Background: The basic motor patterns driving rhythmic limb movements during walking are generated
by networks of neurons called central pattern generators (CPGs). Within motor control systems, neuromodulators
are necessary for proper and efficient CPG function because they induce or regulate essential components
of spinal network activity, including firing parameters of CPG neurons and network synaptic strength, allowing
the network to change/adapt and sometimes to even become functional.
Methods: The goal of this work is to focus on classical and recent findings addressing the role of neuromodulators
such as glutamate, dopamine, acetylcholine and adenosine in eliciting, changing and sometimes terminating
spinal CPG network function in rodents.
Results: Neuromodulatory inputs onto CPG locomotor networks have been additionally related to inducing state
changes such as locomotor timing, phasing and speed, and to the induction/maintenance of actual network function.
These inputs originate from supraspinal centers such as the brainstem and from intraspinal neurotransmission.
The isolated in vitro rodent spinal cord preparation is a powerful model for studies on locomotor network
organization because of its physiological and anatomical accessibility, as well as the incorporation of various
transgenic approaches to identify specific neuronal populations. Both roles are accomplished through the action
of neuromodulators on ionotropic and metabotropic receptors mediating synaptic neurotransmission, which can
be used by neurons that are intrinsic or extrinsic components of a CPG network itself.
Conclusion: This article has hopefully provided a comprehensive overview of some of the main spinal mechanisms
involved in the modulatory control of locomotor activity.