Complex sentence: Inflammatory pathways may also inhibit serotonin activity through a pathway called the "TRYCAT" pathway (tryptophan catabolites), in which the catabolites of tryptophan inhibit serotonin synthesis and deplete tryptophan resulting in CFS symptoms.
Split into simpler sentences: Inflammatory pathways may also inhibit serotonin activity through a pathway called the "TRYCAT" pathway (tryptophan catabolites). Catabolites of tryptophan may inhibit serotonin synthesis and deplete tryptophan resulting in CFS symptoms.