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Biomedical subjects

J L Du

Publications and source records attributed to J L Du.

11 recordsLinked to original sources
PubMed2002

Glycinergic synaptic transmission to bullfrog retinal bipolar cells is input-specific.

Glycinergic inhibitory postsynaptic currents (IPSCs) focally elicited at the dendrites and axon terminals were recorded from bipolar cells in the bullfrog retinal slice, using the whole-cell clamp technique. IPSCs driven by input from interplexiform cells at bipolar cell dendrites (ipc-IPSCs) had a much slower decay time constant (25.2 +/- 7.8 ms) than IPSCs driven by input from amacrine cells at bipolar cell axon terminals (ac-IPSCs) (14.7 +/- 5.5 ms). Furthermore, peak-scaled non-stationary noise analysis revealed that the weighted mean single-channel conductance of the glycine receptors underlying bipolar cell dendritic ipc-IPSCs (20.8 +/- 6.6 pS) was significantly larger than that of those underlying bipolar cell axon terminal ac-IPSCs (12.9 +/- 2.9 pS). These results demonstrate that glycinergic synaptic transmission with different properties at bipolar cell dendrites and axon terminals differentially mediates intraretinal centrofugal signal transfer from the inner retina to the outer retina provided by interplexiform cells and lateral inhibition offered by amacrine cells in the inner retina.

Animals↗
PubMed2001

Sex change in the protandrous black porgy, Acanthopagrus schlegeli: a review in gonadal development, estradiol, estrogen receptor, aromatase activity and gonadotropin.

Black porgy, Acanthopagrus schlegeli Bleeker, a marine protandrous hermaphrodite, is functional male for the first two years of life but begins to sexually change to female after the third year. Testicular tissue and ovarian tissue was separated by connective tissue in the bisexual gonad. This sex pattern provides a very good model to study the endocrine mechanism of sex change in fish. The annual profiles of plasma estradiol, vitellogenin and 11-ketotestosterone concentrations in males were significantly different from those in the three-year-old females. Significantly high levels of plasma estradiol during the prespawning/spawning season and low levels of plasma 11-ketotestosterone during the spawning season were observed in the inversing females. No difference of plasma testosterone levels was observed in males and females. Oral administration of estradiol stimulated high levels of gonadal aromatase activity, plasma gonadotropin II levels and sex change in the two-year-old fish. Exogenous estradiol administered for 5-6 months induced a reversible sex change in one- and two-year-old fish. The sensitive period for estradiol treatment of sex change is from early prespawning to spawning season. Implantation with testosterone for more than a year could not block the natural sex change in three-year-old fish. Exogenous aromatase inhibitors (1,4,6-androstatriene-3,17-dione or fadrozole) suppressed aromatase activity in the brain. Oral administration with aromatase inhibitors for a year further inhibited the natural sex change in three-year-old black porgy and all fish became functional male with spermiation. Estrogen receptor alpha gene in the ovarian tissue of bisexual gonad is significantly less expressed than that in the vitellogenic ovary of female on the basis of reverse-transcription polymerase-chain reaction. There was no difference in the annual profiles of the plasma gonadotropin II levels in the males and natural inversing females. Plasma gonadotropin II levels were significantly higher in estradiol-treated group than those in the control. It is concluded that estradiol, aromatase activity and estrogen receptor in the ovarian tissue play an important role in the natural and controlled sex change in black porgy. The association of gonadotropin and sex change in black porgy is not clear.

Administration, Oral↗
PubMed2001

Estradiol-17beta stimulates gonadotropin II expression and release in the protandrous male black porgy Acanthopagrus schlegeli Bleeker: a possible role in sex change.

