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J Ong

Publications and source records attributed to J Ong.

At least 19 recordsLinked to original sources
PubMed1998

The morpholino-acetic acid analogue Sch 50911 is a selective GABA(B) receptor antagonist in rat neocortical slices.

The pharmacological properties of (+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid (Sch 50911) were evaluated on GABA(B) receptors in rat neocortical slices. The GABA(B) receptor agonist, baclofen, produced a concentration-dependent depression of the frequency of spontaneous discharges in slices maintained in Mg2+-free Krebs medium with an EC50 of 6 microM, reversibly antagonised by Sch 50911 (5, 10 and 25 microM) with an apparent pA2 of 6.0 +/- 0.1. The (-) enantiomer Sch 50910 (500 microM) and the racemic des-methyl analogue Sch 48588 (500 microM) were inactive. In slices preloaded with [3H]GABA, Sch 50911 antagonised GABA(B) autoreceptors, increasing the electrically-stimulated 3H overflow in a concentration-dependent manner, with an IC50 of 3 microM. The maximal effect (148 +/- 10.5%) was found at 10 microM, but at 50 microM the response was reduced to 67 +/- 19%. In contrast, evoked release was unaffected by Sch 50910 (100 microM) whilst Sch 48588 at 100 microM increased the overflow by 51.3 +/- 11.6%. In summary, Sch 50911 is a relatively potent antagonist of considerable potential in studies of GABA(B) receptor function.

Animals↗
PubMed1998

Morpholin-2-yl-phosphinic acids are potent GABA(B) receptor antagonists in rat brain.

The pharmacological properties of morpholin-2-yl-phosphinic acids were evaluated on GABA(B) receptors. In rat neocortical slices maintained in Mg2+-free Krebs medium, baclofen, a GABA(B) receptor agonist, produced a concentration-dependent depression of the frequency of spontaneous discharges with an EC50 of 14 +/- 5.5 microM, which was antagonised reversibly by the morpholin-2-yl-phosphinic derivatives. The order of potency was 3-[(3S,6R)-6-[(cyclohexylmethyl)hydroxyphosphinoylmethyl- morpholin-3-yl]benzoic acid (CGP 76290A) (pA2 = 7.1 +/- 0.05) > its enantiomer 3-[(3R,6S)-6-[(cyclohexylmethyl)hydroxyphosphinoylmethyl]-++ +morpholin-3-yl]benzoic acid (CGP 76291A) (pA2 = 6.8 +/- 0.1) > cyclohexylmethyl-[(2R',5S')-5-(3-nitrophenyl)-morpholin-2-++ +ylmethyl]phosphinic acid (CGP 71978) (pA2 = 6.5 +/- 0.05) > cyclohexylmethyl-[(2R,5S)-5-phenyl-morpholin-2-ylmethyl++ +]phosphinic acid (CGP 71980) (pA2 = 6.3 +/- 0.15) > its enantiomer cyclohexylmethyl-[(2S,5R)-5-phenyl-morpholin-2-ylmethyl++ +]phosphinic acid (CGP 71979) (pA2 = 5.8 +/- 0.1). An open chain analogue of CGP 76290A, CGP 56999A (3-[1(R)-[(3-cyclohexylmethyl-hydroxyphosphinoyl)-2(S)-hydro xypropyl-amino]-ethyl]benzoic acid lithium salt) gave a pA2 of 6.6 +/- 0.2. In GABA(B) receptor binding assays, CGP 71982 (the racemic mixture of CGP 76290A and CGP 76291A), CGP 76290A, CGP 76291A, CGP 71978, CGP 71980 and CGP 71979 had IC50 values against [3H]CGP 27492 binding of 8, 1.85, 69, 124, 326 and 1460 nM, respectively. In electrically-evoked [3H]GABA release from rat cortical slices, CGP 71982, CGP 71978, CGP 71980 and its enantiomer CGP 71979, antagonised GABA(B) autoreceptors with EC150 values of 2.5, 33, 181 and 474 nM, respectively. These compounds form a novel class of potent GABA(B) receptor antagonists.

Animals↗
PubMed1998

3' IgH enhancer elements shift synergistic interactions during B cell development.

