Biomedical subjects

L G Costa

Publications and source records attributed to L G Costa.

At least 109 records · Page 6Linked to original sources

PubMed1992

Inhibition of muscarinic receptor- and G-protein-dependent phosphoinositide metabolism in cerebrocortical membranes from neonatal rats by ethanol.

Phosphoinositide (PtdIns) metabolism activated by cholinergic muscarinic receptors appears to play a role in brain development and has been recently suggested as a possible biochemical target for the developmental neurotoxicity of ethanol (EtOH). Recent experimental evidence indicates that, in rat brain, muscarinic receptor stimulation is coupled to PtdIns hydrolysis through regulatory GTP-binding proteins (G-proteins). We investigated the effect of various alcohol concentrations (10-500 mM) on guanine nucleotide-, fluoride-, and muscarinic-dependent PtdIns hydrolysis in [3H]inositol-labelled cerebral cortical membranes from neonatal (7-day-old) and adult rats. At both ages, EtOH exerted slight inhibitory effects on GTP(S) (100 microM)- and NaF (5 mM)-induced [3H]inositol phosphates accumulation. The presence of GTP(S) was necessary to unmask the stimulatory effect of the muscarinic agonist carbachol. Under these experimental conditions EtOH markedly inhibited carbachol (100 microM)-induced PtdIns hydrolysis. This effect was concentration-dependent and was more pronounced in the cortex from immature animals, where a statistically significant inhibition was observed at EtOH concentrations as low as 50 mM, comparable to the hematic concentrations reached following in vivo administration of doses of ETOH able to induce developmental neurotoxicity. These results confirm that EtOH exerts an age-specific inhibition of muscarinic-dependent PtdIns metabolism and suggest that this action might be exerted through an interaction with receptor-G-protein coupling.

Animals↗

PubMed1992

Comparative studies on the neuro- and reproductive toxicity of acrylamide and its epoxide metabolite glycidamide in the rat.

The neurotoxicity of acrylamide (AA) has been the subject of extensive studies at the morphological and functional levels in both animals and man. The concern for human exposure to monomeric AA derives partly from its extensive use in molecular biology laboratories where, in the United States alone, 100,000-200,000 persons are potentially exposed. Initial work in this laboratory aiming at the development of techniques for using hemoglobin adducts as biomarkers for human exposure to AA, revealed the formation of glycidamide as a reactive epoxide metabolite of acrylamide in the rat (Chem. Res. Toxicol. 3, 406, 1990). In rats treated with 0-100 mg/kg of AA significant dose-rate effects were observed on adduct formation by both AA and glycidamide. The high rate of formation of the metabolite, especially at low doses where approximately 60% of AA was converted to glycidamide in vivo, prompted us to investigate its potential role in the induction of neurotoxic and reproductive effects attributed to AA exposure. In initial neurotoxicological experiments, the effects of the parent compound (8-14 days, 25 and 50 mg/kg/day) and the metabolite (8-14 days, 50 and 100 mg/kg/day) were compared. While at the higher dose both compounds affected the rats' performance on the rotarod, only acrylamide had a significant effect in the hindlimb splay test, which is considered a more sensitive indicator of peripheral neuropathy. On the other hand, a stronger effect was seen for glycidamide than for AA on the male reproductive system, especially on sperm cell viability.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylamide↗

PubMed1991

Regional development of carbachol-, glutamate-, norepinephrine-, and serotonin-stimulated phosphoinositide metabolism in rat brain.

Phosphoinositide metabolism stimulated by activation of cholinergic muscarinic, glutamatergic, alpha-adrenergic and serotoninergic receptors was measured in brain regions of the developing rats. Accumulation of [3H]inositol phosphates ([3H]InsPs) in [3H]inositol-prelabeled slices from cerebral cortex, hippocampus, brainstem and cerebellum was measured as an index of phosphoinositide metabolism. Large age-, neurotransmitter receptor-, and brain region-dependent differences were found. Carbachol-stimulated [3H]InsPs accumulation peaked on postnatal day 7 in cerebral cortex and hippocampus while in cerebellum and brainstem the effect of muscarinic stimulation was maximal at birth and then declined to adulthood. The effect of glutamate also showed a peak on day 7 in hippocampus and brainstem and a developmentally related decrease in cerebral cortex. In the cerebellum, on the other hand, the response to glutamate remained sustained through adulthood. Stimulation of phosphoinositide metabolism by norepinephrine increased with age in hippocampus and cerebral cortex, but decreased in the cerebellum, while the effect of serotonin did not change significantly with age except in cerebellum. These changes in receptor-stimulated phosphoinositide metabolism do not parallel, for the most part, the ontogeny of receptor recognition sites. Activation of the phosphoinositide metabolism pathway leads to an increase in intracellular calcium levels and to stimulation of protein kinase C, which are believed to play significant roles in cellular proliferation and differentiation. Thus, the differential ability of neurotransmitters to stimulate phosphoinositide hydrolysis might play a role in the development of brain regions.

