Tail Flick Test

The mouse tail flick test was performed as described in our earlier work,²² with 52°C water and a 10 second cutoff time to prevent tissue damage. SRI-22141 (0.32-10 mg/kg) or morphine (10 mg/kg) was delivered by the subcutaneous (sc) route and tail flick latencies recorded over a time course. For a subset of experiments, naloxone was delivered by the intraperitoneal (30 mg/kg, ip), intrathecal (10 nmol, it), or intracerebroventricular (10 nmol, icv) route, or naltrindole (10 mg/kg) by the ip route, prior to SRI-22141 injection by the sc route and measurement as above. The procedures for it and icv injections are described in ²².