Search PubMed⌕ Search

Biomedical subjects

S H Chan

Publications and source records attributed to S H Chan.

At least 199 records · Page 11Linked to original sources
PubMed1991

Cytochrome oxidase immunohistochemistry in rat brain and dorsal root ganglia: visualization of enzyme in neuronal perikarya and in parvalbumin-positive neurons.

Histochemical detection of cytochrome oxidase activity has been widely used to deduce patterns of neuronal electrical activity in the CNS. Here we investigated the utility of cytochrome oxidase localization by immunohistochemistry and compared immunostaining with histochemical staining patterns in dorsal root ganglia of the rat. In addition, a limited survey of cytochrome oxidase immunostaining density within what are thought to be highly active parvalbumin-immunoreactive neurons was conducted. The immunohistochemical approach produced granular cytoplasmic immunolabelling in neuronal cell bodies and allowed identification of individual labelled cells in all brain regions including those within dense immunoreactive networks of neuropil. Neuronal somata exhibited a wide range of staining densities which were particularly evident in the hippocampus and dorsal root ganglia. The distribution of neurons intensely immunoreactive for cytochrome oxidase within various structures was consistent with previous histochemical descriptions of enzyme activity. Densitometric measurements of immunohistochemical reaction product in individual neurons of hippocampus, substantia nigra, cerebellum and dorsal root ganglia showed that the rate of product deposition was linear with time under conditions chosen for comparisons of staining density. Quantitative analysis of cytochrome oxidase immunohistochemical and histochemical staining densities within the same cells in adjacent sections of dorsal root ganglion gave a correlation coefficient of r = 0.75 (P less than 0.001). In sections processed immunohistochemically for both cytochrome oxidase and parvalbumin, most but not all parvalbumin-containing cells displayed dense cytochrome oxidase immunolabelling. Conversely, many examples were found of neurons that were densely stained for cytochrome oxidase, but lacked parvalbumin. Immunohistochemistry for cytochrome oxidase reveals the enzyme in neuronal cell bodies with a clarity not usually seen with the histochemical method. Combination of this immunohistochemical approach with simultaneous immunolabelling of other neuronal markers, as shown here in the case of parvalbumin, is expected to assist the elucidation of patterns of activity in neurochemically identified cell types and anatomically defined neural systems.

Animals↗
PubMed1991

A cytogenetic study of 74 nasopharyngeal carcinoma biopsies.

Cells from 102 nasopharyngeal biopsies of patients suspected of Nasopharyngeal Carcinoma (NPC) and family members of NPC patients were cultured. Metaphases were successfully obtained from 74 of the biopsies of which 52 were subsequently histologically confirmed to be NPC. Cytogenetical analysis using Q-banding showed abnormalities in 15 cultures, and these included polyploidy, aneuploidy and marker chromosomes. Of the 15 abnormal cultures, 14 were from confirmed NPC patients and in five of these, a consistent 5q+ abnormally was seen involving 5q31. The only other abnormal chromosome changes seen was in a patient with olfactory neuroblastoma.

Asia, Southeastern↗
PubMed1991

Effects of adrenalectomy and nephrectomy on adrenal regeneration hypertension in the rat.

The involvement of the regenerating adrenal gland and kidney, and the contribution of deoxycorticosterone (DOC) and prostaglandin E2 (PGE2), in the development of adrenal regeneration hypertension (ARH) was evaluated in young female Sprague-Dawley rats. Based on tail-cuff plethysmographic measurement, animals subjected to nephrectomy and adrenalectomy on the right side and adrenal enucleation (removal of the adrenal cortex) on the left side developed significant (P less than 0.05, n = 12) hypertension within 6 weeks following operation. Subsequent left nephrectomy in these ARH rats produced a further elevation, whereas a secondary adrenalectomy resulted in an acute and discernible reduction in blood pressure within 24-36 hours. It is interesting to note that the progressive increase in blood pressure following left nephrectomy was significantly reversed by PGE2 (10 or 20 micrograms/kg, i.p.). At the same time, the reduction in blood pressure after secondary adrenalectomy was significantly retarded by deoxycorticosterone trimethylacetate (2 mg/kg, i.p.). These data demonstrated that both the kidney and the regenerating adrenal cortex are involved in the pathogenesis of ARH. Furthermore, it is probable that the secretion of DOC by the regenerating adrenal cortex is responsible for the elevation in blood pressure, in a process that is balanced by PGE2, possibly secreted by the kidney.

Adrenal Glands↗
PubMed1990

Linkage of a nasopharyngeal carcinoma susceptibility locus to the HLA region.

