Effects of Histamine on Anxiety-related behavior in Morphine sensitized and Naïve Rats

Aim and Background. It has been suggested that histamine have modulator influence on anxiety-related behaviors both in animals and humans. On the other hand, ventral hippocampus (VHC) may be an important brain site in the modulation of fear or anxiety. Materials and Methods. In the present study, the effects of bilateral intra-VHC injections of histamine on anxiety-related behavior have been investigated in morphine-sensitized and naïve rats using a plus-maze model. Sensitization was obtained by subcutaneous injections of morphine, once daily for 3 days and then 5 days free of the drug before test. Results. Our results showed bilateral intra-VHC administration of histamine (2.5, 5 and 7.5μg/rat) decreased %OAT (Open Arm Times) and %OAE (Open Arm Entries) but not locomotor activity that showing an anxiogenic effect. Another results indicated that morphine sensitization increased %OAT and %OAE. Conclusions. Bilateral intra-VHC administration of histamine showed an anxiogenic effect. Moreover, another results indicated that morphine sensitization indicated an anxiolytic response in the presence of histamine.