Expression of NMDA receptor subunits in human peripheral blood lymphocytes in opioid addiction

Glutamate receptors especially the N-methyl-d-aspartate (NMDA)-activated ones have a key role in the development and maintenance of opioid addiction. It has been proposed that the neurotransmitter receptors expression in peripheral blood lymphocytes may be parallel to their expression state in the brain. This study was designed to evaluate the possibility of using the mRNA expression state of NR2A and NR3A subunits of NMDA receptors in human peripheral blood lymphocytes as a peripheral marker in opioid addiction studies. Four groups, each comprising of 20 male individuals participated in the study: opioid addicts, methadone maintained patients, long-term abstinent former opioid addicts, and non-addicted control subjects. Real-time PCR method was used to investigate the mRNA expression level of NR2A and NR3A subunits of NMDA receptors in peripheral blood lymphocytes of all groups. Our data indicated that the mRNA expression of NR2A subunit of NMDA receptors in all three test groups was not statistically different from control subjects. However, the NR3A subunit expression was significantly down-regulated in abstinent subjects reaching 0.14 the amount of the control group. The expression of NR3A subunit was not significantly changed in addicted and methadone maintained individuals in comparison to control subjects. It is concluded that the deficiency in expression of NR3A subunit of NMDA glutamate receptors detected by a peripheral marker may be a risk factor making individuals vulnerable for opioid addiction.