Abstract

The hippocampus is one of the main parts of Limbic system and plays a crucial role in the response of brain to stress. In this study, the effect of nicotine injection on the CA1 region of the hippocampus of mice in responding to inescapable stress was studied. Fifty four adult NMRI male mice were divided randomly into nine groups, comprising a negative control group (without any intervention), two groups as positive controls (receiving 1 ml/mouse and 10 1/4 g/mouse saline, respectively), three groups received Intrahippocampal (CA1) nicotine (getting 1, 5 and 10 1/4 g/mouse nicotine) and three groups received intraperitoneal nicotine (receiving 0.25, 0.5 and 1 mg/kg nicotine). The water and food consumption, body weight, anorexia time, changes in weight of brain and adrenal glands were evaluated. Data were presented as mean standard error of mean (SEM) and analyzed using one-way analysis of variance (ANOVA). Body and brain weight, amount of food and water consumption were decreased following stress, but the adrenal gland weight and anorexia time were increased. The results showed that intraperitoneal administration of nicotine exacerbated the effects of stress in a dose of 1 mg/kg and reduced the effects of stress in doses of 0.5 and 0.25 mg/kg. Intrahippocampal injection of nicotine had no effect on the response to stress and only affects the brain's weight. We conclude that inescapable stress causes extensive changes in animal performance, which is related to nicotinic acetylcholine receptors present on hippocampal pyramidal neurons. On the other hand, nicotinic acetylcholine receptors may modulate the activity of glucocorticoid receptors in the hippocampus neurons and play an important role in moderating stress responses in a dose-dependent manner.