Immunohistochemical Distribution of Urotensins I and II in the Central Nervous System of the Senegal Bichir, Polypterus senegalus

Abstract

Abstract The distribution of the urotensin I (UI)- and II (UII)-like immunoreactants in the central nervous system of the primitive bony fish Polypterus senegalus was studied by means of immunohistochemistry. Noticeably, UI-positive perikarya were present chiefly in the brain stem and the entire spinal cord with the exception of the caudalmost spinal cord segments, and their axons terminated on the wall of the adjacent blood vessels. In the cranial portion, the positive cells were found in the nucleus preopticus, the caudal diencephalon and the medulla oblongata. In contrast, the UII-immunoreactive fibers were distributed in the terminal part of the spinal cord, anterior to the 15th-to-the last vertebra; and a few UII-immunopositive perikarya occurred only in the caudalmost 5 to 6 segments. The most caudal region of the spinal cord showed a simplified or reduced neurohemal structure, where only UII-immunoreactive fibers were found. Accordingly, this area may represent the caudal neurosecretory system of t...