OPRK1 and major depressive disorder: Other post-mortem findings have identified elevated prodynorphin mRNA in the caudate nucleus of suicide victims as compared to healthy volunteers; [64] lower prodynorphin mRNA levels in the amygdala among subjects with MDD and bipolar disorder compared to controls; [65] and no difference in prodynorphin or KOR mRNA between patients with major depressive disorder and healthy volunteers [66].