Sex- and Context-Dependent Modulation of Striatal Cholinergic Interneuron Activity During Novelty Exposure.

Obsessive-compulsive disorder (OCD) involves dysfunction of cortico-striato-thalamo-cortical circuits, with striatal cholinergic interneurons (SCI) regulating output and salience. SCI ablation induces compulsive and repetitive behaviors without affecting balance or coordination in male mice, but sex differences in SCI activity during behaviors remain unknown. C57BL/6 male and female mice were exposed to home-cage (HC), open-field (OF), or hole-board (HB) contexts for 30 min. Thirty minutes later, mice were perfused, brains were collected and sectioned to quantify phosphorylated S6 ribosomal protein (pS6rp), an activity marker, in ChAT+ striatal neurons by double immunohistochemistry. Behavioral analysis showed that males exhibited greater immobility in the OF than females (p=0.043). Immunohistochemical analysis revealed that, in males, pS6rp intensity increased in the OF (p=0.0017) and decreased in the HB (p<0.0001) compared with the HC context, whereas females showed no significant differences across contexts. Sex differences were observed in the OF (p<0.0001) and HC (p=0.027), but not in the HB. In the OF, SCI activity correlated negatively with distance traveled (R²=0.91) and center entries (R²=0.86), and positively with immobility (R²=0.96); no significant correlations were observed in the HB. SCI activity depends on sex and context, with stronger changes in males, highlighting sex as a key factor in OCD-related striatal circuit regulation.