Effects of desipramine and chlorimipramine on buprenorphine analgesia in mice.

The effects of the tricyclic antidepressants desipramine HCI and chlorimipramine HCI on buprenorphine HCI antinociceptive activity were studied in mice using the hot-plate and the tail-flick methods. In the hot-plate test, desipramine caused a transient antinociceptive effect at low doses, but it decreased buprenorphine analgesia. Chlorimipramine in this test caused a more sustained antinociceptive effect, especially at relatively higher doses, and it did not significantly change buprenorphine analgesia. In the tail-flick test, desipramine either reduced or increased the tail-flick latency in a dose-specific manner, and chlorimipramine (10 mg/kg) significantly increased the tail-flick latency. Desipramine (1 mg/kg) caused a decrease followed by an increase in buprenorphine analgesia. Desipramine (5 and 10 mg/kg) caused significant increases in buprenorphine analgesia. All doses of chlorimipramine (1, 5 and 10 mg/kg) caused significant increases in buprenorphine analgesia. Thus, depending on the test employed, buprenorphine analgesia was modified differently by these tricyclics. Biochemical data suggested a greater role for brain 5-hydroxytryptamine (5-HT) than noradrenaline in tricyclic analgesia.