Serotonin (5-HT) containing neuroepithelial cells (NECs) are O2 sensitive chemoreceptors found throughout the skin of larval zebrafish (Danio rerio). Zebrafish larvae are sensitive to changes in ambient PO2 as early as 2 days post fertilisation (dpf) and hyperventilate in response to hypoxia beginning at 3 dpf. Tryptophan hydroxylase (tph) is the rate-limiting enzyme in 5-HT synthesis; three tph paralogs are present in zebrafish (tph1a, tph1b and tph2). Although 5-HT has been implicated as a key neurotransmitter mediating hypoxic hyperventilation, it has not been possible to discern the role of 5-HT specifically contained within the NECs in promoting hypoxic hyperventilation. The purpose of this study was to determine the role of NEC 5-HT in regulating the hypoxic ventilatory response in larval zebrafish. It was hypothesised that 5-HT is a key neurotransmitter released from NECs which contributes to hypoxic hyperventilation. Immunohistochemistry was used to determine the distribution of tph paralogs and their role in 5-HT production in NECs. Tph1a was present in NECs and nerves innervating NECs. Exposure to the non-selective tph inhibitor, para-chlorophenylalanine (pCPA), or translational gene knockdown of tph1a, diminished 5-HT expression within NECs. Exposure to acute hypoxia (PO2 = 30 mmHg) revealed a blunted hypoxic ventilatory response (reduced breathing frequency) in fish exhibiting depleted 5-HT in NECs. The hypoxic hyperventilatory response was rescued with application of 5-HT. The results of these experiments demonstrate that tph1a is responsible for 5-HT production in NECs of larval zebrafish, and that 5-HT released from NECs is involved in establishing their hypoxic hyperventilatory response.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/35196 |
| Date | January 2016 |
| Creators | Jensen, Gregory |
| Contributors | Perry, Steve |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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