The developmental emergence of differential brainstem serotonergic control of the sensory spinal cord

F Schwaller,M Fitzgerald,A H Kanellopoulos

doi:10.1038/s41598-017-02509-2

F Schwaller, M Fitzgerald + Show 1 more

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https://doi.org/10.1038/s41598-017-02509-2

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Abstract

Descending connections from brainstem nuclei are known to exert powerful control of spinal nociception and pain behaviours in adult mammals. Here we present evidence that descending serotonergic fibres not only inhibit nociceptive activity, but also facilitate non-noxious tactile activity in the healthy adult rat spinal dorsal horn via activation of spinal 5-HT3 receptors (5-HT3Rs). We further show that this differential serotonergic control in the adult emerges from a non-modality selective system in young rats. Serotonergic fibres exert background 5-HT3R mediated facilitation of both tactile and nociceptive spinal activity in the first three postnatal weeks. Thus, differential descending serotonergic control of spinal touch and pain processing emerges in late postnatal life to allow flexible and context-dependent brain control of somatosensation.

Highlights

The brain can powerfully modulate the processing of somatosensory information at lower levels of the central nervous system (CNS)
The results show that descending raphe spinal serotonergic pathways, mediated by 5-HT3 receptors (5-HT3Rs) in the spinal dorsal horn, enhance
We used retrograde tracing to demonstrate that serotonergic neurons in the rostroventral medial medulla (RVM) project to the lumbar spinal cord in young rats and that the proportion of spinally projecting serotonergic RVM neurons increases between P10-P16 (Supplementary Fig. 1A and C)

Summary

Introduction

The brain can powerfully modulate the processing of somatosensory information at lower levels of the central nervous system (CNS). There is considerable evidence that supraspinal pathways selectively target high-threshold nociceptive inputs in the spinal dorsal horn[4,5,6,7], but earlier studies suggested that descending PAG-RVM control of spinal somatosensation is not nociceptive-selective and targets non-noxious inputs[8, 9]. This evidence has been largely overlooked in recent studies. Tactile spinal processing throughout life, but are responsible for the endogenous facilitation of nociceptive inputs in young animals, before the emergence of a mature balanced descending control

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