The purpose of this study is to further understand the pharmacology of analgesia to intractable pain states in the human which will hopefully spur drug development in this area. This protocol will determine the effect of acute intrathecal bolus administration of adenosine on response to intradermal capsaicin over time. Adenosine is a naturally occurring neurotransmitter known to be released spinally to produce analgesia. Adenosine and adenosine agonists are highly effective in animal models of neuropathic and inflammatory pain against which standard analgesics are often ineffective. A similar formulation of adenosine which is marketed in Sweden has undergone preclinical toxicity screening, Phase I trials, and is in early Phase II study by a physician investigator there, and initial results show efficacy in patients with neuropathic pain. In this trial of spinal administration of adenosine we will study 40 healthy volunteers. Both male and females will be studied. The volunteer will be trained to estimate pain quantitatively using a Peltier thermode applied to the skin of the arm and leg. Typically, the volunteer is exposed to random thermode temperatures between 38 and 51 degrees Celcius, and the volunteer asked to report the perceived pain in a numerical scoring system of his choice. We will then inject the intradermal (i.d.) capsaicin and ask the volunteer to rate his pain and we will measure his response to capsaicin. We will then adminsiter an intrathecal bolus administration of adenosine and measure it's effect on response to intradermal capsaicin over time.
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