Chronic dichlorvos exposure (6mg/kg b.wt/day) for a period of 8 weeks resulted in significant reduction in body weight gain of the male Wistar rats. However, the dietary intake remained unchanged in experimental animals following dichlorvos treatment. Activity of the synthesizing enzyme of acetylcholine (ACh) ie, choline acetyltransferase, was found to be significantly increased and the activity of hydrolyzing enzyme, acetyl cholinesterase (AChE), was inhibited in all the three brain regions studied. Chronic dichlorvos treatment also caused significant reduction in both high affinity (HA) and low affinity (LA) choline uptake (CU), with maximal effect being observed in the brain stem followed by cerebellum and cerebrum. Muscarinic receptor binding was significantly decreased in brain stem and cerebellum as reflected in the decreased receptor number (Bmax), without any change in the binding affinity (Kd) of the receptors. Dichlorvos treatment caused marked inhibition in cAMP synthesis as indicated by decreased adenylate cyclase activity as well as cAMP levels in cerebrum, cerebellum and brain stem. Our study shows that organophosphates may interact with muscarinic receptor-linked second messenger system and this could be a potential mechanism for the neurotoxic effects observed after repeated exposure to low levels of organophosphates, which are unexplainable on the basis of cholinergic hyperactivity. Toxicology and Industrial Health 2007; 23: 25—37.
Allgaier, C., Choi, B.K. and Hertting, G.1993: Muscarinic receptors regulating electrically evoked release of acetylcholine in hippocampus are linked to pertussis toxin-sensitive G-proteins but not to adenylate cyclase. J Neurochem61, 1043—49.
2.
Aoyagi, T., Wada, T., Kojima, F., Nagai, M., Harada, S., Takeuchi, T. and Hirokawa, K.1990: Increase in aminobutyrate aminotransferase and cholineracetyltransferase in cerebrum of aged rats. Chem Pharm Bull38, 1750—52.
3.
Bakry, N.M.S., El-Rashidy, A.H., Eldefrawi, A.T. and Eldefrawi, M.E.1988: Direct actions of organophosphorus anticholinesterase on nicotinic and muscarinic acetylcholine receptors. J Biochem Toxicol3, 235—39.
4.
Balduini, W., Cimino, M., Reno, F., Marini, P., Princivalle, A. and Cattabeni, F.1993: Effects of postnatal or adult chronic acetyl cholinesterase inhibition on muscarinic receptors, phosphoinositide turnonver and M1 mRNA expression. Eur J Pharmacol248, 281—88.
5.
Bignami, G., Rosik, N., Michalek, H., Milosevic, M. and Gatti, G.I.1975: Behavioural toxicity of anticholinesterase agents: Methodological, neurochemical and neuropsychological aspects. In L aties, V. ed. Behavioural toxicity. Plenum Press: 155—215.
6.
Bonner, T.I.1989: The molecular basis of muscarinic receptor diversity. Trends Neurosci12, 148—51.
7.
Burchfiel, J.L., Duffy, F.H. and Sim, V.M.1976: Persistent effects of sarin and dieldrin upon the primate electroencephalogram. Toxicol Appl Pharmacol35, 265—379.
8.
Carod-Artal, F.J. and Speck-Martins, C.1999: Late onset polyneuropathy due to exposure to organophosphates. Rev Neurol29, 123—37.
9.
Costa, L., Schwab, B.W. and Murphy, S.D.1982: Differential alterations of cholinergic muscarinic receptors during chronic and acute tolerance to organophosphorus insecticides. Biochem Pharmacol31, 3407—13.
10.
Desi, I. and Nagymajtenyi, I.1999: Electrophysiological biomarkers of an organophosphate pesticide, dichlorvos. Toxicol Lett107, 55—64.
11.
Eldefrawi, A.T., Jett, D. and Eldefrawi, M.E.1992: Direct actions of organophosphate anticholinesterases on muscarinic receptors, In Chambers J.E. , Levi, P.E. eds. Organophospates: Chemistry, fate and effects. Academic Press, 257—70.
12.
Ellman, G.L., Courtney, K.D., Anders, V. Jr and Featherstone, R.M.1961: A rapid, new and calorimetric determination of acetylcholinesterase activity. Biochem Pharmacol7, 88—95.
13.
Elnatan, A. and Mitchelson, F.1994: A simple and rapid HPLC assay for quantitating cyclic AMP accumulation in intact cell preparations. J Pharmacol Toxicol Met31, 47—51.
14.
Eskenazi, B., Bradman, A. and Castorina, R.1999: Exposures of children to OP pesticides and their potential adverse health effects. Environ Health Perspect107, 409—19.
15.
