Toxicology Reports 2 (2015) 950–956
Contents lists available at ScienceDirect
Toxicology Reports journal homepage: www.elsevier.com/locate/toxrep
Paraquat exposure induces behavioral deficits in larval zebrafish during the window of dopamine neurogenesis Jayshree Nellore a,∗ , Nandita P. b a b
Department of Biotechnology, Sathyabama University, Jeppiaar Nagar, Rajiv Gandhi Salai Chennai-119, Chennai, Tamilnadu, India Department of Biotechnology, Sathyabama University, Chennai, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 6 April 2015 Received in revised form 29 May 2015 Accepted 11 June 2015 Available online 16 June 2015 Keywords: Cholinergic system Motor defects Paraquat Early life
a b s t r a c t Exposure to environmental risk factors such as herbicides in early life has been proposed to play important roles in the development of neurodegenerative disorders in adult life. To test this hypothesis, we used a zebrafish model to link the herbicide paraquat (PQ) to disease etiology. Strikingly, treatment of 18 hpf embryonic zebrafish with low-dose PQ treatment (0.04 ppm, lower than the accepted human daily exposure) resulted in 50% display of neurodegenerative phenotypes and motor deficits at various developmental stages (segmentation to larval stage). Wide arrays of biomarkers have been employed to delineate the toxic responses which include lipid peroxidation, glutathione (GSH) and apoptosis studies. A decrease in the GSH levels, increase in lipid peroxidation and apoptosis, respectively, were observed at various developmental stages. Unexpectedly, we show that the exposure to paraquat during the window of dopamine neurogenesis causes Parkinsonian like motor defects in later life by perturbing cholinergic system due to oxidative stress. © 2015 Published by Elsevier Ireland Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Neurotransmitter systems work in concert in the vertebrate nervous system to regulate signal transduction pathways that govern processes like behavior [1] . Dysfunction in the dopaminergic nervous system can lead to conditions that feature motor abnormalities. Parkinson’s disease (PD) is a common neurodegenerative disease characterized by the loss of dopamine neurons in the substantia nigra and patients present with extensive motor abnormalities [2]. Neurodevelopmental motor disorders can also result from dopaminergic dysfunction, the most well documented of these being attention deficient hyperactivity disorder (ADHD) [3]. In addition to altered dopaminergic signaling, effects on serotonergic pathways have been identified in PD and ADHD patients [4,5]. The etiology of sporadic dopamine related movement disorders is largely unknown. Epidemiological studies, however suggest environmental factors may contribute. One such risk factor is exposure to chemicals like pesticides. Paraquat has been linked to selec-
Abbreviations: PQ, paraquat; hpf, hours post fertilization; LPO, lipid peroxidation; GSH, glutathione; ADHD, attention deficient hyperactivity disorder; PD, Parkinson’s disease; DTNB, 5 5 -dithiobis-(2- nitrobenzoic acid); EM, embryo medium; ppm, parts per million. ∗ Corresponding author. E-mail address: sree [email protected] (J. Nellore).
tive dopaminergic degeneration, which has been shown to produce parkinsonian syndrome, and thus, are also used in animal models of PD [6]. Interestingly, evidence has shown that neurodegenerative diseases may result from insults during development [7]. More studies need to be conducted in order to evaluate environmental exposures as a causal factor in the onset of movement disorders. Also, it is not clear whether developmental insults on the dopaminergic nervous system are the underlying cause for disorders that occur later in life. Zebrafish may be a useful model in addressing these qualms. In zebrafish, no dopaminergic cells lie in the midbrain; therefore, the nigrostriatal pathway, which extends from the substantia nigra (SN) to the striatum (Str) in mammals, is homologous to the dopaminergic ascending pathway in zebrafish, extending from cells in the posterior tuberculum (PT) to the subpallium (Vd), both of which are present in the forebrain [8]. As determined by tyrosine hydroxylase and dopamine transporter staining, dopamine-containing neurons can first be detected in the posterior tuberculum in the midbrain as early as 18 hpf [9]. Other components of the dopaminergic nervous system such as the spinal cord and ventral diencephalon contain functioning neurons by 24 hpf. Also at 48 hpf, dopaminergic neurons are present in the olfactory bulb, preoptic region, telencephalon, paraventricular organ, and hypothalamus. By 72 hpf, dopaminergic neurons are present in the retina, pretectum, and ventral thalamus, with the tectum gaining
http://dx.doi.org/10.1016/j.toxrep.2015.06.007 2214-7500/© 2015 Published by Elsevier Ireland Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
J. Nellore, N. P. / Toxicology Reports 2 (2015) 950–956
951
dopaminergic neuronal activity by 96 hpf [10]. By the end of 4 days (96 hpf), the full complement of dopaminergic neuronal groups is present in the zebrafish [11] . Relatively few studies have assessed paraquat induced effects on locomotor activity during zebra fish development in small testing environment (e.g., a multi-well microtiter plate) that would be required for large-scale chemical screening in toxicology. Hence, we began investigating the locomotion of zebrafish during development, as well as the factors that affect this activity following paraquat exposure during the window of dopamine neurogenesis i.e., 18 hpf. 2. Materials and methods 2.1. Chemicals DTNB (5,5 - dithiobis-(2-nitrobenzoic acid)), 2 -thiobarbituric acid, methanol, chloroform were purchased from Southern Scientific Corporation, Chennai. Other chemicals that were used were of analytical grade. Paraquat was obtained from Microbial Technology Laboratory, Sathyabama University, Chennai. 2.2. Zebrafish Wild-type adult (
