8 research outputs found
Thyroid and pituitary gland development from hatching through metamorphosis of a teleost flatfish, the Atlantic halibut
Fish larval development, not least the spectacular
process of flatfish metamorphosis, appears to be
under complex endocrine control, many aspects of
which are still not fully elucidated. In order to obtain
data on the functional development of two major
endocrine glands, the pituitary and the thyroid, during
flatfish metamorphosis, histology, immunohistochemistry
and in situ hybridization techniques were applied on
larvae of the Atlantic halibut (Hippoglossus hippoglossus),
a large, marine flatfish species, from hatching
through metamorphosis. The material was obtained
from a commercial hatchery. Larval age is defined as
day-degrees (D =accumulated daily temperature from
hatching). Sporadic thyroid follicles are first detected in
larvae at 142 D (27 days post-hatch), prior to the
completion of yolk sack absorption. Both the number
and activity of the follicles increase markedly after yolk
sack absorption and continue to do so during subsequent
development. The larval triiodothyronine (T3)
and thyroxine (T4) content increases, subsequent to yolk
absorption, and coincides with the proliferation of thyroid
follicles. A second increase of both T3 and T4 occurs
around the start of metamorphosis and the T3 content
further increases at the metamorphic climax. Overall,
the T3 content is lower than T4. The pituitary gland can
first be distinguished as a separate organ at the yolk sack
stage. During subsequent development, the gland becomes
more elongated and differentiates into neurohypophysis (NH), pars distalis (PD) and pars intermedia
(PI). The first sporadic endocrine pituitary cells are observed
at the yolk sack stage, somatotrophs (growth
hormone producing cells) and somatolactotrophs (somatolactin
producing cells) are first observed at 121 D
(23 days post-hatch), and lactotrophs (prolactin producing
cells) at 134 D (25 days post-hatch). Scarce
thyrotrophs are evident after detection of the first thyroid
follicles (142 D ), but coincident with a phase in
which follicle number and activity increase (260 D ).
The somatotrophs are clustered in the medium ventral
region of the PD, lactotrophs in the anterior part of the
PD and somatolactotrophs are scattered in the mid and
posterior region of the pituitary. At around 600 D ,
coinciding with the start of metamorphosis, somatolactotrophs
are restricted to the interdigitating tissue of the
NH. During larval development, the pituitary endocrine
cells become more numerous. The present data on thyroid
development support the notion that thyroid hormones
may play a significant role in Atlantic halibut
metamorphosis. The time of appearance and the subsequent
proliferation of pituitary somatotrophs, lactotrophs,
somatolactotrophs and thyrotrophs indicate at
which stages of larval development and metamorphosis
these endocrine cells may start to play active regulatory
roles.This work has been carried out within the
projects ‘‘Endocrine Control as a Determinant of Larval Quality in
Fish Aquaculture’’ (CT-96-1422) and ‘‘Arrested development: The
Molecular and Endocrine Basis of Flatfish Metamorphosis’’
(Q5RS-2002-01192), with financial support from the Commission
of the European Communities. However, it does not necessarily
reflect the Commission’s views and in no way anticipates its future
policy in this area. This project was further supported by the
Swedish Council for Agricultural and Forestry Research and Pluriannual
funding to CCMAR by the Portuguese Science and
Technology Council
A systematic immunohistochemical survey of the distribution patterns of GH, prolactin, somatolactin, β–TSH, β–FSH, β–LH, ACTH, and α–MSH in the adenohypophysis of Oreochromis niloticus , the Nile tilapia
Fish pituitary plays a central role in the control of growth, development, reproduction and adaptation to the environment. Several types of hormone-secreting adenohypophyseal cells have been characterised and localised in diverse teleost species. The results suggest a similar distribution pattern among the species investigated. However, most studies deal with a single hormone or hormone family. Thus, we studied adjacent sections of the pituitary of Oreochromis niloticus, the tilapia, by conventional staining and immunohistochemistry with specific antisera directed against growth hormone (GH), prolactin (PRL), somatolactin (SL), thyrotropin (beta-TSH), follicle-stimulating hormone (beta-FSH), luteinising hormone (beta-LH), adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (alpha-MSH). The pituitary was characterised by a close interdigitating neighbourhood of neurohypophysis (PN) and adenohypophysis. PRL-immunoreactive and ACTH-immunoreactive cells were detected in the rostral pars distalis. GH-immunoreactive cells were present in the proximal pars distalis (PPD). A small region of the PPD contained beta-TSH-immunoreactive cells, and beta-LH-immunoreactive cells covered approximately the remaining parts. Centrally, beta-FSH-immunoreactive cells were detected in the vicinity of the GH-containing cells. Some of these cells also displayed beta-LH immunoreactivity. The pars intermedia was characterised by branches of the PN surrounded by SL-containing and alpha-MSH-immunoreactive cells. The ACTH and alpha-MSH antisera were observed to cross-react with the respective antigens. This cross-reactivity was abolished by pre-absorption. We present a complete map of the distinct localisation sites for the classical pituitary hormones, thereby providing a solid basis for future research on teleost pituitary