Developmental changes in neurotensin and its metabolites in the neonatal rat

Neurotensin-like immunoreactivity (NT-LI) was measured in the di-, tel- and mesencephalon of rats from embryonic day 15 (E15) through birth (∼E22) until postnatal day 5 (P5) using radioimmunoassay (RIA) and an N-terminal directed polyclonal antibody. NT-LI and NT metabolite-like immunoreactivities (NT 1–8, NT 1–10, NT 1–11 and NT 1–12-LI) were also similarly determined using high performance liquid chromatography (HPLC) coupled with RIA. NT-LI was low at E15 but increased to peak levels at around E20 or birth in the di- and telencephalon, after which the levels declined. Similar, but lower, changes were observed with NT 1–10-LI but not other metabolites while much lower NT-LI and metabolites were observed in the mesencephalon where no transitory changes occurred. The changes in neonatal rat brain NT and metabolites are discussed with respect to the possible neonatal trophic roles of these peptides.