Biology Reference
In-Depth Information
Neuroendocrine axes
Thyrotropic
Somatotropic
Corticotropic
Gonadotropic
CRH ?
Brain
LH/FSH
TSH
ACTH
GH
Pituitary
Peripheral
glands
E2/T
11KT
T4/T3
IGF1
cortisol
Liver
Adrenals
Gonads
Thyroid
Target organs
Metamorphic changes
Figure 4
. Neuroendocrine axes involved in the control of secondary metamorphosis
(smoltifi cation) in salmonid. Smoltifi cation is triggered mainly by thyrotropic and somatotropoic
axes with some synergism of corticotropic axis. Gonadotropic axis is likely inhibitory.
CRH=corticotropin-releasing hormone; TSH=thyrotropin; T4=thyroxine; T3=triiodothyronine;
GH=growth hormone; IGF=insulin-like growth factor; ACTH=corticotropin; LH=luteinizing
hormone; FSH=follicle-stimulating hormone; E2=estradiol; T=testosterone; 11KT=11-
ketotestosterone.
those that control physiological development, followed by 'releasing' factors
(e.g., water temperature or fl ow) that initiate behaviours (McCormick et al.,
1998). Many studies provided evidence that GH was the major endocrine
mediator of the effects of environmental factors (such photoperiod and
temperature) on the timing of smolt development.
Acknowledgements
We thank Nicole Dunn and Sarah Harris (MNHN/University of Keele, UK;
ERASMUS European Program) for their work on the assays of pituitary
hormone mRNAs. Thanks to Jocelyn Rancon (Conservatoire National du
Saumon Sauvage) for providing pictures of salmon parr and smolt.
