Changes in intracranial self-stimulation (ICSS) threshold for quinpirole (QNP)-treated rats and controls. Changes in ICSS thresholds (expressed as percentage of pre-drug values) following the injection of 0.05 mg/kg haloperidol (highHalo), 0.01 mg/kg haloperidol (lowHalo), saline, 0.1 mg/kg d-amphetamine (lowAmph) or 0.5 mg/kg d-amphetamine (highAmph). (a) Animals from both groups (QNP: n = 9; control: n = 9) demonstrate slight increases of stimulation thresholds after lowHalo, saline and even lowAmph treatment, which is most probably due to high activity in the time preceding the ICSS tests. Consequently, threshold shifts were normalized for each rat's individual shift in the saline condition. (b) QNP-treated animals demonstrate a stronger response to an effective dose of d-amphetamine than controls. Error bars represent s.e.m.