Insulin and raclopride combine to decrease short-term intake of sucrose solutions

We have previously reported that the hormone insulin can modulate synaptic function of dopamine neurons. To evaluate whether insulin can alter performance of a task which is dependent on intact dopaminergic signaling, we tested rats in a five minute lick rate task, with a range of concentrations of sucrose or oil solutions. Rats received either ip (t - 15 min) saline or the D2 receptor antagonist raclopride (50 mug/kg), and intraventricular (t - 4 h) saline or insulin (5 mU). Although ineffective on its own, insulin combined with raclopride treatment resulted in significant suppression of sucrose lick rates compared to the saline/saline group. The overall results are consistent with our hypothesis that insulin may modify performance in tasks that are dependent on dopaminergic signaling. (C) 2000 Elsevier Science Inc. All rights reserved.