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M E Reith

Publications and source records attributed to M E Reith.

At least 145 records · Page 8Linked to original sources
PubMed1984

Endogenous material in brain inhibiting [3H]nicotine and [3H]acetylcholine binding.

The supernatant obtained from mouse brain homogenates contains material that inhibits the saturable binding of [3H]nicotine in mouse cerebral cortex. This inhibitory material was further purified by heat denaturation, ultrafiltration through an Amicon PM-10 membrane filter, and gel chromatography on Sephadex G-10. The material inhibited the binding of [3H]acetylcholine with the same potency as it did that of [3H]nicotine. It also had some affinity for the sites that specifically bind [3H]D-Ala, D-Leu enkephalin, but had much lower affinity for the binding sites for [3H]quinuclidinyl benzilate (QNB), [3H]spiroperidol, [3H]naloxone, or [3H]imipramine. Acid hydrolysis destroyed the activity. These preliminary results suggest the presence in brain of "nicotinelike" substances, one of which may be the endogenous ligand for the sites that specifically bind [3H]nicotine.

Acetylcholine↗
PubMed1984

Binding of imipramine and cocaine to a model lipid membrane: comparison with binding to brain membranes.

[3H]Imipramine and [3H]cocaine were concentrated at membranes of liposomes prepared from phosphatidylcholine, cholesterol, and dicetylphosphate. This "binding" has an apparent dissociation constant in the micromolar range and a density close to 2 pmol/micrograms of phosphatidylcholine. The potencies of various drugs in inhibiting the binding to liposomes correlated only weakly with those in inhibiting the high-affinity binding of [3H]imipramine and [3H]cocaine to brain membranes. However, there was a highly significant correlation between the potencies of drugs in inhibiting binding to liposomes and their lipophilic character, indicating the involvement of hydrophobic bonding. Although the amounts of phosphatidylcholine and cholesterol in brain preparations in assays for high-affinity binding to brain membranes were in the same range as those used in our assays with liposomes, the inhibition of the high-affinity binding to brain membranes was only weakly dependent upon the lipophilicity of the inhibiting drug. These results indicate that lipophilicity is but one of the factors in the complex binding interactions between lipophilic substances and integral brain membranes. In addition, the results are in agreement with the suggestion that phosphatidylcholine and cholesterol are not the primary sites of high-affinity binding [3H]imipramine and [3H]cocaine to brain membranes, although it cannot be ruled out that these lipids have different properties in natural biological membranes and in artificial liposome membranes.

Animals↗
PubMed1984

[3H]cocaine binding in brain is inhibited by Tris (hydroxymethyl) aminomethane.

High-affinity binding of [3H]cocaine to membranes of mouse cerebral cortex is inhibited by Tris (hydroxymethyl) aminomethane, the buffer commonly used in receptor binding assays. This inhibition is not due to an effect of ionic strength in general. Comparison of binding in Tris buffer with that in sodium phosphate buffer indicates a more than 4-fold higher Kd in the former buffer, with no differences in the Bmax values.

Animals↗
PubMed1984

Similarities and differences between high-affinity binding sites for cocaine and imipramine in mouse cerebral cortex.

Previously we found close similarities between high-affinity binding sites for [3H]cocaine and those for [3H]imipramine in the mouse cerebral cortex in regard to their association with neuronal uptake of serotonin. In the present study we investigated whether the two ligands bind to the same site. The two ligands had the following high-affinity binding properties in common: localization in both synaptosomal and microsomal fractions; vulnerability to treatment with N-ethylmaleimide, trypsin, and phospholipase A2; and resistance to exposure to dithiothreitol. In contrast, cocaine binding in the cerebral cortex was more sensitive to heat inactivation than imipramine binding. In addition, the mechanism by which cocaine inhibited [3H]imipramine binding differed from that by which imipramine inhibited [3H]cocaine binding. These data suggest that the high-affinity binding sites for [3H]cocaine and [3H]imipramine in the cerebral cortex are distinct entities.

