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Biomedical subjects

S D Murphy

Publications and source records attributed to S D Murphy.

At least 19 recordsLinked to original sources
PubMed2002

DNA sequence and structure: direct and indirect recognition in protein-DNA binding.

MOTIVATION: Direct recognition, or direct readout, of DNA bases by a DNA-binding protein involves amino acids that interact directly with features specific to each base. Experimental evidence also shows that in many cases the protein achieves partial sequence specificity by indirect recognition, i.e., by recognizing structural properties of the DNA. (1) Could threading a DNA sequence onto a crystal structure of bound DNA help explain the indirect recognition component of sequence specificity? (2) Might the resulting pure-structure computational motif manifest itself in familiar sequence-based computational motifs? RESULTS: The starting structure motif was a crystal structure of DNA bound to the integration host factor protein (IHF) of E. coli. IHF is known to exhibit both direct and indirect recognition of its binding sites. (1) Threading DNA sequences onto the crystal structure showed statistically significant partial separation of 60 IHF binding sites from random and intragenic sequences and was positively correlated with binding affinity. (2) The crystal structure was shown to be equivalent to a linear Markov network, and so, to a joint probability distribution over sequences, computable in linear time. It was transformed algorithmically into several common pure-sequence representations, including (a) small sets of short exact strings, (b) weight matrices, (c) consensus regular patterns, (d) multiple sequence alignments, and (e) phylogenetic trees. In all cases the pure-sequence motifs retained statistically significant partial separation of the IHF binding sites from random and intragenic sequences. Most exhibited positive correlation with binding affinity. The multiple alignment showed some conserved columns, and the phylogenetic tree partially mixed low-energy sequences with IHF binding sites but separated high-energy sequences. The conclusion is that deformation energy explains part of indirect recognition, which explains part of IHF sequence-specific binding.

Algorithms↗
PubMed2001

Effective planning and implementation of ecological rehabilitation projects: a case study of the regional municipality of Waterloo (Ontario, Canada).

The literature guides environmental planning and, specifically, how to use ecological rehabilitation projects to achieve long-term planning goals and landscape-scale environmental sustainability. There is, however, a perceived gap between principles in the literature and the use of them by practitioners involved in smaller-scale ecological rehabilitation projects. Using interviews with practitioners involved in 11 projects within the Regional Municipality of Waterloo, Ontario, Canada, we tested whether practitioners used five principles for effective planning and implementation of ecological rehabilitation that we derived from the literature. These five principles were: establishing political and ecological context, using ecologically appropriate objectives and practices, using comparative multidisciplinary and cross-scale approaches, using adaptive planning and implementation, and establishing good communication within and external to projects. Few projects followed all five principles, and practitioners indicated that they used three more project-specific principles: obtaining political/social support, promoting projects and changing attitudes about projects, and securing sufficient and persistent funding to maintain a project's life. While the literature emphasizes that ecological rehabilitation is only effective if projects are coordinated on a watershed basis, most practitioners focused solely on the goals of their specific project. The gap between literature and practice may arise because most practitioners are new to the field of ecological rehabilitation and still are focused on the methods involved. Time pressures force practitioners to obviate the literature and get projects started quickly, lest support evaporate. Complicating these difficulties is decreased support from federal and provincial governments for large-scale environmental planning. It is unclear whether ecological rehabilitation projects in Waterloo Region (at least) will ever become effective at promoting landscape-scale ecological goals or remain smaller-scale stop-gaps.

Animals↗
PubMed1992

Comparative metabolism of methyl parathion in intact and subcellular fractions of isolated rat hepatocytes.

