1. Introduction
Parkinson’s disease (PD) is one of the most prevalent neurological
disorders which affects about 1% of the world population over 60 years
old[1]. The etiology of PD is complex. Although the causes and risk
factors of PD are still unknown, several factors including specific
genes and environmental cues seem to play a role in inducing PD[2],
[3]. Recent studies demonstrated
the involvement of gap junctions and connexin hemichannels in a variety
of neurological diseases, including Alzheimer’s disease (AD) and
PD[4], [5]. Pannexin (Panx) channels have also displayed
aberrant functioning in neurodegenerative disease and may be etiologic
in PD[6]. Panx1 is one of the known members of the Panx family which
are ubiquitously expressed in many organs[7]. They show a widespread
distribution in neurons and astrocytes of all major subdivisions of the
brain including those affected by PD. However, their roles in the
activity of astrocytes and neurons remains to be fully
characterized[8]–[10]. There is evidence supporting a role of
Panx1 channels in oxidative stress, which is considered as one of the
main contributors to the development of a variety of diseases such as AD
and PD[11]–[13]. Yet, the involvement of Panx1 in the etiology
of PD remains to be fully characterized.
In addition to humans and mice, the expression of Panx1 channels has
been identified in other species including zebrafish[14]–[16].
Zebrafish larvae are widely used for studying genetic[17],
behavioral activities[18]–[20] and neurodegenerative
disorders[17], [21], [22]. They offer many advantages
including small size[18], rapid development[23], genetic
homology to humans[24] and optical transparency[25] that
facilitate their use for fundamental and large-scale research. The
optical transparency and rapid neurodevelopment throughout embryogenesis
in zebrafish facilitates study of dopaminergic-related diseases such as
PD[26]–[35]. Zebrafish PD models have been produced relying on
either genetic manipulations[29], [34], [35] or exposure to
different neurotoxins such as 6-hydroxydopamine (6-OHDA) and
1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)[26], [30],
[33].
Here, an association of Panx1 and PD was investigated by comparing
molecular and behavioral properties of Panx1a knockout (KO)
(panx1a-/- ) and wild type (WT)
(panx1a+/+ ) zebrafish using the 6-OHDA model.
We have previously reported different microfluidic techniques to study
the electric-induced behavioral responses of zebrafish larvae,
quantitatively[20], [36]–[39]. The lab-on-chip approach
allows to address challenges of behavioral studies such as providing a
controllable stimulus to evoke the behavioral responses of larvae and
quantifying their quick movements. Here, the electrical stimulus offers
several advantages for behavioral studies as its duration, magnitude and
direction can be accurately modulated to evoke locomotor responses in
zebrafish larvae on demand. Using the electric-induced response duration
(RD) and tail beat frequency (TBF) as quantifying parameters, we
previously discovered significant difference between behavioral
responses of 5-7 days post-fertilization (dpf)panx1a+/+ andpanx1a-/- larvae, suggesting the potential
involvement of Panx1a in electric-induced locomotor response of
zebrafish larvae[20]. This result was exploited to study the role of
Panx1a channels for early stages of the development of Parkinson related
disorders. Here, the electric-induced RD and TBF ofpanx1a+/+ andpanx1a-/- zebrafish larvae in response to
6-OHDA provided insight into Panx1a channels’ involvement in the
etiology of PD. In support of the behavioral analysis quantitative Real
Time-PCR (RT-qPCR) tested the differential expression of tyrosine
hydroxylase expression was also employed to study the molecular events
underlying the behavioral response of zebrafish larvae. This study opens
broad areas of application including on-demand behavioral investigations
of gene functions and chemical toxicity, as proposed in this application
for studying the roles of Panx1a in the etiology of PD.