Role of interaction between Nicotine and dopaminergic D2 receptors of dorsal hippocampus on anxiety behavior

Nicotine can affect anxious behaviors through its direct effect on presynaptic nicotinic receptors. In addition, dorsal hippocampus and D2 dopamine receptors play modulatory role in anxiety behavior, based on previous studies. This study was performed with the aim of evaluating the role of dopaminergic D2 receptors of dorsal hippocampus on anxiety behavior induced by nicotine, in mice. In this experimental study, male laboratory mice were anesthetized with intra-peritoneal injection of ketamine hydrochloride plus xylazine and then were placed in a stereotaxic apparatus. Two stainless-steel cannulas were placed in dorsal hippocampus. All animals were allowed to recover for one week before behavioral tests. The hole-board test was performed for evaluating anxiety-like behaviors. Data was analyzed using one-way analyses of variance followed by Dunnett’s test, using SPSS 17 software. Intra-peritoneal injection of nicotine decreased number of head-dip (p<0.001) but had no effect on locomotion activity (p>0.05) which showed the anxiogenic effect of nicotine. The bilateral intra-dorsal hippocampal injections of ineffective doses sulpiride reversed anxiogenic response induced by nicotine (p<0.01) without affecting locomotion activity (p>0.05). Furthermore, co-administration of ineffective dose of quipirole plus ineffective dose of nicotine increased anxiogenic effects of nicotine (p<0.001) but had no effect on locomotion activity (p>0.05). It seems that dopaminergic D2 receptors of dorsal hippocampus play modulatory role in anxiogenic response induced by nicotine.