the temporal cortex of monkeys that exhibited sustained activity during the delay period of a visual short-term memory task. The activity was highly selective for the pictorial information to be memorized and was independent of the physical attributes such as size, orientation, colour or position of the object. These observations show that the delay activity represents the short-term memory of the categorized percept of a picture.

Action Potentials↗
PubMed1988

The glutamate receptor subtype mediating parallel fibre-Purkinje cell transmission in rabbit cerebellar cortex.

Responses of Purkinje cells to parallel fibre stimulation and to ionophoretically applied glutamate agonists, L-glutamate, L-aspartate, quisqualate, kainate and N-methyl-D-aspartate (NMDA), were extracellularly recorded in a superficial folium of the dorsal paraflocculus of high-decerebrate rabbits. NMDA caused an inhibition of simple spike discharge from Purkinje cells. 2-Amino-5-phosphonovalerate (APV), a selective NMDA receptor antagonist, effectively antagonized this inhibition. However, APV did not antagonize the excitation of Purkinje cells caused by quisqualate or parallel fibre stimulation. By contrast, both kynurenate and gamma-D-glutamylglycine (gamma-DGG) effectively antagonized the excitation of Purkinje cells by parallel fibre stimulation in a dose-dependent manner. Both kynurenate and gamma-DGG also antagonized the excitation of Purkinje cells caused by quisqualate, L-glutamate, L-aspartate or kainate. However, the antagonism was more prominent to L-aspartate and kainate than to quisqualate and L-glutamate. Quisqualate response was antagonized to an extent comparable with the response to parallel fibre stimulation. These results indicate that the receptor for the neurotransmitter at parallel fibre-Purkinje cell synapses is of quisqualate-specific type. The present data are consistent with the evidence that L-glutamate is the endogenous transmitter at these synapses.

2-Amino-5-phosphonovalerate↗
PubMed1986

Aneurysms of the posterior cerebral artery: report of ten cases.

Ten cases of posterior cerebral artery (PCA) aneurysm are presented. There were 13 aneurysms in the 10 patients: 6 saccular, 5 fusiform, 1 broad-based, and 1 giant fusiform serpentine aneurysm. Eight patients underwent operation: clipping for 2 saccular aneurysms, trapping for 1 saccular and 3 fusiform aneurysms, and coating for 2 fusiform or broad-based aneurysms. Microsurgical cerebral revascularization techniques were attempted in 2 cases: after a fusiform aneurysm had been excised, end-to-end anastomosis of the residual two ends of the PCA was performed and, after a giant serpentine aneurysm had been trapped, the superficial temporal artery was anastomosed transcortically to the distal PCA. Two patients died before operation because of rebleeding and vasospasm. Postoperative neurological deficits include contralateral hemiparesis, homonymous hemianopsia, hemihypesthesia, and ipsilateral 3rd nerve palsy. Our results suggest that, despite the good collateral circulation of the PCA, some ischemic events may occur after trapping procedures and that cerebral revascularization techniques may have some benefit in the treatment of unclippable aneurysms in this region.

Adolescent↗
PubMed1986

Staging with CT.

Explore the source record for details and available documents.

Humans↗
PubMed1986

Fusiform posterior cerebral artery aneurysm treated with excision and end-to-end anastomosis. Case report.

A case of a ruptured fusiform aneurysm of the posterior cerebral artery is reported. The aneurysm was excised and end-to-end anastomosis was carried out between the two ends of the posterior cerebral artery. There is no previous report of a posterior cerebral artery aneurysm treated with this technique. The pertinent literature is reviewed and the significance of this technique in the treatment of unclippable cerebral aneurysms is discussed.

Adult↗