IgH gene expression is tightly controlled over the course of B cell development, B cell activation, and the subsequent differentiation of these cells into Ig-secreting plasmacytes. There are several transcriptional enhancers that map within and downstream of the IgH locus, and some of these have been clearly implicated in the developmental regulation of IgH gene assembly and expression. While some of the individual enhancers from this locus have been studied extensively, the functional interactions possible among this group of enhancers have been largely unexplored. In the present study, we have measured the transcriptional activities of combinations of enhancers introduced into B-lineage cell lines at several different developmental stages. We detected a developmental progression in which the 3' enhancers are initially inactive, then become strongly active through synergistic interactions, and finally achieve a strong level of activity with little interdependency. The relative contributions of E mu (the intron enhancer) and of the 3' enhancers also change as a function of developmental stage. We discuss these results in light of parallel studies of developmental changes in transcription factor requirements.

Animals↗
PubMed1998

The gamma-aminobutyric acid uptake inhibitor NO-711 potentiates 3-aminopropylphosphinic acid-induced actions in rat neocortical slices.

In rat neocortical slices maintained in Mg2+-free Krebs medium, the GABAB receptor agonists baclofen and 3-aminopropylphosphinic acid dose-dependently reduced the frequency of spontaneous discharges, 3-aminopropylphosphinic acid being 10 times less potent than baclofen. These were sensitive to the antagonist CGP 52432 (3-[[3,4-dichloro-phenyl)methyl]-amino]propyl](-P-diethoxymethyl)- phosphinic acid) (1, 5 and 10 microM). The GABA uptake inhibitor NO-711 (1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1,2,5,6-tetrahydro-3-+ ++pyridinecarboxylic acid) (5 and 10 microM) produced 2.9 and 9 fold increases in the potency of 3-aminopropylphosphinic acid without affecting baclofen-induced responses. In this study, the low potency of 3-aminopropylphosphinic acid when compared to baclofen, may be attributed to its uptake by NO-711-sensitive GABA transporters.

Animals↗
PubMed1998

Differential effects of phosphonic analogues of GABA on GABA(B) autoreceptors in rat neocortical slices.

The effects of five phosphonic derivatives of GABA on the release of [3H]-GABA from rat neocortical slices, preloaded with [3H]-GABA, were investigated. Phaclofen and 4-aminobutylphosphonic acid (4-ABPA) increased the overflow of [3H] evoked by electrical stimulation (2 Hz) in a concentration-dependent manner, with similar potencies (phaclofen EC50=0.3 mmol/l, 4-ABPA EC50=0.4 mmol/l). At 3 mmol/l, phaclofen increased the release of [3H]-GABA by 82.6+/-8.6%, and 4-ABPA increased the release by 81.3+/-9.0%. 2-Amino-ethylphosphonic acid (2-AEPA) increased the overflow of [3H] by 46.8+/-10.9% at the highest concentration tested (3 mmol/l). In contrast, the lower phosphonic homologue 3-aminopropylphosphonic acid (3-APPA), and 2-amino-2-(p-chlorophenyl)-ethylphosphonic acid (2-CPEPA), a baclofen analogue, did not modify the stimulated overflow. These results suggest that phaclofen, 4-ABPA and 2-AEPA are antagonists at GABA(B) autoreceptors, the latter being the weakest antagonist, whilst neither 3-APPA nor 2-CPEPA are active at these receptors. Since phaclofen, 4-ABPA and 2-CPEPA are antagonists and 3-APPA a partial agonist/antagonist on GABA(B) heteroreceptors, the lack of effect of 3-APPA and 2-CPEPA on [3H]-GABA release in this study suggests that GABA(B) autoreceptors may be pharmacologically distinct from the heteroreceptors.

Animals↗
PubMed1998

Surgery as salvage therapy in chemotherapy-resistant nonseminomatous germ cell tumours.

