Early development of the endocrine system in salmonids : regulation of sex differentiation and ontogeny of the stress response Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kh04ds417

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  • Sex steroids, follicle stimulating hormone (FSH), luteinizing hormone (LH) and gonadotropin releasing hormone (GnRH) were measured in monosex and mixed sex populations of rainbow trout during early development. Steroids declined following fertilization, increased at hatch, then fell and remained constant thereafter. Trends toward differences in steroids between males and females became evident around the time of gonadal differentiation. FSH and GnRH were always detectable whereas LH was not. Peptide hormones were not sexually dimorphic. Given that the brain-pituitary-gonadal axis appears to be intact during the process of sexual differentiation and the dynamics of steroid levels during this process, sex steroids may drive sexual differentiation of rainbow trout. Gynogenetic rainbow trout were sex-reversed to produce XX males by using l7α-methyltestosterone (MT) and l1β- hydroxyandrostenedione (OHA). Steroids were administered by immersion or immersion plus feeding to determine if males with intact sperm ducts could be produced. Immersion in MT resulted in varying degrees of masculinization while immersion plus feeding produced nearly 100% males. The most effective period for steroid immersion was one week post-hatch. Immersion in OHA caused low rates of masculinization, while immersion plus feeding resulted in 70% males. Males produced through both immersion and feeding of MT generally did not develop sperm ducts; whereas animals treated by immersion alone in MT, or those produced with OHA, tended to be functional. Cryopreserved semen from functional males produced 100% female populations. Cortisol was measured in chinook salmon during early development in both stressed and non-stressed fish to determine when the corticosteroidogenic stress response first arises. Levels of cortisol were low in eyed eggs, increased at hatch, decreased 2 weeks later and then remained constant thereafter. Differences in cortisol between stress and control fish were found 1 week after hatch and persisted for the remainder of the study. A decrease in the ability to elicit cortisol was seen 4 weeks after hatch. The decreases in both endogexious cortisol content and magnitude of the stress response may be comparable to developmental events of mammals where corticosteroid synthesis is inhibited to neutralize possible detrimental effects of these hormones during critical periods of development.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-08-23T20:28:56Z (GMT) No. of bitstreams: 1 FeistGrantWilliam2001.pdf: 2758793 bytes, checksum: 257f24d263c35cef51235ee4b621c24e (MD5)
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