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Biomedical subjects

L G Abood

Publications and source records attributed to L G Abood.

At least 19 recordsLinked to original sources
PubMed1992

4-Bromoacetamidoprocaine: an affinity ligand for brain muscarinic and nicotinic cholinergic receptors.

This study describes the synthesis, receptor binding characteristics, and some behavioral effects of p-bromoacetamidoprocaine (BAP), a new affinity ligand for brain muscarinic and nicotinic cholinergic receptors. The reversible binding of [3H]QNB to rat brain membranes was inhibited in a concentration dependent and saturable manner by both procaine and BAP, with Ki values of 4 x 10(-6) and 3 x 10(-7) M, respectively, and complete inhibition at 1 x 10(-5) M. Both procaine and BAP, although at much concentrations, inhibited the binding of [3H]methylcarbamylcholine in a concentration dependent manner, with Ki values of 5 x 10(-5) and 1 x 10(-5) M, respectively, and complete inhibition for both at 1 x 10(-3) M. Plots of the % irreversible inhibition of [3H]QNB, [3H]nicotine, and [3H]MCC vs [BAP] yielded Ki values of 7 x 10(-8), 1 x 10(-4), and 6 x 10(-5) M, respectively. In behavioral studies BAP was able to antagonize the QNB-induced hyperactivity in mice; however, BAP did not appear to alter nicotine-induced seizure activity or other behavioral effects in mice. A plot of the time course of inhibition by BAP for [3H]QNB binding revealed that the inhibition was almost complete within 10 min exposure at 37 degrees. The findings indicate that BAP is a useful affinity ligand for examining the biochemical and functional characteristics of brain cholinergic receptors, particularly the muscarinic which has an affinity near the nM concentration range.

Animals↗
PubMed1992

Opioid receptor antagonist affinity ligands: 6 beta-bromoacetamido-6-desoxynaltrexone and 6 beta-thioglycolamido-6-desoxynaltrexone.

The present study, utilizing thioglycolamido as the reactive group, describes the synthesis and pharmacology of a new opioid antagonist affinity ligand, 6 beta-thioglycolamido-6-desoxynaltrexone (TAN) and compares TAN with a related known compound, 6 beta-bromoacetamido-6-desoxynaltrexone (BAN). Both compounds were tested for their reversible and irreversible inhibition of [3H]naloxone binding to calf brain membranes. Reversible binding of BAN and TAN had Ki values of 1 x 10(-9) and 1 x 10(-10) M, respectively as determined by log probit plots. Irreversible binding was determined after extensive washing to remove all non-covalently bound ligand. At a concentration of 5 x 10(-8) and 1 x 10(-8) M for BAN and TAN irreversible binding was inhibited 50% of the maximum value. A study of the time course of irreversible inhibition of [3H]naloxone binding revealed that maximal inhibition occurred within 5 min with a concentration of 1 x 10(-7) M of either agent. TAN but not BAN when administered systematically to mice produced an antinociceptive effect as measured by the writhing test. When administered intracerebraventricularly BAN did not block morphine-induced analgesia for more than 2 hr; whereas, with a single ED50 dose of 20 nmoles of TAN i.c.v. morphine-induced analgesia was almost completely blocked for a period of over 24 hr, as determined by the tail flick test. Although the SH group of TAN were required for the covalent interaction with opioid receptors, the site of TAN's interaction appears to involve other than protein SH groups.

Affinity Labels↗
PubMed1990

[3H]mecamylamine binding to rat brain membranes. Studies with mecamylamine and nicotine analogues.

Mecamylamine, an antagonist to nicotine, does not compete at the nicotinic recognition site, but is believed to block the ion channel of the nicotinic receptor. The present study demonstrates specific, saturable [3H]mecamylamine binding in rat brain membranes. [3H]Mecamylamine binding was destroyed by heating at 100 degrees and trypsin. Scatchard analysis revealed the presence of two sites with Kd values of 9.6 x 10(-8) and 1.1 x 10(-6) M and Bmax values of 7 x 10(-12) and 3 x 10(-11) mol/mg protein respectively. A good correlation was observed between the Ki values for [3H]mecamylamine binding of a number of mecamylamine and related analogues and their ability to block nicotine-induced prostration in rats and seizures in mice. Inorganic cations, particularly divalent, and various ion channel blockers, such as phencyclidine and verapamil, exhibited a high affinity for the [3H]mecamylamine site. Although mecamylamine did not block nicotine binding, nicotine and its analogues exhibited a high affinity for the [3H]mecamylamine site, a finding which suggests that nicotine acts directly on ion channels as well as the nicotinic cholinergic recognition sites. The data are consistent with the notion that mecamylamine interacts with the open ion channel of the nicotinic receptor.

Animals↗
PubMed1989

Interaction of putative vasopressin receptor proteins of rat brain and bovine pituitary gland with an antibody against a nanopeptide encoded by the reverse message of the complementary mRNA to vasopressin.

An antibody directed against the reverse message of the complementary mRNA for arginine vasopressin was demonstrated to be immunoreactive with 62 and 55 kdalton proteins, obtained by affinity chromatography of rat brain and bovine posterior pituitary extracts and believed to be associated with the vasopressin binding site. A similar pattern of immunoreactivity was seen with an anti-idiotypic antibody for arginine vasopressin.

