UI Biology Researchers Transplant Ears in Frogs to Provide Insight into the Inner Ear and Functional Connections in the Brain

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Karen Thompson (Elliott), Bernd Fritzsch, and Steve Kehoe, UI Department of Biology
November 2, 2018

The inner ear is responsible for the senses of hearing and of balance and gravity perception. It develops out of a layer of tissue just beneath the skin, the otic placode. From this otic placode, both hair cells (which detect sound vibrations and movement) and sensory neurons (which carry the signal from the hair cells to processing centers in the brainstem) develop. Thus, it is crucial that these neurons find the correct target nuclei in the brain for proper sound and balance perception. To understand the principles of navigation by these neurons, the otic placodes were transplanted to other locations in the body in frogs to assess how inner ear sensory neurons can navigate in a novel territory.

Researchers in the Department of Biology at the University of Iowa, in collaboration with Professor Hans Straka and his doctoral student, Clayton Gordy, from Ludwig-Maximilians-Universität München (LMU) in Munich, Germany, found that when the ear was transplanted to the trunk, adjacent to the spinal cord, neurons grew into the spinal cord and projected along existing neuron tracts. However, once they reached the hindbrain, they rerouted to the correct target nuclei for inner ear neurons, suggesting that these neurons are reading signals that direct them to where they need to go. Furthermore, these neurons form functional connections with existing hindbrain circuitry to elicit normal behavioral responses. In addition, neurons can also project toward the hindbrain along other nerve tracts at the periphery. For example, when the ear was transplanted adjacent to the heart, neurons grew along the vagus nerve to reach the hindbrain. 

The results of this paper, which appeared in the Developmental Neurobiology journal, show that there is some degree of plasticity in the hindbrain to accommodate incoming neurons from a novel or additional source. Future studies hope to determine the various signals and mechanisms used by inner ear sensory neurons to find their targets.

Gordy studied under the direction of Professor of Biology, Bernd Fritzsch, at the University of Iowa where he received both his bachelor’s and master’s degrees in biology in the Spring 2016 and Fall 2017 semesters, respectively.The corresponding press release from LMU on this research can be found here.

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