Functional and molecular analysis of proprioceptive sensory neuron excitability in mice

Madden, J.F., Davis, O.C., Boyle, K.A., Iredale, J.A., Browne, T.J., Callister, R.J., Smith, D.W., Jobling, P., Hughes, D.I. and Graham, B.A. (2020) Functional and molecular analysis of proprioceptive sensory neuron excitability in mice. Frontiers in Molecular Neuroscience, 13, 36. (doi: 10.3389/fnmol.2020.00036) (PMID:32477061) (PMCID:PMC7232575)

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Abstract

Neurons located in dorsal root ganglia (DRG) are crucial for transmitting peripheral sensations such as proprioception, touch, temperature, and nociception to the spinal cord before propagating these signals to higher brain structures. To date, difficulty in identifying modality-specific DRG neurons has limited our ability to study specific populations in detail. As the calcium-binding protein parvalbumin (PV) is a neurochemical marker for proprioceptive DRG cells we used a transgenic mouse line expressing green fluorescent protein (GFP) in PV positive DRGs, to study the functional and molecular properties of putative proprioceptive neurons. Immunolabeled DRGs showed a 100% overlap between GFP positive (GFP+) and PV positive cells, confirming the PVeGFP mouse accurately labeled PV neurons. Targeted patch-clamp recording from isolated GFP+ and GFP negative (GFP−) neurons showed the passive membrane properties of the two groups were similar, however, their active properties differed markedly. All GFP+ neurons fired a single spike in response to sustained current injection and their action potentials (APs) had faster rise times, lower thresholds and shorter half widths. A hyperpolarization-activated current (Ih) was observed in all GFP+ neurons but was infrequently noted in the GFP− population (100% vs. 11%). For GFP+ neurons, Ih activation rates varied markedly, suggesting differences in the underlying hyperpolarization-activated cyclic nucleotide-gated channel (HCN) subunit expression responsible for the current kinetics. Furthermore, quantitative polymerase chain reaction (qPCR) showed the HCN subunits 2, 1, and 4 mRNA (in that order) was more abundant in GFP+ neurons, while HCN 3 was more highly expressed in GFP− neurons. Likewise, immunolabeling confirmed HCN 1, 2, and 4 protein expression in GFP+ neurons. In summary, certain functional properties of GFP+ and GFP− cells differ markedly, providing evidence for modality-specific signaling between the two groups. However, the GFP+ DRG population demonstrates considerable internal heterogeneity when hyperpolarization-activated cyclic nucleotide-gated channel (HCN channel) properties and subunit expression are considered. We propose this heterogeneity reflects the existence of different peripheral receptors such as tendon organs, muscle spindles or mechanoreceptors in the putative proprioceptive neuron population.

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/J000620/1, BB/P007996/1 to DH) and the Hunter Medical Research Institute (Glenn Moss grant to BG).
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Boyle, Dr Kieran and Hughes, Dr David I
Authors: Madden, J.F., Davis, O.C., Boyle, K.A., Iredale, J.A., Browne, T.J., Callister, R.J., Smith, D.W., Jobling, P., Hughes, D.I., and Graham, B.A.
College/School:College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
Journal Name:Frontiers in Molecular Neuroscience
Publisher:Frontiers Media
ISSN:1662-5099
ISSN (Online):1662-5099
Copyright Holders:Copyright © 2020 Madden, Davies, Boyle, Iredale, Browne, Callister, Smith, Jobling, Hughes and Graham
First Published:First published in Frontiers in Molecular Neuroscience 13:36
Publisher Policy:Reproduced under a Creative Commons license

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
165961Modulating cutaneous afferent input: Identifying a source of presynaptic (axo-axonic) inputs in the mouse spinal dorsal hornDavid I HughesBiotechnology and Biological Sciences Research Council (BBSRC)BB/J000620/1NP - Centre for Neuroscience
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