Delineating the Diversity of Spinal Interneurons in Locomotor Circuits

Abstract

Locomotion is common to all animals and is essential for survival. Neural circuits located in the spinal cord have been shown to be necessary and sufficient for the generation and control of the basic locomotor rhythm by activating muscles on either side of the body in a specific sequence. Activity in these neural circuits determines the speed, gait pattern, and direction of movement, so the specific locomotor pattern generated relies on the diversity of the neurons within spinal locomotor circuits. Here, we review findings demonstrating that developmental genetics can be used to identify populations of neurons that comprise these circuits and focus on recent work indicating that many of these populations can be further subdivided into distinct subtypes, with each likely to play complementary functions during locomotion. Finally, we discuss data describing the manner in which these populations interact with each other to produce efficient, task-dependent locomotion.

Spinal V3 interneurons and left-right coordination in mammalian locomotion

“…Similar to other genetically defined types of spinal interneuron populations (Bikoff et al, 2016;Deska-Gauthier and Zhang, 2019;Gosgnach et al, 2017), the V3 population is heterogeneous, consisting of sub-populations with different anatomical, physiological and molecular profiles (Borowska et al, 2013(Borowska et al, , 2015. In the present study, however, we did not consider different subtype of V3 neurons.…”

“…The identification of genetically defined interneuron populations has enabled us to characterize their specific functions in locomotor behaviors (Deska-Gauthier and Zhang, 2019;Gosgnach et al, 2017;Goulding, 2009). Until now, however, most experimental data were from genetically eliminating certain group of spinal interneurons without clear understanding of connectivity among the spinal interneurons in spinal circuits (Bellardita and Kiehn, 2015;Crone et al, 2008;Gosgnach et al, 2006;Lanuza et al, 2004;Talpalar et al, 2013;Zhang et al, 2008).…”

Extensive somatosensory and motor corticospinal sprouting occurs following a central dorsal column lesion in monkeys

“…This diverse group of cells receives input from the major descending motor centers in cortex as well as from peripheral afferents, and studies in cats show that they exert influence over a range of contralateral postsynaptic targets (Jankowska, 2008). The network is complex and though progress has been made in terms of genetic identification of some subclasses of commissural interneurons in mice (Gosgnach et al, 2017), and in characterizing functional connectivity in the cat (Jankowska, 2008), little is known about their role in primates (Soteropoulos, Edgley, & Baker, 2013 Summary schematic comparing terminal distribution patterns of CST boutons following different spinal cord lesions. Schematic combines data from monkeys and shows the averaged terminal territory for each lesion group.…”

Somatosensory corticospinal tract axons sprout within the cervical cord following a dorsal root/dorsal column spinal injury in the rat

“…In normal rats, as in primates, S1 CST terminals synapse in the (contralateral) dorsal horn primarily on to the presumed axons/dendrites of intraspinal neuronal populations (Côté, Murray, & Knikou, ; Gosgnach et al, ; Schieber, ; Ziskind‐Conhaim & Hochman, ). Target neurons may include local reflex, long and short range propriospinal (Filli & Schwab, ) and commissural interneuronal populations (Bannatyne, Edgley, Hammar, Jankowska, & Maxwell, ; Jankowska et al, ; Soteropoulos, Edgley, & Baker, ), which in turn connect with motor neurons, and/or regulate (or gate) ascending tracts (i.e., the dorsal columns, spinocerebellar and spinothalamic pathways).…”