Figure 3.

Cyclic tetrapeptide induced antinociception is opioid-receptor mediated. Peak antinociceptive activity of peptides 2 (3 nmol), 3 (10 nmol), 4 (0.3 nmol) and 5 (30 nmol) was determined in the 55°C warm-water tail-withdrawal assay after i.c.v. administration to C57Bl/6J mice (open bars). Naloxone pretreatment (15 nmol i.c.v., striped bars) 25 min prior to peptide administration significantly antagonized the effect of each cyclic tetrapeptide. Tail-withdrawal latencies were measured 30 minutes after injection of the cyclic tetrapeptide. Data represents average % antinociception ± SEM from 7-8 mice. *=significantly different from response of matching administered compound alone, p<0.05, One-way ANOVA followed by Tukey’s HSD post hoc test.