Metabolism of the widely used insecticide methyl parathion by isolated hepatocytes and various subcellular fractions was compared to determine the effects of cellular integrity on the metabolic profile observed. A reverse-phase ion-pair high-performance liquid chromatographic method was developed to separate and quantify methyl parathion and six of its hepatic biotransformation products: methyl paraoxon; desmethyl parathion; desmethyl paraoxon; p-nitrophenol; p-nitrophenyl glucuronide; and p-nitrophenyl sulfate. Most compounds exhibited linear responses and limits of detection below 1 nmol. The chromatographic method was used to determine metabolic profiles of methyl parathion in isolated rat hepatocytes, sonicated hepatocytes, postmitochondrial fraction, microsomes, and cytosol. Isolated hepatocytes produced significantly more desmethyl parathion and p-nitrophenyl sulfate than the subcellular preparations, demonstrating that cellular integrity significantly affects the quantitative metabolic profile observed.

Animals↗
PubMed1991

The formamidine pesticides chlordimeform and amitraz decrease hepatic glutathione in mice through an interaction with alpha 2-adrenoceptors.

Recent studies have provided evidence that formamidine pesticides, such as chlordimeform (CDM; N'-4-chloro-o-tolyl-N,N-dimethylformamidine) or amitraz (AMZ; N'-2-4-(dimethylphenyl)-N-[((2,4-dimethylphenyl)imino)methyl]-N- methanimidamide) exert some of their toxic effects by an interaction with alpha 2-adrenoceptors. Since epinephrine and clonidine have been shown to decrease hepatic glutathione (GSH) by activating alpha 2-adrenoceptors, and alpha 2-antagonists partially antagonize GSH depletion and hepatotoxicity caused by bromobenzene and cocaine, we have investigated whether the formamidines would affect hepatic GSH levels in mice. Both CDM and AMZ decreased hepatic nonprotein sulfydryls (NPSH) to a maximum of about 40%, in a dose-dependent manner. The effect of AMZ was longer lasting than that of CDM. For both compounds, decrease of hepatic NPSH was antagonized by the alpha 2-antagonist yohimbine but not by the alpha 1-antagonist prazosin or the beta-antagonist propanolol. The alpha 2-agonist clonidine also caused a dose-dependent decrease of hepatic NPSH (to a maximum of 40%), which was prevented only by yohimbine. The effects of AMZ, CDM, and clonidine were not additive, suggesting that all compounds act on a common site and/or with a common mechanism. Adrenalectomy or destruction of peripheral sympathetic nerves with 6-hydroxydopamine did not alter the ability of CDM and AMZ to decrease hepatic NPSH. These results indicate that formamidine pesticides can affect the levels of hepatic GSH, possibly through a direct interaction with hepatic alpha 2-adrenoceptors.

Animals↗
PubMed1990

Serum paraoxonase and its influence on paraoxon and chlorpyrifos-oxon toxicity in rats.

Paraoxon and chlorpyrifos-oxon, the active metabolites of the organophosphorus insecticides parathion and chlorpyrifos, respectively, are hydrolyzed by an "A"-esterase, paraoxonase, which is present in the sera of several mammalian species. In this study, we investigated whether levels of serum paraoxonase activity in laboratory animals can influence the in vivo toxicity of paraoxon and chlorpyrifos-oxon. Paraoxonase was found to be 7-fold higher in rabbit serum than in rat serum. The dose of paraoxon required to produce similar signs of toxicity and similar degrees of cholinesterase inhibition in rats and rabbits (0.5 and 2.0 mg/kg, respectively) differed by 4-fold. Paraoxonase was then purified from rabbit serum and 8.35 units was injected in the tail veins of rats, increasing the peak hydrolytic activity of rat serum by 9-fold toward paraoxon and by 50-fold toward chlorpyrifos-oxon. The increase in serum paraoxonase/chlorpyrifos-oxonase activity was long-lasting, with a 2- and 10-fold increase, respectively, still present after 24 hr. Thirty minutes following enzyme injection, rats were challenged with an acute dose of paraoxon or chlorpyrifos-oxon given by the intravenous, intraperitoneal, dermal, or oral route. Cholinesterase activities were measured in plasma, red blood cells, brain, and diaphragm after 4 hr. Rats pretreated with paraoxonase exhibited less inhibition of cholinesterase than vehicle-treated controls following identical doses of paraoxon, particularly when the organophosphate was given iv or dermally. A very high degree of protection, particularly toward brain and diaphragm cholinesterase, was provided by paraoxonase pretreatment in animals challenged with chlorpyrifos-oxon by all routes. These results indicate that levels of serum paraoxonase activity can affect the toxicity of paraoxon and chlorpyrifos-oxon.

