Immunohistochemical Localization of 3-
Hydroxysteroid Dehydrogenase and 5-
Reductase in the Brain of the African
Lungfish Protopterus annectens
MAURA MATHIEU,
1,2
AYIKOE GUY MENSAH-NYAGAN,
1
*
MAURO VALLARINO,
2
JEAN-LUC DO-RE
´
GO,
1
DELPHINE BEAUJEAN,
1
DAVID VAUDRY,
1
VAN LUU-THE,
3
GEORGES PELLETIER,
3
AND HUBERT VAUDRY
1
1
European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and
Molecular Neuroendocrinology, Institut National de la Sante ´ et de la Recherche Me ´dicale
(INSERM U-413), Unite ´ Affilie ´e au Centre National de la Recherche Scientifique (UA
CNRS), University of Rouen, 76821 Mont-Saint-Aignan, France
2
Department of Experimental Biology, Section of Neuroendocrinology and Developmental
Biology, University of Genova, 16132 Genova, Italy
3
MRC Group in Molecular Endocrinology, Laval University Hospital Center,
Que ´bec G1V 4G2, Canada
ABSTRACT
The localization of the enzymes responsible for the biosynthesis of neurosteroids in the
brain of dipnoans has not yet been determined. In the present study, we investigated the
immunohistochemical distribution of 3-hydroxysteroid dehydrogenase (3-HSD) and 5-
reductase (5-R) in the brain and pituitary of the African lungfish Protopterus annectens by
using antibodies raised against type I human 3-HSD and type I human 5-R. The 3-HSD
and 5-R immunoreactivities were detected in cell bodies and fibers located in the same areas
of the lungfish brain, namely, in the pallium, thalamus, hypothalamus, tectum, and periaq-
ueductal gray. Identification of astrocytes, oligodendrocytes, and neurons with antisera
against glial fibrillary acidic protein, galactocerebroside and neurofilaments revealed that, in
the lungfish brain, 3-HSD immunolabeling is expressed exclusively by neurons, whereas the
5-R-immunoreactive material is contained in both neurons and glial cells. In the pituitary
gland, 3-HSD- and 5-R-like immunoreactivity was localized in both the pars distalis and
the pars intermedia. The present study provides the first immunocytochemical mapping of
two key steroidogenic enzymes in the brain and pituitary of a lungfish. These data strongly
suggest that neurosteroid biosynthesis occurs in the brain of fishes, as previously shown for
amphibians, birds, and mammals. J. Comp. Neurol. 438:123–135, 2001. © 2001 Wiley-Liss, Inc.
Indexing terms: 3-HSD; 5-R; neurosteroids; immunocytochemistry; dipnoans; central nervous
system; pituitary
Contract grant sponsor: Institut National de la Sante ´ et de la Recherche
Me ´dicale (INSERM); Contract grant number: U-413; Contract grant spon-
sor: MURST (40%); Contract grant sponsor: Italian Centro Nazionale delle
Ricerche (Italy/France Bilateral Program); Contract grant number:
95.00885.CT04; Contract grant sponsor: Institut National de la Sante ´ et de
la Recherche Me ´dicale and Centro Nazionale delle Ricerche (INSERM/
CNR Exchange Program); Contract grant sponsor: Conseil Re ´gional de
Haute-Normandie.
The first two authors contributed equally to this work.
*Correspondence to: Professor A.G. Mensah-Nyagan, Laboratoire de Neu-
rophysiologie Cellulaire et Inte ´gre ´e, CNRS, UMR 7519, Universite ´ Louis
Pasteur, 21, rue Rene ´ Descartes, 67084 Strasbourg, France.
E-mail: g.mensah@caramail.com
Received 3 August 2000; Revised 28 November 2000; Accepted 11 June
2001
THE JOURNAL OF COMPARATIVE NEUROLOGY 438:123–135 (2001)
© 2001 WILEY-LISS, INC.