Acetylcholine↗

PubMed1991

Two subtypes of enteric non-opioid sigma receptors in guinea-pig cholinergic motor neurons.

In the longitudinal muscle-myenteric plexus preparation (LMMP) of the guinea-pig ileum, the non-opioid sigma receptors agonists, 1,3-di-ortho-tolylguanidine (DTG) and (+)N-allyl-N-normetazocine [(+)SKF 10,047], had opposite effects on nerve-mediated cholinergic contractions caused by electrical field stimulation. DTG (0.1-10 microM) inhibited and (+)SKF 10,047 (0.1-10 microM) markedly enhanced these contractile responses. Both effects were evaluated in the presence (0.5 or 1 microM) of the putative antagonists at central sigma sites: haloperidol, rimcazole, BMY 14802 and dextromethorphan. Haloperidol and dextromethorphan were ineffective. Rimcazole antagonized the effect of both DTG and (+)SKF 10.047. BMY 14802 antagonized the (+)SKF 10.047-mediated excitatory response only. These results suggest that two sigma receptor subtypes are present in enteric cholinergic motor neurons innervating the longitudinal coat. Rimcazole and BMY 14802 may provide useful tools for the characterization of peripheral non-opioid sigma receptors.

Animals↗

PubMed1991

Time-, concentration-, and age-dependent inhibition of muscarinic receptor-stimulated phosphoinositide metabolism by ethanol in the developing rat brain.

We have previously reported that administration of ethanol (EtOH; 4 g/Kg/day) to rats from postnatal day 4 to day 10 causes microencephaly and decreases muscarinic receptor-stimulated inositol metabolism on days 7 and 10. An identical exposure to EtOH of adult rats, which resulted in similar blood EtOH concentrations, did not have any effect on the same system. Initial in vitro studies have shown the presence of a differential sensitivity to EtOH of the phosphoinositide system coupled to muscarinic receptors during development. In the present study we have expanded these findings by investigating the concentration-, time-, and age-dependent effects of EtOH on accumulation of [3H]inositol phosphates ([3H]InsPs) in brain slices. EtOH caused a dose-dependent inhibition of carbachol-stimulated phosphoinositide metabolism in cerebral cortex slices from 7 day-old rats. When the time of incubation with EtOH was increased to 90 minutes, concentrations as low as 50 mM, which are reached following in vivo administration of EtOH, significantly inhibited the muscarinic response. The effect of EtOH was rather specific for the muscarinic receptors, since, even with longer incubation times, the accumulation of [3H]InsPs induced by norepinephrine or serotonin was inhibited only at concentrations of 150-500 mM. The effect of EtOH was more pronounced in cerebral cortex, hippocampus and cerebellum, and less in the brainstem. The potency of EtOH in inhibiting carbachol-stimulated phosphoinositide metabolism was also dependent on the age of the animals. Its effect was maximal in the 7-day-old rat and less pronounced in younger and older animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1991

Interaction of aluminum ions with phosphoinositide metabolism in rat cerebral cortical membranes.

