Partial protection from organophosphate-induced cholinesterase inhibition by metyrapone treatment.

Background: Organophosphates are cholinesterase (ChE) inhibitors with worldwide use as insecticides. Stress response, evidenced by a dramatic and relatively long-lasting (several hours) rise in the plasma glucocorticoid concentration is an integral element of the organophosphate (OP) poisoning symptomatology. In rodents, corticosterone (CORT) is the main glucocorticoid.

Neuroendocrine and behavioral response to amphetamine challenge after exposure to an organophosphorus pesticide.

Objectives: Exposure to various stressors is known to result in sensitization to psychostimulants, a state related to the psychostimulant dependence and addiction. It has been shown in some studies that the rise in corticosterone (CORT) concentration is indispensable for both the induction and the expression of behavioral sensitization. Therefore, it might be suspected that behavioral hyposensitivity to amphetamine (AMPH) is somehow related to a reduced CORT response to the psychostimulant subsequent to the chlorphenvinphos (CVP) intoxication.

Effects of stress pretreatment on the dynamics of blood cholinesterase activity after exposure to an organophosphorus pesticide in the rat.

A single i.p. administration of 1.

Contrasting effects of 4-week inhalation exposure to pseudocumene or hemimellitene on sensitivity to amphetamine and propensity to amphetamine sensitization in the rat.

Objectives: Some data suggest that increased behavioural sensitivity to psychostimulants may develop after exposure to volatile chemicals in common use. The purpose of the present experiment was to find out whether and in what way inhalation exposure to pseudocumene (PS) or hemimellitene (HM) at low concentrations alters behavioural sensitivity to the psychostimulant amphetamine (AMPH), and propensity to develop behavioural sensitization to AMPH.

Material And Methods: Adult male Wistar rats were exposed 6 h/day, 5 days a week for 4 weeks to PS or HEM at 0, 25, 100 or 250 ppm.

Neurobehavioural functions in adult progeny of rat mothers exposed to methylmercury or 2,2', 4,4', 5,5'-hexachlorobiphenyl (PCB 153) alone or their combination during gestation and lactation.

Objectives: Methylmercury (MeHg) and polychlorinated biphenyls (PCBs) are ubiquitous environmental pollutants. Both are neurotoxic, especially for the developing brain. The main source of human exposure to MeHg and PCBs is seafood.

Early developmental effects of separate or combined perinatal exposure to methylmercury (MeHg) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) in the rat.

Objectives: Methylmercury (MeHg) and polychlorinated biphenyls (PCBs) are ubiquitous and persistent environmental pollutants and food contaminants. Both are neurotoxic, especially for the developing nervous system.

Material And Methods: Female rats were exposed from day 7 of pregnancy up to day 21 after the delivery to MeHg in drinking water, PCB 153 per os or MeHg+PCB 153.

Catecholamine levels in the brain of rats exposed by inhalation to benzalkonium chloride.

Objectives: The aim of the study was to obtain quantitative data on the effect of inhalation exposure to benzalkonium chloride (BAC) on the concentration of catecholamines and their metabolites in selected brain structures. Additionally, concentration of corticosterone (CORT) in plasma was estimated.

Material And Methods: Wistar rats were subjected to a single (6-hour) or repeated (3 days, 6 h/day) exposure to BAC aerosol at ca.

[Exposure to neurotoxic substances versus stress].

It has long been known that exposure to a stressor may initiate progressive and long-lasting (or even permanent) functional changes in the central nervous system. They are manifested by an altered, decreased or increased responsiveness of the body not only to the generating stressor, but also to other unrelated stressors. Numerous experimental studies have shown that the sensitivity of the body to chemical stressors may be influenced by a prior exposure to nonchemical stressors, e.

Exposure to chlorphenvinphos, an organophosphate insecticide, prevents from behavioral sensitization to amphetamine.

Objectives: Exposure to organophosphorus (OP) pesticides, irreversible inhibitors of acetylcholinesterase (AChE), may result in long-lasting alterations in the functional state of the central nervous system. In earlier studies, we found that a single exposure of the rat to chlorphenvinphos (CVP), an OP pesticide, made the animal hyposensitive to amphetamine (AMPH) three weeks posttreatment. A repeated administration of AMPH is known to result in a progressive increase in the behavioral sensitivity to the psychostimulant.

[Possible consequences of acetylcholinesterase inhibition in organophosphate poisoning. Discussion continued].

Numerous toxicologists still believe that the only function of acetylcholinesterase (AChE) is to catalyse the hydrolysis of acetylcholine (ACh), and that the toxicity of organophosphorous pesticides (OP) results from their ability to switch this function off. This viewpoint, however, requires revision in the light of the recent findings concerning the AChE structure and function as well as in view of the regulation of the AChE protein synthesis in conditions of stress. There is now no doubt that apart from catalysing the ACh hydrolysis, AChE performs also nonenzymatic functions, trophic (e.

Amphetamine- and scopolamine-induced locomotor activity following treatment with chlorphenvinphos or chlorphyriphos in rats.

