PTGS2 and major depressive disorder: In studies conducted in a lipopolysaccharide-induced murine model of depression, it was demonstrated that lipopolysaccharides (LPS) activated the NF-κB factor in the prefrontal cortex and induced expression of nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2); these activities were normalized after prior administration of HCE.