Effect of MK-912 and PMNPQ on the duration of anesthesia induced by the combination of xylazine (10 mg/kg) and ketamine (80 mg/kg) in PDE4D-deficient (a) and PDE4B-deficient (b) mice (–/–) and their littermates (wild-type, +/+; heterozygote, +/–). Fifteen minutes after the induction of anesthesia, mice were injected with MK-912 (1 mg/kg, subcutaneously), PMNPQ (0.3 mg/kg, subcutaneously), or vehicle (PEG 60%). The duration of anesthesia was assessed by the return of the righting reflex. Results are expressed as mean ± SEM. *Significantly different at P < 0.05.