The orchestration of anuran metamorphosis is initiated and integrated by thyroid hormones, which change dynamically during larval development and which may represent a target of disruption by environmental contaminants. Studies have found that some anurans experience increased rates of development when exposed to the insecticide carbaryl later in larval development, suggesting that this insecticide could affect thyroid hormone-associated biological pathways. However, the time in development when tadpoles are sensitive to insecticide exposure has not been clearly defined nor has the mechanism been tested. In two separate studies, we exposed recently hatched green frog (Lithobates clamitans) tadpoles to a single, three day carbaryl exposure in the laboratory at either 2, 4, 8, or 16 weeks post-hatching. We examined the impact of carbaryl exposure on mRNA abundance patterns in the brains of frogs following metamorphosis months after a single three day exposure (experiment 1) and in tadpole tails three days after exposure (experiment 2) using cDNA microarrays and quantitative real time polymerase chain reaction (QPCR) analyses. For tadpoles reared through metamorphosis, we measured tadpole growth and development, as well as time to, mass at, and survival to metamorphosis. Although carbaryl did not significantly impact tadpole development, metamorphosis, or survival, clear exposure-related alterations in both tail and brain transcript levels were evident when tadpoles were exposed to carbaryl, particularly in tadpoles exposed at weeks 8 and 16 post-hatching, indicating both short-term and long-term alterations in mRNA expression. These results indicate that carbaryl can have long-lasting effects on brain development when exposure occurs at sensitive developmental stages, which may have implications for animal fitness and function later in the life cycle.
Bibliographical noteFunding Information:
We are grateful to Kristina Gaietto, Stacy James, Marcelo Jorge, Peter Kleinhenz, Marek Kobylarz, Louisa Phillips, Sabrina Pittroff, Vicki Rehaume, Nick Webber, Clara Wilson, Neal Sullivan, and Emmette Boone for assistance in experimentation. Animal experiments were carried out in accordance with The Code of Ethics in the World Medical Association. The research was conducted under IACUC Protocol 749 at Miami University and funded by the National Institute of Health AREA Grant #0717088 to MDB and CCH.
Copyright 2013 Elsevier B.V., All rights reserved.
- DNA microarray
- Frog metamorphosis
- MRNA abundance
- Quantitative real-time PCR
- Thyroid hormone