Effects of naloxone, glycyrrhizic acid, dexamethasone and deoxycorticosterone in repetitive stress

1. The present study examined the effect of naloxone (NAL), glycyrrhizic ac id (GCA), deoxycorticosterone (DOC) and dexamethasone (DEX) on daily repeat ed 2 h chronic restrained stress (RS) on the locomotor activity (LA) of rat s tested in the open field arena to elucidate the possible roles of opioids , glucocorticoids and mineralocorticoids in response to stress. 2, Intact and adrenalectomized (ADX) rats were either injected with 0.1 mt of NAL (0.32 mu g/100 g BW), 2. 1 mg/kg DOC or 120 mu g/kg DEX or had 1.0 m g/mL GCA dissolved in their drinking water or normal saline (for the ADX gr oup) dissolved in their drinking water 3, In intact groups, treatment with NAL completely blocked the stress respo nse and treatment with GCA, DOC and DEX partially prevented the stress resp onse. Adaptation occurred on either days 4, 5, 6 or 7 for intact rats treat ed with DEX, DOG, GCA or control rats, respectively. All ADX control rats d ied following the first 2 h RS, Adrenalectomized rats treated with DEX or D OC adapted later compared with intact rats, while rats given either GCA or NAL were unable to block or adapt to chronic RS, 4. These findings demonstrate that the stress response is primarily mediate d by endogenous opioids, in that it is blocked by NAL, Both mineralocortico ids and glucocorticoids, which can art centrally to inhibit endorphins, par tially blocked the stress response. The effect of GCA in intact rats was si milar to that of both DEX and DOC in intact rats. Adrenalectomized rats tre ated with GCA (despite their lack of endogenous corticosterone) showed a st ress response that was significantly different from the other ADX groups, i mplying that GCA had effects independent of endogenous corticosterone.