Contents lists available at ScienceDirect
Toxicology Reports journal homepage: www.elsevier.com/locate/toxrep
Paraquat exposure induces behavioral deficits in larval zebrafish during the window of dopamine neurogenesis Jayshree Nellore a,∗ , Nandita P. b a b
Department of Biotechnology, Sathyabama University, Jeppiaar Nagar, Rajiv Gandhi Salai Chennai-119, Chennai, Tamilnadu, India Department of Biotechnology, Sathyabama University, Chennai, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 6 April 2015 Received in revised form 29 May 2015 Accepted 11 June 2015 Available online 16 June 2015 Keywords: Cholinergic system Motor defects Paraquat Early life
a b s t r a c t Exposure to environmental risk factors such as herbicides in early life has been proposed to play important roles in the development of neurodegenerative disorders in adult life. To test this hypothesis, we used a zebrafish model to link the herbicide paraquat (PQ) to disease etiology. Strikingly, treatment of 18 hpf embryonic zebrafish with low-dose PQ treatment (0.04 ppm, lower than the accepted human daily exposure) resulted in 50% display of neurodegenerative phenotypes and motor deficits at various developmental stages (segmentation to larval stage). Wide arrays of biomarkers have been employed to delineate the toxic responses which include lipid peroxidation, glutathione (GSH) and apoptosis studies. A decrease in the GSH levels, increase in lipid peroxidation and apoptosis, respectively, were observed at various developmental stages. Unexpectedly, we show that the exposure to paraquat during the window of dopamine neurogenesis causes Parkinsonian like motor defects in later life by perturbing cholinergic system due to oxidative stress. © 2015 Published by Elsevier Ireland Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Neurotransmitter systems work in concert in the vertebrate nervous system to regulate signal transduction pathways that govern processes like behavior [1] . Dysfunction in the dopaminergic nervous system can lead to conditions that feature motor abnormalities. Parkinson’s disease (PD) is a common neurodegenerative disease characterized by the loss of dopamine neurons in the substantia nigra and patients present with extensive motor abnormalities [2]. Neurodevelopmental motor disorders can also result from dopaminergic dysfunction, the most well documented of these being attention deficient hyperactivity disorder (ADHD) [3]. In addition to altered dopaminergic signaling, effects on serotonergic pathways have been identified in PD and ADHD patients [4,5]. The etiology of sporadic dopamine related movement disorders is largely unknown. Epidemiological studies, however suggest environmental factors may contribute. One such risk factor is exposure to chemicals like pesticides. Paraquat has been linked to selec-
Abbreviations: PQ, paraquat; hpf, hours post fertilization; LPO, lipid peroxidation; GSH, glutathione; ADHD, attention deficient hyperactivity disorder; PD, Parkinson’s disease; DTNB, 5 5 -dithiobis-(2- nitrobenzoic acid); EM, embryo medium; ppm, parts per million. ∗ Corresponding author. E-mail address: sree [email protected] (J. Nellore).
tive dopaminergic degeneration, which has been shown to produce parkinsonian syndrome, and thus, are also used in animal models of PD [6]. Interestingly, evidence has shown that neurodegenerative diseases may result from insults during development [7]. More studies need to be conducted in order to evaluate environmental exposures as a causal factor in the onset of movement disorders. Also, it is not clear whether developmental insults on the dopaminergic nervous system are the underlying cause for disorders that occur later in life. Zebrafish may be a useful model in addressing these qualms. In zebrafish, no dopaminergic cells lie in the midbrain; therefore, the nigrostriatal pathway, which extends from the substantia nigra (SN) to the striatum (Str) in mammals, is homologous to the dopaminergic ascending pathway in zebrafish, extending from cells in the posterior tuberculum (PT) to the subpallium (Vd), both of which are present in the forebrain [8]. As determined by tyrosine hydroxylase and dopamine transporter staining, dopamine-containing neurons can first be detected in the posterior tuberculum in the midbrain as early as 18 hpf [9]. Other components of the dopaminergic nervous system such as the spinal cord and ventral diencephalon contain functioning neurons by 24 hpf. Also at 48 hpf, dopaminergic neurons are present in the olfactory bulb, preoptic region, telencephalon, paraventricular organ, and hypothalamus. By 72 hpf, dopaminergic neurons are present in the retina, pretectum, and ventral thalamus, with the tectum gaining
http://dx.doi.org/10.1016/j.toxrep.2015.06.007 2214-7500/© 2015 Published by Elsevier Ireland Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
J. Nellore, N. P. / Toxicology Reports 2 (2015) 950–956
951
dopaminergic neuronal activity by 96 hpf [10]. By the end of 4 days (96 hpf), the full complement of dopaminergic neuronal groups is present in the zebrafish [11] . Relatively few studies have assessed paraquat induced effects on locomotor activity during zebra fish development in small testing environment (e.g., a multi-well microtiter plate) that would be required for large-scale chemical screening in toxicology. Hence, we began investigating the locomotion of zebrafish during development, as well as the factors that affect this activity following paraquat exposure during the window of dopamine neurogenesis i.e., 18 hpf. 2. Materials and methods 2.1. Chemicals DTNB (5,5 - dithiobis-(2-nitrobenzoic acid)), 2 -thiobarbituric acid, methanol, chloroform were purchased from Southern Scientific Corporation, Chennai. Other chemicals that were used were of analytical grade. Paraquat was obtained from Microbial Technology Laboratory, Sathyabama University, Chennai. 2.2. Zebrafish Wild-type adult (