OBJECTIVE: To review our experience of surgical staging for residual masses after chemotherapy in patients with nonseminomatous germ cell tumour (NSGCT) and positive tumour markers. PATIENTS AND METHODS: Of 107 patients with metastatic NSGCTs treated surgically after chemotherapy from 1978 to 1995, 30 (median age 30.5 years, range 20-52) had positive tumour markers. These patients were reviewed and the outcome compared with 77 patients who had normal tumour marker values. RESULTS: Of the 77 patients with negative markers undergoing surgical/pathological staging, 71 (92%) became continuously disease-free, including 37 of 50 (74%) with viable NSGCT in excised specimens. Seventeen of 30 (57%) with raised marker levels undergoing similar surgery for chemotherapy-resistant tumour became disease-free, including 11 of 22 with viable NSGCT in the excised specimens. CONCLUSION: Although the outcome after surgery is better in patients with negative tumour markers, it is clear that surgery is curative for patients with localized chemotherapy-resistant masses. There is a need for continued debate on the timing of salvage surgery and subsequent chemotherapy.

Adult↗
PubMed1997

Actions of thienyl analogs of baclofen at GABA(B) receptors in rat neocortical slices.

In rat neocortical slices maintained in Mg2+-free Krebs medium, baclofen and its thienyl analogs, 4-amino-3-(5-chlorothien-2-yl)-butanoic acid (5h), 4-amino-3-(5-methylthien-2-yl)-butanoic acid (5d), 4-amino-3-(5-bromothien-2-yl)-butanoic acid (5f) and 4-amino-3-(thien-3-yl)-butanoic acid (5j) dose-dependently suppressed the spontaneous discharges, antagonised by the GABA(B) receptor antagonist 2-hydroxysaclofen (200 microM). Their relative potencies were baclofen > 5h > 5d > 5f > 5j. These heterocyclic analogs may prove useful as GABA(B) receptor agonists in functional studies.

Animals↗
PubMed1997

Use of intraperitoneal 5-fluorouracil and chlorhexidine for prevention of recurrence of perforated colorectal carcinoma in a rat model.

PURPOSE: Colorectal cancer is a prevalent and mortal disease, resulting in nearly 55,000 deaths in the United States annually. Preoperative or intraoperative spillage of tumor cells because of perforation occurs in up to 10 percent of cases. When this spillage occurs, the chance of recurrence and death is dramatically increased. METHODS: In an effort to reduce the chance of recurrence and death, we used a rat model to evaluate the efficacies of intraperitoneal 5-fluorouracil and chlorhexidine in reducing the incidence of recurrence. Rats were injected with 10 mg/kg azoxymethane subcutaneously weekly for 12 weeks to induce colorectal cancers. At 20 weeks, subtotal colectomies were performed on rats with colorectal tumors and without peritoneal implants or liver metastases. At the time of surgery, a cut portion of the tumor was placed in the abdomen for 30 minutes; the rats then randomly received peritoneal irrigation with 5-fluorouracil, chlorhexidine, or sterile water (control). Eight weeks postoperatively a necropsy was performed. At that time, obvious and suspected recurrences and the anastomotic area were sampled for histologic evaluation. RESULTS: Significant differences were seen with chlorhexidine vs. water for gross tumor (P = 0.05) and microscopic tumor (P < 0.05). 5-Fluorouracil showed a greater rate of abscess formation vs. both control and chlorhexidine (P > 0.05). CONCLUSIONS: Use of chlorhexidine intraperitoneal therapy at the time of the operation for perforated colorectal cancer significantly decreases the frequency of gross tumor recurrence but not total recurrences. Intraperitoneal 5-fluorouracil does not significantly decrease recurrence and may increase the risk of abscess when used intraoperatively.

Animals↗
PubMed1997

A single-centre observational study of surgery and late malignant events after chemotherapy for germ cell cancer.

