Abstract-Relations between neurotoxicants and changes in physiological parameters and behavior were investigated in larval rainbow trout (RBT; Oncorhynchus mykiss) exposed to sublethal concentrations of two organophosphate pesticides (OPs). Fish were exposed to diazinon and malathion in static-renewal experiments. After exposures for 24, 96, or 96 h, followed by 48 h of recovery, individual RBT were videotaped to assess locomotory behaviors. Brain tissue from the same fish was assayed for the physiological endpoints, cholinesterase (ChE) activity, muscarinic cholinergic receptor (MChR) number (B max ), and MChR affinity (K D ). Cholinesterase activity decreased significantly with increasing concentrations of both diazinon and malathion and differed significantly among exposure durations, with 24-and 96-h means less than 48-h recovery means. Decreases in B max with OP concentration were not significant for either chemical, and K D was unaffected. Changes in swimming speed and distance were significantly correlated with changes in ChE activity for both chemicals; rate of turning was significantly correlated with ChE activity in malathion exposures. These results suggest that correlations between physiological and behavioral changes previously seen in mammals also occur in fish.
Pesticides and heavy metals are common environmental contaminants that can cause neurotoxicity to aquatic organisms, impairing reproduction and survival. Neurotoxic effects of cadmium and carbaryl exposures were estimated in larval rainbow trout (RBT; Oncorhynchus mykiss) using changes in physiological endpoints and correlations with behavioral responses. Following exposures, RBT were videotaped to assess swimming speed. Brain tissue was used to measure cholinesterase (ChE) activity, muscarinic cholinergic receptor (MChR) number, and MChR affinity. ChE activity decreased with increasing concentrations of carbaryl but not of cadmium. MChR were not affected by exposure to either carbaryl or cadmium. Swimming speed correlated with ChE activity in carbaryl-exposed RBT, but no correlation occurred in cadmium-exposed fish. Thus, carbaryl exposure resulted in neurotoxicity reflected by changes in physiological and behavioral parameters measured, while cadmium exposure did not. Correlations between behavior and physiology provide a useful assessment of neurotoxicity.
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