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Biomedical subjects

L M Neckers

Publications and source records attributed to L M Neckers.

120 records · Page 7Linked to original sources
PubMed1978

Increased adenylate cyclase activity and rapid weight loss following intraseptal injection of cholera toxin.

Cholera toxin, stereotaxically injected into the medial septal nucleus of the rat, leads within 24 h to a dramatic decrease in body weight and an increase in septal adenylate cyclase activity. Toxin-treated rats drink one-third the water of vehicle-treated animals while excreting two-and-one half times the urine. Food intake over the 24-h period is depressed to 13% of control but feces production was normal. The dramatic increase of urinary output suggests that cholera toxin activates a septal adenylate cyclase system which supressess the release of antidiuretic hormone. Cholera toxin injection into the septum may be a unique alternative to electrical stimulation for investigating septal involvement in the regulation of neuronal and metabolic processes.

Adenylyl Cyclases↗
PubMed1977

Modulation of brain tryptophan hydroxylase activity by brain tryptophan content.

Although hydroxylation of tryptophan (TP) is considered to be the rate-limiting step in serotonin synthesis, the mechanism whereby tryptophan hydroxylase (TPH) participates in the regulation of serotonin synthesis is still in question. Since the brain TP concentration is probably near the Km for tryptophan hydroxylase, changes in brain TP content could affect the rate of its hydroxylation. However, it has not been established whether in vivo the activity of TPH and TP in several brain nuclei and other regions of rat brain after treatments known to lower brain TP levels. Chlorimipramine, loading with neutral amino acids and a TP-deficient diet decreased the TP content of some, but not all, brain regions studied. Whenever TP decrease withe TP injections. Several brain nuclei accumulate TP at different rates after a TP load. These data suggest possible mechanisms for regulation of serotonin synthesis in the face of fluctuating plasma levels of TP.

Amino Acids↗
PubMed1976

Reduction of tryptophan hydroxylase activity and 5-hydroxytryptamine concentration in certain rat brain nuclei after p-chloroamphetamine.

High-pressure liquid chromatography and mass fragmentography have been used to determine tryptophan hydroxylase activity and 5-hydroxytryptamine (5-HT) concentration, respectively, in certain rat brain nuclei. (+/-)-p-Chloroamphetamine (100 mumol/kg i.p.) decreased enzyme activity in 5-HT terminals of the caudate, hippocampus and septum to a minimum level within 3 days. In hippocampus, but not in septum, the enzyme activity and 5-HT content remained maximally depleted (about 80%) for as long as 2 months after the p-chloroamphetamine injection. Of the 5-HT cell body areas investigated, only in the B9 nucleus was the tryptophan hydroxylase activity and 5-HT content still significantly reduced (about 25-50%) at 21 and 60 days after the drug injection. The enzyme activity and 5-HT content of the B7 and B8 nuclei were not significantly different from control values at these times. These results suggest that the primary site of action of p-chloroamphetamine is on nerve terminals followed by secondary effects on serotonergic cell bodies.

Amphetamines↗
PubMedDate not supplied

Influence of olfactory bulbectomy and the serotonergic system upon intermale aggression and maternal behavior in the mouse.

Biochemical parameters in the brains of olfactory bulbectomized male and female mice were studied in two experiments, followed by three experiments in which 5-HTP was injected into bulbectomized males and females to try to block abnormal behaviors. In Experiment 1 bulbectomized male and female mice had significantly less tryptophan hydroxylase in their brains than did sham controls. Neither 5-hydroxtryptophan decarboxylase nor tyrosine hydroxylase activity was affected. In Experiment 2 the rate of synthesis of 5-HT was significantly less in bulbectomized males and females. Since bulbectomy leads to increased pup killing by female mice, the objective of Experiments 3 and 4 was to see whether the injection of 5-HTP into bulbectomized females could block this behavior. The incidence of pup killing was not influenced, but in both studies the latency to kill was significantly prolonged. Olfactory bulbectomy eliminates aggressive behavior in male mice, and the purpose of Experiment 5 was to determine whether 5-HTP treatment could restore normal levels of aggression. No significant effect was found. The data suggest that a dual mechanism is needed to explain the behavioral abnomalities seen in the two sexes; the mechanism in the female appears to be serotonergic while that in the male is still unknown.

5-Hydroxytryptophan↗
PubMedDate not supplied

A c-myc antisense oligodeoxynucleotide inhibits entry into S phase but not progress from G0 to G1.

