The antidepressant-like effect of human opiorphin via opioid-dependent pathways in mice.

In the present study, we investigated the antidepressive activity of opiorphin with central administration in the forced swim test in mice. Intracerebroventricular (i.c.v.) administration of opiorphin (1-6 μg/mouse) dose-dependently decreased the immobility time, which was reversed by nonselective opioid receptor antagonist naloxone, δ-selective naltrindole and μ-selective β-FNA. The data suggested that central administration of opiorphin produced an antidepressant-like effect by activating both μ and δ opioid receptors indirectly. In order to eliminate the possibility of a false-positive result in the forced swim test, locomotor activity was checked in both non-habituated and habituated mice. Opiorphin had no influence on non-habituated mice, though had weak effect on habituated mice. In addition, mice treated with opiorphin did not display any convulsive behaviors.