Ontogeny of the neurotensin-containing neuron system of the rat: immunohistochemical analysis. I. Forebrain and diencephalon.

The ontogeny of the neurotensin (NT) neuron system in the forebrain and diencephalon of the rat was investigated by means of indirect immunofluorescence. NT-positive structures first appear in the primordium of the olfactory bulb, anterior amygdaloid area, piriform cortex, amygdaloid complex, nucleus tractus diagonalis, lateral preoptic area, and lateral hypothalamus, etc., of the fetus of gestational day 16. From this day, NT-positive structures appear gradually in various areas of the forebrain and diencephalon and reach their maximum content on postnatal day 7. In contrast, NT-positive structures decrease slightly in number as the rat grows. However, even in adult rats, numerous NT-positive structures are still identifiable in various areas of the forebrain and diencephalon.