Aluminum (Al) is believed to exert a primary role in the neurotoxicity associated with dialysis encephalopathy and has been suggested to be involved in a number of other neurological disorders, including Alzheimer's disease. Al, complexed with fluoride to form fluoroaluminate (AlF4-), can activate the GTP-binding (G) proteins of the adenylate cyclase and retinal cyclic GMP phosphodiesterase systems. Since an involvement of G-proteins with cerebral phosphoinositide (PtdIns) metabolism has also been suggested, in this study we investigated the interaction of the stable GTP analogue GTP(S), Al salts and NaF with this system. In rat cerebral cortical membranes, GTP(S) dose-dependently stimulated [3H]inositol phosphates ([3H]InsPs) accumulation. This effect was potentiated by carbachol and was partially prevented by the GTP-binding antagonist GDP(S), indicating that CNS muscarinic receptor activation is coupled to PtdIns hydrolysis via putative G-protein(s). GTP(S) stimulation was also inhibited by phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C, which is known to exert a negative feedback control on agonist-stimulated PtdIns metabolism. Both Al salts and NaF mimicked the action of GTP(S) in stimulating PtdIns turnover. Their actions were highly synergistic, suggesting that AlF4- could be the active stimulatory species. However, the stimulatory effects of AlCl3 and/or NaF were not potentiated by carbachol and were not inhibited by GDP(S) and PMA, suggesting that separate sites of action might exist for GTP(S) and AlF4-. In the nervous tissue, activation of PtdIns hydrolysis by Al (probably as AlF4-) may be mediated by activating a regulatory G-protein at a location distinct from the GTP-binding site or by a direct stimulation of phospholipase C.

Aluminum↗

PubMed1991

Formation of hemoglobin adducts of acrylamide and its epoxide metabolite glycidamide in the rat.

A method was developed for the determination of hemoglobin (Hb) adducts formed by the neurotoxic agent acrylamide and its mutagenic epoxide metabolite glycidamide. The method was based on simultaneous measurements of the cysteine adducts formed by these two agents by means of gas chromatography/mass spectrometry in hydrolyzed hemoglobin samples. Rats were injected ip with acrylamide or glycidamide in doses ranging from 0 to 100 mg/kg body wt, and the hemoglobin adduct levels were determined. The hemoglobin binding index of acrylamide to cysteine was found to be 6400 pmol (g Hb)-1/mumol (kg body wt)-1, higher than for any other substance studied so far in the rat, and 1820 pmol (g Hb)-1/mumol (kg body wt)-1 for glycidamide. In rats injected with acrylamide, formation of adducts of the parent compound was approximately linear with dose (0-100 mg/kg), whereas adducts of the epoxide metabolite glycidamide generated a concave curve, presumably reflecting the Michaelis-Menten kinetics of its formation. On the basis of the rate constants for cysteine adduct formation determined in vitro, the first-order rates of elimination of acrylamide and glycidamide from the blood compartment of rats were estimated to be 0.37 and 0.48 hr-1, respectively, using a linear kinetic model. It was further estimated that the percentage of acrylamide converted to glycidamide in the rat decreased from 51% following administration of 5 mg/kg to 13% after a dose of 100 mg/kg. Subchronic treatment of rats with acrylamide (10 mg/kg/day for 10 days or 3.3 mg/kg/day for 30 days) confirmed that the conversion rate of acrylamide to glycidamide, as determined from hemoglobin adduct formation, is higher at low-administered doses. These findings suggest that dose-rate effects may significantly affect risk estimates of this compound and that different low-dose extrapolation procedures should be employed for effects induced by the parent compound acrylamide and those induced by the metabolite glycidamide.

Acrylamide↗

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↗

PubMed1991

Effect of styrene oxide on rat brain glutathione.

Glutathione (GSH) plays a primary role in protecting cells from oxidative stress and in detoxifying foreign compounds. The functions and regulations of GSH in nervous tissue have not been thoroughly investigated. This study examines the effects of styrene oxide, a reactive metabolite of the neurotoxic solvent styrene, on GSH metabolism in six regions of the rat brain (cortex, cerebellum, medulla-pons, hippocampus, striatum and hypothalamus). Control levels of GSH in brain regions ranged from 1.6 mM in medulla-pons to 2.7 mM in striatum. Styrene oxide (100-400 mg/kg, ip) depleted GSH in a dose- and time-dependent manner in all brain regions studied. Histochemical studies indicated a predominantly glial distribution of GSH and confirmed the depletion of GSH by styrene oxide in brain. Studies with [8(-14)C] styrene oxide revealed no differences in the distribution of styrene oxide/metabolites among brain regions. gamma-Glutamylcysteine synthetase, the rate-limiting enzyme in GSH biosynthesis, was not affected by styrene oxide in any brain region, either in vitro or following in vivo administration. Glutathione S-transferase activity in different brain regions, measured using p-nitrostyrene oxide as a substrate, correlated quantitatively with GSH depletion by styrene oxide. Depletion of brain GSH by styrene oxide may contribute to oxidative injury to neuronal and glial cells and may be involved in styrene neurotoxicity.

