Localization of corticotropin-releasing hormone (CRF)-like immunoreactivity in the central nervous system of the elasmobranch fish,Scyliorhinus canicula

Summary The occurrence and localization of immunoreactive corticotropin-releasing factor (CRF) in the brain and pituitary of the elasmobranch fish Scyliorhinus canicula, were studied by means of specific radioimmunoassay and immunohistochemistry using the indirect immunofluorescence method. Brain and pituitary extracts showed a good cross-reactivity with the ovine CRF antiserum, but serial dilutions of tissue samples did not completely parallel the standard curve. Relatively high concentrations of CRF-like material were found within the pituitary, diencephalon, and telencephalon. CRF-like immunoreactive perikarya were observed in the preoptic nucleus and in the nucleus lateralis tuberis. Numerous immunoreactive cells appeared to be of the CSF-contacting type. CRF-like immunopositive fibers were seen to run through the hypothalamus within the ventro-medial floor of the infundibular region. A dense plexus of immunoreactive nerve endings terminated in the median eminence and the neurointermediate lobe of the pituitary. These results indicate that a neurosecretory system containing CRF-like immunoreactivity exists in the brain of elasmobranchs, a group of vertebrates which has diverged early from the evolutionary line leading to mammals. In addition, our data support the notion that a CRF-like molecule is involved in the regulation of corticotropic and melanotropic cell activity in this primitive species of fish.