Kinematics-Based Assessment of Reaching and Grasping Movements in LRN Ablated Animals Identifies a Role for the LRN in Endpoint Stabilization and Reach Timing.

The lateral reticular nucleus (LRN) is positioned to relay motor-related information to cerebellar circuits, but its direct contribution to skilled reaching and grasping remains unclear. Here, we examined skilled forelimb behavior in intact adult female Long-Evans rats after bilateral, cell type-targeted LRN ablation using single-pellet reaching, qualitative scoring, and quantitative three-dimensional kinematic analysis. We assessed whether LRN loss disrupted gross limb transport, endpoint precision, trial-to-trial consistency, and reach timing across pre- and post-surgical recording sessions. LRN-ablated animals continued to generate broadly recognizable pellet-directed reaches, indicating that the LRN is not required for basic reach production. However, group differences emerged in restricted portions of the reach trajectory and were most prominent in pellet-directed endpoint control. Experimental animals showed broader endpoint covariance, greater endpoint spread, and increased trial-to-trial variability, indicating less precise and less reproducible forelimb placement relative to the pellet. These effects were not explained by a single fixed spatial offset, but instead reflected reduced endpoint stabilization accompanied by selective coordinate-specific changes, including altered paw height. Reach duration was also altered, but these timing differences emerged later and were less prominent than the spatial endpoint deficits. Together, these findings suggest that the LRN contributes primarily to the refinement, stabilization, and timing of skilled forelimb movements rather than to gross reach initiation or limb transport. This work provides a direct in vivo model for studying LRN-dependent control of skilled reaching and highlights the value of kinematic analysis for detecting subtle movement deficits beyond retrieval success alone.