Neural mechanisms of hyperalgesia after tissue injury

For more than 25 years, investigators from APL and the Johns Hopkins School of Medicine have collaborated on research aimed at understanding the neural mechanisms of pain sensation. This research is based on correlating results from studies of pain sensations in humans with results from studies of neural activity in anesthetized animals. One aspect of pain that has clinical importance is hyperalgesia-the enhanced pain to stimuli applied to the skin that develops after tissue injury and in certain diseases. We review here the neural mechanisms of hyperalgesia. Primary hyperalgesia, which develops at the site of tissue injury, is associated with an increased sensitivity of the peripheral nerve fibers involved in pain. Secondary hyperalgesia, which develops in uninjured tissue surrounding the site of injury, exhibits symptoms similar to those seen in chronic pain patients and is caused by an enhanced neural responsiveness in the central nervous system.