Fig. 5. Ondansetron (OND) down-regulates morphine-augmented messenger RNA expression in dorsal root ganglia. Mice were treated with saline, morphine, or morphine plus OND during the 4-day treatment protocol. CGRP =α-calcitonin gene-related peptide; PPTA = preprotachykinin-A; NR1 = N-methyl-d-aspartate receptor-1; TRPV1 = transient receptor potential vanilloid-1; ADRB2 =β2-adrenergic receptor; 5-HT3AR = 5-hydroxytryptamine receptor subunit type 3A. Data are presented as mean ± SEM; *P < 0.05; **P < 0.01. Five mice were used in each group.