Faculty Opinions recommendation of Grading movement strength by changes in firing intensity versus recruitment of spinal interneurons.

Distinct types of rhythmic movements that use the same muscles are typically generated largely by shared multifunctional neurons in invertebrates, but less is known for vertebrates. Evidence suggests that locomotion and scratching are produced partly by shared spinal cord interneuronal circuity, although direct evidence with intracellular recording has been lacking. Here, spinal interneurons were recorded intracellularly during fictive swimming and fictive scratching in vivo and filled with Neurobiotin. Some interneurons that were rhythmically activated during both swimming and scratching had axon terminal arborizations in the ventral horn of the hindlimb enlargement, indicating their likely contribution to hindlimb motor outputs during both behaviors. We previously described a morphological group of spinal interneurons (“transverse interneurons” or T neurons) that were rhythmically activated during all forms of fictive scratching at higher peak firing rates and with larger membrane potential oscillations than scratch-activated spinal interneurons with different dendritic orientations. The current study demonstrates that T neurons are activated during both swimming and scratching and thus are components of the shared circuitry. Many spinal interneurons activated during fictive scratching are also activated during fictive swimming (scratch/swim neurons), but others are suppressed during swimming (scratch-specialized neurons). The current study demonstrates that some scratch-specialized neurons receive strong and long-lasting hyperpolarizing inhibition during fictive swimming and are also morphologically distinct from T neurons. Thus this study indicates that locomotion and scratching are produced by a combination of shared and dedicated interneurons whose physiological and morphological properties are beginning to be revealed.

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RORβ Spinal Interneurons Gate Sensory Transmission during Locomotion to Secure a Fluid Walking Gait

Neuron ◽

10.1016/j.neuron.2017.11.011 ◽

2017 ◽

Vol 96 (6) ◽

pp. 1419-1431.e5 ◽

Cited By ~ 28

Author(s):

Stephanie C. Koch ◽

Marta Garcia Del Barrio ◽

Antoine Dalet ◽

Graziana Gatto ◽

Thomas Günther ◽

...

Keyword(s):

Walking Gait ◽

Spinal Interneurons ◽

Sensory Transmission

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Spinal Interneurons

Estrogens and Brain Function ◽

10.1007/978-1-4613-8084-9_4 ◽

1980 ◽

pp. 44-56

Author(s):

Donald W. Pfaff

Keyword(s):

Spinal Interneurons

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Spatiotemporal correlation of spinal network dynamics underlying spasms in chronic spinalized mice

eLife ◽

10.7554/elife.23011 ◽

2017 ◽

Vol 6 ◽

Cited By ~ 24

Author(s):

Carmelo Bellardita ◽

Vittorio Caggiano ◽

Roberto Leiras ◽

Vanessa Caldeira ◽

Andrea Fuchs ◽

...

Keyword(s):

Motor Neurons ◽

Neural Activity ◽

Sensory Input ◽

Mouse Genetics ◽

Spinal Interneurons ◽

Neuronal Mechanisms ◽

Cord Injury ◽

Motor Neuron Excitability ◽

Spinal Network ◽

Opening Up

Spasms after spinal cord injury (SCI) are debilitating involuntary muscle contractions that have been associated with increased motor neuron excitability and decreased inhibition. However, whether spasms involve activation of premotor spinal excitatory neuronal circuits is unknown. Here we use mouse genetics, electrophysiology, imaging and optogenetics to directly target major classes of spinal interneurons as well as motor neurons during spasms in a mouse model of chronic SCI. We find that assemblies of excitatory spinal interneurons are recruited by sensory input into functional circuits to generate persistent neural activity, which interacts with both the graded expression of plateau potentials in motor neurons to generate spasms, and inhibitory interneurons to curtail them. Our study reveals hitherto unrecognized neuronal mechanisms for the generation of persistent neural activity under pathophysiological conditions, opening up new targets for treatment of muscle spasms after SCI.

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Spontaneous neural synchrony links intrinsic spinal sensory and motor networks during unconsciousness

10.1101/2021.01.15.426828 ◽

2021 ◽

Author(s):

Jacob G. McPherson ◽

Maria F. Bandres

Keyword(s):

