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Biomedical subjects

C M Tang

Publications and source records attributed to C M Tang.

At least 73 records · Page 4Linked to original sources
PubMed1993

Psychosis and cannabis abuse in The Gambia. A case-control study.

Cannabis abuse is a major public health problem in The Gambia and other parts of West Africa, and the rise in the incidence of psychotic illness reflects the increased background use of cannabis by the local population. A case-control study was performed to determine the association between psychosis and cannabis abuse in The Gambia and the importance of other risk factors. Out of 234 patients admitted to Campama Psychiatric Unit over 12 months, 210 (90%) were enrolled in a case-control study. Urine was tested for cannabinoid substances and 38% were positive compared with 12% of matched non-psychotic control subjects. Analysis of the matched pairs showed that a positive urinary cannabinoid test, cigarette smoking, alcohol consumption, travel to Europe and family history of mental illness were all significant risk factors for psychotic illness; Koranic education reduced the risk. There was a positive correlation among the psychotic patients between a positive urinary cannabinoid test and the use of alcohol, ataya tea and cigarette smoking; a family history of mental illness showed a negative correlation.

Adult↗
PubMed1993

Benzothiadiazides inhibit rapid glutamate receptor desensitization and enhance glutamatergic synaptic currents.

A distinctive characteristic of the AMPA subset of glutamate receptor channels is their remarkably rapid desensitization. A family of compounds, the benzothiadiazides, is described here that potently inhibit rapid glutamate receptor desensitization. The structure-activity relationships of these compounds are examined and the actions of cyclothiazide (CYZ), the most potent of these compounds, are described in detail. At the macroscopic level CYZ reduced rapid desensitization, enhancing the steady-state and peak current produced by 1 mM quisqualate with EC50 values of 14 and 12 microM, respectively, and shifted the quisqualate peak current concentration-response relation to the left. The slight outward rectification of the steady-state quisqualate current-voltage relationship was reduced by CYZ. At the microscopic level CYZ caused glutamate to induce long bursts of channel openings, and greatly increased the number of repeated openings. At 10 microM CYZ did not have measurable effects on the fast component of deactivation nor did it have statistically significant effects on the distribution of the faster components of glutamate-induced burst duration. In contrast, 10 microM CYZ increased the amplitude and significantly prolonged the duration of the spontaneous miniature EPSCs. The identification and characterization of this new family of gating modifiers may further facilitate the investigation into the mechanisms underlying rapid glutamate receptor desensitization and the physiological roles that it may serve.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1993

[Field studies on different control schemes for hookworm infection].

Three different control schemes including selective chemotherapy, a combination of selective chemotherapy and management of fecal disposal and mass treatment with mebendazole-medicated salt were implemented for the control of hookworm infection in Luwo Town and Taiping Village, Wuming County, Guangxi Zhuang Autonomous Region during 1971-1990. Through ten years of selective chemotherapy, the results showed that the hookworm infection rate dropped from 42.6% to 3.9% and the infection intensity from 425.6 eggs per gram faeces to 1.6 eggs per gram faeces. After seven years of selective chemotherapy combined with management of fecal, the hookworm infection rate dropped from 58.7% to 10.9% and the infection intensity from 111.5 eggs per gram faeces to 8.5 eggs per gram faeces. However, 3 years after the termination of the combined treatment, the hookworm infection rate increased to 14.5%. As for the implementation of the third scheme, mebendazole-medicated salt was given at 100 mg daily for 30 consecutive days or at 50 mg daily for 30 consecutive days. Stool examination was made one year after the treatment, the results showed that the infection rate of the inhabitants dropped from 36% and 36% to 2% and 1.3%, respectively, and the infection intensity dropped from 110.3 and 246 eggs per gram faeces to 1.3 and 0.24 eggs per gram faeces. After three years, the infection rate of inhabitants remained under 2% and the infection intensity under 1 egg per gram faeces. It was concluded that mass treatment with mebendazole-medicated salt might be the most practical scheme for the control of hookworm infection.

Ancylostomiasis↗
PubMed1992

An Aspergillus fumigatus alkaline protease mutant constructed by gene disruption is deficient in extracellular elastase activity.

Invasive pulmonary aspergillosis, usually caused by Aspergillus fumigatus, is a life-threatening condition of immunosuppressed patients. We have created a mutant strain of this fungus that lacks an extracellular alkaline protease (AFAlp). This was accomplished by transformation of A. fumigatus with a plasmid containing a selectable marker for hygromycin B resistance, and a 504 bp segment of the AFAlp gene, obtained by polymerase-chain-reaction-based amplification of A. fumigatus genomic DNA. Approximately 25% of transformants resulted from disruption of the AFAlp gene. SDS-polyacrylamide gel electrophoresis of proteins from the culture filtrate of a strain carrying the AFAlp gene disruption showed that it lacked a major protein of 33 kDa. Furthermore, in contrast to the culture filtrate from wild-type cells, the mutant had undetectable activity on azocollagen and elastin-Congo red, over a broad pH range. This shows that AFAlp accounts for most, if not all, of the extracellular elastinolytic activity of A. fumigatus, and that the mutant strain will be useful in assessing the role of AFAlp in pathogenicity.

