Methods for Assessing Neurotoxicity in Zebrafish - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 116

Figure 10.2 Effects of 6-hydroxydopamine in zebrafish. Two dpf zebrafish were untreated (a) or treated
with 6-hydroxydopamine (b) and stained with anti-tyrosine hydroxylase antibody at 5dpf. TH positive
cells were present in the diencephalon, eyes, and hindbrain (circled). The total number of TH positive
DA neurons in the populations 1 and 2 was 44 4 for wild-type zebrafish (a) and 3 4 for
6-OHDA-treated zebrafish (b) ( P < 0.0001) indicating occurrence of dopaminergic neuron
neurotoxicity.

(Rink and Wullimann, 2001). For quantitative assessment, TH-immunoreactive DA
neurons were counted by microscopy ( n 10). Statistical analysis was performed to

determine significance. Distinct populations of dopaminergic neurons were observed in
the diencephalons of wild-type zebrafish (Fig. 10.2a). After 6-OHDA treatment, the
number of dopaminergic neurons significantly decreased (Fig. 10.2b); total number of
TH positive DA neurons in populations 1 and 2 was 44

¼

4 for wild-type zebrafish and

3 0.0001). These results indicate 6-OHDA-

induced dopaminergic neurotoxicity (Parng et al., 2007). In mammals, 6-OHDA has
been shown to induce oxidative stress and results in neuronal death (Elkon et al., 2004).
Immunostaining using an anti-nitrotyrosine antibody was performed and nitrotyrosine
immunoreactivity was observed in the brain of 6-OHDA-treated zebrafish but not in
untreated controls, suggesting that oxidative stress in response to 6-OHDA treatment
occurs in zebrafish (Parng et al., 2007).

4 for 6-OHDA-treated zebrafish ( P <

10.3.3 Compound Effects on Myelin

Myelin is a dielectric (electrically insulating) material that forms a layer, the myelin
sheath, usually specifically around axons on neurons. Myelin is essential for the
proper functioning of the nervous system. Schwann cells supply the myelin for
peripheral neurons, whereas oligodendrocytes, specifically of the interfascicular type,
supply it to those of the central nervous system. Myelin is considered a defining
characteristic of vertebrates, but it has also arisen by parallel evolution in some
invertebrates. The myelin sheath has been shown to be affected by many compounds.
To assess compound effects on the integrity of the myelin sheath in zebrafish,
expression of myelin basic protein (MBP) was quantified after compound treatment
and whole mount immunostaining. Acrylamide, which has been shown to
cause demyelination in mammals (Harry et al., 1992; LoPachin et al., 1992, 1993;