Introduction
Zebrafish larvae offer several advantages for behavioural studies applicable in examining and creating treatments to combat neurodegenerative and psychiatric disorders. Many microfluidic devices have been designed for manipulation of zebrafish embryos and larvae[1–8] and stimulating them[9–16] to gather information about their neural[15,17] and behavioral[13–16,18,19] activities in controlled microenvironments. Various stimuli such as thermal[9], chemical[20] and fluid flow[11] have been tested. Yet, electrical stimulation comes with a high degree of versatility for studying zebrafish movement. Its properties such as signal magnitude, direction and duration can be modulated with convenience.
Studies have observed no significant impact on model organisms such as nematodes and zebrafish due to small electric signals[12,21]. Some studies have been performed on zebrafish response to electric signal by our lab and others[16,22–24]. While insightful, these experiments were either time consuming with fish tested individually on single-fish microfluidic platforms or uncontrollable and difficult to quantify on conventional multi-well plates and chambers. In this paper, a quadruple-fish microfluidic device was employed to load, partially immobilize, electrically stimulate and monitor behavioral responses of four larvae, simultaneously. The design principles of this device were previously reported by us[6], while in this paper, we focus on the first time application of this multi-fish device to screen the novel effect of various dopaminergic chemicals on the electric behaviour. The electric response of the semi-mobile larvae was analyzed using response duration (RD) and tail beat frequency (TBF) as quantitative phenotypes[16]. The new device reduced the time required for behavioral screening and enabled an increased sample size.
The molecular pathway involved in zebrafish response to electricity is unknown, but dopaminergic (DAergic) pathway is likely involved in this locomotion[24]. A few studies have identified variations in different behaviours of zebrafish when exposed to dopamine (DA) compounds[25–32]. However, not much is known about the behavioural impacts of DA drugs on the electric response of zebrafish larvae. Specifically, the effects of non-selective and selective DA agonists and antagonists on the electric response are unknown.
Our quadruple-fish device was utilized to characterize the acute effects of various DAergic receptor drugs on the electric-induced locomotion of zebrafish larvae. The response of larvae exposed to DA antagonists were compared to those treated with DA agonists. We also examined whether the observed impairment in electric-induced movement due to DA antagonist exposure could be recovered through subsequent treatment with a DA agonist. Our findings elevate the present knowledge about the electric induced behavior of zebrafish larvae and its potential regulation by the DAergic system in the context of a customizable assay platform for on-demand and quantitative behavioral studies.