Animals↗
PubMed1990

Potassium ions potentiate the muscarinic receptor-stimulated phosphoinositide metabolism in cerebral cortex slices: a comparison of neonatal and adult rats.

Activation of cholinergic muscarinic receptors results in an increased turnover of membrane inositol phospholipids. In rat cerebral cortex slices, carbachol- and acetylcholine-induced inositol phosphates ([3H]InsPs) accumulation is maximal in 7 day-old rats and lowest in adults, while the density of muscarinic binding sites increases gradually with age, suggesting the presence of a more effective receptor-effector coupling during neonatal life. In the process of investigating the nature of such differential stimulation, we have studied the effects of potassium ions on muscarinic receptor-stimulated phosphoinositide metabolism during development. Increasing the concentration of K+ from 6 to 12 mM potentiated the stimulating effect of carbachol by 80-100% in adult animals, as previously shown, but only 10-20% in 7 day-old animals, without altering its EC50 values. The differential potentiation by K+ at these two ages was specific for muscarinic receptors, since norepinephrine-stimulated accumulation was potentiated only 18% and 12% in adult and 7 day-old rats, respectively. Two other monovalent cations, rubidium and cesium, had the same effect as K+ on carbachol-stimulated [3H]-InsPs accumulation. The effect of K+ was not antagonized by the K+ channel blocker 4-aminopyridine, but was antagonized by tetraethylammonium (TEA). TEA, however, also interacted with muscarinic binding sites. Omission of calcium from the incubation medium did not influence the potentiating effect of K+ during development was inversely proportional to the stimulation of phosphoinositide metabolism induced by carbachol. These results suggest that the mechanism responsible for the potentiating effect of K+ in adult rats might be already operating in neonatal animals.

Aging↗
PubMed1990

In vitro and in vivo modulation of cholinergic muscarinic receptors in rat lymphocytes and brain by cholinergic agents.

A binding site for 3H-quinuclidinyl benzylate (QNB) has been identified in rat lymphocytes which has the characteristics of a cholinergic muscarinic receptor (Costa, L. G., Kaylor, G. & Murphy, S. D. (1988). Muscarinic cholinergic binding sites on rat lymphocytes. Immunopharmacology, 16, 139-149.) Here we show that prolonged exposures to cholinergic compounds in vitro and in vivo modulate muscarinic receptor binding in lymphocytes as well as in brain tissue. Exposure of rat splenic lymphocytes in vitro to oxotremorine caused a time- and concentration-dependent decrease in the density of 3H-QNB binding sites. This decrease occurred only when incubation with oxotremorine was carried out at 37 degrees C and not at 0-4 degrees C, suggesting that it was not an artifact due to residual, unwashed, oxotremorine. The effect of oxotremorine was mimicked by two other cholinergic agonists, acetylcholine and carbachol, and was antagonized by atropine, which, when present alone, caused an increase in 3H-QNB binding. In vivo exposures to oxotremorine or atropine (both at 20 mg/kg/day for 14 days via an ALZA minipump) caused a significant decrease (20-30%) and increase (13-30%), respectively, of 3H-QNB binding in various brain areas as well as circulating lymphocytes. Repeated administrations of the organophosphorus insecticide disulfoton (2 mg/kg/day for 14 days, i.p.) caused significant reductions (59-88%) of acetylcholinesterase activity in brain, lymphocytes, plasma and red blood cells, as well as a 23-39% decrease of 3H-QNB binding in brain areas and circulating lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗
PubMed1990

Characterization of cholinergic muscarinic receptor-stimulated phosphoinositide metabolism in brain from immature rats.

