Abstract
Our study showed differential expression of the
arginine vasotocin
(
avt
)/
isotocin
(
it
) in the brain and pituitary gland of the euryhaline black porgy (
Acanthopagrus schlegelii
) during osmotic stress. A decrease in serum osmolality and increased cortisol levels were observed after acute transfer from seawater (SW) to freshwater (FW). The increased expressions of
avt
,
avt receptor
(
avtr
:
v1a
), and
isotocin receptor
(
itr
:
itr1)
transcripts on day 1 and
it
and
itr
transcripts on days 7 and 30 were found in the brains and pituitary glands of FW fish. Increased levels of
avt
mRNA in the diencephalon and
avtr
mRNA in the pituitary together with serum cortisol on day 1 of FW exposure indicated activation of the hypothalamic–pituitary–interrenal (HPI) axis. The expression levels of
avtr
and
itr
after FW transfer were increased in the pituitary on days 7 and 30. Furthermore,
in situ
hybridization demonstrated spatially differential expression of
avt
and
itr
transcripts in nucleus preopticus parvocellularis of pars gigantocellularis (PMgc), magnocellularis (PMmc), and parvocellularis (PMpc) of the preoptic area (POA). Positive signals for
avt
and
it
were highly abundant in PMpc after FW exposure. The data suggest involvement of neurohypophysial hormones in the brain (telencephalon and diencephalon) and pituitary for osmotic stress.