Background and purpose: The adrenergic system is known to have modulatory influence on anxiety-related behaviour both in human and animals. Dorsal hippocampus is an important brain site in modulation of neurotransmittery and neuroendocrinology of anxiety. The present study, was designed to evaluate the interactions between adrenergic and opioidergic systems in dorsal hippocampus on anxiety. Materials and methods: The male Wistar rats, weighting 200-250 grams, were used. At the time of surgery the animals were anesthetized and placed in the stereotaxic apparatus and were cannulated bilaterally. The elevated plus-maze was used to measure the anxiety. Percentage of open arm time (OAT%) and open arm entry(OAE%) was used for evaluation of anxiety. Results: Intra peritoneal administration of morphine (6mg/kg) increased the percentage of open arm time (OAT%) in anxiety test, indicating anxiolytic-like effect. Intra dorsal hippocampus infusion of salbutamol, β2-adrenergic receptor agonist, (4μg/rat) increased OAT% in anxiety test, demonstrating anxiolytic-like effect. While co-administration of intra dorsal hippocampus salbutamol (4μg/rat) and ineffective dose of morphine (4mg/kg) showed significant increase of OAT% in anxiety test, thus presenting anxiolytic response. Intra dorsal hippocampus administration of propranolol, β2-adrenergic receptor non-selective antagonist, (4μg/rat) decreased OAT% ,indicating of decrease anxiety-like behaviour. While co-administration of intra dorsal hippocampus propranolol (4μg/rat) and effective dose of morphine (6mg/kg) showed a significant increase of OAT%, presenting anxiolytic response. Co-administration of ineffective doses of morphine (4mg/kg) and propranolol (1μg/rat) with the effective dose of salbutamol (4μg/rat), showed that propranolol could reverse the anxiolytic-like effect of morphine and salbutamol. It should be noted that there are no significant changes in locomotor activity. Conclusion: The results indicate that morphine creates the compromise changes in adrenergic neurons of dorsal hippocampus by changing the effects of β-adrenergic system on anxiety.

Keywords: Anxiety, noradrenergic system, morphine, dorsal hippocampus

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