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Association between human mu-opioid receptor gene polymorphism, pain tolerance, and opioid addiction
Peggy Compton1, Daniel H Geschwind, Maricela Alarcón
1Acute Care Section, UCLA School of Nursing, Los Angeles, California 90095-6918, USA. pcompton@sonnet.ucla.edu
Abstract:
Central to both pain responses and opioid addiction is activity at the micro -opioid receptor. To explore the role of the micro -opioid receptor gene (OPRM) in human pain tolerance and opioid addiction, we examined the relationships among OPRM genotype and experimental pain tolerance in opioid addicts in methadone treatment (n = 50) and healthy normal controls (n = 59). Pain phenotype (pain tolerant vs. pain intolerant) was operationalized as tolerance to a standardized noxious stimulus (either thermal or mechanical), and dichotomized based on distribution. One microsatellite and two single nucleotide polymorphisms, A118G and C17T, in exon 1 were typed to study the OPRM gene. Although the established relationship between the phenotypes of opioid addiction and pain intolerance was validated (P = 0.02), genotype differed neither between addict-affected vs. control, nor pain tolerant vs. intolerant subjects. The variant A118G was absent in all individuals and the C17T polymorphism appeared in only three African-American individuals (two addicts and one control). The absence of this polymorphism, the small sample size and the heterogeneous ethnic backgrounds of participants in the pilot study allow only tentative conclusions based on the results, thus the role of the opioid receptor in pain and opioid reward response remains uncertain.
Insights
The micro-opioid receptor gene (OPRM) was studied in relation to pain tolerance and opioid addiction. No significant genetic differences were found, suggesting the OPRM gene
Area of Science:
- Neuroscience
- Genetics
- Pharmacology
Background:
- The micro-opioid receptor is central to pain perception and opioid addiction.
- Understanding the genetic underpinnings of the micro-opioid receptor gene (OPRM) is crucial for pain and addiction research.
Purpose of the Study:
- To investigate the association between OPRM gene variations and experimental pain tolerance.
- To explore the role of OPRM genotype in individuals with opioid addiction undergoing methadone treatment compared to healthy controls.
Main Methods:
- Genotyping of OPRM gene polymorphisms (microsatellite, A118G, C17T) in 50 opioid addicts and 59 healthy controls.
- Assessment of experimental pain tolerance using standardized thermal or mechanical noxious stimuli.
- Phenotyping of pain tolerance (tolerant vs. intolerant) and opioid addiction status.
Main Results:
- The established link between opioid addiction and pain intolerance was confirmed (P = 0.02).
- No significant differences in OPRM genotype were observed between addicts and controls, or between pain-tolerant and pain-intolerant subjects.
- The A118G variant was absent; C17T polymorphism was rare and observed only in three individuals.
Conclusions:
- The pilot study did not find a direct association between the examined OPRM gene polymorphisms and pain tolerance or opioid addiction.
- Limitations including small sample size, absence of key polymorphisms, and ethnic heterogeneity preclude definitive conclusions.
- The precise role of the OPRM gene in pain and opioid reward pathways requires further investigation.