Tph2, also known as tryptophan hydroxylase 2, is the rate-limiting enzyme in brain serotonin synthesis. Serotonin is involved in numerous physiological, behavioral, and cognitive processes, and Tph2's role in its synthesis makes it biologically significant. Animal models generated by genetic manipulation of Tph2 have been crucial in understanding serotonergic neurotransmission [4].

In Tph2-deficient mice (Tph2 -/-), ethanol consumption increased, suggesting central 5-HT, synthesized by Tph2, modulates drinking behavior [1]. Adult-onset TPH2 deletion in the dorsal Raphe nuclei (DRN) of male mice led to hyperphagia and weight gain, while in females, it affected responses to estrogen-related appetite regulation, indicating a sex-dependent role in energy balance [2]. Also, deletion of TLR4 in Tph2 neurons decreased anxiety-like behaviors in male mice, showing a sex-specific modulation of anxiety-related behaviors [3]. In TPH2-R439H mice (a model with a mutation analogous to that in severely depressed individuals), there were defects in enteric nervous system (ENS) development and gastrointestinal (GI) motility due to reduced 5-HT release from enteric neurons, and Tph2 CKO in APP/PS1 mice increased amyloid plaque load and astrogliosis [5,6].

In conclusion, Tph2 plays essential roles in multiple biological processes. Through gene-knockout and related mouse models, it has been shown to be involved in alcohol-related behaviors, energy balance regulation, anxiety-related behaviors, ENS development, GI motility, and Alzheimer's-related amyloid plaque formation. These findings contribute to understanding the underlying mechanisms of related diseases and biological functions [1,2,3,5,6].