Creatine transporter knockout mice (Slc6a8) show increases in serotonin-related proteins and are resilient to learned helplessness

•Slc6a8−/y mice have increased striatal, hippocampal 5-hydroxyindoleacetic acid and hippocampal tryptophan hydroxylase and monoamine oxidase.•Slc6a8−/y mice and female mice heterozygous for Slc6a8 (Slc6a8+/−) mice are resilient to learned helplessness induction.•Minor alterations in anxiety-like and native-depression-like measures were discovered in Slc6a8−/y and Slc6a8+/− mice.•The results of this study suggest that creatine plays a role in serotonin metabolism, which may manifest as changes in induced depressive-like behaviors.