Tissue and Cell 41 (2009) 75–78
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Tissue and Cell
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Short communication
Orexin-B-like immunoreactivity localized in both luteinizing
hormone- and thyroid-stimulating hormone-containing
cells in the Nile tilapia (Oreochromis niloticus) pituitary
H. Suzuki
a,∗
, A. Matsumoto
a
, T. Yamamoto
b,c
a
Department of Biology, Fukuoka University of Education, Akamabunkyo-machi 1-1, Munakata, Fukuoka 811-4192, Japan
b
Department of Human Biology, Kanagawa Dental College, Inaoka-cho 82, Yokosuka, Kanagawa 238-8580, Japan
c
Research Center of Brain and Oral Science, Kanagawa Dental College, Inaoka-cho 82, Yokosuka, Kanagawa 238-8580, Japan
article info
Article history:
Received 30 January 2008
Received in revised form 3 June 2008
Accepted 17 June 2008
Available online 24 July 2008
Keywords:
Orexin
Pituitary
LH
TSH
Fish
Tilapia
abstract
Immunohistochemical techniques were employed to examine orexin-like immunoreactivities in the pitu-
itary of the Nile tilapia (Oreochromis niloticus). Rabbit anti-orexin-A serum and mouse anti-orexin-B
monoclonal antibodies were used as primary antibodies. Orexin-B immunoreactive cells corresponded
to luteinizing hormone (LH)- or thyroid-stimulating hormone (TSH)-containing cells, and all LH- and
TSH-containing cells were immunoreactive for orexin-B. However, we found no orexin-A immunoreac-
tive cells in the pituitary. In the Nile tilapia, an orexin-B-like substance may be secreted from LH- or
TSH-containing cells and may regulate pituitary function, rather than the orexin-A-like substance in the
pituitaries of Japanese seaperch and medaka.
© 2008 Elsevier Ltd. All rights reserved.
1. Introduction
Orexin-A and orexin-B, also termed hypocretin 1 and hypocretin
2, are novel neuropeptides isolated from the mammalian hypotha-
lamus (de Lecea et al., 1998; Sakurai et al., 1998). Orexin-A and
-B are derived from an identical precursor and consist of 33 and
28 amino acid residues, respectively, with 46% sequence homol-
ogy (Sakurai et al., 1998). Histological studies (Payron et al., 1998;
Cutler et al., 1999; Date et al., 1999; Nambu et al., 1999) and phar-
macological experiments (Sakurai et al., 1998; Edwards et al., 1999;
Sweet et al., 1999) indicated that these peptides may play a role
in the regulation of food consumption. Pharmacological study also
revealed that orexins directly affect secretion of adenohypophy-
seal hormones (Pu et al., 1998; Malendowicz et al., 1999; Tamura
et al., 1999; Kuru et al., 2000; Russell et al., 2000; Kohsaka et al.,
2001; Seoane et al., 2004; Barb and Matteri, 2005; Estienne and
Barb, 2005). In the human pituitary, immunoreactivities of both
orexins have been detected (Blanco et al., 2003). Unlike the human
pituitary, only orexin-A-like immunoreactivity has been detected
in the pituitaries of amphibians (bullfrog, Yamamoto et al., 2004;
∗
Corresponding author. Tel.: +81 940 35 1389; fax: +81 940 35 1716.
E-mail address: spiderhs@fukuoka-edu.ac.jp (H. Suzuki).
Xenopus, Suzuki et al., 2007b) and fishes (medaka, Amiya et al.,
2007; Japanese seaperch, Suzuki et al., 2007a). According to the
peptide sizes and amino acids sequences, orexin-B is more highly
conserved than orexin-A among vertebrates (Alvarez and Sutcliffe,
2002; Kaslin et al., 2004). We surveyed orexin-B-like immunoreac-
tivity in lower vertebrates, and immunoreactivity in the pituitary
has been observed in several freshwater fishes (Nile tilapia, carp
and catfish). In this note, we reported for the first time the pres-
ence of orexin-B-like immunoreactivity in the pituitary of the Nile
tilapia (Oreochromis niloticus).
2. Materials and methods
Seven Nile tilapia (O. niloticus) males about 40 cm in length were
collected in May 2007 at a river in Oita Prefecture, Japan. Before
use, the fish were kept in freshwater tanks under laboratory condi-
tions for 1 week. They were cooled on ice and the pituitaries were
dissected out rapidly. Samples fixed for 24 h with 4% paraformalde-
hyde and 0.2% picric acid in 0.1 M sodium phosphate buffer (PB, pH
6.9), and then cut into 8 m-thick sagittal sections with a cryostat.
Sections were mounted on glass slides.
Immunohistochemistry was performed according to our rou-
tine method (Suzuki et al., 1997). Briefly, the sections were washed
overnight in 0.1 M PB (pH 7.4) containing 0.9% saline (PBS) and
0040-8166/$ – see front matter © 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tice.2008.06.001