Biomedical subjects

T H Phan

Publications and source records attributed to T H Phan.

At least 19 recordsLinked to original sources

PubMed2001

Further studies on the activation of rat median raphe serotonergic neurons by inescapable sound stress.

Previous studies, using a biochemical measure of serotonergic neuronal function, show that inescapable, randomly presented sound pulses activate serotonergic neurons in the rat median raphe but not dorsal raphe nucleus. The present study reveals that this activation also occurs in serotonin projection areas, in hippocampus, nucleus accumbens and cortex but not in caudate nucleus. The selectivity of this response is examined by comparing the response to sound stress with that produced by morphine, a treatment known to selectively activate dorsal raphe but not median raphe serotonergic neurons. Two approaches are used in Sprague-Dawley rat to measure the activation of serotonergic neurons: (1) determination ex vivo of accumulation of 5-hydroxytryptophan (5-HTP) in tissue from the dorsal and median raphe nuclei, hippocampus, cortex, caudate nucleus, and nucleus accumbens following in vivo inhibition of aromatic amino acid decarboxylase; and (2) measurement of extracellular serotonin levels in hippocampus, caudate nucleus, and nucleus accumbens. Sound stress increases 5-HTP accumulation in median raphe nucleus, hippocampus, cortex, and nucleus accumbens, but not dorsal raphe nucleus or caudate nucleus. Sound stress also enhances extracellular serotonin levels in hippocampus and nucleus accumbens, but not caudate nucleus. In contrast, the morphine treatment enhances 5-HTP accumulation in dorsal raphe nucleus, cortex and caudate nucleus, but not in median raphe nucleus, hippocampus or nucleus accumbens. Furthermore, it increases extracellular serotonin levels in only the caudate nucleus. The combined effects of sound stress and morphine on 5-HTP accumulation are identical to those obtained by each treatment individually. These findings provide further support for the presence of serotonergic neurons within the median raphe nucleus that have a unique response profile. These neurons may have an important role in responses or adaptations to stress.

Adaptation, Physiological↗

PubMed2001

Decrease in rat taste receptor cell intracellular pH is the proximate stimulus in sour taste transduction.

Taste receptor cells (TRCs) respond to acid stimulation, initiating perception of sour taste. Paradoxically, the pH of weak acidic stimuli correlates poorly with the perception of their sourness. A fundamental issue surrounding sour taste reception is the identity of the sour stimulus. We tested the hypothesis that acids induce sour taste perception by penetrating plasma membranes as H(+) ions or as undissociated molecules and decreasing the intracellular pH (pH(i)) of TRCs. Our data suggest that taste nerve responses to weak acids (acetic acid and CO(2)) are independent of stimulus pH but strongly correlate with the intracellular acidification of polarized TRCs. Taste nerve responses to CO(2) were voltage sensitive and were blocked with MK-417, a specific blocker of carbonic anhydrase. Strong acids (HCl) decrease pH(i) in a subset of TRCs that contain a pathway for H(+) entry. Both the apical membrane and the paracellular shunt pathway restrict H(+) entry such that a large decrease in apical pH is translated into a relatively small change in TRC pH(i) within the physiological range. We conclude that a decrease in TRC pH(i) is the proximate stimulus in rat sour taste transduction.

Acetic Acid↗

PubMed2001

A novel pharmacological probe links the amiloride-insensitive NaCl, KCl, and NH(4)Cl chorda tympani taste responses.

Chorda tympani taste nerve responses to NaCl can be dissected pharmacologically into amiloride-sensitive and -insensitive components. It is now established that the amiloride-sensitive, epithelial sodium channel acts as a sodium-specific ion detector in taste receptor cells (TRCs). Much less is known regarding the cellular origin of the amiloride-insensitive component, but its anion dependence indicates an important role for paracellular shunts in the determination of its magnitude. However, this has not precluded the possibility that undetected apical membrane ion pathways in TRCs may also contribute to its origin. Progress toward making such a determination has suffered from lack of a pharmacological probe for an apical amiloride-insensitive taste pathway. We present data here showing that, depending on the concentration used, cetylpyridinium chloride (CPC) can either enhance or inhibit the amiloride-insensitive response to NaCl. The CPC concentration giving maximal enhancement was 250 microM. At 2 mM, CPC inhibited the entire amiloride-insensitive part of the NaCl response. The NaCl response is, therefore, composed entirely of amiloride- and CPC-sensitive components. The magnitude of the maximally enhanced CPC-sensitive component varied with the NaCl concentration and was half-maximal at [NaCl] = 62 +/- 11 (SE) mM. This was significantly less than the corresponding parameter for the amiloride-sensitive component (268 +/- 71 mM). CPC had similar effects on KCl and NH(4)Cl responses except that in these cases, after inhibition with 2 mM CPC, a significant CPC-insensitive response remained. CPC (2 mM) inhibited intracellular acidification of TRCs due to apically presented NH(4)Cl, suggesting that CPC acts on an apical membrane nonselective cation pathway.

