Coexistence of corticotropin-releasing factor-like immunoreactivity and vasotocin in perikarya of the preoptic nucleus in the eel.

A corticotropin-releasing factor (CRF)-like system has been identified in eels (Anguilla anguilla, A. rostrata, and A. japonica) with immunocytochemical techniques. Immunoreactive perikarya were located in the preoptic area, in magno- and parvocellular regions of the preoptic nucleus. Fine fibers reached the pituitary and terminated in the neurohypophysis close to the corticotropic cells of the rostral pars distalis and caudally close to the melanocorticotropic cells of the intermediate lobe. Double immunostainings revealed the presence of three subpopulations of perikarya: one population containing only CRF, a second containing only arginine vasotocin (VT), and a third one containing both CRF and VT. This coexistence of CRF and VT was also demonstrated by comparing adjacent sections stained with anti-CRF and anti-VT, respectively. Because antisera used in the present work were carefully absorbed, these data strongly suggest that CRF and VT coexist in some perikarya, at least in the animals studied.