Abstract: This study was designed to determine the effect of the entorhinal cortex on stress response to immobilization in rats. Neurons in the entorhinal cortex were lesioned by bilateral injection of the cell-selective neurotoxin, ibotenic acid (1.5 μg/μl of solution per side). Two weeks later, rats were subjected to immobilization stress. Rats in which ibotenic acid had been injected into the entorhinal cortex showed attenuated expression of c-Fos in the hypothalamic paraventricular nucleus (PVN) and blunted elevation of plasma adrenocorticotropic hormone (ACTH) after immobilization stress compared with rats in which saline had been injected into the entorhinal cortex. The results of this study indicate that the entorhinal cortex is closely involved in the activation of the HPA axis during immobilization stress in rats.

Key words: entorhinal cortex, hypothalamic paraventricular nucleus, c-Fos, adrenocorticotropic hormone, ibotenic acid