Subchronic ephedrine exposure suppresses PPAR signalling and impairs neurobehaviour in adult zebrafish

Abstract

Pharmaceutical contamination of freshwater systems by psychoactive compounds has intensified globally, yet the sub-lethal neurological consequences for resident aquatic fauna remain largely unresolved. Ephedrine (EPH), a centrally active psychoactive compound and controlled precursor substance, is routinely detected in wastewater effluents and surface waters at concentrations from ng/L to μg/L, raising unaddressed questions about its toxicity to fish. Using adult zebrafish as a vertebrate model, we examined the effects of fourteen-day waterborne EPH exposure at two environmentally relevant concentrations (0.05 and 1 μg/L) and one supra-environmental concentration (20 μg/L). Behavioural assessment revealed concentration-dependent locomotor inhibition, heightened anxiety-like behaviour, spatial learning deficits, and impaired social preference. Targeted neurotransmitter profiling identified biphasic alterations of cholinergic, monoaminergic, and amino-acid transmitter pools in brain tissue. Histopathological examination revealed mild changes at the environmentally relevant concentrations and pronounced neuronal injury at 20 μg/L. Whole-brain transcriptomic analysis identified suppression of PPAR signalling as one of the most prominently affected pathways, with marked downregulation of fatty acid oxidation genes (cpt1ab, cpt1cb, acaa1), suggesting disruption of the neuronal energy supply required for synaptic maintenance. These findings indicate that EPH exposure at environmentally relevant concentrations is associated with neurobehavioural, neurochemical, and molecular alterations in adult zebrafish, and provide mechanistic evidence to support the inclusion of stimulant alkaloids in aquatic environmental hazard identification.