OBJECTIVE: To review the impact of surgical staging after treatment on the late malignant events in an unselected group of patients treated with chemotherapy for germ cell cancer of the testis over the last 16 years. PATIENTS AND METHODS: The study comprised 256 patients treated between 1978 and 1994 who were reviewed for late relapse and development of second germ cell and non-germ cell cancer. RESULTS: At diagnosis, 142 patients had clinical stage 2, 30 stage 3 and 84 stage 4 disease; 57 patients relapsed within 20 months of treatment, while late germ-cell cancer relapses (> or = 24 months after treatment) occurred in six patients. Of patients relapsing early or late, 42% and 33%, respectively, received surgery after treatment. Only two of those relapsing late remain progression-free with further treatment. Four patients developed germ cell cancer in the contralateral testis, while six developed second non-germ cell cancers. CONCLUSION: Late events occurred in 6.2% of 256 patients in this series, from 29 to 141 months after treatment. Given that the late relapse rate of six of 256 (2.3%) is less than the incidence of mature teratoma at routine retroperitoneal lymph node dissection, more patients may eventually relapse. These results suggest that there might be a case to evaluate the use of ultrasonographic surveillance of the retroperitoneum and testis at 5, 10 and 20 years, in addition to extending routine surveillance.

Adult↗
PubMed1996

GABAB receptor antagonism by resolved (R)-saclofen in the guinea-pig ileum.

The GABAB receptor antagonist saclofen (3-amino-2-(4-chlorophenyl)propylsulphonic acid) has been resolved by chiral high-performance liquid chromatography. The enantiomer (R)-saclofen, but not (S)-saclofen, reversibly antagonised the (R,S)-baclofen-induced depression of cholinergic twitch contractions in the guinea-pig ileum with an apparent pA2 of 5.3. Also, 2-hydroxy-saclofen was resolved by the same method, its (S)-enantiomer yielding an apparent pA2 of 5.0. This method provides a convenient resolution of these antagonists.

Animals↗
PubMed1996

Testis conservation studies in germ cell cancer justified by improved primary chemotherapy response and reduced delay, 1978-1994.

OBJECTIVE: To investigate the need for the continued encouragement of early diagnosis of germ cell cancer of the testis, in view of the prevailing cure rate of 95%. PATIENTS AND METHODS: The study comprised a retrospective review of 453 unselected and previously untreated patients referred to one centre between 1978 and 1984, comparing the delay from first symptoms with the histological diagnosis. RESULTS: With a delay of < 30 days, 20% of patients had overt metastases at presentation and if the delay was > 4 months. 55% had metastases (chi-squared trend = 15.9, P < 0.001); 18% of Stage-1 patients under surveillance with a delay of < 30 days relapsed, compared with 38% of those with a delay of > 4 months. During the period 1978-1983, 16% of patients were seen after a delay of < 60 days, during the period 1984-1988 the proportion was 22% and during 1989-1994, 31% (chi-squared trend = 8.2, P < 0.004). There was a non-significant trend for a more prolonged delay in those aged < 21 years and > 40 years. Thirty-two patients had chemotherapy with the primary tumour in situ; at orchidectomy, 13 of 18 had no viable malignancy and four of five with viable malignancy also had drug-resistant metastases. Fourteen did not undergo orchidectomy; within a median follow-up of 9 years, one developed a second (histologically different) tumour after 12 years. The outcome of preliminary attempts to use neoadjuvant chemotherapy with or without partial orchidectomy for patients with tumours in a solitary testis is discussed. CONCLUSION: These findings clearly justify the continued encouragement of early diagnosis, possibly best performed as part of an extended educational programme of genital health at puberty. The long-term potential for testis conservation should be explored initially in tumours in a solitary testis.

Adult↗
PubMed1995

3-amino-2-hydroxy-N-(4-nitrophenyl)-propanesulphonamide, a new class of GABAB receptor antagonist in central and peripheral preparations.

Racemic 3-amino-2-hydroxy-N-(4-nitrophenyl)-propanesulphonamide (AHPNS), a sulphonamide analog of GABA, reversibly and competitively antagonised the concentration-dependent depression of cholinergic twitch contractions by baclofen, in the electrically stimulated guinea-pig isolated ileum, with a pA2 of 4.0 +/- 0.2. In the rat neocortex, maintained in Mg(2+)-free medium, AHPNS (100-500 microM) also reversibly antagonised the baclofen (10 microM)-induced suppression of spontaneous discharges. AHPNS is a new class of GABAB receptor antagonist that has central and peripheral blocking actions.

Animals↗
PubMed1995

Immunoglobulin gene transcription ceases upon deletion of a distant enhancer.