The frequency of nasopharyngeal carcinoma is nearly 100-fold higher in southern Chinese than in most European populations. Earlier studies have suggested that an increased risk of nasopharyngeal carcinoma is associated with specific haplotypes in the HLA region: relative risks slightly over twofold were found for haplotypes A2, Bw46 and the antigen B17. We now report a linkage study based on affected sib pairs which suggests that a gene closely linked to the HLA locus confers a greatly increased risk of nasopharyngeal carcinoma. The maximum likelihood estimate is of a relative risk of approximately 21. The relationship between this suspected disease susceptibility gene (or genes) and known viral and environmental aetiological factors remains to be elucidated.

China↗
PubMed1990

Tonic enhancement of the sensitivity of baroreceptor reflex response by endogenous substance P in the rat.

Modulation of baroreceptor reflex (BRR) by endogenous substance P (SP) in the brain was investigated in rats anesthetized with pentobarbital sodium. Intracerebroventricular administration of the undecapeptide (15 or 30 nmol) and its antagonist, (D-Pro2, D-Trp7,9)-SP (30 or 60 nmol) or SP antiserum (1:20), respectively, promoted a significant increase and decrease in the sensitivity of BRR response. Prolonging the endogenous activity of SP with the aminopeptidase blocker, bestatin (200 nmol) or with the endopeptidase-24.11 inhibitor, phosphoramidon (200 nmol) significantly augmented the same reflex. Combining the undecapeptide with either peptidase blocker, moreover, promoted additional potentiation of the BRR response. On the other hand, simultaneous administration of bestatin and (D-Pro2, D-Trp7,9)-SP produced a reduction of the augmented effect of bestatin on the sensitivity of BRR response. Bilateral microinjection of SP (600 pmol) or an antiserum against SP (1:20) into the nucleus tractus solitarius (NTS) elicited respectively an enhancement of and reduction in the BRR response. These data suggest that neurons that contain SP may participate in central cardiovascular control by tonically enhancing the sensitivity of the BRR response, possibly via an action on the NTS.

Animals↗
PubMed1990

Cytochrome oxidase from thermophilic bacterium PS3 contains a fourth protein subunit.

Monoclonal antibodies prepared against subunits II and IV of beef heart cytochrome oxidase were found to cross-react with thermophilic bacterial PS3 oxidase. Each individual antibody affects the enzymatic activity. "Western" blot analyses showed that subunit II antibodies of beef heart recognized subunit II of PS3 and subunit IV antibody likewise recognized a fourth protein subunit on slab gels. This fourth subunit previously thought to be a contaminant or a degradation product has a molecular weight of about 10,500 on SDS-gels, and appears to exist in stoichiometric amount. We have extracted this subunit from slab gels and compared its amino acid composition with that of subunit III.

Amino Acids↗
PubMed1990

Tonic suppression of baroreceptor reflex by endogenous neurotensin in the rat.

We evaluated the modulatory role of endogenous neurotensin (NT) in baroreceptor reflex (BRR) response in Sprague-Dawley rats anesthetized with pentobarbital sodium. Intracerebroventricular (i.c.v.) administration of NT (15 or 30 nmol) significantly reduced the sensitivity of the BRR response. Blocking the endogenous activity of the tridecapeptide with its specific antagonist, (D-Trp11)-NT (4 or 8 nmol) or antiserum against NT (1:20); or inhibiting the aminopeptidases with bestatin (200 nmol), on the other hand, promoted a potentiation of BRR response. When administered together with bestatin (200 nmol), the suppressive effect of NT (15 nmol) on the BRR response was further enhanced, as was the augmentative action of (D-Trp11)-NT (4 nmol). Upon microinjection into the bilateral nucleus tractus solitarius (NTS), NT (600 pmol) and (D-Trp11)-NT (150 pmol) respectively elicited a reduction and enhancement of the BRR response. These results suggest that neurons that contain NT may participate in central cardiovascular regulation by tonically suppressing the BRR, possibly via an action on the NTS where baroreceptor afferents terminate.

Animals↗
PubMed1990

Involvement of coerulospinal noradrenergic pathway in fentanyl-induced muscular rigidity in rats.

Unilateral, site-specific microinjection of fentanyl (2.5 micrograms/50 nl) into the locus coeruleus (LC) in Sprague-Dawley rats anesthetized with ketamine evoked a significant increase in the electromyographic activity recorded from both caudal lateral extensor and gastrocnemius muscles. This correlate of opiate-induced muscular rigidity was appreciably antagonized by a pretreatment with the specific alpha 1-adrenoceptor blocker, prazosin (250 micrograms/kg, i.v.). On the other hand, an equimolar dose (0.65 mumol/kg) of the specific alpha 2-adrenoceptor blocker, yohimbine (0.23 mg/kg, i.v.) failed to prevent the occurrence of fentanyl-induced EMG activation. We suggest that the coerulospinal noradrenergic pathway may be directly involved in the elicitation of muscular rigidity by fentanyl, possibly via alpha 1-adrenoceptors in the spinal cord.

