Projection neuron axon collaterals in the dorsal horn: placing a new player in spinal cord pain processing

Browne, T. J., Hughes, D. I. , Dayas, C. V., Callister, R. J. and Graham, B. A. (2020) Projection neuron axon collaterals in the dorsal horn: placing a new player in spinal cord pain processing. Frontiers in Physiology, 11, 560802. (doi: 10.3389/fphys.2020.560802) (PMID:33408637)

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Abstract

The pain experience depends on the relay of nociceptive signals from the spinal cord dorsal horn to higher brain centres. This function is ultimately achieved by the output of a small population of highly specialised neurons called projection neurons (PNs). Like output neurons in other CNS regions, PNs are invested with a substantial axon collateral system that ramifies extensively within local circuits. These axon collaterals are widely distributed within and between spinal cord segments. Anatomical data on PN axon collaterals has existed since the time of Cajal, however, their function in spinal pain signalling remains unclear and is absent from current models of spinal pain processing. Despite these omissions, some insight on the potential role of PN axon collaterals can be drawn from axon collateral systems of principal or output neurons in other CNS regions such as the hippocampus, amygdala, olfactory cortex and ventral horn of the spinal cord. The connectivity and actions of axon collaterals in these systems have been well defined and used to confirm crucial roles in memory, fear, olfaction and movement control, respectively. We review this information here and propose a framework for characterising PN axon collateral function in the dorsal horn. We highlight that experimental approaches traditionally used to delineate axon collateral function in other CNS regions are not easily applied to PNs because of their scarcity relative to spinal interneurons, and the lack of cellular organisation in the dorsal horn. Finally, we emphasise how the rapid development of techniques such as viral expression of optogenetic or chemogenetic probes can overcome these challenges and allow characterisation of PN axon collateral function. Obtaining detailed information of this type is a necessary first step for incorporation of PN collateral system function into models of spinal sensory processing.

Item Type:Articles
Additional Information:This work was funded by the National Health and Medical Research Council (NHMRC) of Australia (grants 631000, 1043933, 1144638, and 1184974 to BG and RC), the Biotechnology and Biological Sciences Research Council (BB/P007996/1 to DH), and the Hunter Medical Research Institute (grant to BG and RC).
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Hughes, Dr David I
Authors: Browne, T. J., Hughes, D. I., Dayas, C. V., Callister, R. J., and Graham, B. A.
College/School:College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
Journal Name:Frontiers in Physiology
Publisher:Frontiers Media
ISSN:1664-042X
ISSN (Online):1664-042X
Copyright Holders:Copyright © 2020 Browne, Hughes, Dayas, Callister and Graham
First Published:First published in Frontiers in Physiology
Publisher Policy:Reproduced under a Creative Commons license

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
174050Determining the role of calretinin-RorB spinal interneurons in modulating mechanical painDavid I HughesBiotechnology and Biological Sciences Research Council (BBSRC)BB/P007996/1Institute of Neuroscience & Psychology