Aspergillus fumigatus↗
PubMed1992

Diabetes mellitus in The Gambia, west Africa.

A register of diabetic patients attending the Royal Victoria Hospital, Banjul, The Gambia, was kept and data on hospital admissions recorded over a 1-year period. Two hundred and sixty-nine patients (110 men, 159 women) were registered of whom 66 (25%) were receiving insulin. Seventy-five patients (28%: 40 men, 35 women) were newly diagnosed. There were significant differences in age (p less than 0.001) and obesity (p less than 0.001) between men and women and between patients with different types of diabetes. There were 95 hospital admissions (5.2%) related to diabetes, as were a fifth of medical out-patient attendances. Ketoacidosis was the major cause of death while foot infections were more common (p less than 0.01) in women. Diabetes imposed a heavy burden on the health services of The Gambia, a small developing country in West Africa; more than 3.6% of the annual health budget was spent on the treatment of diabetic patients.

Adult↗
PubMed1992

Peripartum cardiac failure in The Gambia.

Twenty-seven patients with peripartum cardiac failure were seen at the Royal Victoria Hospital, Banjul over a 2-year period while one further patient presented 6 months after delivery with a cerebral embolus secondary to a dilated cardiomyopathy. Five (18%, P less than 0.001) patients had twin pregnancies. Seventeen (63%) patients attended for follow-up, of whom eight had evidence of continuing cardiac dysfunction and required treatment with diuretics; two patients were known to have died. In five asymptomatic patients the electrocardiogram had reverted to normal and three patients had further pregnancies without relapse. The bipolar distribution of onset of symptoms in relation to pregnancy was suggestive of two different pathological processes. There was no evidence that cultural habits played any significant part in the aetiology of peripartum cardiac failure in The Gambia.

Adolescent↗
PubMed1991

Modulation of the time course of fast EPSCs and glutamate channel kinetics by aniracetam.

It is generally accepted that glutamate serves as the neurotransmitter at most excitatory synapses in the mammalian central nervous system (CNS). Synaptic release of glutamate may trigger a fast and a slow excitatory postsynaptic current (EPSC). The slow EPSC is mediated by N-methyl-D-aspartate (NMDA) receptor channels, whereas the fast EPSC is mediated by non-NMDA receptor channels. The nootropic agent aniracetam selectively and reversibly slows the desensitization kinetics of non-NMDA channels and lengthens their single-channel open times. Antiracetam also modulates the kinetics of the fast EPSC in a manner that mirrors its action on the kinetics of the non-NMDA channels. These results support the hypothesis that the properties of the non-NMDA glutamate channels rather than the rate of neurotransmitter clearance are the primary determinants of the kinetics of the fast EPSC in the mammalian CNS.

Action Potentials↗
PubMed1990

Modulation of the N-methyl-D-aspartate channel by extracellular H+.

The influence of external [H+] on whole-cell and single-channel currents activated by glutamate agonists was studied in rat hippocampal neurons. In the pH range between 6.6 and 8.0, changes in external [H+] had negligible influence on the amplitude and kinetics of the monovalent ion-carrying currents activated by the agonists quisqualate and kainate. The divalent ion-carrying N-methyl-D-aspartate (NMDA)-activated current, on the other hand, was strongly modulated by extracellular [H+]. Increased external [H+] suppressed, whereas decreased external [H+] enhanced, the NMDA-activated current. Changes in internal [H+] had little or no effect on the NMDA-activated current. Modulation of the NMDA-activated current resulted primarily from changes in the number of channel openings. Neither the unitary conductance nor the individual open dwell-times were significantly affected. These results suggest that the protonation site is on the external aspect of the channel and is far removed from the channel permeation pathway. Because interactions between H+, NMDA, and glycine in activating the current were predominantly noncompetitive, our results suggest that the modulatory effect of H+ was not associated with changes in receptor-agonist affinities. These results suggest that modulation of the NMDA-receptor channel by [H+] may be an intrinsic protective mechanism by which calcium influx into neurons is regulated, particularly in hypoxic/ischemic conditions.

Animals↗
PubMed1989

Outbreak of beri-beri in The Gambia.

