Pain
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Nociceptive primary afferents have the capacity to induce a state of increased excitability or central sensitization in dorsal horn neurones. This contributes to the mechanical hypersensitivity (allodynia) which occurs after peripheral tissue injury where low-mechanothreshold primary afferent activation begins to elicit pain. The relative susceptibility of dorsal horn cells with an apparent exclusive nociceptive input (nociceptive-specific (NS) or high-threshold (HT) cells) and those with a convergent input from low- and high-threshold mechanoreceptors (wide-dynamic-range (WDR) or multireceptive neurones) to sensitivity changes has been disputed. ⋯ In 3 cells, an increase in the response to A-fibre afferents occurred, a novel A-fibre response was recruited in 2 cells and the C-fibre response increased in 2 cells. Cells in the superficial dorsal horn of the rat spinal cord that are normally NS can begin, therefore, to respond to LT primary afferent mechanoreceptors after an increase in central excitability produced by activation of peripheral chemoreceptors. Sensitization of these, as well as of WDR cells, may contribute to the generation of post-injury mechanical pain and reflex hypersensitivity.
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The communication of pain requires a sufferer to encode and transmit the experience and an observer to decode and interpret it. Rosenthal's (1982) model of communication was applied to an analysis of the role of facial expression in the transmission of pain information. Videotapes of patients with shoulder pain undergoing a series of movements of the shoulder were shown to a group of 5 judges. ⋯ The results indicated that although observers can make coarse distinctions among patients' pain states, they (1) are not especially sensitive, and (2) are likely to systematically downgrade the intensity of patients' suffering. Moreover, observers appear to make insufficient use of information that is available in patients' facial expression. Implications of the findings for pain patients and for training of health-care workers are discussed as are directions for future research.