Effect of PDE inhibitors on the duration of anesthesia induced by the combination of xylazine (10 mg/kg) and ketamine (80 mg/kg) in C57BL/6 mice. Fifteen minutes after the induction of anesthesia, mice were injected with (a) increasing doses of vinpocetine (PDE1 inhibitor; n = 5 per dose), EHNA (PDE2 inhibitor; n = 4–8 per dose), milrinone (PDE3 inhibitor; n = 2–6 per dose), PMNPQ (PDE4 inhibitor; n = 5 per dose), dipyridamole (PDE5/6/9/10/11 inhibitor; n = 4–5 per dose) or vehicle (PEG 60%; n = 34); or (b) increasing doses of PMNPQ, (R)-rolipram, (S)-rolipram, CT-2450 (n = 5 per dose tested), or vehicle (PEG 60%; n = 34). The duration of anesthesia was assessed by the return of the righting reflex. Results are expressed as mean ± SEM. *Significantly different from vehicle group at P < 0.05.