Hindlimb muscle spindles inform preparatory forelimb coordination prior to landing in toads

Animals move across a wide range of surface conditions in real-world environments to acquire resources and avoid predation. To effectively navigate a variety of surfaces, animals rely on several mechanisms including intrinsic mechanical responses, spinal-level central pattern generators, and neural commands that require sensory feedback. Muscle spindle 1a afferents play a critical role in providing sensory feedback and informing motor control strategies across legged vertebrate locomotion, which is apparent in cases where this sensory input is compromised. Here we tested the hypothesis that spindle 1a afferents from hindlimb muscles are important for coordinating forelimb landing behavior in the cane toad. We performed bilateral sciatic nerve reinnervations to ablate the stretch reflex from distal hindlimb muscles while allowing for motor neuron recovery. We found that toads significantly delayed the onset and reduced the activation duration of their elbow extensor muscle following spindle 1a afferent ablation in the hindlimbs. However, reinnervated toads achieved similar elbow extension at touchdown compared to their pre-surgery state. Our results suggest that while toads likely tuned the activation timing of forelimb muscles in response to losing 1a afferent sensation from the hindlimbs they were likely able to employ compensatory strategies that allowed them to continue landing effectively with reduced sensory information during takeoff. These findings indicate muscle spindle 1a afferents may contribute to tuning complex movements involving multiple limbs.You will need Microsoft Excel or equivalent (e.g. Google Sheets) to open and read CSV files and any movie or video player that can play .avi files (if you are interested in collected videos).Funding provided by: Army Research LaboratoryCrossref Funder Registry ID: http://dx.doi.org/10.13039/100006754Award Number: W911NF-15-1-058Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100008982Award Number: 105169