Functional Connectivity ◽

Neural Synchrony ◽

Afferent Activity ◽

Resting State Functional Connectivity ◽

Spinal Interneurons ◽

Synaptic Interactions ◽

Large Populations ◽

Neural Transmission ◽

Connection Latencies

AbstractPurposeful functional connectivity during unconsciousness is a defining feature of supraspinal networks. However, its generalizability to intrinsic spinal networks remains incompletely understood. Previously, Barry et al. (2014) used fMRI to reveal bilateral resting state functional connectivity within sensory-dominant and, separately, motor-dominant regions of the spinal cord. Here, we record spike trains from large populations of spinal interneurons in vivo and demonstrate that spontaneous functional connectivity also links sensory- and motor-dominant regions during unconsciousness. The spatiotemporal patterns of connectivity could not be explained by latent afferent activity or by populations of interconnected neurons spiking randomly. We also document connection latencies compatible with mono- and di-synaptic interactions and putative excitatory and inhibitory connections. The observed activity is consistent with a network policy in which salient, experience-dependent patterns of neural transmission introduced during behavior or by injury/disease are reactivated during unconsciousness. Such a spinal replay mechanism could shape circuit-level connectivity and ultimately behavior.

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Spinal microcircuits comprising dI3 interneurons are necessary for motor functional recovery following spinal cord transection

eLife ◽

10.7554/elife.21715 ◽

2016 ◽

Vol 5 ◽

Cited By ~ 20

Author(s):

Tuan V Bui ◽

Nicolas Stifani ◽

Turgay Akay ◽

Robert M Brownstone

Keyword(s):

Spinal Cord ◽

Functional Recovery ◽

Motor System ◽

Motor Training ◽

Prediction Errors ◽

Spinal Interneurons ◽

Motor Activities ◽

Afferent Inputs ◽

To Receive ◽

Sensory Prediction

The spinal cord has the capacity to coordinate motor activities such as locomotion. Following spinal transection, functional activity can be regained, to a degree, following motor training. To identify microcircuits involved in this recovery, we studied a population of mouse spinal interneurons known to receive direct afferent inputs and project to intermediate and ventral regions of the spinal cord. We demonstrate that while dI3 interneurons are not necessary for normal locomotor activity, locomotor circuits rhythmically inhibit them and dI3 interneurons can activate these circuits. Removing dI3 interneurons from spinal microcircuits by eliminating their synaptic transmission left locomotion more or less unchanged, but abolished functional recovery, indicating that dI3 interneurons are a necessary cellular substrate for motor system plasticity following transection. We suggest that dI3 interneurons compare inputs from locomotor circuits with sensory afferent inputs to compute sensory prediction errors that then modify locomotor circuits to effect motor recovery.

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Multiple Effects of Serotonin and Acetylcholine on Hyperpolarization-Activated Inward Current in Locomotor Activity-Related Neurons in Cfos-EGFP Mice

Journal of Neurophysiology ◽

10.1152/jn.01110.2009 ◽

2010 ◽

Vol 104 (1) ◽

pp. 366-381 ◽

Cited By ~ 13

Author(s):

Yue Dai ◽

Larry M. Jordan

Keyword(s):

Spinal Cord ◽

Motor System ◽

Reversal Potential ◽

Rhythmic Activity ◽

Maximal Conductance ◽

Inward Current ◽

Spinal Interneurons ◽

Whole Cell Patch Clamp ◽

Activation Rate ◽

Maximal Activation

Hyperpolarization-activated inward current ( Ih) has been shown to be involved in production of bursting during various forms of rhythmic activity. However, details of Ih in spinal interneurons related to locomotion remain unknown. Using Cfos-EGFP transgenic mice (P6–P12) we are able to target the spinal interneurons activated by locomotion. Following a locomotor task, whole cell patch-clamp recordings were obtained from ventral EGFP+ neurons in spinal cord slices (T13–L4, 200–250 μm). Ih was found in 51% of EGFP+ neurons ( n = 149) with almost even distribution in lamina VII (51%), VIII (47%), and X (55%). Ih could be blocked by ZD7288 (10–20 μM) or cesium (1–1.5 mM) but was insensitive to barium (2–2.5 mM). Ih activated at −80.1 ± 9.2 mV with half-maximal activation −95.5 ± 13.3 mV, activation rate 10.0 ± 3.2 mV, time constant 745 ± 501 ms, maximal conductance 1.0 ± 0.7 nS, and reversal potential −34.3 ± 3.6 mV. 5-HT (15–20 μM) and ACh (20–30 μM) produced variable effects on Ih. 5-HT increased Ih in 43% of EGFP+ neurons ( n = 37), decreased Ih in 24%, and had no effect on Ih in 33% of the neurons. ACh decreased Ih in 67% of EGFP+ neurons ( n = 18) with unchanged Ih in 33% of the neurons. This study characterizes the Ih in locomotor-related interneurons and is the first to demonstrate the variable effects of 5-HT and ACh on Ih in rodent spinal interneurons. The finding of 5-HT and ACh-induced reduction of Ih in EGFP+ neurons suggests a novel mechanism that the motor system could use to limit the participation of certain neurons in locomotion.

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