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Pain Research and Management
Volume 9 (2004), Issue 2, Pages 89-97
http://dx.doi.org/10.1155/2004/150503
Original Article

Alpha-1 Adrenoceptor Hyperresponsiveness in Three Neuropathic Pain States: Complex Regional Pain Syndrome 1, Diabetic Peripheral Neuropathic Pain and Central Pain States Following Spinal Cord Injury

Robert W Teasell1,3,4,5 and J Malcolm O Arnold2,3,4,6

1Physical Medicine and Rehabilitation, University of Western Ontario, Canada
2Internal Medicine, University of Western Ontario, Canada
3Lawson Research Institute, Canada
4University of Western Ontario, Canada
5Parkwood Hospital, St Joseph’s Health Care London, Canada
6London Health Sciences Centre, London, Ontario, Canada

Copyright © 2004 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The pathophysiology of the pain associated with complex regional pain syndrome, spinal cord injury and diabetic peripheral neuropathy is not known. The pain of complex regional pain syndrome has often been attributed to abnormal sympathetic nervous system activity based on the presence of vasomotor instability and a frequently reported positive response, albeit a temporary response, to sympathetic blockade. In contrast, the pain below the level of spinal cord injury and diabetic peripheral neuropathy are generally seen as deafferentation phenomena. Each of these pain states has been associated with abnormal sympathetic nervous system function and increased peripheral alpha-1 adrenoceptor activity. This increased responsiveness may be a consequence of alpha-1 adrenoceptor postsynaptic hypersensitivity, or alpha-2 adrenoceptor presynaptic dysfunction with diminished noradrenaline reuptake, increased concentrations of noradrenaline in the synaptic cleft and increased stimulation of otherwise normal alpha-1 adrenoceptors. Plausible mechanisms based on animal research by which alpha-1 adrenoceptor hyperresponsiveness can lead to chronic neuropathic-like pain have been reported. This raises the intriguing possibility that sympathetic nervous system dysfunction may be an important factor in the generation of pain in many neuropathic pain states. Although results to date have been mixed, there may be a greater role for new drugs which target peripheral alpha-2 adrenoceptors (agonists) or alpha-1 adrenoceptors (antagonists).