A novel key player in cognitive striatal processes: the Pthlh interneurons

Interneurons in the dorsal striatum provide essential modulatory control over the projecting neurons, known as medium spiny neurons (MSNs), regulating the output of this brain structure, which is critical for motor control, decision-making, and learning. The diversity of interneurons has been recently determined based on single-cell transcriptomic analyses identifying novel populations as the Pthlh-expressing interneurons, one of the most abundant and distinctive inhibitory populations in the human and mouse striatum. Here, we generated a novel Pthlhcre knock-in mouse line that enables comprehensive study of this critical population. Quantitative histological analyses show that this line effectively targets the Pthlh interneuron class, which appears as a stable population across age, sex and the anterior-posterior axis. To elucidate their functional role, we performed selective chemogenetic inhibition of Pthlh interneurons, which caused significant impairments in striatum-dependent cognitive functions and reduced exploratory behaviorur. Importantly, selective silencing did not affect basal locomotion, motor coordination, or anxiety-like behavior. Monosynaptic rabies tracing revealed that Pthlh interneurons receive dense local input from MSN subtypes and diverse long-range afferents from thalamic and different cortical regions. We further confirm that this population displays electrophysiological heterogeneity encompassing fast-spiking and fast-spiking-like phenotypes. Overall, our findings establish Pthlh interneurons as a major inhibitory class essential for cognitive processing--but not gross motor function--acting as key integrators of local MSN feedback and thalamocortical signals. The novel Pthlhcre mouse line provides a valuable resource for future studies of inhibitory diversity in basal ganglia function and related neurological disorders.