Animals↗
PubMed1988

Inhibition of phosphoinositide turnover by selective muscarinic antagonists in the rat striatum. Correlation with receptor occupancy.

In the rat corpus striatum, receptor occupancy and the inhibition of phosphoinositide turnover by muscarinic antagonists have been examined under very similar conditions with respect to tissue preparation and buffer composition. The results suggest a good correlation between receptor occupancy and inhibition by muscarinic antagonists, of the carbachol-stimulated turnover of inositol phospholipids, measured by the accumulation of [3H]inositol phosphates in the presence of 5 mM LiCl. In the presence of 10 mM carbachol (CCh), the accumulation of labeled inositol phosphates was increased 8-fold above basal levels (EC50 = 95 microM). Inclusion of antagonists resulted in a dose-dependent inhibition of the 0.1 mM CCh-stimulated inositol phosphate accumulation, with a rank order of potency of atropine greater than trihexyphenidyl greater than pirenzepine greater than or equal to gallamine. Radioligand binding studies with [3H]-l-quinuclidinyl benzilate [( 3H]QNB) in a cell aggregate preparation revealed a single class of saturable, high affinity [3H]QNB binding sites exhibiting a Kd of 74 pM and a Bmax of 2.85 pmol/mg protein. The antagonists examined were able to inhibit the binding of [3H]QNB with the same rank order of potency as for the inhibition of carbachol-stimulated phosphoinositide turnover (atropine greater than trihexyphenidyl greater than pirenzepine greater than or equal to gallamine). Although the inhibition of phosphoinositide turnover and [3H]QNB binding by the nonselective antagonist atropine was best described by interaction at a single site, inhibition of phosphoinositide turnover and [3H]QNB binding by both pirenzepine, which is selective for M1 receptors, and gallamine, which is selective for M2 receptors, is complex. Pirenzepine was much more potent than gallamine for both binding to receptors and inhibiting phosphoinositide turnover. Nonlinear curve-fitting analysis indicated that slope factors for inhibition of phosphoinositide turnover (analogous to Hill coefficient for binding) by only subtype selective antagonists were significantly less than unity. The above-mentioned antagonist interactions together with the apparently multicomponent stimulation of phosphoinositide turnover by carbachol suggest that phosphoinositide turnover may be coupled to more than one muscarinic receptor subtype in the corpus striatum.

Animals↗
PubMed1986

Effects of the affinity ligands 14-beta-chloroacetylnaltrexone and 14-beta-bromoacetamidomorphine on [3H]-dihydromorphine binding sites in rat brain.

The aim of the present study was to examine the inhibitory effects in vitro of the affinity ligands 14-beta-chloroacetylnaltrexone (CAN) and 14-beta-bromoacetamidomorphine (BAM) to characterize the pharmacological specificity of the ligands for high and low affinity opioid binding sites. Rat brain membranes were incubated with 2.0 microM BAM or CAN, or their parent compounds (morphine and naltrexone, respectively) at 37 degrees for 45 min, and the membranes were washed extensively to remove the unbound ligand. The specific binding of 0.3 nM [3H]dihydromorphine ([3H]DHM) was reduced 32 +/- 7% in membranes treated with CAN and BAM, whereas specific binding in preparations treated with morphine and naltrexone was not significantly different from controls. An increased affinity of BAM and CAN relative to morphine and naltrexone could not account for the observed irreversible inhibition, since the relative affinity of CAN was similar to that of naltrexone and that of BAM was 10-fold less active than morphine. Saturation binding assays revealed that the affinity ligands selectively abolished a high affinity binding site (Kd = 0.3 nM, Bmax 95 fmoles/mg protein), which comprised approximately one-third of the total number of sites. The affinity of the remaining site (Kd = 4.0 nM) was not altered significantly. The results indicate that the inhibition caused by the affinity ligands is irreversible and represents inactivation of high affinity opioid binding sites in a relatively selective manner.

Animals↗
PubMed1986

Behavior and receptor changes after kainate lesioning of nodular cerebellum.

A study was undertaken on the effects of kainic acid lesioning on the nodulus of the rat cerebellum on behavior and various brain receptors in conscious, freely moving rats. The basis for the study was the observation that barrel rotation and other motor effects induced by intraventricular administration of vasopressin and nicotine could be elicited by their administration into the nodular area of the cerebellum. Histology revealed a marked destruction of Purkinje, stellate, and Golgi cells in the area surrounding the site of kainate administration, with little effect on the granular cells. Immediately after administering 4-12 ng of kainic acid into the nodular cerebellum, rats exhibited circling movements, barrel rotation, and clonic convulsions accompanied by stereotypic head movements, aggressiveness, and gnawing-biting; effects gradually diminishing over 3 days. Receptor binding studies 4-14 days after kainate lesioning revealed a marked increase in 3H-nicotine and 3H-QNB binding in the surrounding cerebellar region, caudate nucleus, and hypothalamus, with no change in 3H-dihydromorphine binding. The findings are consistent with the hypothesis that nicotinic and muscarinic pathways in the vestibular cerebellum, along with its connection to nigrostriatal dopaminergic systems, are involved in the mediation of barrel rotation, ataxia, and other motor disturbances resulting from administration of vasopressin on nicotine intraventricularly.

