The effect of peripheral GABAA receptor activation on pain and sensitivity in healthy human subjects has never been investigated. However, as earlier studies suggest that activation of peripheral GABAA receptors is anti-nociceptive in rats, it is important to determine if these findings can be translated into human subjects to determine if peripheral GABAA receptors are a viable target for future analgesic drug development.

Subproject I This study will test if oral administration of GABA containing solutions will reduce the pain and sensitivity induced by application of capsaicin to the tongue of healthy human subjects. Thirty, pain-free men (n=15) and women (n=15) for the oral cavity study.

Subproject II This study will test the hypothesis that intramuscular injection of GABA alone will not be painful, but will reduce muscle pain sensitivity in healthy human subjects. Thirty, pain-free men (n=15) and women (n=15) will be recruited for the intramuscular GABA injection studies

Subproject III This study will test the hypothesis that intramuscular injection of GABA with glutamate will decrease the intensity of glutamate-evoked muscle pain in healthy human subjects. Thirty, pain-free men (n=15) and women (n=15) will be recruited for the intramuscular glutamate and GABA injection studies.

Inclusion Criteria:

• Aged 20-40 years
• Free from ongoing or chronic pain
• Adequate conversational English

Exclusion Criteria:

• Pregnancy or intent to become pregnant, breast feeding
• Signs or symptoms of any serious systemic diseases
• Current malignancies
• High blood pressure
• Requirement for chronic administration of psychiatric, analgesic or other medications that might influence their response to pain
• Frequent recreational drug or alcohol use
• Previous neurologic, musculoskeletal or mental illnesses
• Lack of ability to cooperate