Effects of (-)eticlopride and 7-OH-DPAT on the tail-suspension test in mice

The dopamine (DA) D2/D3 antagonist (-)eticlopride (0.02, 0.05 and 0.1 mg/kg), dose-dependently increased immobility in the mouse tail-suspension test. Chronic treatment with the same compound (0.05, 0.1 mg/kg, x 14 days) produced a different effect, decreasing immobility when animals were tested 24 h after the last injection. The DA D3 agonist, 7-OH-DPAT, acutely administered before the same test, behaved biphasically, increasing and decreasing mice immobility at low (0.05 and 0.1 mg/kg) and high (1 and 2 mg/kg) doses, respectively. Chronically administered 7-OH-DPAT reduced the immobility time at 2 mg/kg but not at 0.1 mg/kg. These effects, coupled with measurements of locomotor activity and evaluation of mice behaviour in different conditions, are discussed in the light of putative DA involvement in depressive states and are considered as predicting antidepressant potential.