PLCB1 and major depressive disorder: Treatment with antidepressants has also been shown to decrease levels of PLCB1 activity and expression in the rat cortex and hippocampus,36 yet we saw no difference in PLCB1 levels in CNS tissue from subjects with MDD or BD, many of whom were on antidepressant treatment regimes, suggesting that the rat and human CNS may respond differently to antipsychotic and antidepressant treatments.