TARGET-SPECIFIC DIFFERENCES IN THE DENDRITIC MORPHOLOGY AND NEUROPEPTIDE CONTENT OF NEURONS IN THE RAT SCG DURING DEVELOPMENT AND AGING

Our purpose in this work was to investigate the role of target tissues in the regulation of dendritic morphology from sympathetic neurons du ring, development and aging. Neurons were retrogradely labeled from th ree targets, the iris, the submandibular gland (SMG), and the middle c erebral artery (MCA). They were then fixed and intracellularly injecte d to demonstrate their dendritic arborizations. Dendritic geometry var ied quantitatively in sympathetic neurons innervating different target tissues at all stages of development. Neurons innervating the iris ha d the largest cell bodies and most extensive dendritic arborizations, whereas the vasomotor neurons were the smallest. The number of primary dendrites, however, did not vary significantly between the different neuronal populations. The growth of dendritic arborizations during pos tnatal development and their atrophy in old age were not concordant in the different neuron populations we studied. Neurons innervating the MCA and the iris ceased dendritic growth early in postnatal developmen t, whereas the dendritic complexity of neurons supplying the SMG incre ased well into adulthood. By contrast, dendritic atrophy was seen in a ged MCA- and SMG-projecting neurons but not in those innervating the i ris, suggesting, with other evidence, correlated and distinct patterns of growth and atrophy in axons and dendrites of mature sympathetic ne urons projecting to different targets. Swollen dendrites and protubera nces on cell soma were a prominent feature of aged neurons. In additio n to the target-specific variation in neuronal morphology, we observed diversity in neurotransmitter phenotype. For example, neuropeptide Y was expressed in iridial but not SMG-projecting neurons. These results show a range of age- and target-specific differences in the dendritic morphology and neuropeptide content of sympathetic neurons that may b e a result of differing trophic interactions with their target tissues . (C) 1996 Wiley-Liss, Inc.