TPH2 and major depressive disorder: Therefore, future directions include focusing on wild-type animals and conducting a thorough analysis of metabolic fluctuations in tryptophan (including its conversion to the kynurenine pathway), Tph2 expression, its enzymatic activity, 5-HT levels, its metabolism, release and reuptake, and 5-HT2C receptor editing during different phases of ethanol consumption, with particular emphasis on early and long-term abstinence (assessment of other depression symptoms), as well as relapse-like behavior.