μ-opioid receptor binding potential
may be higher with increasing age and in women [33]. Moreover, in one human experimental
study, region-specific differences in OPRM1 levels between individuals with AA and G
alleles have been demonstrated [34]. Additionally, the OPRM1 genotype may influence stress
responses, immune and pro-inflammatory responses [21,35-37], and reactivity to social
rejection [27]. Also, acute and chronic stress has been suggested to affect available μ-opioid
receptor pools in GABAergic interneurons differentially in female and male rats [38]. Exactly
how this happens is not fully understood.