Background & Aims

Understanding the development and maintenance of pathological pain is critical for the discovery of therapeutic targets. Different forms of pathological pain alter nociceptive processing in the superficial dorsal horn (SDH) of the spinal cord through distinct mechanisms, but these differences are not well understood.1-4 The purpose of this project was to develop and and apply an ex-vivo SDH Ca2+ imaging pipeline to screen different forms of pathological pain.

Methods

We employed several models of pathological pain: acute inflammatory (Capsaicin), protracted inflammatory (Complete Freud’s Adjuvant, CFA), neuropathic (Spared Nerve Injury, SNI), and osteoarthritic (ACL transection, OA). All models exhibited peripheral mechanical hypersensitivity after injury. We captured network wide SDH dynamics of spontaneous and evoked cellular activity, under various pain conditions, using epifluorescent Ca2+ imaging in an ex-vivo
setup.5 To confirm this approach could elucidate alterations in cellular Ca2+ responses, we applied blockers of GABAergic and glycinergic receptor mediated inhibition (bicuculline and strychnine), a model of disinhibition.

Results

We observed that SDH cells exhibited a higher amplitude of Ca2+ response to glutamate in ipsilateral compared to contralateral controls. When glutamate was applied to stimulate neuronal activity, we found that the SDH neurons from Capsaicin, CFA, and SNI models exhibited a higher amplitude of Ca2+ response compared to controls, while the OA model did not elicit a difference in response. Unexpectedly, the number of spontaneously active neurons, in the absence of glutamate, was significantly decreased in the OA, Capsaicin, and CFA models.

Conclusions

Collectively, our findings provide further insight into the diverse manifestations of inflammatory, neuropathic, and osteoarthritic pain across different time scales in the spinal cord.

References

1 Kuner R. (2010). Central mechanisms of pathological pain. Nature medicine, 16(11), 1258–1266. https://doi.org/10.1038/nm.2231

2 Baron, R., Binder, A., & Wasner, G. (2010). Neuropathic pain: diagnosis, pathophysiological mechanisms, and treatment. The Lancet. Neurology, 9(8), 807–819. https://doi.org/10.1016/S1474-4422(10)70143-5

3 Costigan, M., & Woolf, C. J. (2000). Pain: molecular mechanisms. The journal of pain, 1(3 Suppl), 35–44. https://doi.org/10.1054/jpai.2000.9818

4 Luo, C., Kuner, T., & Kuner, R. (2014). Synaptic plasticity in pathological pain. Trends in neurosciences, 37(6), 343–355. https://doi.org/10.1016/j.tins.2014.04.002

5 Doolen, S., Blake, C. B., Smith, B. N., & Taylor, B. K. (2012). Peripheral nerve injury increases glutamate-evoked calcium mobilization in adult spinal cord neurons. Molecular pain, 8, 56. https://doi.org/10.1186/1744-8069-8-56

Presenting Author

Samuel Fung

Poster Authors

Samuel Fung

BSc(Hons)

University of Toronto

Lead Author

Erika Harding

PhD

Hotchkiss Brain Institute, University of Calgary

Lead Author

Jo Anne Stratton

PhD

Montreal Neurological Hospital and Institute, Department of Neurology, McGill University

Lead Author

Stephanie Norlock

MSc

Department of Neuroscience, Carleton University

Lead Author

Jenny Cheung

BSc

Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toront

Lead Author

Hantao Zhang

BSc

Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toront

Lead Author

Jeff Biernaskie

PhD

Hotchkiss Brain Institute, University of Calgary

Lead Author

Michael E Hildebrand

PhD

Department of Neuroscience, Carleton University

Lead Author

Robert P. Bonin

Lead Author

Topics

  • Mechanisms: Biological-Systems (Physiology/Anatomy)