Hydrolysis of phosphoinositides elicited by stimulation of cholinergic muscarinic receptors has been studied in brain from neonatal (7-day-old) rats in order to determine: 1) whether the neonatal rat could provide a good model system to study this signal-transduction pathway; and 2) whether potential differences with adult nerve tissue would explain the differential, age-related effects of cholinergic agonists. Accumulation of [3H] inositol phosphates in [3H]inositol prelabeled slices from neonatal and adult rats was measured as an index of phosphoinositide metabolism. Full (acetylcholine, methacholine, carbachol) and partial (oxotremorine, bethanechol) agonists had qualitatively similar, albeit quantitatively different, effects in neonatal and adult rats. Atropine and pirenzepine effectively blocked the carbachol-induced response with inhibition constants of 1.2 and 20.7 nM, respectively. In all brain areas, response to all agonists was higher in neonatal than adult rats, and in hippocampus and cerebral cortex the response was higher than in cerebellum or brainstem. The relative intrinsic activity of partial agonists was higher in the latter two areas (0.6-0.7) than in the former two (0.3-0.4). Carbachol-stimulated phosphoinositide metabolism in brain areas correlated well with the binding of [3H]QNB (r2 = 0.627) and, particularly, with [3H]pirenzepine (r2 = 0.911). In cerebral cortex the effect of carbachol was additive to that of norepinephrine and glutamate. The presence of calcium (250-500 microM) was necessary for maximal response to carbachol to be elicited; the EC50 value for Ca2+ was 65.4 microM. Addition of EDTA completely abolished the response. Removal of sodium ions from the incubation medium reduced the response to carbachol by 50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

[The effect of pesticides-CDM and AMZ on inhibition of the binding of 3H-clonidine to alpha 2-adrenoreceptor in rat forebrain tissue].

Chlordimeform (CDM) and Amitraz (AMZ) are two formamidine pesticides. CDM and AMZ inhibited the binding of 3H-Clonidine, 3H-Yohimbine to Alpha 2-adrenoreceptor of rat forebrain tissue in vitro with IC50 values of 62-68 mumol/L (CDM) and 95-110 mumol/L (AMZ). In vivo the administration of CDM and AMZ by ip showed the effect of inhibition on the binding and significant correlation of dose-effect r = 0.995 (CDM), 0.884 (AMZ). Time course test indicated that the lasting inhibition effect of CDM following exposure was shorter than AMZ. Similar results were observed with plasma in vitro. Comparing inhibition effects on rat forebrain tissue, directly induced by CDM and AMZ at different doses, with the results from the plasma of treated rats in vitro, there was a significant correlation r = 0.973 (CDM), 0.909 (AMZ). It showed that the inhibition effect of both CDM and AMZ was linked to the concentration of compounds chemical and their metabolites in blood. Time course and washing test indicated that the inhibition effect by CDM and AMZ was reversible.

Amidines↗
PubMed1989

Acute and chronic effects of the pesticide amitraz on alpha 2-adrenoceptors in mouse brain.

There is increasing evidence to suggest that several effects of the formamidine pesticide amitraz (AMZ) in mammals are mediated by its interaction with alpha 2-adrenoceptors. AMZ has been shown to inhibit the binding of [3H]clonidine, a specific ligand for alpha 2-adrenoceptors to mouse brain in vitro and after administration in vivo. In the present study we have further investigated and characterized the effects of acute and chronic administration of AMZ on brain alpha 2-adrenoceptors in mice. AMZ caused a dose-dependent inhibition of [3H]clonidine binding. This inhibition was long-lasting (more than 48 h) following a relatively high dose of AMZ (75 mg/kg), while it was of short duration (2 h) following low doses (7.5 and 12.5 mg/kg). The time course of inhibition of [3H]clonidine binding was correlated with the plasma levels of AMZ and/or its active metabolites, measured with a novel radioreceptor binding technique. The alteration of [3H]clonidine binding was due to a decrease in alpha 2-adrenoceptor affinity, with no change in the density of binding sites, and was reversible in vitro upon repeated washing of the membrane preparation. Repeated administration of 7.5 mg/kg or 12.5 mg/kg AMZ, to yield a total dose of 75 mg/kg, showed no evidence of a cumulative effect on brain alpha 2-adrenoceptors.

