Involvement of opioidergic system of the ventral hippocampus, the nucleus accumbens or the central amygdala in anxiety-related behavior

Abstract

In the present study, the influence of opioidergic system of the ventral hippocampus, the nucleus accumbens or the central amygdala on anxiety-related behaviour was investigated in rats. 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. Bilateral microinjection of different doses of morphine (2.5, 5 and 7.5 μg/rat) into the ventral hippocampus or the nucleus accumbens increased the percentage of open arm time (OAT) and open arm entries (OAE) but not locomotor activity, indicating an anxiolytic response. However, intra-central amygdala administration of the opioid did not show any response. On the other hand, microinjection of a dose of naloxone into the ventral hippocampus (2 μg/rat) or the nucleus accumbens (1 μg/rat) increased open arm time (OAT), but not open arm entry (OAE) which may indicate an anxiolytic effect. Pre-treatment administration of naloxone (0.5, 1 and 2 μg/rat) reversed the anxiolytic effect of morphine (7.5 μg/rat) injected into the ventral hippocampus in a dose-dependent manner. A dose of the antagonist (1 μg/rat) also reduced the morphine response (2.5 μg/rat) when injected in the nucleus accumbens. In conclusion, it seems that the opioidergic system in the ventral hippocampus and the nucleus accumbens are involved in anxiety-related behaviors and the ventral hippocampus may be the main site of action of the anxiolytic properties of morphine. © 2008 Elsevier Inc. All rights reserved