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.