Animals↗
PubMed1988

Alpha 2-adrenoceptors as a target for formamidine pesticides: in vitro and in vivo studies in mice.

While the toxicity in insects of formamidines such as chlordimeform (CDM), its demethylated metabolite DCDM, and amitraz (AMZ) appears to involve activation of an octopamine-sensitive adenylate cyclase, their mechanism of action in mammals remains elusive. There is increasing evidence, however, that alpha 2-adrenoceptors might mediate certain effects of CDM, DCDM, and AMZ. In the present study, we investigated whether formamidines can interact directly with adrenoceptors in mouse forebrain both in vitro and after in vivo administration. Formamidines were potent inhibitors of the binding of [3H]clonidine to alpha 2-adrenoceptors with IC50's of 13 microM, 29 nM, and 130 nM for CDM, DCDM, and AMZ, respectively. Binding of [3H]yohimbine was inhibited with similar potencies. All compounds also inhibited with equal (CDM) or lower potency the binding of [3H]spiperone to dopamine D2 receptors and were weak inhibitors or inactive toward alpha 1- and beta-adrenoceptors, cholinergic muscarinic, GABAA, opiate mu, benzodiazepine, and histamine 1 receptors. Administration of formamidines to mice caused a dose-dependent decrease of [3H]clonidine binding. [3H]Clonidine binding returned to control values within 5 hr following administration of CDM and DCDM, but was still significantly decreased up to 48 hr after AMZ. Among different brain regions, [3H]clonidine binding was decreased to a larger extent in cerebral cortex, hippocampus, and midbrain. In vitro and ex vivo kinetic binding studies indicated that the effect of formamidines on alpha 2-adrenoceptors was due to a decrease in affinity and not to an alteration of the density of [3H]clonidine binding sites. The results of these biochemical studies support the hypothesis that alpha 2-adrenoceptors represent an important target for formamidine neurotoxicity in mammals.

Amidines↗
PubMed1988

Spatial memory impairment and central muscarinic receptor loss following prolonged treatment with organophosphates.

Memory impairment is one of the recurrent complaints of agricultural workers repeatedly exposed to organophosphorus insecticides. In an effort to establish an animal model for such behavioral effects, which would allow studying its underlying biochemical mechanism(s), in this study we evaluated spatial memory in animals following repeated organophosphate exposure. Male Long-Evans rats were given daily i.p. injections of either diisopropylfluorophosphate (DFP; 1 mg/kg/day) or disulfoton (O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate; 2 mg/kg/day) for 14 days. Acetylcholinesterase activity was inhibited 71-77% in the cortex, hippocampus, and striatum of rats treated with DFP, and 73-74% in those treated with disulfoton. Binding of [3H]quinuclidinyl benzilate ([3H]QNB) to cholinergic muscarinic receptors in the same brain areas was reduced 16-28% in organophosphate-treated rats. This decrease was due to a reduction in muscarinic receptor density (Bmax) with no changes in receptor affinity. At the end of the treatment rats were tested for spatial memory using the spontaneous alternation task in a T-maze. Rates of true spontaneous alternation were 64.4, 45.0, and 44.8% in animals which received corn oil, DFP, or disulfoton, respectively (P less than 0.05). These results indicate that prolonged inhibition of acetylcholinesterase caused by repeated organophosphate exposure alters spatial memory functions in rats, as well as causing a loss of muscarinic receptors. Considering the role of the cholinergic system in cognitive processes, these biochemical alterations could be related to the observed behavioral changes and may offer a potential explanation of the memory impairment reported by workers chronically exposed to organophosphates.

Acetylcholinesterase↗
PubMed1987

Interaction of the pesticide chlordimeform with adrenergic receptors in mouse brain: an in vitro study.

