Page 1 - Brain_morphology_2008

ORIGINAL PAPER

Brain morphology and immunohistochemical localization of the
gonadotropin-releasing hormone in the bluefin tuna, Thunnus thynnus

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G. Palmieri, F. Acone, S. Desantis, A. Corriero, G. Ventriglia, P. Addis, S. Genovese, 4
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A. Aprea, D. Spedicato, M. Losurdo, M. Deflorio, A. Di Summa, G. De Metrio 2
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1 Department of Animal Biology, University of Sassari, Sassari; Department of Animal Health and Well-
being, University of Bari, Valenzano; Department of Animal Biology and Ecology, University of Cagliari,
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Cagliari; Institute for Coastal Marine Environment, National Research Council, Mazara del Vallo (TP), Italy
©2008 European Journal of Histochemistry
onadotropin-releasing hormone (GnRH) is
The present study was focused on the morphology of the a key regulator of the pituitary-gonadal
diencephalic nuclei (likely involved in reproductive functions) Gaxis as it stimulates both synthesis and
as well as on the distribution of GnRH (gonadotropin-releas-
ing hormone) in the rhinencephalon, telencephalon and the release of teleost pituitary gonadotropin (GTH)
diencephalon of the brain of bluefin tuna (Thunnus thynnus) (Peter, 1983; Okuzawa and Kobayashi, 1999; Zohar
by means of immunohistochemistry. Bluefin tuna has an and Mylonas, 2001).
encephalization quotient (QE) similar to that of other large Fourteen forms of GnRH have so far been identi-
pelagic fish. Its brain exhibits well-developed optic tecta and
corpus cerebelli. The diencephalic neuron cell bodies fied in different vertebrate species (Pham et al.,
involved in reproductive functions are grouped in two main 2006). In teleost fish, 8 GnRH variants have been
nuclei: the nucleus preopticus-periventricularis and the identified, although two or three of the GnRH forms
nucleus lateralis tuberis. The nucleus preopticus-periventric-
ularis consists of the nucleus periventricularis and the nucle- co-exist in the brain albeit distributed differently
us preopticus consisting of a few sparse multipolar neurons (Pham et al., 2006). Among the Pleuronectiforms
in the rostral part and numerous cells closely packed and and Perciformes, sea bream (sb)GnRH-producing
arranged in several layers in its aboral part. The nucleus lat-
eralis tuberis is located in the ventral-lateral area of the cell bodies in the preoptic area project their axons
diencephalon and is made up of a number of large multipo- mainly to the pituitary, whereas salmon sGnRH-
lar neurones. and chicken cGnRH-producing cells connect differ-
Four different polyclonal primary antibodies against salmon ent areas of the brain through their axons, which,
(s)GnRH, chicken (c)GnRH-II (cGnRH-II 675, cGnRH-II 6)
and sea bream (sb)GnRH were employed in the immunohis- however, do not project to the pituitary (White et
tochemical experiments. No immunoreactive structures were al., 1995; Gonzalez-Martínez et al., 2001; Amano
found with anti sbGnRH serum. sGnRH and cGnRH-II antis- et al., 2002).
era revealed immunoreactivity in the perikarya of the olfac-
tory bulbs, preopticus-periventricular nucleus, oculomotor The localization of GnRH-expressing neurons by
nucleus and midbrain tegmentum. The nucleus lateralis means of immunohistochemistry in many of the
tuberis showed immunostaining only with anti-sGnRH serum. teleost species studied so far has shown that GnRH
Nerve fibres immunoreactive to cGnRH and sGnRH sera were
found in the olfactory bulbs, olfactory nerve and neurohy- neurons are distributed in the tegmentum of the
pophysis. The significance of the distribution of the GnRH- midbrain, in the anterior telencephalon (terminal
immunoreactive neuronal structures is discussed. nerve included), as well as in the caudal telen-
cephalon-preoptic region and in the rostral hypo-
Key words: bluefin tuna (Thunnus thynnus); brain;
gonadotropin-releasing hormone; immunohistochemistry. thalamus (reviewed by Lethimonier et al., 2004).
Reproductive dysfunctions are often exhibited by
Correspondence: Gregorio De Metrio, fish reared in captivity ascribable to captivity-
Department of Animal Health and Well-being,
University of Bari, Valenzano, Italy induced stress (Mylonas and Zohar, 2001), and are
E-mail: g.demetrio@veterinaria.uniba.it due to the absence of GnRH release.The attempts in
Japan to reproduce Pacific bluefin tuna (Thunnus
Paper accepted on January 11, 2008 orientalis) in captivity in the last decade produced
inconsistant results (Doumenge, 1996; Lioka et al.,
European Journal of Histochemistry 2000). Recently, spawning of Atlantic bluefin tuna
2008; vol. 52 issue 1 (Jan-Mar): 19-28
(Thunnus thynnus) reared in captivity in the
Mediterranean has been obtained by the administra-
tion of a GnRH agonist (Corriero et al., 2007;
Mylonas et al., 2007).

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