Electronic Theses and Dissertations

Date

2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biology

Committee Chair

Charles Lessman

Committee Member

David Freeman

Committee Member

Judith Cole

Committee Member

Matthew Parris

Committee Member

Omar Skalli

Committee Member

Thomas Sutter

Abstract

Progestogens are steroid hormones based on progesterone (P4) that play many critical roles in early developmental stage and adult zebrafish (Danio rerio). In addition to their functions in reproduction, they play important roles in the central nervous system (CNS). P4 and its metabolites are known to modulate the excitability of neurons and promote neural inhibition. This dissertation aims to elucidate the physiological and developmental effects of progestogens on zebrafish embryos and larvae. Through the use of motility assays, we report significant findings in this dissertation that suggests both the membrane progesterone receptor (mPR) and GABAA receptor facilitate the rapid deep anesthetic properties of progestogens in larval zebrafish. Exposure to P4, tetrahydrodeoxycorticosterone (THDOC), 5α-dihydroprogesterone (5α-DHP), and the selective mPR agonist, ORG-OD-02-0 (ORG), and other modulators of target receptors revealed the particular mechanisms of the motility effects. Microscopy using polarized lenses to capture the birefringence of the zebrafish larvae show that early embryonic exposure to P4 does not alter the formation or structural organization of the sarcomeres within muscle cells. Confocal microscopy analysis of P4-exposed zebrafish embryos showed that microtubule formation in the brain is slightly altered, suggesting a role that P4 plays in neuron axogenesis and migration. Similarly, the antibody for zebrafish synaptotagmin (znp-1) revealed that motor neuron development may be modified from early P4 exposure. Finally, the ability of P4 and ORG to alter microtubule dynamics in developing zebrafish embryos and larvae was examined. Zebrafish embryos chronically exposed to P4 and ORG contained less acetylated α-tubulin and showed a downregulation of mPRα. Results from these experiments suggest that P4 may induce anesthetic responses through multiple pathways: by activating G-protein signaling associated with the mPR and acting as a PAM on the GABAA receptor. The effects on microtubules during development of the CNS may also impact neuronal development to influence the innervation of motor neurons to skeletal muscles, thereby affecting locomotor abilities and diminishing fitness in the wild.

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Data is provided by the student.

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Open access.

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