CPP morphine preference scores preceding euthanasia.

<p>Mean S+ chamber preference scores (±SEM) during the last 4 preference tests (actual days in brackets) prior to euthanasia (Day −1(1)) in normal (Control) and tumour bearing (Cancer) groups conditioned to Saline or Morphine (2 mg/kg; s/c). Scores above 0.5 indicate an enhanced S+ chamber preference. Note especially the cancer mice conditioned to morphine show enhanced morphine seeking (higher CPP S+ score) than either the saline or tumour control groups (p = 0.005; p<0.001, respectively), but from days −7 to −1 prior to euthanasia their morphine chamber preference also significantly exceeded the morphine preference of controls conditioned to morphine (p = 0.02).