- Title
- The effect of neck muscle inflammation on neuronal excitability in the dorsal horn of the spinal cord
- Creator
- Harris, Belinda Maree
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2012
- Description
- Masters Research - Master of Philosophy (MPhil)
- Description
- Studies on the nociceptive (or pain) system have focused primarily on that of nociception of cutaneous origin, rather than that from deep structures that can also cause pain, such as bone and muscle. From what we do know of muscle pain, however, pain in deep tissues differs not only in sensation, but also in the sensory processing within the central nervous system. Thus, given these differences, it is remiss to suggest that the underlying mechanisms that drive cutaneous pain are also those that drive muscle pain. However, evidence is currently lacking. Further, for those studies that have been conducted on muscle pain, experimental models have focused primarily on limb muscles. This is possibly due to the ease of experimental design. Yet, like cutaneous and muscle pain, differences also exist between appendicular (eg. gastrocnemius) and axial (eg. rectus capitis major) muscles. Due to the structural disparity between the two, it is possible that the major clinical problem of pain syndromes within axial muscles, such as back and neck pain, exists due to these differences. Likewise, in order to model muscle pain of back or neck origin, a disease-specific model needs to be utilised. Accordingly, in order to test the underlying spinal mechanisms that accompany axial muscle pain, the rectus capitis major muscle of the mouse neck was injected with 2% carrageenan (in PBS), and c-Fos activation along with whole-cell patch clamp recordings including intrinsic neuronal properties, discharge patterns, hyperpolarising patterns, subthreshold currents, and spontaneous excitatory post-synaptic currents were obtained in the cervical (C1/C2) superficial dorsal horn (SDH) following an acute (2 hours) time frame. These results were contrasted against a sham-injected (PBS) and control (uninjected) model. Results indicate that following 2 hours of inflammation, neurons show c-Fos activation exclusively within the carrageenan-injection model along the mediolateral aspect of the SDH, ipsilateral to the injected muscle. This neuronal activation was coupled with electrophysiological results which indicate a significantly more depolarised resting membrane potential following carrageenan injection compared to control and PBS injected groups, a reduction in reluctant firer population following current injection protocols, and increase in T-type Ca²⁺ subthreshold currents and a decrease in hyperpolarisation-activated currents, which suggest an increase in spinal cord hyperexcitability. Surprisingly, an increase in decay kinetics was also identified in spontaneous excitatory post-synaptic currents 2 hours following carrageenan muscle injection. This alternatively would suggest a reduction in hyperexcitability. Accordingly, it can be concluded from these sets of experiments that within the isolated spinal cord, and therefore independent of further peripheral or descending input, the SDH of the cervical spinal cord shows attributes of hyperexcitability while still being under some form of inhibitory control following neck muscle inflammation. As such, 2 hours post neck muscle inflammation may be the transition zone between peripheral and central sensitisation, with the inhibitory component identified through faster decay time constant indicating a neuroprotective mechanism is in place within the SDH in the early stages of the process toward central sensitisation.
- Subject
- pain; dorsal horn; neck; spinal cord
- Identifier
- http://hdl.handle.net/1959.13/932045
- Identifier
- uon:11242
- Rights
- Copyright 2012 Belinda Maree Harris
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT02 | Thesis | 8 MB | Adobe Acrobat PDF | View Details Download |