Morphine in changing dosages (range between 10-60 mg twice a day). Opioid titration proceeds as follows: starting at an oral dose of 10 mg twice per day, followed every 5 days by a dose increase of 10 mg twice per day until (1) adequate analgesia had been achieved (as determined by the patients), (2) side effects (severe sedation, nausea or vomiting, constipation, sleep disturbances) limited further titration, or (3) a total of 120 mg per day had been reached.

Milnacipran (Ixel)- a serotonin-norepinephrine reuptake inhibitor (SNRI), will be administrated in changing dosages (range between 12.5-75 mg twice daily). SNRI titration proceeds as follows: starting at an oral dose of 12.5 mg twice per day, followed every 5 days by a dose increase of 12.5 mg twice per day until (1) adequate analgesia had been achieved (as determined by the patients), (2) side effects (severe sedation, nausea or vomiting, constipation, sleep disturbances) limited further titration, or (3) a total of 150 mg per day had been reached.

Heat pain sensitivity will be determined by the use of VAS units (0-100). We'll measure the intensity of pain in response to application of brief experimental heat pain.