Adrenergic Fibers↗
PubMed1990

Detection of integrated hepatitis B virus DNA in hepatocellular carcinoma cell lines by nonradioactive in situ hybridization.

A sensitive and specific nonradioactive in situ hybridization method capable of detecting single-copy integrated hepatitis B virus (HBV) DNA sequences in hepatocellular carcinoma (HCC) cell lines was developed. In situ hybridization of biotinylated HBV (adr, adw) DNA probes with nine different human HCC cell lines were carried out in 96-well microtiter plates. Integration was detected in HCC cell lines HCCM, Hep3B, huH-1, huH-4, and PLC/PRF/5. Detection of single-copy HBV DNA sequences was also achieved in Hep3B and huH-4. HCC cell lines HepG2, HUH-6, HUH-7, Mahlavu, and the non-HCC control MCF-7, gave clear negative results. These results show a 100% correlation with those obtained by Southern blot hybridization assay. The results demonstrate that nonradioactive detection of single-copy integrated HBV DNA sequences in HCC cell lines is possible by the method described, which has potential application for viral genome analysis requiring in situ hybridization.

Carcinoma, Hepatocellular↗
PubMed1990

Interaction between angiotensin III and alpha 2-adrenoceptors of the medulla oblongata involved in cardiovascular regulation in the rat.

We evaluated, in adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium, possible interaction between angiotensin III (AIII) and the alpha 2-adrenoceptors in the medulla oblongata that are involved in cardiovascular regulation. The hypotensive and negative chronotropic and inotropic actions of the alpha 2-adrenoceptor agonist, guanabenz, were used as our experimental index. Intracerebroventricular (i.c.v.) administration of AIII (100 or 200 pmol) significantly attenuated the cardiovascular suppressive effects of the aminoguanidine compound (25 or 50 micrograms/kg, i.v.). Bilateral microinjection of AIII (20 or 40 pmol) to the nucleus reticularis gigantocellularis (NRGC), a medullary site believed to be intimately related to the antihypertensive action of guanabenz, produced similar results. In addition, i.c.v. administered AIII (200 pmol) altered the effects of guanabenz on the arterial pressure-related neurons in the NRGC, in a manner that paralleled the blunted vasodepressive action of the aminoguanidine compound by the heptapeptide. When applied microiontophoretically, AIII also significantly decreased the responsiveness of arterial pressure-related neurons in the NRGC to guanabenz. These findings suggest that AIII may interact with the alpha 2-adrenoceptors located in the NRGC that are involved in central cardiovascular regulation.

Angiotensin II↗
PubMed1990

Detection of tumour antigens in sera of patients with hepatocellular carcinoma using monoclonal antibodies.

A total of 70 serum samples taken from patients with hepatocellular carcinoma (HCC), acute viral hepatitis and cirrhosis and normal individuals were tested in a binding inhibition immunofluorescence assay using 5 mouse monoclonal antibodies (2G9, 3H11, 3H12, 1C7, 3H5) specific for hepatoma cells. Seven out of the 30 HCC sera (23.3%) inhibited the binding of one of these antibodies, 3H11. This detection of antigen 3H11 or antigens of similar structure in HCC sera was significantly more frequent than in control sera (1/40 = 2.5%) (Fisher's exact test, p = 0.009; df = 1, relative risk calculated by the odds ratio in a 2 x 2 table = 12.0). The presence of this antigen was unrelated to the hepatitis B surface antigen and alphafetoprotein status. Thus it would be of value particularly for the detection of hepatitis B negative or alphafetoprotein negative liver cancers.

Acute Disease↗
PubMed1990

Tonic reduction in central alpha 2-adrenoceptor activity by endogenous angiotensin III in the rat.

We evaluated the possible interactions between central alpha 2-adrenoceptors and endogenous angiotensin III (AIII) in Sprague-Dawley rats anesthetized with pentobarbital sodium (50 mg/kg, i.p.). The cardiovascular suppressive effects of the alpha 2-adrenoceptor agonist, guanabenz, were used as our experimental index for alpha 2-adrenoceptor activity. Intracerebroventricular (i.c.v.) administration of AIII (100 or 200 pmol) attenuated the hypotensive and negative inotropic and chronotropic actions of guanabenz (100 micrograms/kg, i.v.). Blocking the endogenous activity of the heptapeptide with its specific antagonist, Ile7-AIII (50 or 100 nmol, i.c.v.), on the other hand, potentiated the circulatory inhibitory efficacy of the aminoguanidine compound. These modulatory effects were essentially duplicated by bilateral microinjection of AIII (20 or 40 pmol) or Ile7-AIII (10 or 20 nmol) into the nucleus reticularis gigantocellularis (NRGC), a medullary site that is critically involved in the cardiovascular suppressive actions of guanabenz. I.c.v. injection of bestatin (200 nmol) also reduced the circulatory depressive potency of guanabenz. This effect was respectively enhanced and reduced when the aminopeptidase inhibitor was given simultaneously with AIII (200 pmol) and Ile7-AIII (100 nmol). These results suggest that the endogenous AIII may exert a tonic inhibition on the alpha 2-adrenoceptors in in the NRGC that are involved in cardiovascular regulation.