Fonnum, F.1966: A radiochemical method for the estimation of choline acetyltransferase . Biochem J100, 479—84.
16.
Glowinski, J. and Iversen, L.L.1966: Regional studies of catecholamines in the rat brain. J Neurochem13, 655—69.
17.
Gray, E.G. and Whittaker, V.P.1962: The isolation of nerve endings from brain: An electron microscopic study of cell fragments derived by homogenization and centrifugation . J Anat96, 79—88.
18.
Guler, K., Tascioglu, C. and Ozbey, N.1996: Organophosphate poisoning: Israel. J Med Sci32, 791—95.
19.
Hertz, L.1969: The biochemistry of brain tissue. In Bitter, E.E. and Bitter, N. eds. The biological basis of medicine. Academic Press, 3—37.
20.
Horowitz, S.H., Stark, E. and Marshall, A.1999: Multidrug modality assessment of peripheral nerve function in organophosphate pesticide applications. J Occup Environ Med41, 405—408.
21.
Huff, R.A. and Abou-Donia, M.B.1995: In vitro effect of chlorpyrifos oxon on muscarinic receptors and adenylate cyclase. Neurotoxicol16, 281—90.
22.
Huff, R.A., Corcoran, J.J., Anderson, J.K. and Abou-Donia, M.B.1994: Chlorpyrifos oxon binds directly to muscarinic receptors and inhibits cAMP accumulation in rat striatum. J Pharmacol Exp Ther269, 329—35.
23.
Jokanovic, M., Kosanovic, M. and Maksimovic, M.1996: Interaction of organophosphorus compounds with carboxyle sterases in the rate. Archives of Toxicology70(7): 444—50.
24.
Jones, D.H. and Matus, A.I.1974: Isolation of synaptic plasma membranes from brain by combined floatation density gradient centrifugation. Biochem Biophys Acta356, 276—87.
25.
Julka, D., Sandhir, R. and Gill, K.D.1995: Altered cholinergic metabolism in rat CNS following aluminium exposure: Implications on learning performance. J Neurochem65, 2157—64.
26.
Kaufer, D., Friedman, A., Seidman, S. and Soreq, H.1999: Anticholinesterases induce multigenic transcriptional feedback response suppressing cholinergic neurotransmission. Chem Biol Interact119—120, 349—60.
27.
Khym, J.X.1975: An analytical system for rapid separation of tissue nucleotides at low pressure on conventional anion exchangers. Clin Chem21, 1245—52.
28.
Kobayashi, H., Yuyama, A. and Chiba, K.I.1986: Cholinergic system of brain tissue in rats poisoned with the organophosphate O,O-dimethyl O-(2,2-dichlorovinyl) phosphate. Toxicol Appl Pharmacol82, 32—39.
29.
Kwong, T.C.2002: Organophosphate pesticides: biochemistry and clinical toxicology. Ther Drug Monit24, 144—49.
30.
Lambert, D.G., Burford, N.T. and Nahorski, S.R.1992: Muscarinic receptor subtypes: Inositol phosphates and intracellular calcium. Biochem Soc Trans20, 130—35.
31.
Liu, J., Chakraborti, T. and Pope, C.2002: In vitro effects of organophosphorus anticholinesterases on muscarinic receptor-mediated inhibition of acetylcholine release in rat striatum. Toxicol Appl Pharmacol178, 102—108.
Lowry, O.H., Rosebrough, N.J., Farr, A.L. and Randall, R.J.1951: Protein measurement with the folin-phenol reagent. J Biol Chem193, 265—75.
34.
Marchi, M., Ruelle, A., Andriolli, G.C. and Raiteri, M.1990: Pirenzipine-insensitive muscarinic autoreceptors regulate acetylcholine release in human neocortex. Brain Res520, 347—50.
35.
Maroni, M., Colosio, C., Ferioli, A. and Fait, A.2000: Biological monitoring of pesticide exposure: a review. Introduction. Toxicol143, 111—18.
36.
McKinney, M., Anderson, D., Forray, C. and El-Fakahany, E.E.1989: Characterization of the striatal M2 muscarinic receptor mediating inhibition of cyclic AMP using selective antagonists: A comparison with brainstem M2 receptor. J Pharmacol Expt Ther250, 265—72.
37.
Milby, T.1971: Prevention and management of organophosphate poisoning . J Am Med Assoc216, 2131—33.
38.
Nicklas, W.J., Purzkin, S. and Berl, S.1973: Effect of vinblastine and colchicines on uptake and release of putative neurotransmitters by synaptosomes and on brain actinomycin-like protein. J Neurochem20, 109—22.
39.
Plotkin, D.A. and Jarvik, L.F.1986: Cholinergic dysfunction in Alzheimer's disease: cause or effect? Prog. Brain Res65, 91—102.
