Nitric oxide synthase in the caudal neurosecretory system of the teleost Oreochromis niloticus

This study provides evidence that, within the caudal neurosecretory system of the teleost Oreochromis niloticus, neurons express nitric oxide synthase (NOS)-like molecules. The presence of NOS-like molecules was demonstrated by means of NADPH-diaphorase (NADPHd) staining and NOS immunohistochemistry. In the caudal spinal cord, NOS-positive neurosecretory cell bodies and neurosecretory fibers were observed. In addition, NOS-positive structures were found in the urophysis which correspond to neurosecretory axon terminals. Cellular co-localization of NOS and ovine corticotropin-releasing factor (oCRF) immunoreactivities confirmed that the NOS-positive structures belong to the caudal neurosecretory system. The present results suggest that NO may participate in the caudal neuroendocrine function.