Vagus nerve stimulation (VNS) is effective in a rat model of antidepressant action

Depression is a common but debilitating illness that afflicts a large population and costs the US economy a staggering $40 billion dollars per year. Clinical studies have demonstrated that vagus nerve stimulation (VNS) is an effective treatment for medication-resistant depression. Understanding VNS's antidepressant mechanisms is key to improving the therapy and selecting the best surgical candidates, and demonstration that VNS is effective in a validated test of antidepressant activity allows us to elucidate these mechanisms in a cost-effective manner. In the present study, Wistar Kyoto rats were implanted with a cuff electrode on the left cervical vagus nerve. The next day, they were placed into a water-filled Plexiglas cylinder for 15 min. After this forced-swim session, one of three treatment conditions were administered over 4 consecutive days: 30 min per day of continuous VNS, 10 mg/kg of desipramine twice per day, or three daily electroconvulsive shocks (ECS). Yoked controls underwent sham procedures, but received no treatment. On the fourth day, the rats were given a 5-min, videotaped swim test. A blinded observer used the videotape to calculate the percentage of time that the rats were immobile (an index of depression) during the swim test. VNS significantly reduced immobility time as compared to unstimulated controls, indicating good antidepressant efficacy. This reduction did not differ statistically from that obtained from rats treated with either desipramine or ECS, two standard antidepressant treatments. These results indicate that VNS is an effective antidepressant in the forced-swim test, allowing us to now investigate possible therapeutic mechanisms.