| Abstract: | The distribution of cholinergic neurons was studies in the brain steam, medulla and rostral spinal cord of the salmon Onchorynchus masu using histochemical choline acetyltransferase (ChAT) detection. Cholinergic neurons were observed in the isthmus, cranial nerve motor nuclei and spinal cord. In order to characterize several cholinergic nuclei observed in the isthmus of O. masu, their projections were studied by application of 1,1'-dioctadecyl-3,3,3',3,'-tetramethylindocarbocyanine perchlorate (DiI) to selected structures of the brain. The secondary gustatory nucleus projected mainly to the lateral hypothalamic lobes, whereas the nucleus isthmi projected to the optic tectum and parvocellular superficial pretectal nucleus, as it was earlier described for the other teleost group. In addition, the other isthmic cholinergic nuclei in O. masu may be homologous to the meso-pontine system of mammals. We conclude that the cholinergic systems of teleosts show many primitive features that have been presented during evolution, together with exclusive to the group characteristics. |