Amiloride↗

PubMed1999

Molecular and biochemical characterization of the involvement of cyclin-dependent kinase A during the early development of tomato fruit.

Following fruit set, the early development of tomato (Lycopersicon esculentum Mill.) fruit comprises two distinct phases: a cell division phase and a consecutive phase of cell expansion until the onset of ripening. In this study, we analyzed cytological and molecular changes characterizing these early phases of tomato fruit development. First we investigated the spatial and temporal regulation of the mitotic activity during fruit development. The DNA content of isolated nuclei from the different fruit tissues was determined by flow cytometry analysis. The results confirm the data of mitotic activity measurements and show that cell differentiation, leading to expanded cells, is characterized by endoreduplication. Second, we isolated two cDNAs, named Lyces;CDKA1 (accession no. Y17225) and Lyces;CDKA2 (accession no. Y17226), encoding tomato homologs of the cyclin-dependent kinase (CDK) p34(cdc2). Tomato CDKA gene expression was followed at both the transcriptional and translational levels during fruit development. The transcripts for Lyces;CDKA1 and Lyces;CDKA2 and the corresponding CDKA proteins are predominantly accumulated during the phase of cell division between anthesis and 5 d post anthesis (DPA). In whole fruits, the maximum CDK activity was obtained between 5 and 10 DPA. The determination of the kinase activity using protein extracts from the different fruit tissues was in agreement with mitotic activity analysis. It showed the particular disappearance of the activity in the gel tissue as early as 15 DPA. The overall data of CDK activity measurements suggest a strong post-translational regulation of CDK at the temporal and spatial levels during early tomato fruit development.

Amino Acid Sequence↗

PubMed1999

Is arcA3 a possible mediator in the signal transduction pathway during agonist cell cycle arrest by salicylic acid and UV irradiation?

Progression of BY-2 tobacco cells through the cell cycle was followed after treatments with ultra violet (UV) and salicylic acid (SA) used as a potent inhibitor of the octadecanoid pathway which can mediate response to UV irradiation. Cells in S phase were more sensitive than G0/G1 or G2 cells to UV irradiation. Although SA efficiently blocked cells in G0/G1 or G2, it did not block S phase synchronized cells. UV and SA applied simultaneously to cells in G0/G1 delayed the cell cycle progression more than each one separately. Therefore UV irradiation and SA act as agonists to arrest BY-2 cells at cell cycle entry. To further investigate the signalling pathway mediating UV response, we complemented a UV-sensitive Escherichia coli strain with a Nicotiana xanthi cDNA expression library. A cDNA (arcA3) whose coding sequence is identical to the 2,4-D induced arcA cDNA cloned by Ishida et al. (1993) was isolated. We show that arcA3 transcription is induced at cell cycle entry but not directly by the 2,4-D treatment. Moreover, arcA3 transcription is induced prior to the restriction point as shown with the CDK inhibitor roscovitine. The arcA3 transcription level is increased by UV irradiation but prevented by SA. Indeed, addition of SA prior to UV irradiation blocks the induction of arcA3 transcription. This suggests that arcA3 gene is modulated in both UV and SA responses, the SA effect preceding the UV step. Since arcA3 is 67% similar to RACK1 (functional homology), a rat intracellular receptor for protein kinase C, and possesses identical PKC fixation motifs, it is hypothesised that the arcA3 gene is involved in UV and SA cell cycle arrest.

Bacterial Outer Membrane Proteins↗

PubMed1999

[Diagnostic imaging of tracheobronchial tuberculosis. Apropos of a case].