Animals↗

PubMed1991

A pilot study of occupational and environmental risk factors for Parkinson's disease.

Increasingly, the etiology of Parkinson's disease (PD) has been linked to exposures to environmental toxicants. This epidemiologic pilot study used a self-administered questionnaire among 34 PD cases and 22 other neurology clinic control patients. All subjects were at least 40 years old. Risk factors investigated included occupation, well-water use, pesticide use, metal exposures, medical history, smoking, alcohol consumption, and drug use. Twenty-six percent of the male PD cases reported having been employed in farming versus eleven percent for male controls (OR = 3.1, 95% C.I. = 0.3 to 35). Sixteen percent of male cases versus none of the controls reported employment as welders. No clear trends involving exposure to either occupational or home pesticides emerged. In assessing occupational exposures to metals, aluminum and copper exposures tended to be more common among male cases than male controls. Additionally, as reported in other studies, smoking showed an inverse relationship with PD. Although the findings reported here are provocative, these results are statistically imprecise and must be interpreted cautiously because of the small number of subjects included in the study.

Adult↗

PubMed1991

Muscarinic M2 receptors in rat brain labeled with [3H] AF-DX 384.

The muscarinic antagonist AF-DX 384 (5,11-dihydro-11-(((2-(2-((dipropylamino)methyl)-1- piperidinyl)ethyl)amino)carbonyl)-6H-pyrido(2,3b)(1,4)-benzodiazepin+ ++-6-one methansulfonate) was used to label cholinergic muscarinic receptors of the M2 subtype in rat brain. In the brainstem [3H] AF-DX 384 labeled a single population of binding sites with Kd = 3-4 nM and Bmax = 430-610 fmol/mg of protein. The pharmacological profile of these sites was similar to that observed with the muscarinic M2 agonist [3H] AF-DX 116. Muscarinic M2 receptors were unequally distributed in rat brain regions: in brainstem, about 80% of total muscarinic receptors (measured with [3H] quinuclidinyl benzilate) were labeled by [3H] AF-DX 384, while in other brain areas they represented only a fraction of total binding. Because of its high specific binding, high affinity and specificity, [3H] AF-DX 384 represents a useful novel ligand to study M2 receptors in brain tissue.

Animals↗

PubMed1991

Interaction of short chain aliphatic alcohols with muscarinic receptor-stimulated phosphoinositide metabolism in cerebral cortex from neonatal and adult rats.

Muscarinic receptor-stimulated phosphoinositide metabolism has been recently suggested as a possible target for the neurotoxic effects of ethanol during brain development. Since two other alcohols, tertiary butanol and n-propanol, have been shown to cause microencephaly in the rat when administered during the brain growth spurt, in the present study we investigated the in vitro effects of five short chain aliphatic alcohols on muscarinic receptor-stimulated phosphoinositide metabolism in cerebral cortical slices from 7 day-old rats. In neonatal animals all alcohols tested inhibited carbachol (1 mM)-stimulated [3H]inositol phosphates accumulation in a dose- and time-dependent manner. The order of potency was t-butanol greater than n-propanol greater than or equal to iso-propanol greater than ethanol greater than methanol. After 90 min of incubation, ethanol, n-propanol and t-butanol caused a significant inhibition of muscarinic receptor-stimulated inositol metabolism at doses as low as 15 - 50 mM, comparable to the blood concentrations reached after in vivo administration of doses able to induce developmental neurotoxicity. The inhibitory effect of ethanol was additive to that of iso-propanol or t-butanol. Differently from these effects in 7 day-old rats, in cortical slices from adult animals methanol and ethanol had no effect on carbachol-stimulated phosphoinositide metabolism, while the two propanol isomers and t-butanol were less effective than in neonatal animals. These results suggest that muscarinic receptor-coupled phosphoinositide metabolism might be a common neurochemical target for the developmental neurotoxicity of short chain aliphatic alcohols.

Alcohols↗

PubMed1990

Developmental neurotoxicity of ethanol: in vitro inhibition of muscarinic receptor-stimulated phosphoinositide metabolism in brain from neonatal but not adult rats.

