Immunohistochemical localization of 3β‐hydroxysteroid dehydrogenase and 5α‐reductase in the brain of the African lungfish Protopterus annectens

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 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 5 alpha-reductase (5 alpha-R) in the brain and pituitary of the African lungfish Protopterus annectens by using antibodies raised against type I human 3 beta-HSD and type I human 5 alpha-R. The 3 beta-HSD and 5 alpha-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 periaqueductal gray. Identification of astrocytes, oligodendrocytes, and neurons with antisera against glial fibrillary acidic protein, galactocerebroside and neurofilaments revealed that, in the lungfish brain, 3 beta-HSD immunolabeling is expressed exclusively by neurons, whereas the 5 alpha-R-immunoreactive material is contained in both neurons and glial cells. In the pituitary gland, 3 beta-HSD- and 5 alpha-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.

Immunohistochemical localization and biological activity of 3β-hydroxysteroid dehydrogenase and 5α-reductase in the brain of the frog, Rana esculenta, during development

“…localization of 5a-R in the CNS of rat and African lungfish (Mathieu et al, 2001). Immunocytochemical studies at the electron microscope level have shown that the immunoreactive material is distributed in the cytoplasm, in agreement with the expected localization of 5a-R in the microsomal fraction .…”

“…for the immunocytochemical localization of 3b-HSD in the brain of fish (Mathieu et al, 2001) and adult frog (Mensah-Nyagan et al, 1994;Do Rego et al, 1998). Besides, immunohistochemical studies conducted with the same antiserum in the rat and human testis, ovary and adrenal gland have previously shown that the immunoreactivity was exclusively associated with steroidogenic cells .…”

“…In particular, neuroanatomical studies have demonstrated the occurrence of several steroidogenic enzymes in the central nervous system (CNS) of most vertebrate taxa including fishes Callard, 1985, 1988;, lungfishes (Mathieu et al, 2001), amphibians (Mensah-Nyagan et al, 1994Beaujean et al, 1999;Takase et al, 1999;Do Rego et al, 2007a), birds Usui et al, Frog 3b-HSD 5a-R Immunohistochemistry Pulse-chase Brain Ontogeny…”

Brain steroid contents in the catfish Heteropneustes fossilis: sex and gonad stage-specific changes

“…In the spawning phase, the E 2 level was low with higher amounts of T level. Mathieu et al (2001) have shown the presence of two key steroidogenic enzymes (3b-HSD and 5a-reductase) in the brain and pituitary of a lungfish. P450 C17 is a key steroidogenic enzyme in the production of androgens and, therefore, is also indispensable for the production of estrogens (that are produced from the aromatization of androgens).…”

Neuroactive steroids: State of the art and new perspectives

“…The biological activity of 3b-HSD has also been detected in primary cultures of rodent oligodendrocytes and neurons [167]. The expression of 3b-HSD protein and/or mRNA has been reported in various brain regions of several classes of vertebrates including fish [187,188], amphibians [189], birds [190] and mammals [191][192][193][194]. 3b-HSD was also localized in the PNS, particularly in dorsal root ganglion neurons and in Schwann cells of sciatic nerve [122,195,196].…”