Ontogeny of Brain Neurotensin in the Rat: A Radioimmunoassay Study

: Concentrations of neurotensin‐like immunoreactivity in several discrete brain areas were measured by radioimmunoassay in rats of different ages (2, 5, 10,20, 30, and 60 days). Neurotensin‐like immunoreactivityincreased steadily from 2 to 30 days of age in the hypothalamus and then plateaued, while the preoptic area andamygdala concentrations peaked at 30 days of age. Brain‐stem neurotensin‐like immunoreactivity concentrationsincreased from 2 to 10 days of age and decreased from20 to 60 days of age. Several other regions showed nosignificant age‐associated changes in neurotensin‐like im‐munoreactivity.