Distribution and characterization of neuropeptide Y‐like immunoreactivity in the brain of the crested newt

The newt brain represents a simplified model for the increasingly complex vertebrate neuronal organization. The localization of neuropeptide Y‐like (NPY‐like) containing neurons in the brain of Triturus cristatus was studied by means of indirect immunofluorescence, peroxidase‐antiperoxidase, and avidin‐biotin techniques using a highly specific antiserum. NPY‐like positive cell bodies were observed in several areas, most notably in the telencephalon (primordium hippocampi and amygdaloid complex), the preoptic and suprachiasmatic areas, the hypothalamus, the dorsal thalamus, the tegmentum, and the rhombencephalon (laterolateral grey column and raphe area). Nerve fibres were particularly abundant in the pallium, striatum, septum, amygdaloid, preoptic neuropils, and pars intercalaris diencephali. Bundles of NPY‐immunoreactive fibres also were visualized in the dorsal thalamus and in the posterior hypothalamus. The pars intermedia lacked any NPY‐like positive fibres. Neuronal processes also were found in the tectum mesencephali and in the body of the cerebellum. A prominent NPY‐like fibre network was observed in the octavolateralis. Concentrations of NPY measured by means of a specific radioimmunoassay were threefold higher in the hypothalamus (15.2 ± 1.3 ng/mg proteins) than in the rhombencephalon (4.9 ± 0.3) and the mesencephalon (4.3 ± 0.2). The concentration found in the telencephalon was 2.1 ± 0.3 ng/mg proteins. Sephadex G‐50 gel chromatography of whole brain extracts indicated the presence of high molecular weight forms of NPY‐like material in addition to the authentic peptide. Both amphibian and mammalian NPY peptides had an apparent molecular weight of 4,000 daltons, as evidenced by immunoblotting analysis. High‐performance liquid chromatography demonstrated, however, that the newt peptide was slightly less hydrophobic than porcine NPY. The present findings indicate that NPY‐immunoreactive neurons are widely distributed in the brain of urodeles. Our data indicate that the NPY molecule has been relatively well preserved during evolution.