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The Effects of Acute Exposure to Neuroactive Drugs on the Locomotor Activity of Larval Zebrafish
Citation:
IRONS, T., R. C. MACPHAIL, D. L. HUNTER, AND S. J. PADILLA. The Effects of Acute Exposure to Neuroactive Drugs on the Locomotor Activity of Larval Zebrafish. Presented at TestSmart DNT 2 Developmental Neurotoxicity Meeting, Reston, VA, November 12 - 14, 2008.
Impact/Purpose:
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Description:
In an effort to develop a rapid in vivo screen for EPA’s prioritization of toxic chemicals, we have begun to characterize the locomotor activity of zebrafish (Danio rerio) larvae using prototypic drugs that act on the central nervous system. Initially, we chose to define the behavioral profile of ethanol, d-amphetamine, and cocaine because all three are known to increase locomotion at low doses and decrease locomotion at high doses in rodents. Our goal was to determine if immature zebrafish (6 days post-fertilization) showed a similar response. Zebrafish embryos/larvae were individually maintained in 96-well microtiter plates at 26°C and under a 14:10 light:dark cycle with lights on at 0830 hr. Non-lethal concentrations of ethanol (1.0 – 4.0% v/v), d-amphetamine sulfate (0.08 – 20.00 μM) or cocaine hydrochloride (0.2 – 50.0 μM) were administered to the larvae by immersion. Each drug was screened on individual plates, with all doses and controls represented. A total of 12 – 48 larvae were exposed to each drug concentration. Locomotor activity was assessed beginning 20 minutes into exposure using a Noldus video activity monitor and Ethovision 3.1 software to track each animal under either visible light or dark (infrared) conditions for 70 minutes using alternating light and dark periods, each of 10-minute duration. Untreated animals displayed activity in the dark that was markedly higher than that in the light. Acute ethanol exposure increased activity in the light: the group exposed to 2% ethanol was 700% more active than controls. The larvae exposed to 4% ethanol remained immobile under both lighting conditions. d-Amphetamine exposure increased activity in the dark to a maximum of 150% of control at 0.73 μM, then decreased activity to 66% of control at the highest dose (20 μM). Animals exposed to cocaine did not exhibit increased activity; however, those that received the higher concentrations showed marked hypoactivity in the dark periods (10% of control at 50 μM). In general, the pattern of response was similar for the compounds: low concentrations of either ethanol or d-amphetamine increased activity, while higher concentrations of all three drugs decreased activity. Because the ethanol effects occurred mainly in light, while those with d-amphetamine and cocaine occurred in the dark, changing the lighting conditions throughout testing proved to be advantageous. These results indicate that very young zebrafish are sensitive to neuroactive drugs, and that their response to acute exposure is similar to those obtained in rodent tests of motor activity. T.D. Irons is supported by the NIH NIGMS Initiative for Maximizing Student Diversity and the NIEHS National Research Service Award (T32 ES007126). This is an abstract of a proposed presentation; the information does not necessarily reflect Agency policy.