Immunohistochemical Localization of Neuropeptide y pOsitive Cell Bodies and Fibres in Forebrain and Pituitary of the African Catfish, Clarias Gariepinus

Abstract

The present study reveals the topographic distribution of NPY-immunoreactive perikarya and fibres in the forebrain of the African catfish, Clarias gariepinus, at the light microscopic level. Our interest was mainly focussed on the possible participation of NPY in the hypothalamo-hypophyseal axis. Different procedures were tested, i.e. on immersion-fixed and paraffin-embedded brains as well as after perfusion-fixation and cryosectioning of the frozen brains. Possible cross-reactivity between the NPY-antiserum and FMRFamide was tested and could be excluded. NPY-immunoreactive perikarya were concentrated in a distinct area of the telencephalon, i.e. the nucleus entopeduncularis (NE). Especially the frontal and lateral parts of the telecephalon were richly innervated by NPY-ir fibres. A second distinct concentration of NPY-ir fibres was found in the area ventralis pars medialis of the telecephalon, known to contain GnRH-ir perikarya. The nucleus praeopticus posterioris (NPP) was densely innervated by NPY-positive fibres. The pituitary hardly showed innervation by NPY-positive fibres, which were then restricted to the neurointermediate lobe. The proximal pars distalis (PPD), containing the gonadotropic (GTH) cells, was devoid of NPY-ir fibres. The results of this immunohistochemical study indicate the possibility of an indirect regulation of the GTH-cells by NPY at the level of the brain, rather than a direct regulation via innervation by NPY fibres.