Adult spinal Dmrt3 neurons receive direct somatosensory inputs from ipsi‐ and contralateral primary afferents and from brainstem motor nuclei

Abstract

In the spinal cord, sensory‐motor circuits controlling motor activity are situated in the dorso–ventral interface. The neurons identified by the expression of the transcription factor Doublesex and mab‐3 related transcription factor 3 (Dmrt3) have previously been associated with the coordination of locomotion in horses (Equus caballus, Linnaeus, 1758), mice (Mus musculus, Linnaeus, 1758), and zebrafish (Danio rerio, F. Hamilton, 1822). Based on earlier studies, we hypothesized that, in mice, these neurons may be positioned to receive sensory and central inputs to relay processed commands to motor neurons. Thus, we investigated the presynaptic inputs to spinal Dmrt3 neurons using monosynaptic retrograde replication‐deficient rabies tracing. The analysis showed that lumbar Dmrt3 neurons receive inputs from intrasegmental neurons, and intersegmental neurons from the cervical, thoracic, and sacral segments. Some of these neurons belong to the excitatory V2a interneurons and to plausible Renshaw cells, defined by the expression of Chx10 and calbindin, respectively. We also found that proprioceptive primary sensory neurons of type Ia2, Ia3, and Ib, defined by the expression of calbindin, calretinin, and Brn3c, respectively, provide presynaptic inputs to spinal Dmrt3 neurons. In addition, we demonstrated that Dmrt3 neurons receive inputs from brain areas involved in motor regulation, including the red nucleus, primary sensory–motor cortex, and pontine nuclei. In conclusion, adult spinal Dmrt3 neurons receive inputs from motor‐related brain areas as well as proprioceptive primary sensory neurons and have been shown to connect directly to motor neurons. Dmrt3 neurons are thus positioned to provide sensory–motor control and their connectivity is suggestive of the classical reflex pathways present in the spinal cord.

Genome assembly of the foot-flagging frog, Staurois parvus: a resource for understanding mechanisms of behavior

“…DMRT3 is expressed in the interneurons of networks important for limb locomotion and coordination, and inhibiting this gene resulted in abnormal gait and locomotor ability in mice ( Perry et al . 2019 ; Vieillard et al . 2023 ).…”

The Characteristics, Distribution, Function, and Origin of Alternative Lateral Horse Gaits

“…The resulting truncated protein transcription factor (possessing only 300 out of 474 amino acids) lacks the ability to produce regular interneuronal bursts in the spine and thereby induce horses to transition from a slow walk to an intermediate speed diagonally coordinated trot, and finally to an asymmetrical contralaterally-coordinated canter/gallop at fast speeds. Instead, horses with the mutated A-allele tend to transition from a slow walk to an intermediate speed laterally-coordinated running walk, rack, broken pace, or hard pace [ 205 , 206 ]. In other words, horse breeds that possess the A-allele (such as the Icelandic, Mangalarga Marchador, Paso Fino, Tennessee Walking Horse, and Saddlebred), when they wish to travel faster, tend to employ alternative lateral gaits based upon the same lateral sequence footfall pattern found in the walk (LH, LF, RH, RF) rather than transitioning to a diagonal trot or asymmetrical gallop.…”