Acquisition of spontaneous electrical activity during embryonic development of gonadotropin-releasing hormone-3 neurons located in the terminal nerve of transgenic zebrafish (Danio rerio).
There are multiple populations of gonadotropin-releasing hormone (GnRH) neurons that have distinct physiological and behavioral functions. Teleost fish have a population of GnRH3 neurons located in the terminal nerve (TN) associated with the olfactory bulb that is thought to play a neuromodulatory role in multiple physiological systems, including olfactory, visual, and reproductive. We used transgenic zebrafish in which the GnRH3 promoter drives expression of a green fluorescent protein to identify GnRH3 neurons during development in live embryos. Unlike with hypophysiotropic GnRH neurons of zebrafish, TN-GnRH3 neurons are of neural crest origin and are one of the first populations of GnRH neurons to develop in the early embryo. Using a combination of optical imaging and electrophysiology, we showed that during the first 3 days post-fertilization, TN-GnRH3 neurons increase in number, extend neural projections, move in association with tissue expansion, and acquire an adult-pattern of spontaneous action potential firing. Early during development, about half of the neurons were quiescent/non-firing. Later, at 3 days post-fertilization, there was an increase in the proportion of neurons showing action potential firing and an increase in the number of neurons that showed an adult-like tonic or beating pattern of action potential firing with a firing frequency similar to that seen in adult TN-GnRH3 neurons. This study represents the first neurophysiological investigation of developing GnRH neurons in live embryos--an important advancement in understanding their potential non-reproductive roles during embryogenesis.
Ramakrishnan
Siddharth
S
Department of Physiology, David Geffen School of Medicine, University of California-Los Angeles, Los Angeles, CA 90095, United States.
Lee
Wenjau
W
Navarre
Sammy
S
Kozlowski
David J
DJ
Wayne
Nancy L
NL
D000818:Animals; D030801:Animals, Genetically Modified / Q000196:embryology / Q000378:metabolism; D004594:Electrophysiology; D047108:Embryonic Development / Q000235:genetics / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007150:Immunohistochemistry; D009432:Neural Crest / Q000196:embryology; D009474:Neurons / Q000378:metabolism*; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology* / Q000378:metabolism*
C448022:gonadotropin-releasing hormone-III; D049452:Green Fluorescent Proteins; D007987:Gonadotropin-Releasing Hormone; D011761:Pyrrolidonecarboxylic Acid