BACKGROUND: The hippocampus regulates the hypothalamic-pituitary-adrenal axis through negative feedback. The hypothalamic paraventdcular nucleus receives neuronal input from the hippocampus via the fix.OBJECTIVE: To explore whether the negative feedback effect of the hippocampus on the hypothalamic-pituitary-adrenal axis is contributed to the inhibitory effect of mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) in the hippocampus on the paraventricular nucleus via the fomix.DESIGN, TIME AND SETTING: Randomized, controlled, animal experiment. The study was performed at the Department of Histology and Embryology, China Medical University between September 2006 and September 2008.MATERIALS: Rabbit anti-rat anti-MR and rabbit anti-rat anti-GR antibodies were purchased from Santa Cruz Biotechnology, USA. Rabbit anti-rat anti-corticotrophin releasing hormone (CRH) and rabbit anti-rat anti-arginine vasopressin antibodies were purchased from Wuhan Boster.METHODS: A total of 90 male, Wistar rats were randomly divided into model and sham-surgery groups (n=45). Fix transection was performed in the model group, while the sham-surgery group underwent surgery, but no fix transection.MAIN OUTCOME MEASURES: Immunohistochemistry was used to examine MR and GR expression in the hippocampus, as well as CRH and anti-arginine vasopressin in the paraventricular nucleus. West blot was used to measure alterations in MR, GR, and CRH protein expression following fomix transection.RESULTS: Compared with the sham-surgery group, there were no obvious changes in MR and GR expression in the hippocampus, or CRH and anti-arginine vasopressin expression in the paraventricular nucleus within 4 days of fix transection. However, after 7-10 days, significantly decreased MR and GR expression in the hippocampus, and increased CRH and anti-arginine vasopressin expression in the paraventricular nucleus were observed (P < 0.05-0.01).CONCLUSION: Negative feedback from the hippocampus on the hypothalamic-pituitary-adrenal axis might be mediated through the fix, and the corticosterone actions mediated by hippocampal corticosteroid receptors indirectly modulated the hypothalamic-pituitary-adrenal axis.