Abstract
Elaborate behaviours are produced by tightly controlled flexor-extensor motor neuron activation patterns. Motor neurons are regulated by a network of interneurons within the spinal cord, but the computational processes involved in motor control are not fully understood. The neuroanatomical arrangement of motor and premotor neurons into topographic patterns related to their controlled muscles is thought to facilitate how information is processed by spinal circuits. Rabies retrograde monosynaptic tracing has been used to label premotor interneurons innervating specific motor neuron pools, with previous studies reporting topographic mediolateral positional biases in flexor and extensor premotor interneurons. To further investigate the spatial organization of premotor interneurons, we used several different viral approaches for retrograde transsynaptic tracing. In contradiction to previous reports, we consistently found that premotor interneurons are not organized into topographic groups related to their innervation of flexor or extensor motor neuron pools. We conclude that the premotor spinal neurons controlling different muscles are spatially intermingled and operate in the absence of clear spatial patterns among the flexor-extensor circuit components.
Competing Interest Statement
RMB is a co-founder of Sania Therapeutics, Inc and consults for Sania Rx Ltd
Footnotes
↵§ co-senior authors
New participating labs added new experiments (Figures 8 to 12) to the original version. Introduction and discussion completely rewritten in light of new findings
