This study will examine how the brain processes pain signals and how the different parts of the brain work with each other in response to painful stimuli. A better understanding of how people experience pain may be helpful in developing more effective treatments.

Healthy normal volunteers, patients requiring third molar (wisdom tooth) extraction, and patients with persistent pain due to disease, injury or other reason may be eligible for this study.

Participants will receive one or more of the following sensory stimuli, which may cause brief discomfort or pain:

- Heat/Cold - applied by an electronically controlled device that touches the skin, or by temperature-controlled water baths, or by a thermally controlled brass cylinder the subject grasps

- Capsaicin (active ingredient in hot chili peppers) - injected in a small volume of fluid under the skin or into a muscle

- Mechanical stimulation - brushings or vibrations that do not normally cause pain

- Ischemic stimulation - inflation of a blood pressure cuff on the arm or leg for up to 30 minutes

These stimuli will be applied both before and during positron emission tomography (PET) scanning. This test shows which parts of the brain are active and which are not and is important for studying how different parts of the brain work together to feel and react to specific sensations. For this procedure, the subject lies on a table in the PET scanner while a series of scans are taken during different sensory conditions. At the beginning of each scan, radioactive water is injected into an arm vein through a catheter (a thin plastic tube). A special camera records the arrival and disappearance of the radiation in various brain areas, creating a picture of the brain's activity in various regions. Oral surgery patients may have PET scans both before and after their wisdom tooth extraction. Alfentanil, a commonly used narcotic pain reliever, will also be given during the PET procedure to determine how the brain responds to sensory stimuli while under the effects of a pain killer.

Participants will also have a magnetic resonance imaging (MRI) scan of the brain to help interpret the PET results. MRI uses a magnetic field and radio waves to show structural and chemical changes in tissues. During the scan, the subject lies on a table in a cylindrical machine (the scanner). He or she can speak with a staff member via an intercom system.

Some sensory studies may require placing an arterial and/or intravenous line. Following injection of a local anesthetic, a catheter is placed in an artery in the arm. At regular intervals during various sensory stimuli, small blood samples are drawn from the artery to measure blood gases and other substances. Samples may also be drawn from a catheter placed in a vein.

Subjects may also have ultrasound monitoring to evaluate blood flow in the arteries, veins and brain. A gel is spread over the skin above the blood vessel and a hand-foot-and-mouth device is placed on the gel. The device emits high-frequency sound waves to produce a picture of the speed of blood flow in the artery and the diameter of the vessel.

Condition	Treatment or Intervention
Healthy Hyperalgesia Pain Peripheral Nervous System Disease	Drug: Oxygen-15 Water  Drug: Capsaicin

Regional cerebral blood flow (rCBF) will be measured while normal subjects, patients with post-operative pain, and patients with neuropathic abnormalities of pain sensation are exposed to a battery of somatosensory stimuli that activate known pathways subserving touch, temperature and pain sensations. Patients with reflex sympathetic dystrophy and other abnormalities that cause persistent pain, hyperalgesia or allodynia (pain sensation to a normally non-noxious stimulus) will be examined with and without applied experimental stimuli. Data from the patients groups will be compared to those of normal controls. In addition, an ultra-short-acting opioid analgesic will be administered to normals and select patients in order to map opioid-dependent modifications of pain-induced neural activity. Activation of several somatosensory modalities in conjunction with high resolution positron emission tomography (PET), adjunctive structural imaging with magnetic resonance imaging (MRI) and analgesic drug manipulations will functionally, anatomically, and pharmacologically characterize the physiology and pathophysiology of nociceptive in human beings.

Genders Eligible for Study:  Both

Accepts Healthy Volunteers

Criteria

INCLUSION CRITERIA
Healthy Normal Volunteers between the ages of 18 and 80 years
Certain Chronic Pain Patients
EXCLUSION CRITERIA
Structural or Functional Brain Defects
Metallic Surgical Implants
Chronic Drug Treatments

Maryland
      National Institute of Dental And Craniofacial Research (NIDCR), 9000 Rockville Pike,  Bethesda,  Maryland,  20892,  United States; Recruiting

Study ID Numbers:  920243; 92-D-0243
Record last reviewed:  July 21, 2004
Last Updated:  July 21, 2004
Record first received:  November 3, 1999
ClinicalTrials.gov Identifier:  NCT00001307
Health Authority: United States: Federal Government
ClinicalTrials.gov processed this record on 2004-11-08