Behavior and brain size of larval zebrafish exposed to environmentally relevant concentrations of betamethylamino- L-alanine (BMAA)

Harmful algal blooms (HABs) release toxic compounds in water and are
increasing in frequency worldwide. The neurotoxin
β-methylamino-L-alanine (BMAA) is released by HABs and has
garnered much attention over the past twenty years due to
its association with human neurodegenerative disorders, but its
effects on wildlife are still largely unknown. This study
characterized the effects of chronic exposure to environmentally
relevant concentrations of BMAA on the behavior and brain size
of developing zebrafish (Danio rerio). Zebrafish were
continuously exposed to 0, 1, 10, or 100 μg/L waterborne BMAA
between 0- and 5-days post-fertilization (dpf) before the onset
of exogenous feeding. At 5 dpf, locomotion and responses to vibrational
and visual stimuli were assessed. Following behavioral testing,
larvae body and brain size were measured. Survival between 0 and
5 dpf did not differ between treatments. Moreover, BMAA exposure
did not affect thigmotaxis, startle response
magnitude, habituation to repeated presentation of vibrational
startling stimuli, or relative brain size. A moderate increase in
overall activity was observed in larvae exposed to 10 ug/L BMAA
under light, but this effect was not seen in dark conditions, indicating
that visual processing may have been affected by chronic BMAA
exposure. Thus, our results show that passive continuous exposure
to environmentally relevant concentrations of BMAA prior to first
feeding in zebrafish does not affect overall brain development,
locomotion, anxiety, and motor neuron-mediated reflexes, but
suggest targeted neurotoxicity within the visual system.