Chlorpyrifos and malathion have opposite effects on behaviors and brain size that are not correlated to changes in AChE activity

Abstract

Organophosphates, a type of neurotoxicant pesticide, are used globally for the treatment of pests on croplands and are therefore found in a large number of conventional foods. These pesticides are harmful and potentially deadly if ingested or inhaled in large quantities by causing a significant reduction in acetylcholinesterase (AChE) activity in the central and peripheral nervous system. However, much less is known about the effects of exposure to small quantities of the pesticides on neural systems and behavior during development. In the current study we used zebrafish larvae in order to determine the effects of two of the most widely used organophosphates, chlorpyrifos and malathion, on zebrafish behavior and AChE activity. Embryos and larvae were exposed to the organophosphates during different time points in development and then tested at 5 days post-fertilization for behavioral, neurodevelopmental and AChE abnormalities. The results of the study indicate that chlorpyrifos and malathion cause opposing behaviors in the larvae such as swim speed (hypoactivity vs. hyperactivity) and rest. Additionally, the pesticides affect only certain behaviors, such as thigmotaxis, during specific time points in development that are unrelated to changes in AChE activity. Larvae treated with malathion but not chlorpyrifos also had significantly smaller forebrain and hindbrain regions compared to controls by 5 days post-fertilization. We conclude that exposure to very low concentrations of organophosphate pesticides during development cause abnormalities in behavior and brain size.

Age matters: Developmental stage of Danio rerio larvae influences photomotor response thresholds to diazinion or diphenhydramine

“…Similar decreases in locomotion or PMR behaviors have been reported for larval zebrafish following exposure to DZN (Scheil et al, 2009; Yen et al, 2011) and other organophosphate insecticides across a variety of ages (Levin et al, 2004; Pérez et al, 2013; Richendrfer et al, 2012; Şişman, 2010; Tilton et al, 2011). However, this trend may not hold true for all cases, as previous work has indicated that specific types of behavioral responses may be compound specific among different organophosphates (Richendrfer and Creton, 2015). …”

Developmental neurotoxicity of succeeding generations of insecticides

“…Other effects in larvae include decreased dopamine and serotonin levels and increased transmitter turnover (Eddins and others 2010), decreased swimming activity (Jin and others 2015; Levin and others 2004; Yen and others 2011) and decreased habituation of swimming over time (Levin and others 2004). Reduced anxiety-related behavior (thigmotaxis) by CPF is unrelated to changes in AChE activity (Richendrfer and Creton 2015; Richendrfer and others 2012). The assessment of adult fish indicates reduced dopamine levels, spatial learning impairments, increased swimming activity and increased sensorimotor response (startle response) (Eddins and others 2010; Levin and others 2003; Sledge and others 2011).…”

Effects of EGCG and Chlorpyrifos on the Mortality, AChE and GSH of Adult Zebrafish: Independent and Combination

“…Chlorpyrifos bond with cholinesterase by covalent [7,8] resulting in the accumulation of acetylcholine in the nervous system [8,9]. They causes irreversible inhibition of AChE, which leads to neuronal overstimulation and death [9].…”

“…Their tests show that 300 nM (≈ 0.1 mg/L) Chlorpyrifos exposure over 5 days inhibited AChE activity by over 80%. Richendrfer et al [8] observed that Larvae treated with 0.1 mM (≈ 35.0mg/L) Chlorpyrifos had decreased more than 30% of levels of AChE. Recent researches showed that Chlorpyrifos could destroy oxygen free radical balance and form oxidative stress [3,11,12].…”

“…Chlorpyrifos causes the toxic effects on the brain size [8] and the tissue of liver of zebrafish [12]. Gomez et al [14] evaluated the effect of Chlorpyrifos exposure on metabolic profiles of zebrafish muscle and observed the induction of muscle exhaustion as well as the oxidative stress and the general disruption of neurotransmitter metabolism.…”