Abstract:
:Gonadotropin-releasing hormone (GnRH) of vertebrates is now believed to have multiple functions in addition to its role as a hypophysiotropic hormone, as originally defined. Recently, it has been shown that GnRH occurs also in the ascidians, which are considered ancestral chordates. Here the author shows that GnRH induces spawning of gametes from mature individuals of Ciona intestinalis. Ciona accumulates mature gametes in the gonoducts and maintains them until spawning is triggered by a photoperiodic cue(s). Injection of synthetic tunicate GnRH-I or -II into various sites of mature individuals effectively induced gamete release (spawning), although the former was more potent. Gamete release often occurred on a larger scale than in spontaneous spawning. However, moderate gamete release, similar to spontaneous spawning, was often triggered by exogenous tunicate GnRH. GnRH in vivo apparently is released from the GnRH-containing neurons that are distributed from the region of the cerebral ganglion to the proximal part of the ovary along the dorsal strand within the blood sinus; this indicates that both forms of tunicate GnRH may be the actual inducers of spawning. It is suggested that, in the ancestral chordate, GnRH neurons release GnRH prior to the spawning and the released GnRH acts directly on the epithelium of gonoducts or functions as a neuromodulator of other neurons innervating the gonoducts to induce spawning.
journal_name
Gen Comp Endocrinoljournal_title
General and comparative endocrinologyauthors
Terakado Kdoi
10.1006/gcen.2001.7728keywords:
subject
Has Abstractpub_date
2001-12-01 00:00:00pages
277-84issue
3eissn
0016-6480issn
1095-6840pii
S0016-6480(01)97728-7journal_volume
124pub_type
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