- Title
- The role of calretinin positive interneurons in spinal sensory coding
- Creator
- Smith, Kelly
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The spinal cord dorsal horn (DH) represents an important area in the processing of sensory information. As the first point in the central nervous system (CNS) where peripheral signals input, our understanding of information processing that occurs here is crucial if we are to better manage sensory dysfunction. Chapter 1 details this background along with emphasising the significant heterogeneity that exists in this region, which has made the elucidation of specific DH circuit’s difficult. Fortunately, advances in molecular and genetic techniques have facilitated the targeting of individual neuron populations. Building from this technology, experiments in this thesis examine the role of a specific population of DH neurons that can be identified by expression of the calcium binding protein calretinin (CR). CR has previously been shown to be expressed on a sub population of excitatory interneurons, however little work has been done to identify their role in spinal pain processing. Chapter 2 first examines the electrophysiological and morphological properties of CR+ neurons in the DH. In this analysis I identified two functionally and morphologically distinct populations of CR+ neurons, referred to as Typical and Atypical. Typical CR neurons exhibited features consistent with excitatory interneurons, including high frequency spontaneous excitatory input, delayed action potential (AP) discharge patterns, A-type potassium currents and central, radial or vertical cell morphologies. While, Atypical CR neurons showed inhibitory interneuron characteristics, including low frequency spontaneous excitatory input, tonic AP discharge patterns, Ih currents and islet-like morphology. The spontaneous inhibitory input received by these two populations of CR+ neurons also differed. Typical, excitatory CR neurons receive mixed inhibition from both GABAergic and glycinergic sources, whereas, inhibition of the inhibitory CR+ neurons was glycine dominant (Chapter 3). In order to look at the functional connections of CR+ neurons within the DH I used channel rhodopsin assisted circuit mapping. These experiments identified a high level of connectivity both amongst CR+ neurons and to other, unidentified populations. Importantly, among the identified connections CR+ neurons provided input to identified projection neurons, the functional output cells of the dorsal (sensory) spinal cord. To further resolve the postsynaptic targets of CR+ neurons I next applied spinal optogenetic stimulation in anaesthetised mice, before undertaking c-Fos immunohistochemistry to label activated populations and identify them with neurochemical markers of known DH subpopulations. This showed that, in addition to projection neurons (identified here by NK-1R labelling), CR+ neurons activated a substantial inhibitory population, and selective populations of excitatory interneurons. Finally, I developed a surgical approach to chronically implant a fibre optic probe over the spinal cord. This allowed me to assess the behavioural phenotype associated with spinal CR+ neuron activation. These results showed that in awake and behaving animals CR+ neuron activation generates a strong nocifensive behavioural response that outlasts optogenetic stimulation, shifts over the body surface, potentiates when stimulation is repeated, is blocked by morphine administration, and produces a conditioned place aversion. Overall, my thesis provides a thorough characterisation of CR+ DH neurons at a single cell, circuit and behavioural level. This has greatly contributed to our understanding of sensory processing in the spinal cord, particularly excitatory interneurons, an important population, which has not previously been studied in this level of detail.
- Subject
- calretinin positive interneurons; spinal sensory coding; spinal cord; sensory information; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1355332
- Identifier
- uon:31446
- Rights
- Copyright 2018 Kelly Smith
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 3 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 234 KB | Adobe Acrobat PDF | View Details Download |