Initiation of T-lymphocyte proliferation by mitogen or antigen involves a cascade of gene activation events. Thus, by the time mitogen-activated T cells have reached the G1/S interface, many genes that are transcriptionally silent in G0, like the c-myc, IL-2, IL-2 receptor (IL-2R) and transferrin receptor (TfR) genes, have been transcriptionally activated. To understand the role of the individual genes in the activation process, one must be able to interfere specifically with the expression or function of each particular gene product. In this way, by blocking the IL-2R with an antibody, it has been demonstrated that IL-2/IL-2R interaction is required to induce TfR expression in activated T cells. When the function or expression of intracellular proteins is to be blocked, however, the need to introduce antibodies into the cytoplasm of viable cells, although possible, is a limiting factor. We have taken another approach, namely the exogenous addition to bulk cell cultures of small antisense oligomers. Sequence-specific antisense oligodeoxyribonucleotides have been reported to inhibit intracellular viral replication without interfering with cellular protein synthesis. Similarly, rabbit globin mRNA translation in a cell-free system and in rabbit reticulocytes has been inhibited by oligomers complementary to the globin mRNA initiation codon region. Recently, a pentadecadeoxyribonucleotide complementary to the initiation codon and four downstream codons of human c-myc mRNA was reported to inhibit the proliferation of the human leukaemic cell line HL-60 specifically. We report here that the same c-myc complementary oligonucleotide inhibits mitogen-induced c-myc protein expression in human T lymphocytes and prevents S phase entry. Interestingly, c-myc antisense treatment did not inhibit G0 to G1 traversal as assessed by morphologic blast transformation, transcriptional activation of the IL-2R and TfR genes, or induction of 3H-uridine incorporation.

Cell Division↗
PubMedDate not supplied

Detection of functional interferon alpha receptors in human neuroendocrine tumor cell lines using a new monoclonal antibody.

While first described as antiviral agents, interferons (IFNs) exhibit significant antiproliferative and antitumor effects as well. IFN alpha has been successfully used in clinical trials to treat several malignancies, including leukemias and certain solid tumors. While many cell types have been studied for IFN alpha receptor expression, very little is known about receptor expression on human neuroendocrine cells. Using a novel anti-IFN alpha receptor monoclonal antibody, we examined IFN alpha receptor expression in 10 human cell lines derived from tumors of neuroendocrine origin, including neuroblastoma, neuroepithelioma and small cell lung carcinoma. All cell lines studied displayed a similar pattern of IFN alpha receptor expression and 5 of 8 cell lines demonstrated reduced thymidine incorporation following IFN alpha treatment. Addition of exogenous IFN alpha caused a decrease in IFN alpha receptor expression, while differentiating agents, such as phorbol esters and retinoic acid, induced an increase in receptor number without altering receptor affinity.

Antibodies, Monoclonal↗
PubMedDate not supplied

The role of Bcl-2 protein and autocrine growth factors in a human follicular lymphoma-derived B cell line.

We have shown that the ability of the human follicular lymphoma-derived cell line SU-DHL-6 to proliferate and survive in vitro depends on both Bcl-2 expression and multiple autocrine growth factors. Treatment with Bcl-2 antisense (AS Bcl-2) decreased Bcl-2 protein levels. However, a cytotoxic effect was seen only at very restricted cell densities. Below such densities cells underwent spontaneous death without any treatment, while above these cell densities no cytotoxic effect of AS Bcl-2 could be seen. The conditioned medium of SU-DHL cells supported the survival and growth of these cells cultivated at low cell densities and partially reversed the cytotoxicity associated with Bcl-2 depletion. RT/PCR analysis revealed autocrine expression of IL-1 beta, IL-2, IL-5 and TNF-beta in SU-DHL cells. Neutralizing antibodies against these cytokines inhibited SU-DHL proliferation. Thus, development of autocrine GF secretion may be the second step in the pathogenesis of follicular lymphomas.

B-Lymphocytes↗
PubMedDate not supplied

Sensitive and simple bioassay for human tumour necrosis factor-alpha.

A simple, sensitive, and specific in vitro bioassay is described for human tumour necrosis factor alpha (TNF-alpha). The system employs the U937 cell line incubated with 10 ng/ml actinomycin D for maximum sensitivity. This method allows the detection of less than 0.6 pg/ml of TNF-alpha and the log dose-response curve is linear at concentrations 0.6-250 pg/ml TNF-alpha. Highly sensitive subclones of U937 were obtained which were capable of detecting as little as 0.1 pg/ml TNF-alpha. Finally, this bioassay demonstrates specificity by discriminating between TNF-alpha and TNF-beta.

Biological Assay↗