Abstract
The mechanisms involved in generation of rhythmic locomotor activity in the mammalian spinal cord remain poorly understood. These mechanisms supposedly rely on both intrinsic properties of constituting neurons and interactions between them. A subset of Shox2 neurons was suggested to contribute to generation of spinal locomotor activity, but the possible cellular basis for rhythmic bursting in these neurons remains unknown. Ha and Dougherty (2018) recently revealed the presence of bidirectional electrical coupling between Shox2 neurons in neonatal spinal cords, which can be critically involved in neuronal synchronization and generation of populational bursting. Gap junctional connections found between functionally-related Shox2 interneurons decrease with age, possibly being replaced by increasing interactions through chemical synapses. Here, we developed a computational model of a heterogeneous population of neurons sparsely connected by electrical or/and chemical synapses and investigated the dependence of frequency of populational bursting on the type and strength of neuronal interconnections. The model proposes a mechanistic explanation that can account for the emergence of a synchronized rhythmic activity in the neuronal population and provides insights into the possible role of gap junctional coupling between Shox2 neurons in the spinal mechanisms for locomotor rhythm generation.
Highlights
The mammalian spinal cord contains neuronal circuits that can generate locomotor-like oscillations in the absence of supraspinal and afferent inputs
The major focus of the present study was on the specific roles of, and possible cooperation between, neural interactions and persistent sodium current (INaP)
We started by simulating a pair of neurons operating in different regimes and connected by bidirectional gap junctions or unidirectional excitatory chemical synapses in order to investigate the effect of the type and strength of connections and the presence/absence of incorporating the persistent sodium current (INaP) conductance on the activity of both neurons
Summary
The mammalian spinal cord contains neuronal circuits that can generate locomotor-like oscillations in the absence of supraspinal and afferent inputs. These circuits include rhythm-generating kernels capable of producing, maintaining, and coordinating populational rhythmic activity. No single genetically identified neuron type has been found to be solely responsible for rhythm generation in the spinal cord, the genetically identified Shox interneurons have been suggested to be involved in locomotor rhythmogenesis (Dougherty et al, 2013). Later investigations provided evidence that a subpopulation of Shox neurons, the Shox non-V2a neuron type, may belong to the rhythm-generating kernel in the neonatal rodent spinal cord and be involved in generation of locomotor rhythmic activity (Dougherty et al, 2013; Kiehn, 2016).
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