The distribution of 'extraurophyseal' urotensin I-immunoreactivity in the central nervous system of Catostomus commersoni after urophysectomy.

The occurrence and distribution of the fish neuropeptide urotensin I-immunoreactive (IR-UI) perikarya and fibres was investigated by peroxidase-anti-peroxidase immunohistochemistry in paraffin and vibratome sections of the central nervous system of urophysectomized and control fishes. IR-UI neurones not described previously were found in the area ventralis telencephali pars dorsalis, in the area pretectalis and in two unidentified brainstem nuclei of control and urophysectomized fishes. In urophysectomized fishes a 4-fold increase in the number of parvocellular IR-UI neurons was observed in the nucleus lateralis tuberis, whereas no significant differences were seen in other IR-UI neuronal groups. A functional relationship between IR-UI 'extraurophyseal' (i.e. brain) and caudal neurosecretory systems is suggested.