Fig 1: Knock-down of CB2R expression by siRNA increases the sensitivity to cisplatin-induced hearing loss. (A) Rats were administered either scramble siRNA (0.9 µg) or increasing doses of CB2R siRNA (0.3, 0.6, and 0.9 µg) by trans-tympanic injections. The animals were sacrificed 48 h later and mRNA was assessed for CB2R expression by real-time RT-PCR. CB2R siRNA knocked down CB2R gene expression by ~50 and ~80% using 0.6 µg and 0.9 µg, respectively. Data are represented as % expression ± SEM (n = 3). *p < 0.05 vs. scramble siRNA and **p < 0.05 vs. CB2R siRNA 0.6 µg. (B) Baseline ABR was recorded in rats administered with either a scramble siRNA or CB2R siRNA by trans-tympanic injections for 48 h. Cisplatin (11 mg/kg, i.p.) was then administered and post-ABR was recorded 72 h later. There was no significant change in ABR threshold shift in the animals treated with scramble siRNA or CB2R siRNA alone. Pre-treatment with CB2 siRNA (0.9 µg) followed by cisplatin significantly potentiated cisplatin-induced hearing loss at 8 and 16 kHz. Data are represented as mean ± SEM. *p < 0.05 vs. scramble siRNA and **p < 0.05 vs. cisplatin (n = 6, one-way ANOVA).