Transient neurotensin high-affinity binding sites in the human inferior olive during development

High-affinity binding sites for neurotensin 1-13 are found transiently in the human inferior olive during development. An in vitro membrane binding assay demonstrates, in the fetus, a specific binding to a single population of sites (Kd = 561 pM) which are levocabastine-insensitive and possess a Bmax value of 71 fmol/mg protein. No specific binding is present in the adult. Film radioautography shows, in fetuses of 15 weeks, a labelling in the whole inferior olive. At 25 weeks and at 33 weeks, the labelling is concentrated in the ventral lamella of the principal olive and in the caudal accessory olives. At birth and until 1 month of age, the labelling is still detected in the medial part of the ventral lamella of the principal olive. The labelling disappears after 3 months of age, is absent at 4 and 6 months and remains absent in the adults from 55 to 81 years of age. At the light microscopic level, the labelling is located mostly outside olivary neuronal cell bodies suggesting its presence on afferent nerve fibers. This ontogeny and localization of the binding sites in the inferior olive is quite different from that of the neurotensin 1-13 nerve terminals.