CX3CL1 and bipolar disorder: Moreover, a quantitative assessment of fractalkine and CX3CR1 using immunoblotting and polymerase chain reaction (PCR) on post-mortem brain samples from individuals diagnosed with either SZ or bipolar disorder and their age-matched non-psychiatric controls revealed a significant reduction in levels of fractalkine in the prefrontal cortex of individuals with SZ compared to both the bipolar disorder and control groups.