Differential distribution of urocortin- and corticotropin-releasing factor-like immunoreactivities in the rat brain

Urocortin, a novel 40 amino acid neuropeptide, is a member of the corticotr opin-releasing factor family. With 45% homology to corticotropin-releasing factor, urocortin binds with similar affinity to the corticotropin-releasin g factor-1 and corticotropin-releasing factor-2 receptors and may play a ro le in modulating many of the same systems as corticotropin-releasing factor . To assess whether urocortin and corticotropin-releasing factor are locali zed in the same regions of the brain, we compared the distribution of uroco rtin- and corticotropin-releasing factor-like immunoreactivities in the rat central nervous system. Polyclonal antibodies to rat corticotropin-releasi ng factor and rat urocortin were generated and utilized to map the distribu tion of corticotropin-releasing factor- and urocortin-like immunoreactiviti es throughout the rat forebrain and brainstem. Characterization of the anti bodies by radioimmunoassay showed no crossreactivity with related peptides. Male Sprague-Dawley rats were treated with colchicine for 18-24 h. Followi ng colchicine treatment, the rats were perfused with paraformaldehyde-lysin e-periodate fixative and their brains removed. Serial coronal sections were taken throughout the rat brain and processed for either corticotropin-rele asing factor- or urocortin-like immunoreactivity. Urocortin-like immunoreac tivity shows a discrete localization within several regions including the s upraoptic nucleus, the median eminence, Edinger-Westphal nucleus and the sp henoid nucleus. This is in contrast to the more abundant corticotropin-rele asing factor-like immunoreactivity. Regions containing high levels of corti cotropin-releasing factor immunoreactivity include the lateral septum, para ventricular nucleus of the hypothalamus, median eminence and locus coeruleu s. There are a few regions that contain both urocortin-immunoreactive and cort icotropin-releasing factor-immunoreactive cells, such as the supraoptic nuc leus and the hippocampus. Therefore, urocortin and corticotropin-releasing factor appear to have different distribution patterns which may be indicati ve of their respective physiological functions. (C) 1999 IBRO. Published by Elsevier Science Ltd.