Mutant huntingtin expression in somatostatin-positive interneurons contributes to neurophysiological and behavioral phenotypes in BACHD mice.

Huntington's Disease (HD) is caused by expansion of the polyglutamine stretch in the widely expressed Huntingtin (HTT) protein. HD patients have motor, psychiatric, and cognitive changes due to changes in a variety of neural circuits. Somatostatin-expressing interneurons (SST-INs) can regulate neural circuits largely by inhibiting their target cells. Behaviorally, brain-wide inhibition of SST-INs increased anxiety in mice. Silencing striatal SST-INs caused a decrease in movement in the open field. Mutant HTT (mHTT) expressing mice exhibit abnormal motor, cognitive and psychiatric-like changes as well as electrophysiological changes in a variety of neurons, including striatal SST-INs. However, it is unknown whether cell autonomous expression of mHTT in SST-INs contributes to HD-associated behavioral phenotypes or causes abnormal electrophysiological changes in striatal SST-INs. To address these questions, we reduced mHTT expression in SST-INs throughout the brain of BACHD mice. Our findings show that brain-wide reduction of mHTT in SST-INs rescues anxiety-like behavior in male BACHD mice in the light-dark box, without improving performance in the open field or on the rotarod. Additionally, expression of mHTT in striatal SST-INs cell autonomously drives their increased excitability.