Eurological disorder [43]. In zebrafish, it has been reported that ethanol causes abnormal development of motor neurons and muscle fibers [25]. The neurotoxic effect of lindane has also been well documented [26,44] and chronic 125-65-5 exposure of low dose lindane causes neurobehavioral, neurochemical, and electrophysiologrcal efects in rat brain [45]. Our observations in the present study are consistent with the general mode of the action of these six chemicals. All of the five neurotoxins, acetaminophen, atenolol, atrazine, ethanol and lindane, 
showed sensitive inhibition of axon growth. In contrast, mefenamic acid has a significant neuroprotective effect by inhibition 12926553 of glutamate-induced cell toxicity in vitro and reduces ischemic stroke in vivo in rats [33]. Our observation is also consistent with its neural protectant role as the toxic concentrations (10 and 50 mg/L) of mefenamic acid, which caused statistically very significant edema, light pigmentation and shorter body length, apparently had no effect on the axon growth. It is apparent that all of these six chemicals show dosagedependent toxicity in essentially all the endpoints observed (Table S1). In the present study, we demonstrated that, compared to the recommended DarT endpoints, axon length, which can be observed and measured in Tg(nkx2.2a:mEGFP) fry, is about 10 fold more sensitive than the most sensitive endpoints recommended in DarT. Thus, with the ease and direct observable features of GFP expression, the Tg(nkx2.2a:mEGFP) transgenic zebrafish provides a convenient and highly sensitive tool for screening and testing neurotoxic compounds, which will be applicable in environmental monitoring and pharmaceutical production. As there are a large number of fluorescent transgenic zebrafish with fluorescent protein reporter gene Benzocaine biological activity expression in specific organs and tissues [10,11], our study may open a new avenue to test other useful fluorescent transgenic zebrafish for development of specific toxicological assays for different categories of chemicals. In particular, as exampled here, all of the toxicological assays in fluorescent transgenic zebrafish can be accomplished within 5 days after fertilization and before feeding stage, which is considered an in vivo test system alternative to adult animals, thus reducing the use of animals in toxicological tests.Supporting InformationTable S1 Comparison of sensitivity of lethal andsublethal DarT endpoints and axon length measurements in Tg(nkx2.2a:mEGFP) the treatment. (DOCX)Figure 6. Lowest effective concentrations of neurotoxins for shortening of motoneuron axons. doi:10.1371/journal.pone.0055474.gTransgenic Zebrafish for Neurotoxin TestAcknowledgmentsThis work was supported by the Singapore National Research Foundation under its Environmental Water Technologies Strategic Research Programme and administered by the Environment Water Industry Programme Office (EWI) of the PUB, grant number R-154-000-328-272.Author ContributionsConceived and designed the experiments: 
XZ ZG. Performed the experiments: XZ. Analyzed the data: XZ ZG. Contributed reagents/ materials/analysis tools: XZ ZG. Wrote the paper: XZ ZG.
Aging strongly affects brain morphology, which may contribute to cognitive change over time [1,2]. Good et al. [1] reported that aging predominantly and substantially affects gray matter (GM), and that GM volume decreased linearly with age. Others have reported that several of the age-associated changes in brain volume are probably nonlin.Eurological disorder [43]. In zebrafish, it has been reported that ethanol causes abnormal development of motor neurons and muscle fibers [25]. The neurotoxic effect of lindane has also been well documented [26,44] and chronic exposure of low dose lindane causes neurobehavioral, neurochemical, and electrophysiologrcal efects in rat brain [45]. Our observations in the present study are consistent with the general mode of the action of these six chemicals. All of the five neurotoxins, acetaminophen, atenolol, atrazine, ethanol and lindane, showed sensitive inhibition of axon growth. In contrast, mefenamic acid has a significant neuroprotective effect by inhibition 12926553 of glutamate-induced cell toxicity in vitro and reduces ischemic stroke in vivo in rats [33]. Our observation is also consistent with its neural protectant role as the toxic concentrations (10 and 50 mg/L) of mefenamic acid, which caused statistically very significant edema, light pigmentation and shorter body length, apparently had no effect on the axon growth. It is apparent that all of these six chemicals show dosagedependent toxicity in essentially all the endpoints observed (Table S1). In the present study, we demonstrated that, compared to the recommended DarT endpoints, axon length, which can be observed and measured in Tg(nkx2.2a:mEGFP) fry, is about 10 fold more sensitive than the most sensitive endpoints recommended in DarT. Thus, with the ease and direct observable features of GFP expression, the Tg(nkx2.2a:mEGFP) transgenic zebrafish provides a convenient and highly sensitive tool for screening and testing neurotoxic compounds, which will be applicable in environmental monitoring and pharmaceutical production. As there are a large number of fluorescent transgenic zebrafish with fluorescent protein reporter gene expression in specific organs and tissues [10,11], our study may open a new avenue to test other useful fluorescent transgenic zebrafish for development of specific toxicological assays for different categories of chemicals. In particular, as exampled here, all of the toxicological assays in fluorescent transgenic zebrafish can be accomplished within 5 days after fertilization and before feeding stage, which is considered an in vivo test system alternative to adult animals, thus reducing the use of animals in toxicological tests.Supporting InformationTable S1 Comparison of sensitivity of lethal andsublethal DarT endpoints and axon length measurements in Tg(nkx2.2a:mEGFP) the treatment. (DOCX)Figure 6. Lowest effective concentrations of neurotoxins for shortening of motoneuron axons. doi:10.1371/journal.pone.0055474.gTransgenic Zebrafish for Neurotoxin TestAcknowledgmentsThis work was supported by the Singapore National Research Foundation under its Environmental Water Technologies Strategic Research Programme and administered by the Environment Water Industry Programme Office (EWI) of the PUB, grant number R-154-000-328-272.Author ContributionsConceived and designed the experiments: XZ ZG. Performed the experiments: XZ. Analyzed the data: XZ ZG. Contributed reagents/ materials/analysis tools: XZ ZG. Wrote the paper: XZ ZG.
Aging strongly affects brain morphology, which may contribute to cognitive change over time [1,2]. Good et al. [1] reported that aging predominantly and substantially affects gray matter (GM), and that GM volume decreased linearly with age. Others have reported that several of the age-associated changes in brain volume are probably nonlin.
