• Nociceptive threshold evaluated with sternal electronical Von Frey mechanical stimulation. The stimulation will increase until the volunteer presses a trigger when the stimulation becomes painful. [ Time Frame: 5 min after injection, and every 15 min during 1 hour ] [ Designated as safety issue: No ]
  

• Non invasive blood pressure (SBP, DBP), heart rate, respiratory rate, pulse oxymetry and cognitive functions evaluation (sedation score). [ Time Frame: all along the experimentation ] [ Designated as safety issue: Yes ]
  

• Principal Objective : "Evaluate fentanyl "ultra low doses" effects on human volunteer's nociceptive threshold depending on their prior pain and opioid experience."
• Secondary Objective : "Confirm the innocuousness of this test (the 3 "ultra low doses" used in this trial will be 10 to 1,000 fold lower than low doses use for anesthesia and analgesia) and to find the fentanyl ultra low dose that could be used to develop a pain sensitisation predictive test."
• Study design : Bicentric, prospective, randomized, double-blind study.

Inclusion criteria :

In both groups:

• 18-40 years old male volunteer
• weight: 60 to 85 kg
• ASA score: 1
• Informed consent obtained from the patient
• Gender : Male

In "operated" group:

- At least one history of peripheral surgery under general anesthesia with opioid in the past five years

Exclusion criteria :

In both groups:

• The patient do not accept inclusion to the study
• Drug or alcohol abuse history
• Chronic use of analgesic drugs or history of chronic pain
• Analgesic or opioid consumption within the 12hs preceding the fentanyl or placebo injection
• Neurological and/or psychiatric disorder, inability to give informed consent
• Psychological trauma within the two year preceding the inclusion
• Any contraindication to fentanyl use
• Use of any medication interacting with fentanyl
• Exclusion period from the national healthy volunteer register
• Gender : Female

In "healthy" group:

- Any history of general anesthesia or surgery

• Study plan: comparing two groups that only defer by their surgical and opioid prior experience and will receive three fentanyl ultra low doses (10 to 1,000 fold lower than low doses use for anesthesia and analgesia) and placebo (cross over administration, one week wash out period).
• Number of subjects : 48