An extensive amount of studies indicate that conditioned pain modulation (CPM) test paradigms can be of use to evaluate the efficacy of the endogenous pain inhibition pathway in healthy controls and pain patients. A number of studies indicate that the autonomic nervous system (ANS) responds to painful stimulation by parasympathetic activity withdrawal and up-regulation of sympathetic activity (flight-or-fight mode), but it remains unknown whether these responses predict individual pain susceptibility or CPM efficacy and whether different pain modalities evoke different physiological stress responses, i.e. do individuals with low pain tolerance exhibit more vigorous ANS responses when subjected to controlled acute pain stimuli, and do high ANS responsiveness to pain coincide with altered psychophysical pain levels/CPM efficacy.

This study aims to investigate the effect of ANS responsiveness on CPM paradigms and to investigate if an exogenous, pharmaceutically induced decrease in the sympathetic drive of the ANS will yield decreased CPM efficacy.

Inclusion Criteria:

• Healthy subjects

Exclusion Criteria:

• Drug addiction defined as the use of cannabis, opioids or other drugs
• Previous history of neurologic, musculoskeletal, mental illnesses or a chronic pain condition
• Lack of ability to cooperate
• Current use of medications that may affect the trial, e.g., analgesics, anti-inflammatory drugs
• Consumption of alcohol, caffeine, nicotine or painkillers the morning and until termination of the study on the study day
• Recent history of acute pain affecting the lower limb
• Participation in other pain trials throughout the study period
• Known diagnosis of cardio vascular diseases (low blood pressure, heart conditions)
• Asthma
• Decreased function of liver and kidneys
• Diabetes