Dose-Dependent Cardiac Responses of Daphnia magna to Neuroactive Substances

<div> This study quantifies the cardiac responses of Daphnia magna to ethanol (12-25%), caffeine, nicotine, and sugar, revealing significant dose-dependent effects. Mean heart rates demonstrated ethanol-induced bradycardia at concentrations ≥14% (p&lt;0.001), with severe depression at 25% (104.7 ± 56 bpm), consistent with its GABAergic inhibitory role in aquatic invertebrates (Cahill, 2006). Caffeine and nicotine exhibited pronounced tachycardia (286 ± 62 bpm and 270 ± 34 bpm, respectively), aligning with their known receptor antagonism (Tkaczyk et al., 2021). Sugar, included as an osmotic control, induced mild stimulation (261 ± 52 bpm), suggesting potential metabolic effects. These findings underscore Daphnia's sensitivity to neuroactive pollutants and support its use in ecotoxicological risk assessment (OECD, 2019). </div>