Genetic Disruption of Both Tryptophan Hydroxylase Genes Dramatically Reduces Serotonin and Affects Behavior in Models Sensitive to Antidepressants

Katerina V Savelieva,Indrani Rajan,Thomas H Lanthorn,Emily Cullinan,Qi Yang,Shulei Zhao,Vladimir M Pogorelov,Alessandro Bartolomucci

doi:10.1371/journal.pone.0003301

Katerina V Savelieva, Indrani Rajan + Show 6 more

Open Access

https://doi.org/10.1371/journal.pone.0003301

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Journal: PloS one	Publication Date: Oct 15, 2008
Citations: 278	License type: CC BY 4.0

Affiliation: Lexicon Pharmaceuticals (United States)

Abstract

The neurotransmitter serotonin (5-HT) plays an important role in both the peripheral and central nervous systems. The biosynthesis of serotonin is regulated by two rate-limiting enzymes, tryptophan hydroxylase-1 and -2 (TPH1 and TPH2). We used a gene-targeting approach to generate mice with selective and complete elimination of the two known TPH isoforms. This resulted in dramatically reduced central 5-HT levels in Tph2 knockout (TPH2KO) and Tph1/Tph2 double knockout (DKO) mice; and substantially reduced peripheral 5-HT levels in DKO, but not TPH2KO mice. Therefore, differential expression of the two isoforms of TPH was reflected in corresponding depletion of 5-HT content in the brain and periphery. Surprisingly, despite the prominent and evolutionarily ancient role that 5-HT plays in both vertebrate and invertebrate physiology, none of these mutations resulted in an overt phenotype. TPH2KO and DKO mice were viable and normal in appearance. Behavioral alterations in assays with predictive validity for antidepressants were among the very few phenotypes uncovered. These behavioral changes were subtle in the TPH2KO mice; they were enhanced in the DKO mice. Herein, we confirm findings from prior descriptions of TPH1 knockout mice and present the first reported phenotypic evaluations of Tph2 and Tph1/Tph2 knockout mice. The behavioral effects observed in the TPH2 KO and DKO mice strongly confirm the role of 5-HT and its synthetic enzymes in the etiology and treatment of affective disorders.

Highlights

The neurotransmitter serotonin (5-HT) has been implicated in a variety of physiological functions in both the peripheral and central nervous systems
G418/FIAU resistant ESC clones for Tph1 deletion were analyzed by southern hybridization of SpeI (s) digested genomic DNA blot with a 244 bp 59 external probe (Fig. 1A) generated using: 59GCT CTT CTA AAA CGT CCA GTA G 39 and 59GTC TGA GTA AGA TTA AAC AAT CCG 39 as primer pairs
Results from testing Tph2 knockout (TPH2KO) mice in the open field (OF) revealed that total distance traveled did not differ between KO and wild type (WT) mice (Fig. 2A)

Summary

Introduction

The neurotransmitter serotonin (5-HT) has been implicated in a variety of physiological functions in both the peripheral and central nervous systems. Serotonin is an important modulator of the gastrointestinal system via the enteric nervous system [7]. Given the wide range of functions that it modulates, one might expect the depletion of 5-HT to have serious consequences for development and maintenance of viability: some evidence exists that peripheral serotonin is important for proper embryonic development [8]. Impaired or altered 5-HT neurotransmission appears to be a central dysfunction leading to depressive and anxiety symptoms. A number of primary therapeutics for depression, anxiety, and some neurological conditions, such as emesis and irritable bowel syndrome, affect the activity of the 5-HT system [15,16,17]

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