Insulin affects dopamine overflow in the nucleus accumbens and the striatum

To better characterize the central nervous system response to peripheral in sulin administration, male Sprague-Dawley rats were fitted with microdialys is probes in the nucleus accumbens (NAC; n = 23) and striatum (STR; n = 22) . Awake intact rats were injected with either 0, 200, 400, or 600 mU regula r insulin i.p. Dopamine overflow was measured for at least 2 h postinjectio n. In the NAG, four postinjection samples were collected once every 30 min. In the STR, eight postinjection samples were collected, once every 20 min. Dopamine baselines in the NAC and STR were 9.22 pg +/- 2.02 and 10.33 pg /- 2.22 per sample, respectively. In the nucleus accumbens, dopamine releas e was significantly greater in the group treated with 600mU insulin (203 +/ - 38% of baseline at 30 min). In the STR, increased dopamine release was ob served in the groups treated with 200 and 400 mU insulin, whereas a suppres sion of a dopamine release was observed in the group treated with 600 mU. T hese data demonstrate that the metabolic state induced by peripheral insuli n injection causes dopamine metabolism to change in both the NAC and STR, a nd at least in part support the hypothesis that insulin may have reinforcin g properties in its effect on NAC dopamine release. (C) 1999 Elsevier Scien ce Inc.