Tertiapin blunts the analgesic effect of high-dose morphine in wild-type mice. The analgesic effect of morphine (0, 0.1, 0.3, 1, and 3 nmol) coadministered intrathecally with either saline (white circles) or 30 pmol of tertiapin (black circles) was measured in wild-type mice. Preinjection and postinjection tail-flick latencies were measured at 49°C (A), 52.5°C (B), and 55°C (C), and normalized ΔTF latency (nΔTF latency) was calculated as described (see Materials and Methods). Separate cohorts of mice were used for each drug condition. Groups were balanced with respect to gender, and sizes ranged from 11 to 16 mice per drug condition. *p < 0.05, tertiapin versus saline; **p < 0.05, 3 versus 1 nmol of morphine.