The Innervation Of Adrenal Homolog In Teleosts: Histological, Cytological And Immunohistochemical Research

The innervation of catecholaminergic and steroidogenic cells of the adrenal homolog in four teleost species was studied by histological and cytological analysis and in two species the immunoreaction for TH, PNMT and nNOS was also investigated. The results obtained suggest that, as in mammals, the adrenal homolog is innervated by preganglionic cholinergic fibres running into the splanchnic nerve and by intrinsic fibres originating from ganglionic neurons located on the surface or inside the head kidney where the adrenal homolog is localized. In the trout ganglionic neurons and nerve fibres are often positive to nNOS suggesting an involvement of NO in the regulation of cellular activity. Under the E.M. the chromaffin cells of all the studied species appear innervated and the nerve endings show typical presynaptic specializations. Nerve fibres can also be found close to the interrenal cells, but no endings with synaptic specializations have ever been observed. The possibility of a paracrine, non-synaptic modulatory role of nerve fibres in the regulation of steroid secretion was suggested.