The objective of the present study was to investigate the in vivo effects of sex steroids (estradiol-17beta, E(2); testosterone, T) and the nonaromatizable androgen 5alpha-dihydrotestosterone (DHT) on the levels of gonadotropin II (GTH II) in plasma and pituitary and on aromatase activity in 2-year-old male black porgy, Acanthopagrus schlegeli, during the prereproductive season. Black porgy GTH II and GTH II beta subunits were purified and anti-GTH II beta serum was induced. A specific radioimmunoassay for black porgy GTH II was developed. cDNA GTH II beta was also cloned from a black porgy pituitary cDNA library for use as a probe for Northern analysis. Male fish were divided into eight groups (n = 64): control; E(2) (3 doses, 2.4 ng, 72 ng, and 2.2 microg/g body weight); T (2 doses, 72 ng and 2.2 microg/g body weight); and DHT (2 doses, 72 ng and 2.2 microg/g body weight). Fish were injected with the respective vehicle or different doses of material on days 0, 8, and 16. Plasma was collected at 4-day intervals from days 4 to 20. Plasma GTH II concentrations were significantly increased (up to 45-fold) in the E(2) group from days 4 to 20 in a dose-dependent manner. In a further experiment during the late reproductive season, plasma GTH II levels increased at 4 h and on days 1 and 2 following a single injection of 1.0 microg E(2)/g body weight (on day 0). Androgens (T or DHT) had little or no effect on plasma GTH II. Pituitary GTH II contents on day 20 were significantly lower in the 72-ng E(2) and 2.2-microg E(2) groups but not in the 2.4-ng E(2) group compared with the control group. Pituitary GTH II beta mRNA levels were significantly stimulated in the 72-ng and 2.2-microg E(2) groups on day 20. Gonadal aromatase activity was not significantly changed in any of the treated or control groups. It is concluded that GTH II secretion in black porgy is regulated by an estrogen-specific effect. Increased plasma GTH II levels or other factors in addition to E(2) might be involved in the regulation of gonadal aromatase activity and sex change in protandrous black porgy.

Amino Acid Sequence↗
PubMed2001

Regulation of plasma gonadotropin II secretion by sex steroids, aromatase inhibitors, and antiestrogens in the protandrous black porgy, Acanthopagrus schlegeli Bleeker.

Plasma gonadotropin II (GTH II) concentrations were significantly higher (approx. 15-20-fold) in estradiol-17beta (E(2)) treated (1.0 microg or 2.5 microg g(-1) body weight) female black porgy from days 4 to 12 compared with the control. E(2) (1 microg g(-1) wt.) had a stronger stimulation on plasma GTH II in early recrudescent phase (low GSI) males (11-fold) than in high GSI and late spermiating males (2.6-fold, P< 0.05). No effect of androgens (testosterone, T; 5alpha-dihydrotestosterone, DHT) on plasma GTH II levels was observed either sex. The levels of plasma GTH II were stimulated in 1,4,6-androstatriene-3,17-dione (ATD, 1 microg g(-1), 2 microg g(-1) body wt.) and fadrozole-treated (1 microg g(-1), 3 microg g(-1) body wt.) groups compared to control. Tamoxifen (1 microg g(-1), 3 microg g(-1) body wt.) but not enclomiphene could stimulate high GTH II levels in plasma. In another experiment of ATD in combination with T, T treatment further attenuated the ATD stimulation of plasma GTH II levels. We concluded that GTH II secretion is positively regulated by an estrogen-specific effect in female and male black porgy. Gonadal stage had significant effects on the responsiveness of GTH II to E(2) stimulation in males. A negative aromatase-dependent feedback control of plasma GTH II levels was also suggested in the protandrous black porgy, Acanthopagrus schlegeli.

Animals↗
PubMed2000

Profiles of gonadal development, sex steroids, aromatase activity, and gonadotropin II in the controlled sex change of protandrous black porgy, Acanthopagrus schlegeli Bleeker.

