FMRFamide immunoreactivity in the brain and pituitary of Carassius auratus (Cyprinidae, Teleostei).

Neurons immunoreactive for the molluscan cardioactive peptide FMRFamide (FMRFi) in the brain of Carassius were demonstrated immunohistochemically with the peroxidase-antiperoxidase technique (PAP) and three antisera against this tetrapeptide. FMRFi perikarya were consistently found in the ganglion of the nervus terminalis, in some scattered neurons of the nucleus entopeduncularis, in the nucleus praeopticus pars magno- and parvocellularis, the nucleus ventromedialis, the nucleus posterior periventricularis, nucleus recessus lateralis and posterior. Some weak FMRFi neurons occurred in the rostral mesencephalic tegmentum and in the region of the nucleus gustatorius secundus. Both the medullary Mauthner neurons and the cerebellar Purkinje cells were only weakly immunoreactive for FMRFamide, while a group of intensely FMRFi rhombencephalic perikarya, presumably the nucleus motorius nervi vagi, occurred subependymally next to the fourth ventricle. FMRFi fibres and nerve endings occurred in the bulbus olfactorius, in the tractus opticus, and in the central parts of the dorsal, medial and ventral telencephalon. Some FMRFi fibres traversed through the commissura anterior while others occurred close to the hypothalamic nuclei, in the medial layers of the tectum opticum, in the brain stem, in the vagal lobe and in the ventral medulla oblongata. The present results are compared to the FMRFi structures in other fish brains.