We report a new case of tracheo-bronchial tuberculosis. Diagnosis was suggested on CT examination first and then confirmed by endoscopy and bacteriological examinations. We discuss the possible mechanisms of stenosis. We present the radiological features of tracheo-bronchial tuberculosis, mainly helical CT features and we discuss and illustrate differential diagnosis. We emphasize the role of 3 D and multiplanar reconstructed CT images that may help visualizing the stenosis at different levels, its craniocaudal extent as well as the boundaries between the stenosis and surrounding tissues. Moreover helical CT appears superior to bronchofibroscopy in diagnosing peribronchial infiltration.

Adolescent↗

PubMed1998

Variation in genome organization of the plant pathogenic fungus Colletotrichum lindemuthianum.

The genome structure of Colletotrichum lindemuthianum in a set of diverse isolates was investigated using a combination of physical and molecular approaches. Flow cytometric measurement of genome size revealed significant variation between strains, with the smallest genome representing 59% of the largest. Southern-blot profiles of a cloned fungal telomere revealed a total chromosome number varying from 9 to 12. Chromosome separations using pulsed-field gel electrophoresis (PFGE) showed that these chromosomes belong to two distinct size classes: a variable number of small (< 2.5 Mb) polymorphic chromosomes and a set of unresolved chromosomes larger than 7 Mb. Two dispersed repeat elements were shown to cluster on distinct polymorphic minichromosomes. Single-copy flanking sequences from these repeat-containing clones specifically marked distinct small chromosomes. These markers were absent in some strains, indicating that part of the observed variability in genome organization may be explained by the presence or absence, in a given strain, of dispensable genomic regions and/or chromosomes.

Ascomycota↗

PubMed1996

Neurotensin inhibits the activation of midbrain serotonergic neurons produced by random inescapable sound.

Previous studies indicate that exposure of rats to randomly presented, inescapable loud sound, referred to as sound stress, increases central serotonin turnover as well as the ex vivo activity of tryptophan hydroxylase (EC 1.14.16.4), the rate-limiting enzyme in serotonin biosynthesis. The purpose of this investigation was to determine whether intracerebroventricular (i.c.v.) administration of neurotensin (NT), a tridecapeptide found within the midbrain raphe, influences the activation of the midbrain serotonergic neurons by sound stress. Accumulation of 5-hydroxytryptophan (5-HTP) in vivo, in the presence of the aromatic amino acid decarboxylase inhibitor, NSD 1015 (m-hydroxybenzylhydrazine, 100 mg/kg i.p.) given immediately before a 30 min sound stress, was used as an index of in vivo tryptophan hydroxylase activity. Sound-stressed rats had significantly higher levels of 5-HTP in cortex and midbrain compared to sham-stressed controls. NT (0.01-3.3 nmol total), given i.c.v., 5 min prior to 30 min sound stress, completely blocked the enhanced accumulation of 5-HTP, but had no effect on basal accumulation of 5-HTP, except at the highest doses of 1.0 or 3.3 nmol, which others have previously shown to inhibit basal serotonergic metabolism. NT (0.3 and 3.3 nmol) blocked the increase in cortical tryptophan hydroxylase activity, ex vivo, in response to 30 min sound stress, without affecting basal enzyme activity. These and other recent data suggest a possible role for endogenous NT in the regulation of serotonergic neuronal activity within the midbrain raphe.

5-Hydroxytryptophan↗

PubMed1995

A clinical trial on diagnostic scoring system of choriocarcinoma and invasive mole in Vietnam.