Chlordimeform (N'(4-chloro-o-tolyl)-N, N-dimethylformamidine; CDM) is a formamidine insecticide acaricide whose major active metabolite is its N-monomethyl analog, desmethylchlordimeform, (DCDM). While their pesticidal action in invertebrates appears to be related to activation of octopamine receptors, their mechanism of action in mammals has not been established. Because of similarities between octopamine and adrenergic receptors and suggestions of CDM and DCDM action on adrenoceptors, the in vitro interactions of CDM and DCDM with adrenoceptors were studied. In mouse brain membrane preparations CDM inhibited the binding of [3H]-clonidine to alpha 2- adrenoceptors and of [3H]-WB4101 to alpha 1-adrenoceptors with IC50 values of 18.2 and 87 microM, respectively. DCDM was a much more potent inhibitor, with IC50 values toward alpha 2-, and alpha 1-adrenoceptors of 44 nM and 1 microM, respectively. Both compounds were only weak inhibitors of the binding of [3H]-dihydroalprenolol to beta-adrenoceptors and of [3H]-quinuclidinyl benzilate to muscarinic receptors and were inactive toward benzodiazepines and gamma aminobutyric acid (GABAA) receptors. Inhibition of [3H]-clonidine binding by both compounds was competitive, as indicated by a decreased receptor affinity without changes in receptor density. Interaction of CDM and DCDM with [3H]-WB4101 binding, on the other hand, was more complex, and not of the competitive type. These results show that CDM and its metabolite DCDM can interact directly in vitro with alpha-adrenergic receptors, suggesting that these receptors could mediate some of the effects of CDM and DCDM in vivo.

Amidines↗
PubMed1987

Developmental changes in muscarinic receptor-stimulated phosphoinositide metabolism in rat brain.

Muscarinic receptor-stimulated phosphoinositide hydrolysis was investigated in rat brain during ontogeny by measuring the accumulation of [3H]inositol phosphates ([3H]InsPs) in cerebral cortex slices at various ages. Experiments with carbachol and acetylcholine showed that [3H]InsPs accumulation was maximal in 7-day-old rats (1477 +/- 98% of basal) and lowest in adult (75 days) rats (428 +/- 24% of basal). No differences were found in the EC50 values for both cholinergic agonists. This effect appeared to be mediated by the M1-muscarinic receptor subtype as it was blocked by pirenzepine with Ki = 29.1 +/- 7.1 nM (adults) and 87.9 +/- 18.2 nM (7-day-old rats). Incorporation of [3H]inositol into phospholipid decreased from day 3 to adulthood; however, when data of [3H]InsPs release were corrected for the incorporation at a given age, the highest stimulation by cholinergic agonists was still observed in 7-day-old rats. Among the other neurotransmitters tested (norepinephrine, histamine and serotonin), all known to stimulate phosphoinositide metabolism, none had the same developmental profile of [3H]InsPs accumulation as cholinergic agonists. In contrast to carbachol- and acetylcholine-stimulated phosphoinositide hydrolysis, the density of muscarinic binding sites, measured by [3H]quinuclidinyl benzilate binding, increased from day 3 to day 75. Acetylcholinesterase activity also increased during development. The dissociation of receptor binding sites from receptor-stimulated phosphoinositide metabolism suggests the presence of a more effective receptor-effector coupling at specific times of neonatal development, particularly 1 week. Furthermore, the fact that maximal stimulation of phosphoinositide hydrolysis coincides with the period of brain growth spurt in the rats suggests that this system in the cerebral cortex might be involved in the processes of cell division and differentiation.

Acetylcholine↗
PubMed1986

Effect of diethylmaleate and other glutathione depletors on protein synthesis.

