ORGANIZATION, DEVELOPMENT, AND EFFECTS OF INFRAORBITAL NERVE TRANSECTION ON GALANIN BINDING-SITES IN THE TRIGEMINAL BRAIN-STEM COMPLEX

Previous experiments from this laboratory have indicated that transect ion of the infraorbital nerve (ION, the trigeminal [V] branch that sup plies the mystacial vibrissae follicles) at birth and in adulthood has markedly different effects on galanin immunoreactivity in the V brain stem complex. Adult nerve transection increases galanin immunoreactivi ty in the superficial layers of V subnucleus caudalis (SpC) only, whil e neonatal nerve transection results in increased galanin expression i n vibrissae-related primary afferents throughout the V brainstem compl ex. The present study describes the distribution of binding sites for this peptide in the mature and developing V ganglion and brainstem com plex and determines the effects of neonatal and adult ION damage and t he associated changes in galanin levels upon their distribution and de nsity. Galanin binding sites are densely distributed in all V brainste m subnuclei and are particularly dense in V subnucleus interpolaris an d the superficial layers of SpC. They are present at birth (P-0) and t heir distribution is similar to that in adult animals. Transection of the ION in adulthood and examination of brainstem 7 days later indicat ed marked reductions in the density of galanin binding sites in the V brainstem complex. With the exception of the superficial laminae of Sp C, the same reduction in density remained apparent in rats that surviv ed >45 days after nerve cuts. Transection of the ION on P-0 resulted i n no change in the density of galanin binding sires in the brainstem a fter either 7 or > 60 days survival. These results indicate that dense ly distributed galanin binding sites are present in the V brainstem co mplex of both neonatal and adult rats, that they are located in region s not innervated by galanin-positive axons, and that their density is not significantly influenced by large lesion-induced changes in the pr imary afferent content of their natural ligand.