Animals↗
PubMed1979

Development of muscarinic cholinergic receptors in inbred strains of mice: identification of receptor heterogeneity and relation to audiogenic seizure susceptibility.

The concentrations and biochemical properties of muscarinic acetylcholine receptors in the brains of two highly inbred strains of mice, DBA/2J and C57BL/6J, have been studied using [3H]quinuclidinyl benzilate (QNB), a potent and specific receptor antagonist. As is the case with rat brain, murine muscarinic receptors exist in at least two forms, which differ in their affinities for receptor agonists but which have the same high affinity for receptor antagonists. Carbamylcholine binding to mouse neural membranes can be resolved into two components with KDs of 5.2 times 10(-7) and 7.9 times 10(-5) M. There is a regional heterogeneity of brain receptors with respect to their distribution between these high and low agonist affinity forms. Brain stem and hypothalamus receptors display binding properties that would be expected if over 60% of their receptors were in the high affinity state, while only 30-40% of cortex, striatum and thalamus receptors appear to be in the high affinity form. Hippocampal receptors display the least amount of high agonist affinity character. Saturation curves and Scatchard plots of QNB binding at 2, 14, 21 and 42 days postnatal age in both strains indicate no differences or changes in the affinity or nature of the binding with age. Significant increases in QNB binding per mg membrane protein were observed between 14 and 42 days in the cortex, hippocampus, striatum, thalamus and hypothalamus, but not in the midbrain-pons-medulla region. In the hippocampus the DBA mice had significantly more QNB binding. In the hypothalamus decreases with age in total binding were noted in DBA, while slight increases were noted in C57. Compared to C57, hippocampal receptors in DBA displayed lower agonist affinity at 14 and 21 days, a trait which was not apparent when DBA had outgrown their audiogenic seizure sensitivity at 42 days. The differences in receptor density and agonist state distribution between the two strains may be related to audiogenic seizure sensitivity.

Acoustic Stimulation↗
PubMed1979

Evidence for a noncholinergic site for nicotine's action in brain: psychopharmacological, electrophysiological and receptor binding studies.

In an effort to investigate the possibility of noncholinergic nicotine sites within the brain, psychopharmacological, biochemical and eletrophysiological studies were undertaken with nicotine and various newly synthesized derivatives of nicotine and piperidine. When 1-10 micrograms of (-)-nicotine was injected into the region of the lateral ventricle of rats through implanted cannulae, there resulted a characteristic prostration immobilization syndrome, which was accompanied by seizures and tremors at the higher dose range. The (+)-isomer possessed 1/100 the activity of the natural (-)-isomer. The syndrome could be prevented by pre-treatment, intraventricularly, with the N-benzyl and N-p-nitrophenylazido derivates of either nicotine or piperide. A variety of neurotransmitters and psychotropic agents, including acetylcholine and anticholinergic drugs, were without antagonistic action. After nicotine, recordings of spontaneous electrical activity from electrodes chronically implanted into the region of the dorsal hippocampus showed a marked decrease in the amplitude and number of 6-8 sec discharges, and the change was correlated with the behavioral syndrome. Receptor binding studies were performed with rat brain slices and various neural preparations using 3H-nicotine, 125I-alpha-bungarotoxin and 14C-d-tubocurarine as ligands; and only with 3H-nicotine was it possible to demostrate any competitive effect with the various nicotine and piperidine antagonists. It was possible to demonstrate stereospecific or specific nicotine binding to only glass fiber filters and, to a lesser extent, brain slices, but not to cell-free preparations. It was concluded that there existed specific noncholinergic sites for nicotine's action which have not been hitherto described.

Animals↗
PubMed1978

Phospholipid changes in synaptic membranes by lipolytic enzymes and subsequent restoration of opiate binding with phosphatidylserine.

A study has been made of the role of phosphatidylserine in stereospecific opiate binding to neural membranes, utilizing specific lipolytic enzymes to attack the lipid. At very low concentrations phospholipase A2 from bee venom will preferentially hydrolyze C22:6-fatty acid; and even after a few percent of the total phosphatidylserine is hydrolyzed, opiate binding is greatly inhibited. The addition of brain phosphatidylserine will restore opiate binding; however, when the inhibition approaches 50% restoration is only partial. Exposure of membranes to phosphatidylserine decarboxylase will partially inhibit opiate binding; and the binding returns to the control level after the addition of phosphatidylserine. The partial inhibition of opiate binding by low concentrations of Triton X-100, which presumably remove lipids, can be partially reversed by phosphatidylserine. The binding of 3H-naloxone, an opiate antagonist, is similar to agonists in its behavior towards phospholipases and phosphatidylserine; however, binding of naltrexone, also an antagonist, is far less responsive. It is concluded that the phosphatidylserine associated with the opiate receptor is the C18:0, 22:6-diacyl form, which is closely associated with protein.

Animals↗