Peptidergic innervation of the locus coeruleus cells in the human brain

The immunocytochemical localization of corticotropin-releasing factor (CRF), thyrotropin-releasing hormone (TRH), substance P (SP), neuropeptide Y (NPY), and neurotensin (NT) were studied in the human locus coeruleus (LC) using the avidin-biotin complex (ABC) technique. The brains were obtained from 3 adult male human subjects of 36-61 years old. All of these peptides studied were present in nerve fibers and varicosities throughout the entire nucleus, where they distributed unevenly. The highest density of immunoreactive neuronal networks was generally observed in the middle and to a lesser extent in the caudal part of the nucleus, while only scattered fibers were seen in the rostral part of the LC. Among the investigated neuronal peptides, the CRF-immunopositive network was the most dense, less dense immunostaining with TRH and NPY antisera while only few SP- and NT-immunoreactive fibers were present in the nucleus. Cell bodies immunostained for the above peptides were not seen in the LC. Per analogiam with rats, fibers immunostained in the LC may be of both intrinsic and extrinsic origins.