Neuropeptide Y (NPY) expression is up-regulated in the rat inferior olive during development

THE aim of this study was to analyse the developmental expression of the neuropeptide Y (NPY) in the rat inferior olivary (IO) complex by immunoperoxidase and immunofluorescence techniques. The spatial distribution of NPY-immunoreactivity (IR) did not vary during development, whereas NPY-IR intensity levels varied significantly. The peak of NPY-IR expression occurred during the second postnatal week, but differed in intensity in individual IO subnuclei, the highest levels being present in the dorsal fold of the dorsal accessory olive and in the ventro-lateral outgrowth. In the adult, NPY-IR could only he rescued in colchicine pretreated animals, but its distribution overlapped the one found during development. These findings show that NPY-IR is transiently up- regulated, during development, in specific compartments of the IO complex, and that the peptide is rescued in the same specific olivocerebellar compartments in the adult. These observations are here taken to support the hypothesis that NPY may exert different trophic- differentiating and/or neuromodulatory roles during development, when its expression is transiently up-regulated, or at adult stages, when it can be rescued, according to the different biological contexts.