These mice demonstrate a range of behavioral and neurophysiological abnormalities that resemble symptoms of human anxiety disorders. They are characterized by reduced aggression, increased anxiety like behavior, altered behavioral despair responses and reduced social interaction

Reproduced with permission from John Wiley & Sons, Inc.

Kalueff et al, 2007: Anxious like behavior of WT mice (SERT+/+), heterozygous (SERT +/-) and homozygous (SERT -/-) serotonin transporter knockout in the open field test. Frequency in the arena center (left), duration in arena center (middle) and time in center/ time in periphery are measured.  A clear inverse relationship is demonstrated between levels of SERT gene expression and levels of anxiety in all three parameters.

References:

Holmes A, Lit Q, Murphy DL, Gold E, Crawley JN (2003) Abnormal anxiety-related behavior in serotonin transporter null mutant mice: The influence of genetic background. Genes Brain Behav 2(6):365-380

Kalueff AV, Fox MA, Gallagher PS, Murphy DL (2007) Hypolocomotion, anxiety and serotonin syndrome-like behavior contribute to the complex phenotype of serotonin transporter knockout mice. Genes Brain Behav 6(4):389-400