Objectives: Effects of acute exposure to organophosphorous pesticides (OPs), chlorphenvinphos (CVP) or chlorphyriphos (CPF) on amphetamine (AMPH)- or scopolamine (SCOP)-induced open-field locomotion were compared in rats.

Materials And Methods: CVP and CPF were administered intraperitoneally, both at doses resulting in about 50% inhibition of erythrocyte acetylcholinesterase (rbcAChE). The pesticide groups did not differ one from another in the magnitude of the acute behavioral effects.

Organic solvents and the dopaminergic system.

Organic solvents pose a considerable health risk for humans. It is due to their ability to cross biological barriers and indisputable toxicity on the one hand, and the wealth of applications and large production and consumption volumes on the other. The primary target of the toxic action of organic solvents is the nervous system.

Behavioral sensitivity to amphetamine or scopolamine after acute administration of nicotine in the rat.

Objectives: Earlier experiments have revealed that a single pretreatment of the rat with chlorphenvinphos (CVP) at a subtoxic dose (1.0 mg/kg, about 1/10 of DL50) makes the animal hyposensitive to the locomotor stimulating effect of amphetamine (AMPH) or scopolamine (SCOP) given three weeks postexposure. Such a hyposensitivity did not develop after a single or multiple (at short intervals) dosing with oxotremorine (OXO), a direct muscarinic agonist, which suggests that it was not mediated by muscarinic receptors.

Pretreatment with footshock alters some effects of subsequent organophosphate exposure.

Pre-exposure to non-chemical stressors may alter a subject's vulnerability to chemical stressors. We found recently that rats given a subtoxic dose of chlorfenvinphos (CVP), an organophosphorus pesticide, develop behavioral hyposensitivity to amphetamine (AMPH). The present experiments were performed in order to find out whether pre-exposure to a non-chemical stressor several days prior to CVP exposure could influence this effect of the pesticide.

Alteration in behavioral sensitivity to amphetamine after treatment with oxotremorine. Effect of dose and test environment.

Our earlier experiment revealed that rats pretreated once with an anticholinesterase develop hyposensitivity to amphetamine (AMPH). One of the likely causes of this effect might be a transient hyperexcitation of the central muscarinic receptors. It has appeared, however, that rats pretreated with oxotremorine (OX), a muscarinic agonist, show an augmented behavioral response to AMPH weeks later.

Assessment of long-term neurotoxic effects of exposure to mesitylene (1,3,5-trimethylbenzene) based on the analysis of selected behavioral responses.

Trimetylbenzene isomers: pseudocumene, hemimellitene and mesitylene, are major components of numerous commercial solvents and high-grade fuels. In our earlier research on rats we have proved that inhalation exposure to pseudocumene or hemimellitene at concentrations close to the MAC value results in behavioral changes detectable many weeks after cessation of the exposure. The aim of our present study is to determine whether exposure to mesitylene causes effects similar to those observed for pseudocumene and hemimellitene.

Behavioral sensitivity to amphetamine after repeated exposure to an organophosphorous pesticide in the rat. Effect of coexposure to restraint.

In the work environment, chemical stressors coexists frequently with physical or psychological stressors. The purpose of the present experiment was to find out whether the effects of a repeated exposure to chlorphenvinphos (CVP), an organophosphorus pesticide, could be modified by a concurrent exposure to restraint, a psychological stressor. The experiment was performed on male Wistar rats.

Behavioral sensitization to amphetamine induced by a single i.p. dose of oxotremorine in the rat.

Earlier experiments have revealed that rats treated with a single dose of chlorphenvinphos (CVP), an irreversible acetylcholinesterase inhibitor, are hyposensitive to amphetamine (AMPH) given three weeks after CVP. Exposure to CVP results in an excess of acetylcholine with subsequent overactivation of the nicotinic as well as muscarinic cholinergic receptors. The purpose of the present experiment was to find out whether a selective activation of muscarinic receptors could induce behavioral hyposensitivity to AMPH.

Behavioural responsiveness to amphetamine or scopolamine following repeated exposure to chlorphenvinphos in rats.

A number of reports indicate that exposure to organophosphates (OPs), inhibitors of acetylcholinesterase (AChE), may result in long-lasting neurobehavioural alterations suggestive of an increased cholinergic tone. It is known that rats with cholinergic hyperreactivity are behaviourally hyposensitive to cholinergic antagonists and dopaminergic agonists. The purpose of the present study was to find out whether a similar trait would develop in rats exposed to chlorphenvinphos (CVP), an OP pesticide, in the past.

[Petit-mal epilepsy in laboratory rats, issues that an experimenter should be remember].

A certain proportion of laboratory rats of various strains is characterized with a heritable, abnormally high propensity for spontaneous, nonconvulsive electrocortical seizures. The seizures have form of bursts of spike-wave discharges (SWD) reminiscent of the human petit-mal epilepsy. The experimenter is usually unaware of this fact.