Selective innervation of NK1 receptor–lacking lamina I spinoparabrachial neurons by presumed nonpeptidergic Aδ nociceptors in the rat

Baseer, N., Al-Baloushi, A. S., Watanabe, M., Shehab, S. A.S. and Todd, A. J. (2014) Selective innervation of NK1 receptor–lacking lamina I spinoparabrachial neurons by presumed nonpeptidergic Aδ nociceptors in the rat. Pain, 155(11), pp. 2291-2300. (doi: 10.1016/j.pain.2014.08.023) (PMID:25168670) (PMCID:PMC4247378)

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Abstract

Fine myelinated (Aδ) nociceptors are responsible for fast, well-localised pain, but relatively little is known about their postsynaptic targets in the spinal cord, and therefore about their roles in the neuronal circuits that process nociceptive information. Here we show that transganglionically transported cholera toxin B subunit (CTb) labels a distinct set of afferents in lamina I that are likely to correspond to Aδ nociceptors, and that most of these lack neuropeptides. The vast majority of lamina I projection neurons can be retrogradely labelled from the lateral parabrachial area, and these can be divided into 2 major groups based on expression of the neurokinin 1 receptor (NK1r). We show that CTb-labelled afferents form contacts on 43% of the spinoparabrachial lamina I neurons that lack the NK1r, but on a significantly smaller proportion (26%) of those that express the receptor. We also confirm with electron microscopy that these contacts are associated with synapses. Among the spinoparabrachial neurons that received contacts from CTb-labelled axons, contact density was considerably higher on NK1r-lacking cells than on those with the NK1r. By comparing the density of CTb contacts with those from other types of glutamatergic bouton, we estimate that nonpeptidergic Aδ nociceptors may provide over half of the excitatory synapses on some NK1r-lacking spinoparabrachial cells. These results provide further evidence that synaptic inputs to dorsal horn projection neurons are organised in a specific way. Taken together with previous studies, they suggest that both NK1r+ and NK1r-lacking lamina I projection neurons are directly innervated by Aδ nociceptive afferents.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Todd, Professor Andrew
Authors: Baseer, N., Al-Baloushi, A. S., Watanabe, M., Shehab, S. A.S., and Todd, A. J.
College/School:College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
Journal Name:Pain
Publisher:Elsevier
ISSN:0304-3959
ISSN (Online):1872-6623
Copyright Holders:Copyright © 2014 The Authors
First Published:First published in Pain 155(11):2291-2300
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
644161Defining pain circuitry in health and diseaseAndrew ToddWellcome Trust (WELLCOME)102645/Z/13/ZINP - CENTRE FOR NEUROSCIENCE
644162Defining pain circuitry in health and diseaseAndrew ToddWellcome Trust (WELLCOME)102645/Z/13/ZINP - CENTRE FOR NEUROSCIENCE