Tamara King co-authors article on neuropathic pain in the 'Journal of Pain'

Tamara King, Ph.D., assistant professor of biomedical sciences, co-authored an article titled “Descending Facilitation Maintains Long-Term Spontaneous Neuropathic Pain,” which was published in the August 2013 issue of the Journal of Pain.

The article looks at the mechanisms giving rise to the long-lasting spontaneous pain, or pain at rest, which is a hallmark feature of neuropathic pain.  While hypersensitivity to touch and cold is a well-described consequence of nerve injury, the chronic nature of neuropathic pain is poorly understood.   The authors’ studies show that thermal hypersensitivity resolves within 35 to 40 days following nerve injury but tactile sensitivity remains elevated even after 580 days (about 19 months).

This long-term hypersensitivity to touch appears to result from an increased number of neurons being activated in the spinal cord, an indication of spinal sensitization.  The effect is blocked by a lesion to the dorsolateral funiculus, part of a descending pathway from the brain to the spinal cord that modulates incoming neuronal activity from peripheral tissues.

The study’s finding, therefore, indicates that such descending pathways play a role in sensitizing the spinal cord following nerve injury and making it more responsive to potentially painful and even benign stimuli.

Similarly, the authors use a conditioned place preference paradigm to investigate spontaneous pain, or pain at rest, that is not evoked by tactile or thermal stimuli.  They found that 40-60 days following nerve injury, animals show a significant preference for a chamber that is paired with blockade of descending pain facilitatory pathways from the rostral ventromedial medulla (RVM).

These findings demonstrate that spontaneous pain persists after recovery of thermal hypersensitivity, suggesting different underlying mechanisms driving these pain states.  In addition, the data indicate that nerve-injury induced tactile hypersensitivity and spontaneous pain persist longer than thermal hypersensitivity and that both are maintained by descending facilitation.

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