40.
Prendergast, M.A., Terry, A.V. Jr and Buccafusco, J.J.1997: Chronic, low-level exposure to diisopropylfluorophosphate causes protracted impairment of spatial navigation learning. Psychopharmacology129, 183—91.
41.
Rouse, S.T., Edmunds, S.M., Gilmor, M.L. and Levey A.I.2000: Localization of M(2) muscarinic acetylcholine receptor protein in cholingeneric and non-cholinegic terminals in rat hippocampus. Neuroscience Letters284(3): 182—6.
42.
Russell, R.W., Carson, V.G., Booth, R.A. and Jenden, D.J.1981: Mechanisms of tolerance to the anticholinesterase, DFP: acetylcholine levels and dynamics in the rat brain. Psychopharmacology20, 1197—201.
43.
Russell, R.W., Carson, V.G., Jope, R.S., Booth, R.A. and Macri, J.1979: Development of behavioural tolerance: A search for subcellular mechanism. Psychopharmacology66, 155—58.
44.
Russell, R.W., Booth, R.A., Lauretz, S.D., Smith, C.A. and Jenden, D.J.1986: Behavioural, neurochemical and psychological effects of repeated exposures to subsynaptomatic levels of anticholinesterase, soman . Neurobehav Toxicol Teratol8, 675—85.
45.
Rydel, R.E. and Green, L.1988: cAMP analogs promote survival and neurite outgrowth in cultures of rat sympathetic and sensory neurons independently of nerve growth factors. Proc Natl Acad Sci USA85, 1257—61.
46.
Salomon, Y., Londos, C. and Rodbell, M.1974: A highly sensitive adenylate cyclase assay. Anal Biochem58, 541—48.
47.
Sarin, S. and Gill, K.D.1998: Dichlorvos induced alterations in glucose homeostasis: possible implications on the state of neuronal function in rats. Mol Cell Biochem199, 87—92.
48.
Sarin, S. and Gill, K.D.2000: Biochemical characterization of dichloruos-induced delayed neurotoxicity in rat. IUBMBLife49(2): 125—30.
49.
Savage, E.P., Keefe, T.J., Mounce, L.M., Heaton, R.K., Lewis, J.A. and Brucar, P.J.1988: Chronic neurological sequelae of acute organophosphate pesticide poisoning. Arch Environ Health43, 38—45.
50.
Scaps, P., Demuynck, S., Descamps, M. and Dhainert, A.1997: Effect of organophosphate and carbonate pesticides on acetyl cholinesterase and cholineacetyltransferase activities of the poilychaete nervis diversicolor. Arch Environ Contam Toxicol33, 203—208.
51.
Silveira, C.L.P., Eldefrawi, A.T. and Eldefrawi, M.E.1990: Putative M2 muscarinic receptors of rat heart have high affinity for organophosphorus anticholinesterase. Toxicol Appl Pharmacol103, 474—81.
52.
Steenland, K.1996: Chronic neurological effects of organophosphate pesticides . Br Med J 312, 1312—13.
53.
Sultatos, L.G.1994: Mammalian toxicology of organophosphorus pesticides. J Toxicol Environ Health43, 271—89.
54.
Szerb, J.C.1977: Characterization of presynaptic muscarinic receptors in central cholinergic neurons. In Jenden, D.J. ed. Cholinergic mechanisms and psychopharmacologyPlenum Press, 49—60.
55.
Volpe, L.S., Biagioni, T.M. and Marquis, J.K.1985: In vitro modulation of bovine caudate muscarinic receptor number by organophosphates and carbamates. Toxicol Appl Pharmacol78, 226—34.
56.
Ward, T.R. and Mundy, W.R.1996: Organophosphorus compounds preferentially affect second messenger systems coupled to M2/M4 receptors in rat frontal cortex. Brain Res Bull39, 49—55.
57.
Weiler, M.H.1989: Characterization of muscarinic receptors modulating acetylcholine release in the rat neostriatum. Experientia Suppl 57, 204—11.
58.
Woodruff, T.J., Kyle, A.D. and Bois, F.V.1994: Evaluating health risks from occupational exposure to pesticides and the regulatory response. Environ Health Perspec102, 1088—96.
59.
Yamamura, H.I. and Snyder, S.H.1974: Muscarinic cholinergic binding in rat brain. Proc Natl Acad Sci USA71, 1725—29.
60.
Zheng, Q., Olivier, K., Wan, Y.K., and Pope, C.N.2000: Comparative cholinergic neurotoxicity of oral chlorpygrifos exposures in preweanling and adult rats. Toxicological Sciences55(1): 124—32.