Angiotensin III↗
PubMed1990

Aetiology of nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC), a rare tumour in most parts of the world, occurs in high frequencies in China and South East Asia and is particularly high among the Southern Chinese. In certain parts of China the incidence may reach 50 per 10(5) per year while in most other ethnic groups the incidence is very low, e.g. among Caucasians the incidence is less than 1 per 10(5) per year. These marked geographic and racial differences in incidence have stimulated much research into the aetiology of this cancer. Potential aetiological factors will have to explain this 50-100 fold difference in incidence. Both genetic and various environmental factors have been postulated. This paper discusses the role of the Histocompatibility Locus Antigen (HLA), Epstein Barr Virus and chemical carcinogen including salted fish in the development of NPC.

Adolescent↗
PubMed1989

Involvement of postsynaptic alpha 2-adrenoceptors and guanine nucleotide-binding protein in guanabenz-induced cardiovascular suppressant effects in the rat.

In adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium, pretreatment with the catecholamine-depleting agent, reserpine (150 micrograms, i.c.v.) significantly antagonized the hypotensive and negative inotropic and chronotropic effects of guanabenz, either given intravenously (100 micrograms/kg) or microinjected bilaterally (5 micrograms) into the nucleus reticularis gigantocellularis (NRGC), a medullary site of action for this centrally acting antihypertensive agent. Pretreating animals with microinjection of the selective norepinephrine neurotoxin, DSP4 (50 micrograms), into the bilateral NRGC, on the other hand, did not appreciably blunt the cardiovascular suppressive actions of the aminoguanidine compound. I.c.v. administration of pertussis toxin (2.5 micrograms), which potentially blocks the action of two guanine nucleotide-binding proteins (Gi and Go), significantly antagonized the circulatory inhibitory effects of guanabenz (100 micrograms/kg, i.v.). More specifically, this blocking effect was still apparent upon microinjecting pertussis toxin (250 ng) into the bilateral NRGC. These data suggest that both pre- and postsynaptic alpha 2-adrenoceptors, and a pertussis toxin sensitive G-protein(s) (Gi and/or Go), in the NRGC are crucial to the expression of the cardiovascular suppressant actions of guanabenz.

Animals↗
PubMed1989

Passive electrical properties of spontaneously active neurons in the nucleus reticularis gigantocellularis of the cat.

We evaluated in chloralose-urethane anesthetized cats the passive electrical properties of 25 spontaneously active neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Compared to other mammalian brain regions, these reticular cells in general possessed higher input resistance, shorter membrane time constant and first equalizing time constant, and longer somatodendritic electrotonic length factor. It is discussed that, by providing a synaptic machinery for quick and sensitive response to afferent inputs and an efficacious interplay between temporal and spatial summation, these electrical membrane properties may account for the spontaneous and irregular discharge pattern characteristic of the NRGC neurons.

Action Potentials↗
PubMed1989

Involvement of locus coeruleus and noradrenergic neurotransmission in fentanyl-induced muscular rigidity in the rat.

Whereas muscular rigidity is a well-known side effect that is associated with high-dose fentanyl anesthesia, a paucity of information exists with regard to its underlying mechanism(s). We investigated in this study the possible engagement of locus coeruleus of the pons in this phenomenon, using male Sprague-Dawley rats anesthetized with ketamine. Under proper control of respiration, body temperature and end-tidal CO2, intravenous administration of fentanyl (50 or 100 micrograms/kg) consistently promoted an increase in electromyographic activity recorded from the gastrocnemius and abdominal rectus muscles. Such an induced muscular rigidity by the narcotic agent was significantly antagonized or even reduced by prior electrolytic lesions of the locus coeruleus or pretreatment with the alpha-adrenoceptor blocker, prazosin. Microinjection of fentanyl (2.5 micrograms/50 nl) directly into this pontine nucleus, on the other hand, elicited discernible electromyographic excitation. It is speculated that the induction of muscular rigidity by fentanyl may involve the coerulospinal noradrenergic fibers to the spinal motoneurons.

Adrenergic Fibers↗