The effects of histaminergic agents in the ventral hippocampus of rats in the plus-maze test of anxiety-like behaviours

It has been suggested that histamine have modulatory influence on anxiety-related behaviours both in animals and humans. Ventral hippocampus (VHC) may also be an important brain site in the modulation of fear or anxiety. In the present study, the effects of histaminergic agents on anxiety-related behaviours in the rats, using plus-maze test has been investigated. Intra-VHC administration of histamine (2.5, 5 and 7.5 μg/rat) decreased %OAT and %OAE but not locomotor activity, showing an anxiogenic response. Pretreatment of animals with either pyrilamine, a H1 receptor antagonist (10 μg/rat), or ranitidine, a H2 receptor antagonist (10 μg/rat) reverse anxiogenic response of histamine (2.5, 5 and 7.5 μg/rat). However, intra-VHC microinjection of higher doses of pyrilamine (40 μg/rat) or ranitidine (20 and 40 μg/rat) alone increased anxiety-like behaviours in rats. Our results showed that histamine may modulate anxiety-like behaviours via H1 and H2 receptors in the ventral hippocampus of the rats.