POSTNATAL-DEVELOPMENT OF [D-ALA(2)]DELTORPHIN-I-LIKE IMMUNOREACTIVE STRUCTURES IN THE RAT-BRAIN

[D-Ala(2)]deltorphin-I, a highly selective ligand for delta opioid rec eptors, is a heptapeptide originally purified from frog skin. Previous immunohistochemical studies indicate that [D-Ala(2)]deltorphin-I-like molecule(s) may be present in adult rat brain, including specific neu ronal cells and fibers partially overlapping with the mesocortical and nigrostriatal dopaminergic systems. Here, we examined the development al aspect of such immunoreactive brain structures in early postnatal r ats. In newborn to al-day-old rats, positive staining in the brain occ urred mainly in subpopulations of neurons and occasionally in tanycyte s. On postnatal day 0, neuronal cell bodies containing [D-Ala(2)]delto rphin-I-like immunoreactivity were found in various brain regions, inc luding the olfactory tubercle, ventral pallidum, hippocampus, ventral tegmental area, pars compacta of the substantia nigra, supramammillary nucleus, and dorsal raphe nucleus. Immunoreactive nerve fibers were o bserved in the main and accessory olfactory bulbs, olfactory tubercle, prelimbic area, anterior cingulate cortex, neostriatum, accumbens, la teral septal nucleus, lateral habenular nucleus, and superior collicul us. As pups grew, positive staining of cell bodies decreased gradually in both density acid intensity, and those in the olfactory tubercle a nd ventral pallidum were no longer visible on postnatal day 14. On pos tnatal day 21, positive cells were found only in the ventral midbrain, including the pars compacta of the substantia nigra, ventral tegmenta l area, A8 region, and supramammillary nucleus. Positive fibers also d ecreased in density with age except in the accessory olfactory bulb, o lfactory tubercle, prelimbic area, and anterior cingulate cortex. (C) 1994 Wiley-Liss, Inc.