Animals↗
PubMed1983

Imipramine does not act as a false transmitter in the rat hypothalamus.

[3H]Imipramine was accumulated by rat hypothalamic slices mostly by a passive low-affinity process. Accumulated [3H]imipramine was released by 60 mM potassium, but the release was small and was not Ca2+-dependent. Imipramine induced some release of [3H]norepinephrine. None of these events were abolished by pretreatment of the rats with reserpine. These results do not favor the view that imipramine acts as a false transmitter in the rat hypothalamus. Rather, imipramine appears to be accumulated in an extragranular pool from which it releases extragranular norepinephrine.

Animals↗
PubMed1983

High- and low-affinity binding of [3H]imipramine in mouse cerebral cortex.

Binding of [3H]imipramine in mouse cerebral cortex was found to be nonhomogeneous. Competition experiments, Scatchard analysis, and Hill plots are compatible with the existence of binding with high (nanomolar) and low (micromolar) affinity. Low-affinity binding could be eliminated by the use of low concentrations of imipramine as the competing ligand. In contrast to the high-affinity binding, the low-affinity binding was found to be unrelated to the neuronal uptake system for serotonin.

Animals↗
PubMed1983

A portion of [3H]cocaine binding in brain is associated with serotonergic neurons.

Three lines of evidence are brought forward in support of an association in the brain cortex of some, but not all, of the cocaine binding sites with serotonergic nerve terminals. The first is based upon the significant correlation observed between the inhibition of cocaine binding by various drugs and the inhibition of neuronal uptake of serotonin in the mouse cerebral cortex. The second is based upon the demonstration of cocaine binding in human blood platelets, a model system for central serotonergic neurons. The third comes from experiments in which rats were treated with p-chloroamphetamine and 5,7-dihydroxytryptamine (serotonin neurotoxins), 6-hydroxydopamine (catecholamine neurotoxin), or p-chlorophenylalanine (inhibitor of tryptophan hydroxylase). Only the serotonin neurotoxins decreased the binding of [3H]cocaine in the rat cerebral cortex, but to a lower extent than the binding of [3]imipramine, which is known to be associated with serotonergic terminals. In contrast to the cocaine binding in the mouse cerebral cortex, the binding in the rat cerebral cortex included a considerable portion of low-affinity binding that was relatively unaffected by lesions of serotonergic neurons.

Animals↗
PubMed1982

On the interaction between nicotine and cycloheximide.

This study examined whether the nicotine-induced reversal of the amnestic effect of cycloheximide is due to an interaction between nicotine and cycloheximide on brain protein synthesis, and whether it involves the sites in brain that saturably bind [3H]nicotine. Nicotine did not reverse the cycloheximide-induced inhibition of protein synthesis, both in in vivo (intact animal) and in vitro (brain slice), suggesting that on-going protein synthesis is not necessarily involved in memory consolidation. The nicotine binding sites were not affected by in vivo or in vitro treatment with cycloheximide in the presence or absence of nicotine.

Animals↗
PubMed1982

Effects of prenatal administration of nicotine on amino acid pools, protein metabolism, and nicotine binding in the brain.

The effects of nicotine on brain protein metabolism and on the properties of the nicotine binding site were investigated in newborn animals exposed to nicotine during gestation. Brain protein synthesis rates measured in vivo were lower by 18% in newborn of treated animals. Protein degradation rates measured in vitro in the presence of nicotine were lower by 13%. The effect was specific for L-(-)nicotine, since D-(+)nicotine, nicotinic acid, or nicotinamide had no effect on degradation rates. Newborn brain amino acid levels, mainly nonessential amino acids and amino acids of putative neurotransmitter function, were changed somewhat; an increase in the level of taurine (13%), threonine (21%), serine (35%) and glycine (35%), and a decrease in lysine (14%) was observed in the offspring of nicotine treated animals (0.5 mg/kg, s.c., 2 x daily throughout gestation). These changes could not account for the decrease in protein metabolism. Nicotine binding was higher by 25% in the offspring of animals exposed to nicotine during gestation. No such increase was found after treatment of adult rats with nicotine, indicating that the properties of the nicotine binding site change with age.