The alpha, beta-unsaturated carbonyl compound diethylmaleate (DEM) depletes glutathione (GSH) from liver and other tissues, and for this reason it is often used in toxicological research to study the GSH-mediated metabolism of xenobiotics. In addition to GSH depletion, however, DEM has been shown to have other nonspecific effects, such as alteration of monooxygenase activities or glycogen metabolism. In this study we found that DEM (1 ml/kg) inhibited protein synthesis in brain and liver, following in vivo administration to mice. Protein synthesis was measured as the incorporation of [3H]valine into trichloroacetic acid-precipitable material. Administration of DEM also decreased body temperature by 2-3 degrees. By increasing the environmental temperature from 22 degrees to 35 degrees the hypothermic effect of DEM was prevented, without affecting its ability to deplete GSH from brain and liver. Furthermore, when mice were maintained at 35 degrees, DEM still caused a significant decrease in protein synthesis, suggesting that this effect was only partially due to hypothermia. To test whether inhibition of protein synthesis was related to GSH depletion, groups of animals were dosed with the alpha, beta-unsaturated carbonyl phorone (diisopropylidenacetone) or the specific inhibitor of GSH synthesis, buthionine sulfoximine (BSO). Phorone decreased GSH in liver and brain; however, it had no effect on protein synthesis. BSO decreased GSH levels in liver and kidney, but not in brain, and did not have any effect on protein synthesis in any of these tissues, nor did it cause any hypothermia. Furthermore, when hepatic GSH content was decreased by in vivo administration of DEM or BSO, there was no inhibition of protein synthesis measured in vitro. These results indicate that, at the dose normally used to deplete GSH from various tissues. DEM also exerts an inhibitory effect on protein synthesis, which appears to be only partially due to its hypothermic effect, and is independent from GSH depletion. BSO, which, in our experimental conditions, lacks this and other nonspecific effects, might be a good alternative for studies aimed at characterizing the role of GSH in the metabolism and toxicity of chemicals.

Animals↗
PubMed1986

Interaction of choline with muscarine receptor-stimulated phosphoinositide metabolism in the rat brain.

Previous receptor binding studies had shown that choline can interact with low potency with muscarine cholinoceptors. In the present study we have investigated whether choline is capable of functionally activating muscarine receptors by investigating its ability in stimulating the hydrolysis of phosphoinositides, a response believed to be coupled in brain to the M1 subtype of muscarine receptors. The results indicated that choline was only a very weak inducer of inositol phosphates (InsPs) accumulation in rat cerebral cortex slices as compared with acetylcholine or charbachol. Maximal increase of InsPs accumulation, at a choline concentration of 10 mM, was only 39 +/- 7%, as compared with the 4- to 6-fold stimulation induced by the other compounds. This effect of choline was not modified by physostigmine nor by the uptake inhibitor hemicholinium-3. At high concentrations, however, choline antagonized the stimulatory effect of acetylcholine and carbachol, suggesting that it might act as a partial agonist at this subtype of muscarine receptors, similar to what has been observed with oxotremorine. Choline had no effect on noradrenaline-stimulated InsPs accumulation.

Acetylcholine↗
PubMed1986

Cholinergic and opiate involvement in the antinociceptive effect of diisopropylfluorophosphate.

The organophosphate diisopropylfluorophosphate (DFP; 3 or 6 mg/kg, IP) caused a dose-related antinociception in mice which was antagonized by the muscarinic antagonist scopolamine. The opiate antagonist naloxone antagonized the antinociceptive effect of the highest dose of DFP, but did not affect the antinociception caused by 3 mg/kg DFP. Twenty-four hours after the administration of DFP, reaction time in animals which received a 3 mg/kg dose did not differ from control. However, reaction time was still significantly higher than control in mice administered 6 mg/kg DFP twenty-four hours earlier. This residual antinociception was antagonized by naloxone but not by scopolamine, suggesting that it was opioid in nature. These results suggest that antinociception induced by a low dose of DFP is primarily due to a cholinergic mechanism, while higher doses appear to affect also the opiate system. Since we have previously shown that DFP (6 mg/kg) increases met-enkephalin levels in brain, it is possible that high doses of DFP might interfere with enkephalin metabolizing enzymes. This conclusion cannot be extended to the organophosphate disulfoton, whose antinociception, even at high doses, appears to involve only an interaction with the cholinergic system.

Analgesics↗