Biology Reference
In-Depth Information
6.3.1.1.2 TSH
Fridberg et al. (1981) reported that TSH-producing cells
in the Atlantic
salmon were more numerous in presmolts and smolts than in parr salmons,
and had cytological features indicating an increased activity. However,
Nishioka et al. (1982) showed no gross or ultrastructural changes of these
cells during smoltifi cation in coho salmon.
Martin et al. (1999) found that FW smolts had a lower concentration of
TSH β subunit than parrs. Following a cohort of Atlantic salmon parrs in
aquaculture at the Conservatoire National du Saumon Sauvage (Chanteuges,
France), we could reveal, by quantitative real-time PCR, that TSHβ mRNA
levels reached a peak in April at the time of parr-to-smolt transformation,
i.e., when Atlantic salmons switched from positive to negative rheotactic
behaviour (Fig. 3).
7.5
TSH
GH1
GH2
5.0
2.5
0.0
0
50
100
150
200
250
300
Day of the year
Figure 3
. Changes in pituitary TSHβ, GH1 and GH2 mRNA during smoltifi cation of Atlantic
salmon. Arrows indicate the time when salmons shift from positive to negative rheotaxism
in April. GH=growth hormone; TSH=thyrotropin.
6.3.1.1.3 CRH
CRH was shown to be potent stimulator of TSH secretion by coho salmon
pituitary cells in culture, whereas TRH was not (Larsen et al., 1998). CRH
being the stimulatory hypothalamic factor of the corticotropic axis, its
involvement in smoltifi cation is discussed in 2.1.3 part.
