Developmental exposure to domoic acid disrupts startle response behavior and circuitry

Abstract

Harmful algal blooms produce potent neurotoxins that accumulate in seafood and are hazardous to human health. Developmental exposure to the harmful algal bloom toxin, domoic acid (DomA), has behavioral consequences well into adulthood, but the cellular and molecular mechanisms are largely unknown. To assess these, we exposed zebrafish embryos to DomA during the previously identified window of susceptibility (2 days post-fertilization) and used the well-known startle response circuit as a tool to identify specific neuronal components that are targeted by exposure to DomA. Exposure to DomA reduced the probability of eliciting a startle after auditory/vibrational or electrical stimuli and led to the dramatic reduction of one type of startle, short latency c-start (SLC) responses. Furthermore, DomA-exposed larvae had altered kinematics of both SLC and long latency c-start (LLC) startle responses, exhibiting shallower bend angles and slower maximal angular velocities. Using vital dye staining, immunolabelling, and live imaging of transgenic lines, we determined that while the sensory inputs were intact, the reticulospinal neurons required for SLC responses were absent in most DomA-exposed larvae. Furthermore, axon tracing revealed that DomA-treated larvae also showed significantly reduced primary motor neuron axon collaterals. Overall, these results show that developmental exposure to DomA leads to startle deficits by targeting specific subsets of neurons. These findings provide mechanistic insights into the neurodevelopmental effects of excess glutamatergic signaling caused by exposure to DomA. It further provides a model for using the startle response circuit to identify neuronal populations targeted by toxin or toxicant exposures.Summary statementWe used the zebrafish startle response as a tool to identify sensory-motor deficits and the loss of specific neural populations after developmental exposure to the harmful algal bloom toxin domoic acid.GRAPHICAL ABSTRACT

Neurological mechanism of sensory deficits after developmental exposure to non-dioxin-like polychlorinated biphenyls (PCBs)

“…The experiment was repeated twice with cohorts from separate breeding events. Vibro-acoustic startle response was assessed as described previously (Panlilio et al 2021). Briefly, the acoustic stimuli were delivered by a vibrational exciter producing acoustic vibrations at a frequency of a 1000 Hz for a duration of 2 ms at four different amplitudes (32, 38, 41, 43 dB).…”

“…Adult zebrafish were fed brine shrimp and Gemma Micro 300 pellets (Skretting) every day. In this study, we used wild-type zebrafish of the AB strain obtained from Zebrafish International Resource Center (ZIRC), as well as several transgenic lines: the photoconvertible calcium indicator line Tg[elavl3:CaMPARI(W391F+V398L)] jf9 kindly provided by Jessica Plavicki (Brown University, USA), and the transgenic lines Tg(cntn1b:EGFP-CAAX) (Panlilio et al 2021) labeling axons, Tg(olig2:EGFP) vu12 (Park et al 2007;Shin et al 2003) marking oligodendrocyte precursor cell bodies, Tg(sox10:mRFP) (Takada et al 2010) marking oligodendrocyte lineage cells, as well as Tg(mbp:EGFP-CAAX) (Almeida et al 2011) and Tg(mbp:EGFP) (gift from Dr. Kelly Monk, generated by Dr. Charles Kaufman in the laboratory of Dr. Leonard Zon, Harvard Medical School, Boston, MA) marking myelin sheaths. Zebrafish eggs were obtained by pairwise breeding and kept in 0.3x Danieau's (17 mM NaCl, 0.2 mM KCl, 0.12 mM MgSO 4 , 0.18 mM Ca(NO 3 ) 2 and 1.5 mM HEPES, pH 7.6) in glass vials at a density of 10 individuals per 10 mL, at a constant water temperature of 28 ± 1˚C and standard 14-h light/10-h dark cycle.…”

Orphan cytochrome P450 20A1 CRISPR/Cas 9 mutants and neurobehavioral phenotypes in zebrafish

“…Vibroacoustic startle latency was assessed as described previously [21, 22] and the same set-up was used to test for startle habituation as a form of non-associative learning in 6 dpf larval zebrafish. For each trial, 16 larvae with inflated swim bladders were distributed in a 4×4 acrylic well-plate which was mounted on a minishaker (Brüel & Kjaer, Vibration Exciter 4810) connected to an amplifier (Brüel & Kjaer, Power Amplifier Type 2718).…”