Responses of brain and pituitary immunoreactive corticotropin-releasing factor in surgically interrenalectomized eels: immunocytochemical study.

Interrenal (IR) cell islets, mainly located in the anterior and posterior cardinal veins, can be surgically removed in the eel. Immunocytochemical studies showed that sham operation slightly affected the distribution of immunoreactive corticotropin-releasing factor (ir-CRF) in the preoptic nucleus (PON) and neurohypophysis (NH). Surgically interrenalectomized (IRX) eels showed a significant increase in the cross-sectional area of the magno- and parvocellular perikarya of the PON and a noticeable decrease in their immunostaining after 8-9 days. In the pituitary, the immunostaining of the rostral nerve fibers facing the corticotropic (ACTH) cells was greatly reduced whereas ir-CRF in the caudal NH was not clearly affected. Immunostaining of the ACTH cells was strongly reduced and that of melanocorticotrops slightly decreased. These data suggest that the suppression of cortisol synthesis is responsible for the stimulation of the CRF ir-perikarya and the CRF release along the rostral pars distalis, inducing ACTH cell degranulation. However, the stressed condition of these eels may accentuate the response to IRX. The neurointermediate lobe, although slightly affected, does not seem to be directly controlled by the plasma cortisol level. These results are compared to those obtained after a pharmacological IRX produced by metopirone.