OBJECTIVES: The aim was to discriminate preoperatively invasive mole (IM) and choriocarcinoma (CC) in patients with gestational trophoblastic neoplasm (GTN) for early and satisfactory treatment in Vietnam. METHODS: In 1990, 122 patients with GTN treated at TUDU Hospital were retrospectively analysed to make a differential diagnosis between CC and IM by using the JSOG scoring system and these results were later compared with postoperative histopathological findings. Furthermore, to raise the predictive diagnostic value for CC, the authors modified the JSOG system and devised a scoring system of TUDU hospital which results were compared with that of the JSOG ones. From the end of 1990 to March 1993, in 151 patients with GTN who underwent surgery, preoperative and postoperative diagnoses of CC and IM were prospectively compared using the JSOG and the modified scoring system. The comparative data were statistically analysed using the t-test, chi 2 test and Fisher test. The sensitivity, specificity, and the positive and negative predictive value, and false positive and false negative were calculated and compared. RESULTS RETROSPECTIVE STUDY: In making a predictive diagnosis of 122 patients with findings of trophoblastic tumors, the authors found some differences in possibility of CC of the following subfactors: latent period, primary lesion, pulmonary metastases, metastases except pulmonary metastases and hCG rerise. So, a modified scoring system of TUDU hospital was devised. PROSPECTIVE STUDY: Of 151 Vietnamese patients with GTN using the JSOG scoring system and the modified system, a diagnostic probability in 108 cases predicted choriocarcinoma by JSOG scoring system was 61%, while that of invasive mole in 43 cases was 62.8%. Accordingly, the false positive rate for invasive mole of 64 cases predicted choriocarcinoma was 38.9%. According to the modified scoring system, of 75 patients predicted choriocarcinoma, 69 patients were histologically confirmed choriocarcinoma. Therefore, the diagnostic specificity was high (94.20%) and the false positive rate was low (5.3%), while of 76 patients predicted invasive mole, 13 patients were histologically diagnosed as choriocarcinoma. Accordingly, the false negative rate was low (13.1%). CONCLUSION: The modified JSOG scoring system is of more diagnostic value in the preoperative differentiation between CC and IM in Vietnam.

Choriocarcinoma↗

PubMed1994

Sound stress activation of tryptophan hydroxylase blocked by hypophysectomy and intracranial RU 38486.

The rapidly reversible increase in cortical or midbrain tryptophan hydroxylase activity observed ex vivo after exposure of rats to 1-h sound stress was blocked by hypophysectomy, but not sham hypophysectomy, and restored by dexamethasone administration to the hypophysectomized animals (500 micrograms/day i.p. for 3 days). The response to sound stress was also lost with deafferentation of the hypothalamus. These results indicate that hypothalamic control of adrenal glucocorticoids is required for the serotonergic response to sound stress. The glucocorticoid antagonist, RU 38486, given intracerebroventricularly (200 micrograms/day for 4-5 days) or bilaterally, into the region of the central nucleus of the amygdala (100 micrograms 15 min before stress), blocked the sound stress-induced increase in tryptophan hydroxylase activity. In contrast, the antimineralocorticoid, RU 26752, was without effect. The block obtained with RU 38486 suggests that glucocorticoid is required by the neurons that relay the effects of sound stress to the rostrally projecting serotonergic neurons.

Acoustic Stimulation↗

PubMed1994

Intracranial dehydroepiandrosterone blocks the activation of tryptophan hydroxylase in response to acute sound stress.

Bilateral infusion of dehydroepiandrosterone (DHEA) given intracerebroventricularly blocked the sound stress-induced increase in tryptophan hydroxylase activity observed ex vivo in midbrain and cortex but had no effect on the level of tryptophan hydroxylase activity from sham-stressed rats. DHEA (20 micrograms total dose) given bilaterally into the region of the central nucleus of the amygdala, 30 min prior to 1 h sound stress, also blocked the increase in enzyme activity in a dose-dependent manner. The DHEA treatment did not alter the activation of the enzyme seen in vitro in the presence of phosphorylating conditions. The effect of DHEA was steroid specific in that other sex steroids, such as estrogen, androgens, or progesterone, were without any effect. Coadministration, 20 micrograms each, of the potent glucocorticoid agonist, RU 28362, with DHEA 30 min prior to 1 h sound stress completely blocked the DHEA suppressive effect on sound stress-induced increases in tryptophan hydroxylase activity. The results obtained suggest that DHEA blocks this increase in tryptophan hydroxylase activity by antagonizing the effects of glucocorticoid.

Acoustic Stimulation↗

PubMed1993

Evidence that corticotropin-releasing factor within the extended amygdala mediates the activation of tryptophan hydroxylase produced by sound stress in the rat.

