The candidate's long term goal is to become an independent investigator at an academic research institution to study the effects of hormones and endocrine disrupting compounds on the development and activity of brain circuits. He has received excellent training in neuroendocrinology, neuroplasticity, and behavioral neuroscience. He now plans to complement this knowledge and technical expertise with training in in vivo analysis of the role of endocrine disruptors on neuronal structural plasticity and brain circuit connectivity using targeted manipulation of gene expression via electroporation, time-lapse 2-photon imaging, neuronal reconstruction and structural analysis, electrophysiology and quantification of thyroid hormone levels. During this training period the candidate will enroll in courses and seminars to improve his management abilities, communication skills and technical literacy. By the end of this award, he will have gained the skills and training that will be needed for establishing his own lab. He wil also have the publication record and preliminary data on hand to write a R01 proposal with a high likelihood of funding. Most of the training during the mentored phase will occur at The Scripps Research Institute (TSRI) under the supervision of Dr. Hollis Cline. Dr. Cline has taken a multidisciplinary approach to studying molecular and cellular mechanisms that govern the development of the visual system in Xenopus laevis tadpoles, including in vivo time-lapse 2 photon imaging, in vivo electrophysiological recordings of visual responses, calcium-imaging and behavior. Her laboratory has been at the forefront of developing exciting new techniques to study the factors that regulate circuit development. Her laboratory is located in the Dorris Neuroscience Center, which is an outstanding intellectual environment consisting of 14 faculty members and more than 100 postdocs and other scientists. Some of the candidate's proposed experiments will benefit from training from a co-mentor, Dr. Ardem Patapoutian, a TSRI faculty member with expertise in biophysics of the TRPA1 channels, which the candidate will use to manipulate neuronal activity. In addition, the candidate will learn techniques to measure thyroid hormone levels in the laboratory of Dr. Robert Denver at the University of Michigan at Ann Arbor. Dr. Denver is a leading expert in endocrine disruption and physiology and will be an invaluable co-mentor to this project. The goal of this research project is determine the effects of endocrine-disrupting compounds on brain development. Compounds that are used in the production of industrial and consumer products can accumulate in the environment and even be found in human blood and tissue in measurable quantities. There is increasing evidence that some of these compounds can affect hormone metabolism and action, including thyroid hormone, which plays an important role in brain development. Yet little is known about how environmental toxins that disrupt thyroid hormone function affect development of brain circuits. The candidate will determine the effects of thyroid hormone disrupting compounds on CNS development, using the visual system in Xenopus laevis tadpoles, an ideal experimental system for these studies because the external development of the animal provides easy access to the developing brains for observation and manipulation. The candidate will treat tadpoles with the active thyroid hormone triiodothyronine, methimazole (a thyroid hormone antagonist), and several thyroid hormone disrupting compounds. I will assess several parameters of brain development, including neural stem cell proliferation, differentiation and survival, and the development of neuronal structure and circuit connectivity. In addition, he will develop and characterize the use of microspheres as a local thyroid hormone delivery system and use this system to target particular hormone treatments to the retina or the optic tectum. These experiments will allow him to disambiguate the site of hormone action within the developing brain and to localize the sites of action and effects of thyroid hormone disrupting compounds on brain development. These will be important advances in the fields of environmental toxicology, neuroendocrinology and brain development. Furthermore, these experiments will establish the Xenopus retino-tectal system as an ideal model to screen thyroid hormone disrupting compounds for effects on brain development.

Public Health Relevance

Very little is known about how thyroid hormone disrupting compounds affect brain development, even though these compounds can be found in measureable quantities in human blood and tissue. The goal of this project is to determine how these compounds affect brain development using Xenopus laevis tadpoles as a model species.

National Institute of Health (NIH)
National Institute of Environmental Health Sciences (NIEHS)
Career Transition Award (K99)
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Special Emphasis Panel (ZES1)
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Hollander, Jonathan
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Scripps Research Institute
La Jolla
United States
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McKeown, C R; Thompson, C K; Cline, H T (2017) Reversible developmental stasis in response to nutrient availability in the Xenopus laevis central nervous system. J Exp Biol 220:358-368
Honarmand, Mariam; Thompson, Christopher K; Schatton, Adriana et al. (2016) Early developmental stress negatively affects neuronal recruitment to avian song system nucleus HVC. Dev Neurobiol 76:107-18
Thompson, Christopher K; Cline, Hollis T (2016) Thyroid Hormone Acts Locally to Increase Neurogenesis, Neuronal Differentiation, and Dendritic Arbor Elaboration in the Tadpole Visual System. J Neurosci 36:10356-10375
Faulkner, Regina L; Wishard, Tyler J; Thompson, Christopher K et al. (2015) FMRP regulates neurogenesis in vivo in Xenopus laevis tadpoles. eNeuro 2:e0055