Antidepressant-like activity of flunarizine in modified tail suspension test in rats

Flunarizine, a Ca(2+) channel blocker, crosses blood brain barrier (BBB), antagonizes calcium influx and interferes with neurotransmitter system. Flunarizine 20 mg/kg exhibited significant antidepressant activity in our previous study using forced swim test (FST) in mice, which was contradictory to the findings of other authors. Hence, the present study was designed to strengthen the results of our previous study, using the modified tail suspension test (TST) in rats.

Aim of this study was to evaluate the antidepressant activity of flunarizine versus standard antidepressant drug fluoxetine in modified TST in rats.

The study approved by Institutional Animal Ethics Committee was conducted using 24 adult albino rats (n = 6 in each group). Antidepressant effect of normal saline (0.1 ml/100 g), fluoxetine (10 mg/kg, intraperitoneally (ip)), and flunarizine (2 and 10 mg/kg, ip) was evaluated by using modified TST in rats. Thirty minutes after administration of all test drugs the duration of immobility was recorded for a period of 5 min in all rats by using modified TST. The data was analyzed by Student's t-test and one-way analysis of variance (ANOVA) and P < 0.05 was considered significant.

Mean duration of immobility was significantly reduced in fluoxetine and flunarizine (10 mg/kg, ip) group as compared to the normal saline, that is, 160.33, 175.17, and 226.83 s, respectively (P < 0.05). Decrease in immobility with flunarizine (10 mg/kg, ip) was statistically significant compared with normal saline, but was not found to be significant when compared to fluoxetine (P > 0.05). Also, currently used human dose of flunarizine when extrapolated to rats (i. e., 2 mg/kg, ip) failed to show significant antidepressant effect in modified TST in rats.

The results of the present study indicate antidepressant-like activity of flunarizine.