Mood alterations in mouse models of Spinocerebellar Ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by abnormal expansion of glutamine-encoding CAG repeats in the Ataxin-1 (ATXN1) gene. SCA1 is characterized by progressive motor deficits, cognitive decline, and mood changes including anxiety and depression, with longer number of repeats correlating with worse disease outcomes. While mouse models have been very useful in understanding etiology of ataxia and cognitive decline, our understanding of mood symptoms in SCA1 has lagged. It remains unclear whether anxiety or depression stem from an underlying brain pathology or as a consequence of living with an untreatable and lethal disease. To increase our understanding of the etiology of SCA1 mood alterations, we used the elevated-plus maze, sucrose preference and forced swim tests to assess mood in four different mouse lines. We found that SCA1 knock-in mice exhibit increased anxiety that correlated with the length of CAG repeats, supporting the idea that underlying brain pathology contributes to SCA1-like anxiety. Additionally, our results support the concept that increased anxiety is caused by non-cerebellar pathology, as Purkinje cell specific SCA1 transgenic mice exhibit decreased anxiety-like behavior. Regarding the molecular mechanism, partial loss of ATXN1 may play a role in anxiety, based on our results for Atxn1 haploinsufficient and null mice.