title: Impaired anterior swim bladder inflation following exposure to the thyroid peroxidase inhibitor 2-mercaptobenzothiazole part I: Fathead minnow.
abstract: In the present study, a hypothesized adverse outcome pathway linking inhibition of thyroid peroxidase (TPO) activity to impaired swim bladder inflation was investigated in two experiments in which fathead minnows (Pimephales promelas) were exposed to 2-mercaptobenzothiazole (MBT). Continuous exposure to 1mg MBT/L for up to 22 days had no effect on inflation of the posterior chamber of the swim bladder, which typically inflates around 6 days post fertilization (dpf), a period during which maternally-derived thyroid hormone is presumed to be present. In contrast, inflation of the anterior swim bladder, which occurs around 14dpf, was impacted. Specifically, at 14dpf, approximately 50% of fish exposed to 1mg MBT/L did not have an inflated anterior swim bladder. In fish exposed to MBT through 21 or 22dpf, the anterior swim bladder was able to inflate, but the ratio of the anterior/posterior chamber length was significantly reduced compared to controls. Both abundance of thyroid peroxidase mRNA and thyroid follicle histology suggest that fathead minnows mounted a compensatory response to the presumed inhibition of TPO activity by MBT. Time-course characterization showed that fish exposed to MBT for at least 4 days prior to normal anterior swim bladder inflation had significant reductions in anterior swim bladder size, relative to the posterior chamber, compared to controls. These results, along with similar results observed in zebrafish (see part II, this issue) are consistent with the hypothesis that thyroid hormone signaling plays a significant role in mediating anterior swim bladder inflation and development in cyprinids, and that role can be disrupted by exposure to thyroid hormone synthesis inhibitors. Nonetheless, possible thyroid-independent actions of MBT on anterior swim bladder inflation cannot be ruled out based on the present results. Overall, although anterior swim bladder inflation has not been directly linked to survival as posterior swim bladder inflation has, potential links to adverse ecological outcomes are plausible given involvement of the anterior chamber in sound production and detection.
authors: Student Services Contractor, U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Krysta R
authors: KR
authors: Nelson
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA; University of Minnesota-Twin Cities, Water Resources Center, 1985 Lower Buford Circle, St. Paul, MN 55108, USA. Electronic address: aschroed@crk.umn.edu.
authors: Anthony L
authors: AL
authors: Schroeder
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Gerald T
authors: GT
authors: Ankley
authors: Oak Ridge Institute for Science and Education (ORISE) Research Participation Program, U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Brett R
authors: BR
authors: Blackwell
authors: Badger Technical Services, U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201 Congdon Blvd., Duluth, MN 55804, USA.
authors: Chad
authors: C
authors: Blanksma
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Sigmund J
authors: SJ
authors: Degitz
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Kevin M
authors: KM
authors: Flynn
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Kathleen M
authors: KM
authors: Jensen
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Rodney D
authors: RD
authors: Johnson
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Michael D
authors: MD
authors: Kahl
authors: Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors: Dries
authors: D
authors: Knapen
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Patricia A
authors: PA
authors: Kosian
authors: Oak Ridge Institute for Science and Education (ORISE) Research Participation Program, U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Rebecca Y
authors: RY
authors: Milsk
authors: Student Services Contractor, U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Eric C
authors: EC
authors: Randolph
authors: Student Services Contractor, U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Travis
authors: T
authors: Saari
authors: Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors: Evelyn
authors: E
authors: Stinckens
authors: Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors: Lucia
authors: L
authors: Vergauwen
authors: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201Congdon Blvd., Duluth, MN 55804, USA.
authors: Daniel L
authors: DL
authors: Villeneuve
mesh_terms: D000400:Air Sacs / Q000187:drug effects*; D000818:Animals; D052160:Benzothiazoles / Q000633:toxicity*; D003530:Cyprinidae / Q000196:embryology*; D004625:Embryo, Nonmammalian / Q000187:drug effects; D038081:Organogenesis / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity; D015027:Zebrafish / Q000196:embryology
chemical_list: D052160:Benzothiazoles; D014874:Water Pollutants, Chemical; C005563:captax
keywords: Adverse outcome pathway; Cyprinid; Endocrine disruption; Fish early life stage; Swim bladder