Exploring acute-to-chronic neuropathic pain in rats after contusion spinal cord injury

May 30, 2017Experimental neurology

Changes in nerve pain from short-term to long-term after spinal cord injury in rats

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Abstract

65% of individuals with spinal cord injury experience chronic pain.

Current pain management strategies are inadequate for many spinal cord injury patients.
Different types of contusion spinal cord injuries in rats lead to varying levels of neuropathic pain.
Female rats showed modest mechanical sensitivity and prolonged sensitivity to heat after specific spinal injuries.
Male rats exhibited sensitivity to touch following spinal injuries, while both sexes had heightened sensitivity to heat.
Acute morphine treatment did not worsen chronic pain symptoms in the rat models used.
Unilateral spinal cord injuries caused temporary sensitivity to touch without affecting heat sensitivity.

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Spinal cord injury (SCI) causes chronic pain in 65% of individuals. Unfortunately, current pain management is inadequate for many SCI patients. Rodent models could help identify how SCI pain develops, explore new treatment strategies, and reveal whether acute post-SCI morphine worsens chronic pain. However, few studies explore or compare SCI-elicited neuropathic pain in rats. Here, we sought to determine how different clinically relevant contusion SCIs in male and female rats affect neuropathic pain, and whether acute morphine worsens later chronic SCI pain. First, female rats received sham surgery, or 150kDyn or 200kDyn midline T9 contusion SCI. These rats displayed modest mechanical allodynia and long-lasting thermal hyperalgesia. Next, a 150kDyn (1s dwell) midline contusion SCI was performed in male and female rats. Interestingly, males, but not females showed SCI-elicited mechanical allodynia; rats of both sexes had thermal hyperalgesia. In this model, acute morphine treatment had no significant effect on chronic neuropathic pain symptoms. Unilateral SCIs can also elicit neuropathic pain that could be exacerbated by morphine, so male rats received unilateral T13 contusion SCI (100kDyn). These rats exhibited significant, transient mechanical allodynia, but not thermal hyperalgesia. Acute morphine did not exacerbate chronic pain. Our data show that specific rat contusion SCI models cause neuropathic pain. Further, chronic neuropathic pain elicited by these contusion SCIs was not amplified by our course of early post-trauma morphine. Using clinically relevant rat models of SCI could help identify novel pain management strategies.

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Exploring acute-to-chronic neuropathic pain in rats after contusion spinal cord injury

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