Developmental selenomethionine and methylmercury exposures affect zebrafish learning.
Methylmercury (MeHg) is a ubiquitous environmental pollutant and has been shown to affect learning in vertebrates following relatively low exposures. Zebrafish were used to model long-term learning deficits after developmental MeHg exposure. Selenomethionine (SeMet) co-exposure was used to evaluate its role in neuroprotection. Embryos were exposed from 2 to 24h post fertilization to (1) MeHg without SeMet, (2) SeMet without MeHg and (3) in combination of MeHg and SeMet. In case (1), the levels of MeHg were 0.00, 0.01, 0.03, 0.06, 0.10, and 0.30 microM. In case (2), the levels of SeMet were 0.00. 0.03, 0.06, 0.10, and 0.30 microM. In case (3), co-exposure levels of (MeHg, SeMet) were (0.03, 0.03), (0.03, 0.06), (0.03, 0.10), (0.03, 0.30), (0.10, 0.03), (0.10, 0.06), (0.10, 0.10), and (0.10, 0.30) microM. Learning functions were tested in individual adults, 4 months after developmental exposure using a spatial alternation paradigm with food delivery on alternating sides of the aquarium. Low levels of MeHg (<0.1 microM) exposure delayed learning in treated fish; fish exposed to higher MeHg levels were unable to learn the task; SeMet co-exposure did not prevent this deficit. These data are consistent with findings in laboratory rodents. The dorsal and lateral telencephalon are the primary brain regions in fish involved in spatial learning and memory. Adult telencephalon cell body density decreased significantly at all MeHg exposures >0.01 microM MeHg. SeMet co-exposure ameliorated but did not prevent changes in telencephalon cell body density. In summary, MeHg affected both learning and brain structure, but SeMet only partially reversed the latter.
Department of Psychology, University of Wisconsin-Milwaukee, Milwaukee, WI 53204, United States.
Leigh E
LE
Smith
Michael J
MJ
Carvan
John A
JA
Dellinger
Jugal K
JK
Ghorai
Donald B
DB
White
Frederick E
FE
Williams
Daniel N
DN
Weber
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000254:growth & development / Q000503:physiopathology; D049109:Cell Proliferation / Q000187:drug effects; D019610:Cytoprotection / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005260:Female; D007858:Learning / Q000187:drug effects / Q000502:physiology; D007859:Learning Disabilities / Q000139:chemically induced / Q000188:drug therapy* / Q000503:physiopathology; D008297:Male; D008767:Methylmercury Compounds / Q000037:antagonists & inhibitors* / Q000633:toxicity; D018696:Neuroprotective Agents / Q000494:pharmacology* / Q000627:therapeutic use; D009483:Neuropsychological Tests; D020258:Neurotoxicity Syndromes / Q000188:drug therapy* / Q000503:physiopathology; D009498:Neurotoxins / Q000037:antagonists & inhibitors / Q000633:toxicity; D012645:Selenomethionine / Q000494:pharmacology* / Q000627:therapeutic use; D013028:Space Perception / Q000187:drug effects / Q000502:physiology; D013687:Telencephalon / Q000187:drug effects / Q000254:growth & development / Q000503:physiopathology; D016896:Treatment Outcome; D015027:Zebrafish
D008767:Methylmercury Compounds; D018696:Neuroprotective Agents; D009498:Neurotoxins; D012645:Selenomethionine