Non-endocrine corticotropin-releasing factor (CRF) is believed to be involved in mediating stress behaviors in rats. The present study investigated the role of CRF in mediating the activation of tryptophan hydroxylase, the rate-limiting enzyme in serotonin synthesis, produced in response to sound stress. Bilateral injections of 0.5-3.0 micrograms of CRF directed towards the central nucleus of the amygdala increased tryptophan hydroxylase activity measured ex vivo when compared to vehicle-injected controls. This increase in enzyme activity, like that due to sound stress, was reversed in vitro by alkaline phosphatase. Intra-amygdala CRF (0.5 microgram) also enhanced the in vivo accumulation of 5-hydroxytryptophan (5-HTP) following the administration of m-hydroxylbenzylamine (NSD-1015, 200 mg/kg). The activation of tryptophan hydroxylase, produced by intra-amygdala CRF, was blocked by the CRF receptor antagonist alpha-helical CRF9-41 (10 micrograms). Additionally, the 5-HT1A agonist, gepirone, given either systemically (10 mg/kg) or intracerebrally into the region of the dorsal raphe (14 micrograms), blocked the tryptophan hydroxylase response to CRF. CRF did not increase tissue levels of 5-hydroxyindole acetic acid (5-HIAA) or the ratio of 5-HIAA to serotonin (5-HT) within the striatum of the same animals in which tryptophan hydroxylase activity was quantified, an effect produced by sound stress. Thus, while intra-amygdala CRF failed to mimic the sound stress response in its entirety, these data suggest that CRF is involved in mediating the activation of tryptophan hydroxylase produced by sound stress within the midbrain serotonin neurons.

Acoustic Stimulation↗

PubMed1992

Effect of gepirone on increases in tryptophan hydroxylase in response to sound stress.

Pretreatment (15 min) of male rats with gepirone given parenterally (10 mg/kg i.p.) or intracranially into the dorsal raphe nucleus (14 or 21 micrograms) blocks the rapidly reversible increase in brain tryptophan hydroxylase activity and 5-hydroxyindolamine acetic acid tissue levels seen in vitro after 1-h acute sound stress. Chronic gepirone treatment over 28 days (40 mg/day s.c.) prevents the stable enzyme activity increase induced by repeated sessions of sound stress, and the rapidly reversible increase always observed following sound stress. The gepirone metabolite, 1-(2-pyrimidinyl)-1-piperazine, is inactive in each of these experiments. Transient blood pressure elevations occur with each sound presentation, but no persistent hypertension is observed with repeated sound-stress exposures. Gepirone may block the sound stress-induced biochemical increases by its inhibition of serotonergic neuronal firing in the dorsal raphe nucleus that is mediated by its agonist action at the somatodendritic (5-HT1A) autoreceptors.

Animals↗

PubMed1990

The increases in rat cortical and midbrain tryptophan hydroxylase activity in response to acute or repeated sound stress are blocked by bilateral lesions to the central nucleus of the amygdala.

Sound stress (SS) (120-dB pulses of 100 ms duration, every min for 1 h) produces an elevation of in vitro cortical or midbrain tryptophan hydroxylase activity from male Sprague-Dawley rats that is abolished, in vitro, by incubation of the enzyme preparation with alkaline phosphatase. SS, when repeated on 3 different occasions, the first 2 sessions 24 h apart and the 2nd and 3rd session separated by 48 h, produces a stable increase in the in vitro enzyme activity that is unaffected by alkaline phosphatase. Bilateral lesions to the central nucleus of the amygdala block both increases in enzyme activity obtained in response to acute and repeated SS, but leave enzyme activity from sham-stressed rats unaffected.

Amygdala↗

PubMed1990

Increases in the activity of tryptophan hydroxylase from rat cortex and midbrain in response to acute or repeated sound stress are blocked by adrenalectomy and restored by dexamethasone treatment.

