Circulating Glutamate/Anandamide ratio differs after 30 minutes arm-cycling in chronic pain subjects compared with healthy controls 

Niclas Stensson1, Anna Grimby-Ekman2
1 Pain and Rehabilitation Centre, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
2 Health Metrics unit, Public health and community medicine, Sahlgrenska Academy
Background and aims
The acute biochemical effect of physical exercise during chronic pain conditions are not fully understood. However, the endocannabinoid system has been suggested to play a role exercise-induced reward and pain inhibition. 
Altered glutamate levels, but also normalized levels, has been reported after physical exercise programs in chronic pain conditions. Moreover a linkage between the endocannabinoid system and glutamatergic pathways has been suggested.  
The aim of this study was to examine the effect of 30 minutes of dynamic load arm-cycling on levels of lipid mediators related to the endocannabinoid system and glutamate, in plasma from chronic pain subjects and controls. 
Methods 
Pain assessments and plasma levels of arachidonoylethanolamide (Anandamide) and 2-aracidonoylglycerol, oleoylethanolamide, palmitoylethanolamide, stearoylethanolamide, and glutamate from 21 subjects with chronic neck pain (chronic pain group) and 11 controls were analysed pre and post a 30 minute dynamic load arm-cycling intervention. 
Results
Pain intensity was significantly different between groups pre and post exercise. Anandamide levels were significantly decreased in controls, but not in the chronic pain group post exercise. Correlation existed between anandamide and glutamate in control group post exercise, and in the chronic pain group pre exercise. Moreover, a statistically significant increase in the glutamate/anandamide ratio existed in controls compared with the chronic pain group.
Conclusion
The glutamate/anandamide ratio increased significantly post exercise in controls, which resulted in a significant difference between groups post exercise. This might reflect an altered relationship between glutamate and anandamide on systemic level in chronic pain, which needs to be further investigated.

CIRCULATING GLUTAMATE/ANANDAMIDE RATIO DIFFERS AFTER 30 MINUTES ARM-CYCLING IN CHRONIC PAIN SUBJECTS COMPARED WITH HEALTHY CONTROLS