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.