The in vitro effects of ethanol (EtOH) on muscarinic receptor-stimulated phosphoinositide metabolism were measured in cerebral cortex slices of adult and 7-day-old rats. EtOH (500 mM) caused a significant decrease (32-43%) of maximal accumulation of [3H]inositol phosphates (InsPs) induced by carbachol, and a 2-fold increase in its EC50 in 7-day-old rats, but had no effect in adult rats. The effect of EtOH on [3H]InsPs accumulation in neonatal rats was significant at a concentration as low as 150 mM. The inhibitory effect of EtOH was maximal in cerebral cortex and hippocampus and lower in cerebellum, while no effect was observed in the brainstem. While carbachol- and acetylcholine-stimulated phosphoinositide metabolism were inhibited by EtOH, EtOH had no effect on norepinephrine-, histamine-, and serotonin-stimulated phosphoinositide hydrolysis. These results are qualitatively and quantitively similar to those previously found following in vivo administration of EtOH to developing and to adult rats, suggesting that the muscarinic receptor-stimulated phosphoinositide metabolism might represent a target for EtOH-induced developmental neurotoxicity.

Aging↗

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

Characterization of ouabain-induced phosphoinositide hydrolysis in brain slices of the neonatal rat.

The effect of the Na/K-ATPase inhibitor ouabain on phosphoinositide (Ptdlns) hydrolysis was studied in rat brain cortical slices. Ouabain induced a dose-dependent accumulation of inositol phosphates (InsPs) which was much higher in neonatal rats (1570 +/- 40% of basal) than in adult animals (287 +/- 18% of basal). For this reason, all experiments were conducted with 7 day-old rats. Strophantidin caused a similar stimulation of Ptdlns hydrolysis, although it was less potent than ouabain. The order of potency for ouabain-stimulated InsPs accumulation in brain areas was hippocampus greater than cortex greater than brainstem greater than cerebellum. The effect of ouabain was not blocked by antagonists for the muscarinic, alpha1 -adrenergic and glutamate receptors. Also ineffective were the K+ channel blockers 4-aminopyridine and tetraethylammonium, the sodium channel blocker tetrodotoxin, and the calcium channel blocker verapamil, whereas the Na/Ca exchanger blocker amiloride partially antagonized the effect of ouabain. The accumulation of InsPs induced by ouabain was additive to that of carbachol and norepinephrine, as well as to that induced by high K+ and veratrine, but not to that of glutamate. Removal of Na+ ions from the incubation buffer completely prevented the accumulation of InsPs induced by ouabain. The effect of ouabain was also dependent upon extracellular calcium and was under negative feedback control of protein kinase C. Despite the higher effect of ouabain on Ptdlns hydrolysis of immature rats, the density of [3H]ouabain binding sites, as well as the activity of Na/K-ATPase were higher in adult animals. Furthermore, a poor correlation was found between ouabain-stimulated Ptdlns hydrolysis and [3H]ouabain binding in brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

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

Na+/K(+)-ATPase in rat brain and erythrocytes as a possible target and marker, respectively, for neurotoxicity: studies with chlordecone, organotins and mercury compounds.

Due to the inaccessibility of human nerve tissue for direct biochemical evaluation, there appears to be a need to identify peripheral markers which will reflect toxicity to the central nervous system by relatively non-invasive means. The aim of this study was to investigate whether the enzyme Na+/K(+)-ATPase in erythrocytes could be used as a marker for effects on the same enzyme in brain tissue. The compounds chosen to test this hypothesis were the pesticide chlordecone, the organotin compounds triethyltin and tributyltin, mercuric chloride and methyl mercury. All compounds were found to inhibit in vitro Na+/K(+)-ATPase activity in rat brain (IC50s = 0.9-56 microM) and in rat erythrocytes (IC50s = 1.2-66 microM) with similar potencies. However, administration of these compounds in vivo at high doses produced no significant inhibition of either brain or erythrocyte Na+/K(+)-ATPase activity, despite observed symptoms of neurotoxicity. Dialysis experiments indicated that dissociation of the compounds by dilution during tissue preparation was not responsible for the lack of detectable in vivo inhibition. Measurements of metal concentrations in brain by atomic absorption spectrometry after in vivo administration of triethyltin, mercuric chloride and methyl mercury indicated that levels of these compounds were too low to inhibit significantly NA+/K(+)-ATPase activity. These results suggest that inhibition of Na+/K(+)-ATPase activity might not represent the mechanism responsible for the neurotoxicity of these compounds, and that erythrocyte Na+/K(+)-ATPase activity is not a useful marker for neurotoxicity following acute exposures.

Animals↗