P.2.027 - Inducible tryptophan hydroxylase 2 knockout mice as model for anxiety and fear like behaviour

Abstract

Background The amygdaloid nuclei are involved in expression of anxiety and fear responses. Malfunctioning of these nuclear complexes may be due in part to dysregulation serotonin (5-HT) neurotransmission. However the neural mechanisms involved are yet to be fully deciphered. Constitutive tryptophan hydroxylase 2 knockout mice (Tph2-/-) which lack 5-HT from embryonic stages of development show increased aggression and altered anxiety and fear responses in aversive contexts[1]. Still, it is unclear whether the observed phenotypes are attributed to abnormal development resulting from 5-HT deficiency or to a specific requirement for 5-HT in adulthood [2]. Inducible Cre-mediated recombination of Tph2 during adulthood, which permits time specific depletion of brain 5-HT may decipher the specific role of 5-HT in the regulation of emotional responses. Aim Characterization of a mouse model for effect of acute brain serotonin depletion on anxiety and fear-like behavior. Methods Mice (10-12weeks old) expressing Cre-recombinase under the Tph2 specific promoter and with Exon V of Tph2 flanked by loxP sites were injected with tamoxifen (2mg, daily for 5 consecutive days) to induce conditional Tph2 deletion (Tph2 icko). Four weeks after injection, immunohistochemistry and high performance liquid chromatography were performed (HPLC) to assess the efficiency of Cre-mediated recombination of Tph2 in raphe nuclei. The mice were subjected to behavioural testing including elevated plus maze, light-dark box, open-field and fear conditioning in an automated fear conditioning chamber. Afterwards, brains were fixed in 4% PFA and used for immunofluorescence staining of 5HT. Data are represented as mean±SEM and Students’ t-test was use to compared means between Tph2 icko mice and sham controls (Tph2CON). A p-value less than 0.05 was regarded as significant. Results The Tph2 icko mice showed significant (p Conclusion Cre-mediated inducible Tph2 deletion may be able to model the impact of central 5HT depletion on anxiety- and fear-like behavior in a time-specific manner.