The effects of histaminergic agents in the ventral hippocampus of rats in the elevated plus‐maze test of anxiety

Abstract

There are reports indicating that histamine & histaminergic agents can change anxiety-related behaviors both in animals and humans. Ventral hippocampus (VHC)is an important brain site in the modulation of fear or anxiety. In the present study, we have investigated the effects of intra-VHC microinjection of histaminergic agents on anxiety-related behaviors in rats, using elevated plus-maze test of anxiety. Intra-VHC administration of histamine at the doses of 2.5,5 and 7.5μg/rat decreased%OAT and %OAE but not locomotor activity, showing an anxiogenic response. Intra-ventral hippocampus microinjection of pyrilamine, a H1 receptor antagonist and ranitidine, a H2 receptor antagonist,(10,20 and 40μg/rat) decreased anxiety in our experiments. In another series of experiments, Histamine at doses of 2.5,5 and 7.5μg/rat was pretreatment with pyrilamine and ranitidine dose of 10μg/rat. The results showed that pyrilamine could significantly reverse the anxiogenic effect of histamine at doses of 5 and 7.5μg/rat and ranitidine could significantly reverse the anxiogenic effect of histamine at doses of 7.5μg/rat. Our results showed that histamine may modulate anxiety via H1 & H2 receptors in the ventral hippocampus of the rats.