Loss Of Ahi1Impairs Neurotransmitter Release In Mouse Brains

Objective To investigate whether Ahi1KO mice have depressive phenotype andfurther explore the role of neurotransmitters in the mechanisms of depressive behaviors.Methods Western blot analysis was used to determine the expression levels of Ahi1inAhi1KO mice and control mice (Ahi1heterozygote). Tail suspension test, forcedswimming test, and sucrose preference test were used to examine depressive phenotype inmice. The contents of neurotransmitters including serotonin (5-HT),5-hydroxy indoleacetic acid (5-HIAA), dopamine (DA),4-hydroxy-3-methoxyphenylacetic (HVA),dihydroxyphenylacetic acid (DOPAC), glutamate and gamma amino acid butyric acid(GABA) were measured by high performance liquid chromatography (HPLC). Wemeasured the monoamine oxidase activity (MAO) in the brainstem of control and Ahi1KOmice by an enzyme linked immunosorbent assay method (ELISA). In order to studywhether these mice responded to known anti-depressant impramine, Mice were treatedwith imipramine or normal saline intraperitoneally for3weeks. Three weeks later, thechange of behaviors was evaluated by forced swimming test and tail suspension test, thechanges of neurotransmitters were examined by HPLC.Results Western blot analysis revealed that there was almost no Ahi1expression inAhi1KO mice (P＜0.05).Tail suspension test and forced swimming test shown thatsignificant decrease of immobility time was found in Ahi1KO mice compared with controlmice (P＜0.05). In sucrose preference test, total consumed liquid and the percentage ofconsumed sucrose water was markedly decreased in Ahi1KO mice (P＜0.05).At postnatalday4, there was no difference for the content of serotonin in control and Ahi1KO mice(P>0.05). However, after postnatal day10、1month and2month，serotonin level wassignificantly increased in control mice, while only a slight increase of serotonin wasobserved in Ahi1KO mice. Similarly, dopamine level was not significantly elevated inAhi1KO mice as in control mice after postnatal day4, but dopamine level was muchlower in Ahi1KO mice after postnatal day10d、1m compared with control mice (P＜0.05). Glutamate and GABA levels were not influenced in control and Ahi1KO mice at4d,10d(P>0.05). We further measured serotonin levels in the cortex, hippocampus, hypothalamus,brainstem, and amygdale at1-m-old mice, the level of serotonin and the metabolite ofserotonin5-HIAA was decreased in Ahi1KO mice compared with control mice (P＜0.05).However, the ratio of5-HIAA to serotonin, namely serotonin turnover, was markedlyelevated in Ahi1KO mice(P＜0.05). Similar tendency was also observed in dopamine, themetabolite of dopamine (DOPAC and HVA).MAO activity was significantly increased inAhi1KO mice compared with control mice(P＜0.05).After imipramine treatment for3weeks, immobility time of Ahi1KO mice in forced swimming test and tail suspension testwas significantly decreased(P＜0.05). Serotonin level was elevated(P＜0.05), however,dopamine level was not changed (P>0.05).Conclusion Ahi1KO caused depressive behaviors in mice.In Ahi1KO mice, thecontent of depression-related neurotransmitter such as5-HT and DA was decreased,however, the level of amino acid neurotransmitters (such as glutamate and GABA) werenot influenced. MAO activity was elevated in Ahi1KO mice, which may result in thedecrease of monoamine in brains. Imipramine alleviated the depressive phenotype;moreover, the content of5-HT in Ahi1KO mice was partly restored. Therefore, Ahi1KOmice are a genetic model of depression for the mechanistic study and a useful tool toscreen anti-depressants.