Aging↗
PubMed1982

Comparison of the properties of central and peripheral binding sites for cocaine.

Cocaine and its analogs bound saturably to membranes of brain and liver of mice. The binding sites on membranes of liver had a lower affinity for cocaine than those of brain. In addition, there were striking differences between the two tissues in regard to the relative potencies of cocaine analogs in competing with [3H]cocaine for binding. In comparison with the binding sites in brain, those in liver had only moderate stereospecificity, and they discriminated less between the centrally active compounds and the centrally inert analogs.

Animals↗
PubMed1981

Strain differences in opiate receptors in mouse brain.

Various opiate ligands were bound to brain membranes of mice of the Recombinant Inbred System. The specific binding of low levels of [3H]naloxone, [3H]dihydromorphine and [3H]ethylketocyclazocine was disturbed in a similar fashion among the inbred strains, and in a pattern different from that observed for [3H](D-Ala2,D-Leu5)-enkephalin. The results indicate that the inbred strains differ in mu- and delta-type binding and support the concept of multiple opiate receptors in mouse brain.

Animals↗
PubMed1981

Noncholinergic, saturable binding of (+/-)-[3H]nicotine to mouse brain.

(+/-)-[3H]Nicotine was bound saturably to crude particulate, and synaptosomal-mitochondrial fraction from mouse brain. Scatchard and Hill plots of the binding data are in agreement with the existence of two independent classes of binding sites with high (Kd of 0.1-0.4 microM) and low(Kd is 20 microM) affinities, although negative cooperativity or a two-step model of ligand-receptor interaction cannot be ruled out. Nicotinic or muscarinic agonists and antagonists had little or no affinity for the nicotine binding sites, suggesting that nicotine binds in brain to noncholinergic sites. The binding did not display stereospecificity; this is consistent with the similarity in the pharmacological effects of (-)- and (+)-nicotine. Our results indicate that binding studies with [3H]nicotine should be interpreted with extreme caution.

Animals↗
PubMed1981

Binding of [3H]cocaine in mouse brain: kinetics and saturability.

Kinetic experiments indicate that association of [3H]-cocaine to its binding site in brain occurs rapidly (seconds). Dissociation of membrane-bound cocaine is also rapid, with a dissociation half-life in seconds; this raises the question of whether membrane-bound cocaine is released during the time required for rapid filtration of tissue-containing filters. Results from experiments with increasing numbers of filter-washes indicate that there is no significant loss of [3H]-cocaine saturably bound to brain membranes within the time-scale of the rapid filtration procedure. In addition, saturation analysis of binding data obtained with the filtration procedure and with the centrifugation method give similar estimates of the affinity (dissociation constant: 0.8 microM) and the maximal binding (5 pmol/mg of protein) of cocaine. However, the nonspecific binding and the experimental error in the saturable binding are considerably greater in centrifugation assays than in filtration assays.

Animals↗
PubMed1980

Endogenous peptide(s) inhibiting [3H]cocaine binding in mouse brain.

The supernatant fraction of centrifuged homogenate of brain tissue contains material that inhibits the saturable binding of [3H]cocaine to crude mouse brain membranes. This material was subjected to heat treatment to remove protein; further purification was achieved by filtering through an Amicon UM-10 membrane ultrafilter and gel filtration of the ultrafiltrate on Sephadex G-25. Sensitivity to acid hydrolysis and peptidase action indicates that the inhibitory activity resides in peptide material with low molecular weight. The partially purified inhibitor has similar effects to that of cocaine on the specific binding of various ligands to opiate and nonopiate receptors in mouse brain membranes.

Animals↗