The objectives of the present study were to investigate the effects of oral administration of estradiol-17 beta (E(2)) on the sex steroids and gonadotropin II (GTH II) in plasma, aromatase activity in gonad and brain, and sex change in protandrous black porgy, Acanthopagus schlegeli Bleeker. Two-year-old black porgy were divided into two groups, one fed a control diet and the other a diet mixed with E(2) (4.0 mg/kg feed) for 7 months. Significantly higher GSI was observed in the E(2) group. Fish treated with E(2) showed complete suppression of spermatogenesis and spermiation and induced sex change with vitellogenic oocytes and large primary oocytes. Lower levels of plasma 11-ketotestosterone and higher levels of plasma vitellogenin were shown in the E(2) group. Higher gonadal aromatase activity in concordance with elevated plasma levels of GTH II was observed in the E(2) group. The highest aromatase activity in the forebrain in the control group was observed in January. Higher aromatase activity in forebrain, midbrain, and hindbrain was also detected in the E(2) group than the control group. The change of aromatase activity in brain was more susceptible than that in gonad. The data showed that the increase of plasma GTH II levels and gonadal aromatase activity may be important to the controlled sex change by administration in black porgy.

Animals↗
PubMed2000

Subcellular localization and complements of GABA(A) and GABA(C) receptors on bullfrog retinal bipolar cells.

gamma-Aminobutyric acid (GABA) receptors on retinal bipolar cells (BCs) are highly relevant to spatial and temporal integration of visual signals in the outer and inner retina. In the present work, subcellular localization and complements of GABA(A) and GABA(C) receptors on BCs were investigated by whole cell recordings and local drug application via multi-barreled puff pipettes in the bullfrog retinal slice preparation. Four types of the BCs (types 1-4) were identified morphologically by injection of Lucifer yellow. According to the ramification levels of the axon terminals and the responses of these cells to glutamate (or kainate) applied at their dendrites, types 1 and 2 of BCs were supposed to be OFF type, whereas types 3 and 4 of BCs might be ON type. Bicuculline (BIC), a GABA(A) receptor antagonist, and imidazole-4-acetic acid (I4AA), a GABA(C) receptor antagonist, were used to distinguish GABA receptor-mediated responses. In all BCs tested, not only the axon terminals but also the dendrites showed high GABA sensitivity mediated by both GABA(A) and GABA(C) receptors. Subcellular localization and complements of GABA(A) and GABA(C) receptors at the dendrites and axon terminals were highly related to the dichotomy of OFF and ON BCs. In the case of OFF BCs, GABA(A) receptors were rather evenly distributed at the dendrites and axon terminals, but GABA(C) receptors were predominantly expressed at the axon terminals. Moreover, the relative contribution of GABA(C) receptors to the axon terminals was prevalent over that of GABA(A) receptors, while the situation was reversed at the dendrites. In the case of ON BCs, GABA(A) and GABA(C) receptors both preferred to be expressed at the axon terminals; relative contributions of these two GABA receptor subtypes to both the sites were comparable, while GABA(C) receptors were much less expressed than GABA(A) receptors. GABA(A), but not GABA(C) receptors, were expressed clusteringly at axons of a population of BCs. In a minority of BCs, I4AA suppressed the GABA(C) responses at the dendrites, but not at the axon terminal, implying that the GABA(C) receptors at these two sites may be heterogeneous. Taken together, these results suggest that GABA(A) and GABA(C) receptors may play different roles in the outer and inner retina and the differential complements of the two receptors on OFF and ON BCs may be closely related to physiological functions of these cells.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2000

Expression of GABA transporters on bullfrog retinal Müller cells.

gamma-Aminobutyric acid (GABA) transporters (GATs) are involved in regulating GABAergic transmission through the high-affinity uptake and release of GABA. In the present work, the expression of different subtypes of GATs (GAT-1, GAT-2, and GAT-3) on Müller cells was investigated both immunocytochemically and electrophysiologically in the bullfrog retina. Double-labeling experiments of glial fibrillary acidic protein (GFAP), a specific marker for Müller cells, and GATs showed that the somata, major processes, endfeet, and even branchlets of almost all Müller cells strongly expressed GAT-1 on the membrane, whereas the main trunks and endfeet of about 80-90% Müller cells were moderately GAT-2 labeled. No GAT-3 immunoreactivity was observed in Müller cells. Meanwhile, using the whole-cell recording technique, GAT-mediated currents were recorded from Müller cells in the retinal slice preparation, and they were reversibly blocked by removal of extracellular Na(+) and spread more or less evenly over the surface of these cells. Furthermore, the GATs on the Müller cells were sensitive to both nipecotic acid and beta-alanine, GABA uptake blockers. Taken together, the complementary immunocytochemical and electrophysiological results suggest that bullfrog Müller cells express functional GAT-1 and GAT-2, which may regulate GABAergic transmission by either taking up or releasing GABA, or both.

