Ontogeny of (D-Ala(2))-deltorphin I-like immunoreactive neurones in foetalrat brain

Foetal rat brain from embryonic day (ED) 12-22 was immunohistochemically st udied to describe the time of first appearance and further distribution pat terns of (D-Ala(2))-deltorphin-I-immunoreactive (DADTI-IR) nerve elements. The primary antiserum used in this study was a polyclonal antibody against DADTI previously used in adult and postnatal rat brain mapping. DADTI-IR ne rve elements first appeared in the neuroepithelium of ventral mesencephalon on ED 13. From there, positive cell bodies migrated towards the mantle lay er until they invaded the whole ventral mesencephalic tegmentum. They then reached their definitive position, corresponding to a subpopulation of the A8, A9 and A10 dopaminergic neurones that had been constantly observed also in the adult age. From ED 15-17, DADTI-positive nerve fibres appeared in t he medial forebrain bundle, the neostriatum anlage, the accumbens nucleus, the olfactory tubercle, the fasciculus retroflexus, and the prefrontal cort ex. All these locations have also been found in adult rats. From ED 14 onwa rds, transient DADTI-IR somata and nerve fibres were observed in retinal ne uroepithelium, optic pathways as far as the superior colliculus, CA3 hippoc ampal field, reticular formation in the medulla oblongata. All these locati ons gradually disappeared either before birth (medulla oblongata) or within the first 3 weeks after birth. These results suggest that the DADT-like mo lecule recognised by our antibody has during the embryonic development a re gulatory function in neuronal growth and differentiation. (C) 2000 Publishe d by Elsevier Science B.V. All rights reserved.