In 1988, an outbreak of beri-beri occurred in The Gambia during the rainy season. At least 140 people were affected, and 22 died. A clear response to thiamine was observed in 8 patients who were in hospital, and the outbreak resolved after distribution of thiamine in the community. Gradual replacement of traditional cereals with imported milled rice may have increased susceptibility to beri-beri.

Adolescent↗
PubMed1989

Quisqualate activates a rapidly inactivating high conductance ionic channel in hippocampal neurons.

Glutamate activates a number of different receptor-channel complexes, each of which may contribute to generation of excitatory postsynaptic potentials in the mammalian central nervous system. The rapid application of the selective glutamate agonist, quisqualate, activates a large rapidly inactivating current (3 to 8 milliseconds), which is mediated by a neuronal ionic channel with high unitary conductance (35 picosiemens). The current through this channel shows pharmacologic characteristics similar to those observed for the fast excitatory postsynaptic current (EPSC); it reverses near 0 millivolts and shows no significant voltage dependence. The amplitude of the current through this channel is many times larger than that through the other non-NMDA (N-methyl-D-aspartate) channels. These results suggest that this high-conductance quisqualate-activated channel may mediate the fast EPSC in the mammalian central nervous system.

Animals↗
PubMed1989

[Mebendazole-medicated-salt in the control of hookworm infection].

From 1984-1987, mass application of mebendazole-medicated salt was studied for the control of hookworm infection in 5 pilot areas (Wuming, Shanlin, Bobai, Guilin and Rongxian Counties) in Guangxi Zhuang Autonomous Region. The dosages of mebendazole (mixed with salt) administered were 15mg, 25mg, 30mg, 40mg, 50mg, 30mg, 70mg, 80mg, 100mg or 200mg per person per day for 15, 20 or 30 days. The results showed that 40mg/day for 15-20 days could result in stool egg negative conversion rates of 92.3 to 94.4%, while 50mg/day for 30 days resulted in 96.9 to 100%. Concurrently, the hookworm infection rate in pilot areas dropped by 57.9-71.7% in a short time; whereas the stool egg negative conversion rate of Ascaris lumbricoides was as high as 99.1% to 100% at the same dosage, when the dosage of 100mg/day for 30 days was given, the egg negative reversion rate for Trichuris trichiura was 97.6%. Promising result was also recorded concerning the tolerance of the medicated salt, as the side effects in the inhabitants were mild. In conclusion, the authors considered that the application of mebendazole-medicated salt was a simple and effective measure in controlling hookworm infection, especially in the light of solving the problem of incomplete mass detection and selected mass treatment. Furthermore, it is much more economic from the cost-effect point of view.

Female↗
PubMed1988

Amiloride selectively blocks the low threshold (T) calcium channel.

More than one type of voltage-gated calcium channel has been identified in muscle cells and neurons. Many specific organic and inorganic blockers of the conventional, slowly inactivating high threshold (L) calcium channel have been reported. No specific blockers of the low threshold (T) channel have been as yet identified. Amiloride, a potassium sparing diuretic, has now been shown to selectively block the low threshold calcium channel in mouse neuroblastoma and chick dorsal root ganglion neurons. The selective blockade of the T-type calcium channel will allow identification of this channel in different tissues and characterization of its specific physiological role.

Amiloride↗
PubMed1986

Glutamate depolarization of glial cells in Necturus optic nerve.

L-Glutamate, 10(-5) to 10(-2) M, depolarized glial cells in the normal and axon-free optic nerve of Necturus by up to 80 mV. The depolarization was maintained if lithium, but not tetramethylammonium, replaced sodium in the bathing solution. It was not blocked by either strophanthidin or tetrodotoxin. The response was accompanied by a membrane conductance increase and was followed by a strophanthidin-sensitive hyperpolarization. These results suggest that the depolarization resulted from sodium entry. D-Glutamate and L-aspartate were less potent but produced a comparable depolarization. gamma-Aminobutyric acid, glycine, taurine or glutamine (up to 10(-3) M) were ineffective.

Amino Acids↗
PubMed1985

Coupling and uncoupling of amphibian neuroglia.

Glial cells in the optic nerve of Necturus are coupled to each other by low resistance pathways which also permit the diffusion of the fluorescent dye Lucifer Yellow CH among the cells. The spread of dye is readily observed as nuclei of cells distant from the site of intracellular injection are stained. By contrast, horseradish peroxidase does not traverse the intercellular pathways. This protein remains in the injected cell. The addition of weak acids (carbonic or propionic) to the bathing medium reversibly uncouples the glia; it blocks the spread of ionic current and Lucifer Yellow among the cells. A block of ionic coupling will block the spatial buffering of potassium by the glial syncytium.

Animals↗