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Review
. 2012:2012:964843.
doi: 10.1155/2012/964843. Epub 2012 Aug 1.

Activity-dependent plasticity of spinal circuits in the developing and mature spinal cord

Behdad Tahayori  1 , David M Koceja
Affiliations
Review

Activity-dependent plasticity of spinal circuits in the developing and mature spinal cord

Behdad Tahayori et al. Neural Plast. 2012.

Abstract

Part of the development and maturation of the central nervous system (CNS) occurs through interactions with the environment. Through physical activities and interactions with the world, an animal receives considerable sensory information from various sources. These sources can be internally (proprioceptive) or externally (such as touch and pressure) generated senses. Ample evidence exists to demonstrate that the sensory information originating from large diameter afferents (Ia fibers) have an important role in inducing essential functional and morphological changes for the maturation of both the brain and the spinal cord. The Ia fibers transmit sensory information generated by muscle activity and movement. Such use or activity-dependent plastic changes occur throughout life and are one reason for the ability to acquire new skills and learn new movements. However, the extent and particularly the mechanisms of activity-dependent changes are markedly different between a developing nervous system and a mature nervous system. Understanding these mechanisms is an important step to develop strategies for regaining motor function after different injuries to the CNS. Plastic changes induced by activity occur both in the brain and spinal cord. This paper reviews the activity-dependent changes in the spinal cord neural circuits during both the developmental stages of the CNS and in adulthood.

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Figures

Figure 1
Figure 1
Presynaptic inhibition to Ia fibers. (i) Schematic diagram of different inputs to Ia afferents and alpha motoneurons. Proprioceptive input from Ia fiber can be selectively suppressed by presynaptic inhibition through PAD interneurons. The interneuron which makes axoaxonic connection with Ia fiber is GABAergic and regarded as last-order PAD IN. This interneuron is under the influence of an excitatory interneuron which is referred to as first-order PAD IN. This first-order PAD IN receives inputs from both descending tracts and from peripheral afferents [15]. In such a case, different inputs can interact to control the Ia input to motoneurons without affecting the intrinsic properties of motoneurons. (ii) During presynaptic inhibition, the normal activity of the muscle can remain unchanged, while the reflex gain reduces. In this example, standing with prism goggles (PV condition) suppressed the H-reflex in comparison to normal vision (NV) standing condition (a), while there was no change in the soleus and tibialis anterior muscle EMG activity (b). This is most likely due to the presynaptic inhibition of Ia fibers which spares the background activity of motoneurons. Part II adapted with permission from [16].
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