Animals↗
PubMed1997

The endocrine mechanism of sex reversal in the protandrous black porgy, Acanthopagrus schlegeli: a review.

Black porgy, Acanthopagrus schlegeli Bleeker, a marine protandrous hermaphrodite, is a functional male for the first 2 years of life but begin to sexually reverse to female after the third year. This sex pattern provides a very good model to study the mechanism of sex reversal in fish. The gonad at 5 month of age consisted of testicular tissue with few primary oocytes at 5 month of age. The ovarian tissue became dominant at 18 months of age during the non-spawning season. Testicular and ovarian tissues were separated by connective tissue. Plasma estradiol-17 beta(E2), vitellogenin and 11-ketotestosterone (11-KT) profiles in males were significantly different from those in the 3-year-old reversing females. Peak levels of plasma E2 in the reversing females occurred during the early prespawning season (in October). Lower levels of plasma E2 were, however, observed in the males. Plasma 11-KT levels significant decreased but no changes of plasma testosterone were detected in the reversing females. Exogenous E2 suppressed the testicular development but induced the gonadal aromatase activity, ovarian development and sex reversal in 2-year-old black porgy. Exogenous T and LHRH analog did not have effects on the sex reversal. Higher concentrations of pituitary GtH II and mRNA of GtH II-beta subunit were detected in the reversed females. These data suggested that E2 and gonadal aromatase closely associated to the occurrence of sex reversal. A working model of the sex reversal in black porgy is proposed.

Animals↗
PubMed1995

Electron-electron spin-spin interaction in spin-labeled low-spin methemoglobin.

Nitroxyl free radical electron spin relaxation times for spin-labeled low-spin methemoglobins were measured between 6 and 120 K by two-pulse electron spin echo spectroscopy and by saturation recovery electron paramagnetic resonance (EPR). Spin-lattice relaxation times for cyano-methemoglobin and imidazole-methemoglobin were measured between 8 and 25 K by saturation recovery and between 4.2 and 20 K by electron spin echo. At low temperature the iron electron spin relaxation rates are slow relative to the iron-nitroxyl electron-electron spin-spin splitting. As temperature is increased, the relaxation rates for the Fe(III) become comparable to and then greater than the spin-spin splitting, which collapses the splitting in the continuous wave EPR spectra and causes an increase and then a decrease in the nitroxyl electron spin echo decay rate. Throughout the temperature range examined, interaction with the Fe(III) increases the spin lattice relaxation rate (1/T1) for the nitroxyl. The measured relaxation times for the Fe(III) were used to analyze the temperature-dependent changes in the spin echo decays and in the saturation recovery (T1) data for the interacting nitroxyl and to determine the interspin distance, r. The values of r for three spin-labeled methemoglobins were between 15 and 15.5 A, with good agreement between values obtained by electron spin echo and saturation recovery. Analysis of the nitroxyl spin echo and saturation recovery data also provides values of the iron relaxation rates at temperatures where the iron relaxation rates are too fast to measure directly by saturation recovery or electron spin echo spectroscopy. These results demonstrate the power of using time-domain EPR measurements to probe the distance between a slowly relaxing spin and a relatively rapidly relaxing metal in a protein.

Cyclic N-Oxides↗
PubMedDate not supplied

Multifrequency electron paramagnetic resonance of irradiated L-alanine.

The radical generated by gamma-irradiation of crystalline L-alanine was examined by continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) at 1.8, 3.2, 4.9, 9.1 and 19.4 GHz. The spin-flip satellite lines that make a prominent contribution to the saturated spectra at 9.1 GHz are less conspicuous at lower frequencies because of overlap with the allowed transitions. The spin-lattice relaxation times measured by long-pulse saturation recovery and phase memory times measured by electron spin echo increase with increasing microwave frequency.

Alanine↗