Tactile skin stimulation increases dopamine release in the nucleus accumbens in rats

We investigated the effect of mild (non-noxious) tactile stimulation (stroking) of skin on dopamine (DA) release in the nucleus accumbens (NAc) of rats. A coaxial microdialysis probe was stereotaxically implanted in the NAc and perfused with modified Ringer's solution. Dialysate output from consecutive 5-min periods was injected into a high-performance liquid chromatograph and DA was measured using an electrochemical detector. Bilateral tactile stimulation of the back for 5 min significantly increased DA release in conscious and anesthetized animals. Increased DA release was observed by stimulation of the contralateral, but not ipsilateral, back. DA secretion was also increased with stimulation of the forelimb, hindlimb, and abdomen. These effects were abolished after lesioning the ventral tegmental area (VTA). In contrast, noxious stimulation (pinching) of these areas had no effect on DA secretion. In conclusion, innocuous mechanical stimulation of the skin increases DA release in the contralateral NAc via the VTA.