The effects of GAL-021 infusion on morphine-induced analgesia in rats. The analgesic effects of morphine and GAL-021 were assessed using the tail-flick latency test. The latency to flick the tail in response to a thermal stimulus was measured before and at fixed time points after starting morphine (1.5 mg/kg IV, bolus) and vehicle, GAL-021 (0.3 mg kg⁻¹ min⁻¹, 60 min, IV), and simultaneous morphine (1.5 mg/kg IV, bolus) + GAL-021 (0.3 mg kg⁻¹ min⁻¹, 60 min, IV) infusion. Morphine increased tail-flick latencies, and this effect persisted for 45-min post-injection. GAL-021 infusion alone had no effect on tail-flick latencies. However, in combination, GAL-021 and morphine elicited analgesia of longer duration compared with morphine alone. ^*Different from GAL-021 alone; ^†different from morphine and vehicle infusion (two-way ANOVA with Bonferroni multiple comparisons test, P < 0.05). Values are means ± SD, n = 6 per group.