Immunohistochemical localization of urotensins I and II in the caudal neurosecretory neurons of the carp Cyprinus carpio and the sharks Heterodontus japonicus and Cephaloscyllium umbratile.

Using antisera to urotensins I and II (UI and UII), in the carp, Cyprinus carpio, three types of caudal neurosecretory neurons were identified: those with both UI- and UII-immunoreactivities, those with only UI-immunoreactivity and those with only UII-immunoreactivity. The last type of neurons exceeded the other types in number, while neurons immunoreactive with both UI and UII antisera were relatively few. The axons of neurons of these three types terminated around the capillaries in the urophysis. In the cat shark, Heterodontus japonicus and the swell shark, Cephaloscyllium umbratile, two types of neurons were identified: those with both UI- and UII-immunoreactivities and those with only UII-immunoreactivity. Neurons of the former type were greater in number than the latter. The axons of neurons of both types terminated in the neurohemal areas.