Locomotor Assessment of 6-Hydroxydopamine-induced Adult Zebrafish-based Parkinson's Disease Model

The limitations of current treatments in delaying dopaminergic neuronal loss in Parkinson's disease (PD) raise the need for alternative therapies that can restore these neurons. Much effort is currently directed toward a better understanding of neuroregeneration using preclinical in vivo models. This regenerative capability for self-repair is, however, inefficient in mammals. Non-mammalian animals like zebrafish have thus emerged as an excellent neuroregenerative model due to its capability to continuously self-renew and have a close brain homology to humans. As part of the effort in elucidating cellular events involved in neuroregeneration in vivo, we have established the 6-hydroxydopamine (6-OHDA)-induced adult zebrafish-based PD model. This was achieved through the optimized intracerebroventricular (ICV) microinjection of 99.96 mM 6-OHDA to specifically ablate dopaminergic neurons (DpN) in the ventral diencephalon (Dn) of zebrafish brain. Immunofluorescence indicated more than 85% of DpN ablation at day three postlesion and full restoration of DpN at lesioned site 30 days postlesion. The present study determined the impairment and subsequent recovery of zebrafish swimming behavior following lesion by using the open field test through which two parameters, distance traveled (cm) and mean speed (cm/s), were quantified. The locomotion was assessed by analyzing the recordings of individual fish of each group (n = 6) using video tracking software. The findings showed a significant (p < 0.0001) reduction in speed (cm/s) and distance traveled (cm) of lesioned zebrafish 3 days postlesion when compared to sham. The lesioned zebrafish exhibited full recovery of swimming behavior 30 days postlesion. The present findings suggest that 6-OHDA lesioned adult zebrafish is an excellent model with reproducible quality to facilitate the study of neuroregeneration in PD. Future studies on the mechanisms underlying neuroregeneration as well as intrinsic and extrinsic factors that modulate the process may provide important insight into new cell replacement treatment strategies against PD.