Biology Reference
In-Depth Information
a)
2.0
1.5
1.0
0.5
0.0
A
B
C
D
E
Silver
Yellow
Intermediate
Eel stages
b)
200
T4
T3
150
100
50
0
Yellow
Silver
Intermediate
Eel stage
Figure 3
. Lack of involvement of thyrotropic axis in the control of eel silvering. During
the process of silvering, no activation of thyrotropic axis is observed; as there is no change
of pituitary TSH β mRNA levels (a) nor plasma T4 and T3 levels (b). TSH=thyrotropin;
T4=thyroxine ; T3=triiodothyronine.
critical, probably due to the fact that even at the yellow stage eels are able
to pass into seawater.
Studies focusing on GH cell regulation have shown that basal release
and synthesis of GH persist
in vitro
, in the absence of secretagogues or
serum, using organ-cultured pituitaries (European eel: Baker and Ingleton,
1975; Japanese eel: Suzuki et al., 1990) or primary cultures of pituitary cells
(European eel: Rousseau et al., 1998, 1999; rainbow trout: Yada et al., 1991;
turbot: Rousseau et al., 2001). All these observations lead to the suggestion
that the major control of these cells
in vivo
is an inhibitory control (Rousseau
