Effects of soman and sarin on high affinity choline uptake by rat brain synaptosomes

Brain regional heterogeneity and toxicological mechanisms of organophosphates and carbamates

The brain is a well-organized, yet highly complex, organ in the mammalian system. Most investigators use the whole brain, instead of a selected brain region(s), for biochemical analytes as toxicological endpoints. As a result, the obtained data is often of limited value, since their significance is compromised due to a reduced effect, and the investigators often arrive at an erroneous conclusion(s). By now, a plethora of knowledge reveals the brain regional variability for various biochemical/neurochemical determinants. This review describes the importance of brain regional heterogeneity in relation to cholinergic and noncholinergic determinants with particular reference to organophosphate (OP) and carbamate pesticides and OP nerve agents.

Age-related effects of chlorpyrifos and parathion on acetylcholine synthesis in rat striatum

We compared the in vivo effects of two organophosphorus (OP) insecticides, chlorpyrifos (CPF) and parathion (PS) on acetylcholine (ACh) synthesis in neonatal, juvenile and adult rats. Basal levels of ACh synthesis were highest in adult rats, intermediate in juveniles and lowest in neonates. Following high (maximum tolerated dosage) subcutaneous exposure to either insecticide, relatively similar degrees of cholinesterase inhibition were noted, but the time to peak reduction varied among the age groups. CPF had no effect on ACh synthesis in neonates, increased synthesis in juveniles and decreased synthesis in adults, but only in the low dose group. PS had more consistent effects on ACh synthesis, decreasing transmitter synthesis in neonates (24 h after dosing) but increasing synthesis in juveniles and adults at both 4 and 24 h after exposure. Selective changes in neurotransmitter synthesis may contribute to differential age-related toxicity of these agents.

Effects of single or repeated administration of a carbamate, propoxur, and an organophosphate, DDVP, on jejunal cholinergic activities and contractile responses in rats

Wistar rats were injected once or repeatedly for 10 days with dichlorvos (DDVP, 5 mg kg-1), propoxur (10 mg kg-1), oxotremorine (0.1 mg kg-1) or atropine (5 mg kg-1). Animals were killed 20 min or 24 h after single or consecutive injections, respectively, for determinations of cholinergic activities and contractile responses to acetylcholine (ACh) of the jejunum. Single treatments: while DDVP and propoxur decreased acetylcholinesterase (AChE) activity, oxotremorine and atropine did not. Although DDVP, propoxur and oxotremorine increased levels of ACh, atropine decreased them. Contractile responses to ACh were enhanced by DDVP and reduced by oxotremorine and atropine. The Bmax value of binding of [3H]quinuclidinyl benzylate (QNB) to muscarinic ACh receptors was decreased by atropine. Consecutive treatments: DDVP and oxotremorine decreased AChE activity markedly and slightly, respectively. Although DDVP and oxotremorine increased levels of ACh, propoxur decreased them. Without affecting the contractile responses, DDVP caused a reduction and propoxur and atropine caused an increase in the Bmax value for binding of [3H]QNB. Both the contractile responses and the value of Bmax for binding of [3H]-QNB were decreased by oxotremorine. In summary, propoxur and DDVP showed similar effects mainly through their anticholinesterase properties in the case of single injection, but DDVP had similar effects to those of oxotremorine and propoxur had similar effects to those of atropine in the case of repeated injection.

Effects of diisopropyl phosphofluoridate, sarin and soman on the accessibility of proteins, in the electroplax membrane, to lactoperoxidase-catalyzed iodination

Anticholinesterases (anti-ChE) have some effects on biological properties including behavior, vision, and electroencephalograms, which are often long lasting and which do not appear to be due to cholinesterase (ChE; EC 3.1.1.7) inhibition, but which may be due to alterations in the organization and/or functioning of the cellular membrane. We assessed the effects of anti-ChE agents on the asymmetric organization of proteins in the innervated (excitable) and in the non-innervated (non-excitable) plasma membrane of the electroplax from the electric eel. Lactoperoxidase-catalyzed iodination (LCI) was carried out under impenetrable conditions in intact electroplax (where protein exposure on the external surface is monitored) and in split electroplax (where total protein labeling on both the external and internal monolayers of the plasma membrane bilayer is monitored). Labeling in split electroplax was much greater than in intact electroplax for all molecular weight groupings of proteins (30,000 to greater than 200,000). The anti-ChE agents diisopropyl phosphofluoridate (DFP; 10(-3) M), sarin (10(-4) M) and soman (10(-4) M, 10(-6) M, 2.5 x 10(-9) M) did not alter permeability, protein content or the electrophoretic pattern of the plasma membrane proteins of the electroplax. DFP, sarin and 10(-6) M soman (but not 2.5 x 10(-9) M or 10(-4) M soman) increased labeling of some of the molecular weight fractions in the non-innervated plasma membrane as monitored by LCI in intact electroplax. Under these same conditions, DFP and 10(-4) M soman increased labeling in the innervated plasma membrane while 10(-6) M soman decreased labeling. When LCI was carried out in split electroplax, 10(-4) M soman caused a decrease in labeling in both the innervated and non-innervated plasma membrane indicating a decrease of exposed proteins on the cytoplasmic surface of the plasma membrane. These concentrations of the anti-ChE agents caused almost complete ChE inhibition in the electroplax cells, except for 2.5 x 10(-9) M soman which caused little or no inhibition. These results suggest that alterations in protein asymmetry, as monitored by LCI of accessible proteins, are not directly due to ChE inhibition. These changes in organization of membrane proteins could contribute to a variety of effects of anti-ChE agents which are not due to ChE inhibition.

Effect of soman and sarin on phosphatidylcholine asymmetry in the electroplax from the electric eel

Some effects of organophosphorus anticholinesterase compounds that are unrelated to cholinesterase inhibition and that are sometimes long lasting may be due to alterations at the cellular membrane level. Phosphatidylcholine exchange protein was used to assess the effects of sarin and soman on phosphatidylcholine asymmetry in the inner and outer leaflets of the plasma membrane bilayer of the electroplax. Exposure of electroplax (30 min in vitro) to soman (10(-4), 10(-6) M) or sarin (10(-4), 10(-6), 5 x 10(-9) M) increased the percentage of phosphatidylcholine in the outer monolayer of the innervated plasma membrane bilayer and decreased the percentage in the inner monolayer. These changes by sarin were observed at concentrations that produced 100% cholinesterase inhibition (10(-4), 10(-6) M) and at a concentration (5 x 10(-9) M) where no inhibition occurred, suggesting that these effects are not directly due to cholinesterase inhibition. A 1-week exposure of live eels to soman (10(-8) M) in vivo caused an increase in phosphatidylcholine labeling in the outer monolayer of the innervated and noninnervated surfaces of the electroplax. Two weeks after stopping exposure to soman, increased labeling was still observed, suggesting that this may be a long-term effect. Because the organophosphates did not increase the permeability of the electroplax, all of these changes in labeling appear to be due to a redistribution of phosphatidylcholine from the inner to the outer monolayer of the plasma membrane bilayer.