Effect of hypophysectomy on the hypothalamic corticotropin-releasing factor (CRF) neuronal system in the eel: immunocytochemical study.

Male and female eels were hypophysectomized by a buccal approach and examined either 2 and 7 weeks (males) or 4 and 5 months (females) later. Intact and sham-operated eels served as controls. Fish were killed by decapitation, and the brains fixed in sublimated Bouin-Hollande solution and embedded in paraffin wax. Frontal and sagittal sections were immunostained by the peroxidase-antiperoxidase method, using antisera against cortiotropin-releasing factor (CRF) or arginine vasotocin (AVT). Immunoreactive (ir)-CRF was detected in parvo- and magnocellular perikarya of the preoptic nucleus. Sham hypophysectomy did not affect ir-CRF in cell bodies and fibres. After hypophysectomy, mainly after 4 or 5 months, there was an apparent increase in the number of ir-CRF cells. The intensity of immunostaining in the cell bodies was variable but not significantly different from the controls, but the two ventral axonal tracts were much thicker and contained more immunoreactive material than in sham-operated eels, while ir-CRF accumulated close to the sectioned pituitary stalk. The existence of negative feedback by cortisol on the CRF neurons is discussed.