Localization of aromatase in the brain of the male African catfish, Clarias gariepinus (Burchell), by microdissection and biochemical identification

Aromatase activity was determined in small discrete areas of the brain of the African catfish, Clarias gariepinus, by a radiometric assay. The fore‐and midbrain were divided into eighteen 500‐μm transverse sections. From these sections several punches (0.3 mg of tissue) were taken and incubated with [19‐3H]‐androstenedione. The aromatase activity, calculated from the release of tritium label during aromatization, is expressed in pmol mg−1 tissue hour−1. The highest activity (3.7 pmol) was detected in the preoptic region. The more caudally located area tuberalis, including the nucleus lateralis tuberis and the nucleus recessus lateralis, also showed a relatively high activity (2.5 pmol). A similar activity was found in the most rostral part of the telencephalon and the dorsal parts of the mesencephalon, i.e., the tectum opticum and torus semicircularis (2.3 pmol). A moderate aromatase activity was observed in remaining parts of the brain, except the cerebellum and hindbrain, in which aromatase activity was hardly detectable (0.1–0.3 pmol). It is concluded that a high aromatase activity is present in regions known to be involved in the regulation of reproduction. Since both the torus semicircularis and the tectum opticum display a high aromatase activity, it is suggested that also these structures are involved in reproductive processes.