Nitrate (NO3−) and nitrite (NO2−) are endocrine disruptors to downregulate expression of tyrosine hydroxylase and motor behavior through conversion to nitric oxide in early development of zebrafish

Abstract

With a view to consider the increasing concern over nitrogen pollution in the aquatic environment, we investigated effects of nitrate (NO3(-)) and nitrite (NO2(-)) on the activity of dopaminergic neuron in zebrafish embryos and larvae. Both nitrate and nitrite exposure decreased the expression of tyrosine hydroxylase (TH) in dopaminergic neurons at 48hpf. Only nitrite decreased the response to tactile stimulation at 72hpf, whereas both nitrate and nitrite decreased the swimming activity at 6dpf. When the embryos were exposed to nitrate or nitrite together with an estrogen receptor blocker (ICI 182,780), the decreases in TH expression and motor behavior caused by nitrate or nitrite alone were reversed suggesting the effects of nitrate and nitrite were mediated through estrogen receptor (ER). The result of co-incubation with an oxidoreductase inhibitor, diphenyleneiodonium, indicated the conversion to nitric oxide (NO) is likely to be responsible for the effects of nitrate and nitrite, which was further supported by the increased staining for NO after exposure. The present study demonstrates that nitrate and nitrite are neurotoxicants acting as an endocrine disruptor possibly through conversion to NO to downregulate the activity of dopaminergic neuron in early development of zebrafish.

Long‐term water quality data explain interpopulation variation in responsiveness to stress in sticklebacks at both wastewater effluent‐contaminated and uncontaminated sites

“…However, the present study suggests that a similar interpopulation range of stress axis reactivity occurs at sites where there are no significant (known) upstream inputs of wastewater, implying that the causal factor(s) is not uniquely associated with WWTP effluent. These data suggest either that 1) the contaminants concerned are among the major water quality determinands known to be present in both WWTP–contaminated and uncontaminated rivers (NO 3 , for example, may have endocrine‐disrupting activity in fish ) or 2) micropollutants, assumed to be primarily associated with treated wastewater inputs , are present within rivers uncontaminated by WWTP effluents to a greater degree than assumed. In either case, it will be necessary to investigate the mechanism underlying variation in stress axis reactivity between populations of sticklebacks, both to provide information on the nature of the causal factor(s) responsible for these effects and to better understand the functional implications of variations in the magnitude of the stress response at both the individual and the population levels.…”

Modulation of the stress response in wild fish is associated with variation in dissolved nitrate and nitrite

“…Teleost fish may utilise NO as a modulator of endocrine activity (Lal and Dubey 2013), and at least two of three NO synthase (NOS) isoforms are present in fish (see references in Mueller and O'Brien 2011). Exogenous inorganic N can affect NO levels in fish: exposure of zebrafish (Danio rerio) to nitrate (Jannat et al 2014) or nitrite results in an increase in circulating levels of NO (Jannat et al 2014;Jensen 2007). Indeed, nitrite itself may be directly involved in signalling within the endocrine system (Bryan et al 2005) in addition to acting as a substrate for the formation of NO.…”

Integrating Behavior and Physiology Into Strategies for Amphibian Conservation

“…However, because aquatic urban habitats often accumulate toxic contaminants that can affect amphibians at sublethal levels (Sievers et al, 2018a,b), behavioral and physiological assays can be additional tools in the conservation toolbox with which to assess effects of urban-associated contaminants and may serve as early warning signals of potential population declines. Although the specific contaminants that may have affected corticosterone in Mondelli (2016) are not known, exposure to nitrate and nitrite affects behavior, physiology, and survival in some aquatic species (Hecnar, 1995;Jannat et al, 2014;Pottinger, 2017). An important next step in this research will be to examine potential links among specific contaminants, physiology and behavior.…”