Association between the cannabinoid receptor gene (CNR1) and the P300 event-related potential

In our prior study we observed a significant association between homozygosity for the greater than or equal to 5 alleles of a microsatellite polymorphism of cannabinoid receptor gene (CNR1) and drug dependence. Decreased amplitude of the P300 wave of evoked related potentials (ERP) has long been shown to be associated with alcohol and drug dependence. The P300 wave reflects attentional resource allocation and active working memory. Since marijuana intoxication has a potent blocking effect on short-term memory we examined the association between the CNR1 alleles and the P300 wave amplitude at three electrodes in 35 alcohol and drug addicts, by MANOVA. There was a significant decrease in amplitude of the P300 wave for all three electrodes (P = 0.028) that was most marked for the frontal lobes (P = 0.008) in subjects homozygous for the CNR1 greater than or equal to 5 repeat alleles. Multivariate regression analysis indicated the CNR1 gene contributed to 20% of the variance of the frontal lobe P300 wave amplitude.