The tissue-specific E mu enhancer within the immunoglobulin heavy chain (IgH) locus has recently been shown to be essential for efficient V region gene assembly in early B lineage cells. However, we and others have shown that late stage, Ig-secreting cells can produce IgH in the absence of E mu. In the present study we have explored the notion that another enhancer found in the far 3' region of the IgH locus (3' alpha E) takes on an important regulatory role in cells that have reached this terminal stage in B cell development. The technique of homologous recombination was used to disrupt the 3' alpha E region in an E mu-deficient, Ig gamma 2a-secreting cell line. Loss of 3' alpha E completely abolished Ig heavy chain gene expression, demonstrating that transcription of this gene was dependent upon sequences that reside over 70 kb downstream. The ability of these sequences to function efficiently in the absence of E mu may also provide an explanation for deregulated c-myc expression in many Ig-secreting tumors.

Animals↗
PubMed1995

The (S)-enantiomer of 2-hydroxysaclofen is the active GABAB receptor antagonist in central and peripheral preparations.

In the guinea-pig isolated ileum, (RS)-(+/-)-baclofen induced a depression of cholinergic twitch contractions, reversibly and competitively antagonised by (S)-2-hydroxysaclofen (pA2 = 5.2 +/- 0.2), but not by (R)-2-hyroxysaclofen. The depression of excitatory field potentials by baclofen ( 5 mu M) in rat CA1 hippocampal slices was antagonised by (S)-2-hydroxysaclofen (100 mu m) (pA2 = 4.3), whilst in rat neocortex, (S)-2-hyroxysaclofen (50-500 mu M) antagonised the baclofen (10 mu M)-induced suppression of spontaneous discharges, the (R)-enantiomer being inactive. These results show that (S)-2-hydroxysaclofen is the active antagonist at central and peripheral GABAB receptors.

Animals↗
PubMed1995

Interactions of N-ethylmaleimide and aluminium fluoride with GABAB receptor function in rat neocortical slices.

Interactions of N-ethylmaleimide and aluminium fluoride (AlF - 4) with GABAB receptors have been examined using spontaneously discharging rat neocortical slices. The suppression of discharges by the GABAB receptor agonist baclofen (5-10 mu M) was irreversibly prevented by N-ethylmaleimide (10-50 mu M) and its analog N-phenylmaleimide (10-50 mu M), whilst superfusion of slices with NaF (10 mM) and AlCl3 (100 mu M) to form a fluoroaluminate (AlF - 4) complex markedly potentiated the action of baclofen. The lipoxygenase inhibitors, nordihydroguaiaretic acid (10-50 mu M) and eicosatetraynoic acid (10-50 mu M) or the phospholipase A2 inhibitor bromophenacylbromide (50-100 mu M) did not affect the response to baclofen. The depressant action of baclofen is evidently mediated through G-proteins, but is not dependent on arachidonic acid metabolites.

Aluminum Compounds↗
PubMed1995

GABAB receptors.

GABAB receptors are a distinct subclass of receptors for the major inhibitory transmitter 4-aminobutanoic acid (GABA) that mediate depression of synaptic transmission and contribute to the inhibition controlling neuronal excitability. The development of specific agonists and antagonists for these receptors has led to a better understanding of their physiology and pharmacology, highlighting their diverse coupling to different intracellular effectors through Gi/G(o) proteins. This review emphasises our current knowledge of the neurophysiology and neurochemistry of GABAB receptors, including their heterogeneity, as well as the therapeutic potential of drugs acting at these sites.

Baclofen↗
PubMed1995

Characterization of GABAB ligands in vivo.

1. While GABAB antagonists have been examined in vitro, very few have been tested in vivo. A range of GABAB antagonists were tested against baclofen-induced muscle relaxation and hypothermia. 2. The GABAB antagonists exhibited a range of in vivo activity profiles. 3. CGP 35348 showed clear antagonist effects, while BPBA and 4-ABPA appeared to have agonist properties. 4. Phaclofen, 2-hydroxysaclofen, 3-APPA and 9G seemed to have little effect in this system at the doses tested. 5. Differences between in vivo and in vitro activity could be explained by differences in blood-brain barrier permeability, or possible differences in affinities for the sub-classes of GABAB receptors.

Animals↗