Ontogeny of Projections from the Motor Cortex Governing Whisker and Neck Movements to the Striatum in the Rat

Corticostrial or cortico-basal ganglia circuitry plays an important role in integrating sensory and motor information, developing appropriate goal-directed behavior, promoting the maturation of GABAergic interneurons in the striatum, and regulating the nigrostriatal pathways. Dysfunction of this circuitry has been seen in some movement disorders. However, the dynamic changes of this circuitry in early life are not fully elucidated. Previous studies demonstrated that projections from motor cortices of caudal forelimb and jaw-lip-tongue areas to the striatum developed postnatally with terminal-like fibers evident at postnatal day 7. Here we report the development of the projections from the motor cortex governing whisker and neck movements to the striatum. Corticostriatal projections from this area were mainly ipsilateral and also underwent a progressive, postnatal development. The pyramidal tract and its collaterals to the dorsal striatum appeared on the day of birth (postanatal day 0 (P0)), peaked on P6 in density, and continued to be tuned until P36. The intertelencephalic projections in the dorsolateral striatum were established between P6 and P12 and continued to be refined between P20 and P36. Neurons in this motor cortex sent their axons to the contralateral motor cortex via the corpus callosum at the age between P6 and P12. Our results suggest that the time window between P6 and P12 is critical for the development of the projections from the motor cortex governing whisker and neck movement to the striatum in the rat. The overall process of the development of this circuitry appears to correspond to the functional development of whisker movement and locomotor activities. ### Competing Interest Statement The authors have declared no competing interest. * ADHD : attention-deficit and hyperactivity disorder CP : cerebral palsy DiI : 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate GABA : gamma-aminobutyric acid WGA-HRP : horseradish peroxidase conjugated with wheat germ agglutinin