Acid sphingomyelinase controls dopamine activity and responses to appetitive stimuli in mice

Alcohol use disorder and depression show a high comorbidity at clinical level with no treatment available selectively for this condition. A hyperfunction of acid sphingomyelinase (ASM) and resulting ceramide overload were recently identified as one pathway into this comorbidity. Here we analyzed the involvement of ASM, one of the main enzymes involved in ceramide synthesis, in the molecular control of monoaminergic systems in their basal activity and in response to pharmacological and natural reinforcers. The effects of alcohol and a palatable food on the extracellular levels of dopamine (DA), serotonin (5-HT), and noradrenaline (NE) were measured by in-vivo microdialysis in ASM overexpressing mice (tgASM). We found reduced basal extracellular DA levels in the nucleus accumbens (Nac) and dorsal hippocampus (DH) of tgASM mice with little effect on 5-HT and NE levels. In contrast, ASM overexpression potentiated the DA response to alcohol (2 g/kg, i.p.) in the DH and Nac, but reduced NE responses. DA and NE responses to a food stimulus were not altered in tgASM mice, but the Nac 5-HT response was enhanced. An immunohistochemical analysis of the DH showed a preserved dopaminergic and serotonergic innervation in tgASM mice and in mice that consumed alcohol for one month. These findings suggest a direct modulation of monoaminergic basal activity and/or responses to reinforcing stimuli by the sphingolipid regulatory enzyme ASM in mice.