Biology Reference
In-Depth Information
6.3.3.2.3 Osmoregulation
Prolonged cortisol treatment in pre-smolt coho salmon caused an increase
in gill Na+/K+-ATPase activity, while treatment of smolts had no effect
(Richman et al., 1985). In young Atlantic salmon, cortisol treatment seems
not to stimulate gill Na+/K+-ATPase activity, while ACTH does, but both
ACTH and cortisol increased the SDH activity in gill cells from pre-smolts;
neither hormone increased the size or abundance of gill chloride cells
(Langdon et al., 1984). Cortisol treatment improved the development of
hypoosmoregulatory mechanisms in rainbow trout (Madsen, 1990d) and
enhanced the hypoosmoregulatory response to GH in rainbow and sea
trouts (Madsen, 1990b, c).
Intraperitoneal injections of cortisol were able
to increase juxtaglomerular cell number and size during smoltifi cation of
masu salmon (Mizuno et al., 2001a).
In coho salmon, acute administration of cortisol resulted in a reduction
in corticosteroid receptor numbers for 72h with no change in affi nity, while
chronic treatment resulted in a decrease in both concentration and affi nity
(Maule and Schreck, 1991; Shrimpton and Randall, 1994). In Atlantic salmon,
Mazurais et al. (1998) also demonstrated that short-term treatment with
cortisol (injections for up to 24 hours) induced a signifi cant decrease of gill
GR transcripts within 12 hours, but long-term treatment (implants for up
to 26 days) did not induce any changes.
Using primary cultures of gill tissue, Tipsmark et al. (2009) demonstrated
the stimulatory effect of cortisol on the expression of FW- (27a and 30) and
SW-induced (10e) claudins (tight junction proteins); this effect was blocked
by RU486, suggesting the involvement of a glucocorticoid type receptor.
Similarly, injections of FW salmon with cortisol increased the expression
of claudin 10e, 27a and 30.
Using tissue culture of FW-adapted sockeye salmon intestine, Veillette
and Young (2005) were able to show that cortisol maintained Na+/K+-
ATPase activity, which declined in controls. Slow-release implants of
cortisol during 7 days stimulated Na+/K+-ATPase activity in pyloric
coeca and posterior region of the intestine (Veillette and Young, 2005). In
Atlantic salmon, cortisol implants stimulated the intestinal fl uid absorption
(Jv) during the parr and postsmolt stages to a rate comparable to that of
control in the smolt stage, when Jv of controls was`low; conversely, RU 486
(corticosteroid antagonist) implants inhibited Jv only during the peak smolt
period, when Jv of controls was elevated (Veillette et al., 1995).
6.3.3.2.4 Migratory behaviour/downstream migration
In juvenile Chinook salmon, central administration of CRH caused a dose-
dependent increase in locomotor activity, which was prevented by the use