Exposure of male Sprague-Dawley rats to acute sound stress (2 s, 110 dB sound pulses presented randomly every minute for 1 h) increases the in vitro activity of cortical and midbrain tryptophan hydroxylase by an alkaline phosphatase-reversible mechanism. Repeated exposure to sound stress on three separate days produces a stable increase in enzyme activity that persists 24 h after the termination of the stress and is insensitive to alkaline phosphatase. Adrenalectomy abolishes both increases in enzyme activity to acute or repeated sound stress but does not change baseline levels of enzyme activity. The synthetic glucocorticoid, dexamethasone, (500 micrograms/day i.p.) given for 3 days or 5 out of 6 days, starting day 3 after adrenalectomy, restores the increases in enzyme activity in adrenalectomized rats exposed, respectively, to acute or repeated sound stress. The mineralocorticoid, aldosterone (5 micrograms/day s.c.), does not substitute for dexamethasone in acutely sound-stressed, adrenalectomized rats. Dexamethasone does not alter control levels of enzyme activity in either adrenalectomized rats or rats with intact adrenals (sham-adrenalectomized), but is required to allow the increase in enzyme activity in response to acute or repeated sound stress to be expressed. The effect of the glucocorticoid, thus, appears to be a permissive one.

Acoustic Stimulation↗

PubMed1989

Blockade of morphine-induced increases in brain tryptophan hydroxylase activity by systemic pretreatment with CCK-8: no reversal by vagotomy.

The treatment of rats with CCK-8 suppresses the behavioral responses to subsequent injection of opiates. We have investigated the possibility that peripherally administered CCK-8 can also suppress a neurochemical response to opiates, namely the increase in brain tryptophan hydroxylase (TrpH) activity and tissue 5-hydroxyindole acetic acid (5-HIAA) which results from morphine administration. While morphine sulfate (4 mg/kg s.c.) roughly doubled brain TrpH activity and tissue 5-HIAA 40 min after injection, pretreatment with CCK-8 (5 micrograms/kg i.p., 10 min prior to morphine) completely abolished this neurochemical change induced by morphine. Doses of CCK-8 as low as 1 microgram/kg were effective in blunting the morphine-induced increase in cortical TrpH activity, but the desulfated form was ineffective at doses of 5 and 100 micrograms/kg. Subdiaphragmatic vagotomy did not prevent the effect of CCK-8.

Animals↗

PubMed1989

Increase in the activity of tryptophan hydroxylase from cortex and midbrain of male Fischer 344 rats in response to acute or repeated sound stress.

Exposure of male Fischer 344 rats to an acute sound stress consisting of 100 dB tones of 2-s duration presented at random 60-s intervals for 2 h, increased cortical and midbrain tryptophan hydroxylase activity, measured in vitro, 50% over that from sham-stressed animals. This increase in enzyme activity was observed when animals were killed immediately, but not 1 h, after termination of the sound stress. It was non-additive with the increase in activity induced by incubation of enzyme under phosphorylating conditions and could be reversed in vitro with alkaline phosphatase. Graded increases in enzyme activity were obtained with increments of sound intensity (90-120 dB). In contrast to acute stress, chronic sound stress (110 dB) repeated over a period of 1, 2 or 6 weeks (3 sessions per week each of 2-h duration) produced a 50% increase in cortical enzyme activity that persisted 24 h after the termination of the stress and was not reversed by alkaline phosphatase. However, a further increase in enzyme activity could be produced if the chronically stressed animals were exposed to an acute 2-h stress (110 dB) immediately before being killed. This additional increase in activity was reversible in vitro by alkaline phosphatase and non-additive with that produced by incubation under phosphorylating conditions. In summary, acute sound stress produced a prompt, reversible activation of tryptophan hydroxylase. Repeated exposure to sound stress induced a persistent increase in enzyme activity that was detected 24 h after the last stress.

Acoustic Stimulation↗

PubMed1987

Activation of cortical tryptophan hydroxylase by acute morphine treatment: blockade by 6-hydroxydopamine.

Acute morphine produced a dose-dependent, naloxone-sensitive, reversible increase in tryptophan hydroxylase activity in low speed supernatants of midbrain, pons-medulla and cerebral cortex but not spinal cord. The increase in cortical enzyme activity was blocked by 6-hydroxydopamine pretreatment, could be reversed in vitro by incubation with alkaline phosphatase and was non-additive with the increase in enzyme activity induced in the presence of phosphorylating conditions. Morphine administration produced an increase in Vmax but no change in Km of cortical enzyme for substrate, tryptophan, or the artificial reduced pterin cofactor, 6-methyl-5,6,7,8-tetrahydropterin. The failure of morphine to increase spinal tryptophan hydroxylase activity despite enhancement of enzyme activity in medulla indicates regional differences in responsiveness of the enzyme to in vivo activation.

Alkaline Phosphatase↗