Histaminergic system of the lateral septum in the modulation of anxiety-like behaviour in rats

The central histaminergic system is known to have modulatory influence on anxiety-related behaviour both in animals and humans through histamine H1 and/or H2 receptors. In the present study, the effects of intra-lateral septal microinjections of histaminergic agents on anxiety-related behaviours in male Wistar rats have been investigated. As a model of anxiety, the elevated plus-maze which is a useful test to investigate the effects of anxiogenic or anxiolytic drugs in rodents was used. Intra-lateral septal administration of histamine (0.5 and 1 μg/rat) decreased the percentage of open arm entries and open arm time but not locomotor activity, showing an anxiogenic response. The intra-lateral septal injections of different doses of the histamine H1 receptor antagonist, pyrilamine (5, 10 and 20 µg/rat) or the histamine H2 receptor antagonist, ranitidine (5, 10 and 20 µg/rat) could not significantly alter the anxiety-like parameters in the plus-maze test. However, intra-lateral septal injections of different doses of pyrilamine (10 and 20 μg/rat) or ranitidine (10 and 20 μg/rat) significantly reversed histamine (1 µg/rat)-induced anxiogenic effect. The results may indicate that the histaminergic system of lateral septum modulate anxiety-like behaviour through histamine H1 and H2 receptors.