Comparison of neurobehavioral effects of methylmercury exposure in older and younger adult zebrafish (Danio rerio).
It is widely recognized that the nature and severity of responses to toxic exposure are age-dependent. Using active avoidance conditioning as the behavioral paradigm, the present study examined the effect of short-term methylmercury (MeHg) exposure on two adult age classes, 1- and 2-year-olds to coincide with zebrafish in relatively peak vs. declining health conditions. In Experiment 1, 2-year-old zebrafish were randomly divided into groups and were exposed to no MeHg, 0.15% ethanol (EtOH), 0.01, 0.03, 0.1, or 0.3 μM of MeHg (in 0.15% ethanol) for 2 weeks. The groups were then trained and tested for avoidance responses. The results showed that older zebrafish exposed to no MeHg or EtOH learned and retained avoidance responses. However, 0.01 μM or higher concentrations of MeHg exposure impaired avoidance learning in a dose-dependent manner with 0.3 μM of MeHg exposure producing death during the exposure period or shortly after the exposure but before the avoidance training. In Experiment 2, 1-year-old zebrafish were randomly divided into groups and were exposed to the same concentrations of MeHg used in Experiment 1 for 2 weeks. The groups were then trained and tested for avoidance responses. The results showed that younger zebrafish exposed to no MeHg, EtOH, or 0.01 μM of MeHg learned and retained avoidance responses, while 0.1 or 0.3 μM of MeHg exposure impaired avoidance learning in a dose-dependent manner. The study suggested that MeHg exposure produced learning impairments at a much lower concentration of MeHg exposure and more severely in older adult compared against younger adult zebrafish even after short exposure times.
Department of Psychology, Grand Valley State University, Allendale, MI 49401, USA. xux@gvsu.edu
Xiaojuan
X
Xu
Daniel
D
Weber
Michael J
MJ
Carvan
Ryan
R
Coppens
Crystal
C
Lamb
Stefan
S
Goetz
Lillian A
LA
Schaefer
D000367:Age Factors; D000375:Aging; D000704:Analysis of Variance; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D001522:Behavior, Animal / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D007859:Learning Disabilities / Q000139:chemically induced*; D018782:Maze Learning / Q000187:drug effects; D008767:Methylmercury Compounds / Q000633:toxicity*; D011930:Reaction Time / Q000187:drug effects; D013997:Time Factors; D015027:Zebrafish
D008767:Methylmercury Compounds