Pain
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(1) Electrophysiological properties of dorsal horn neurones have been investigated in decerebrate, immobilized spinal rats rendered polyarthritic by intradermal injection of Freund's adjuvant. Since arthritis is associated with pronounced erythema and oedema of the foot sole and ankle areas, this particular study was devoted to the induced modifications of responses of units driven by cutaneous inputs. It allowed comparison with previous studies performed in healthy animals. (2) Superficial dorsal horn cells could be separated in: those driven from non-oedematous skin and which had properties similar to those observed in healthy animals; and those driven from oedematous skin and which characterized by unclassical electrophysiological properties such as: (a) a relatively high level of background activity, frequently with bursting pattern and sometimes exhibiting dramatic increases; these neurones are normally silent in healthy animals; (b) a high degree of responsivity to light mechanical stimuli associated with a clear decrease in threshold. ⋯ Responses to radiant heat showed an increase in threshold, sometimes associated with a very high degree of adaptation. (6) Another group of neurones displayed fading responses to repetitive mechanical stimuli. All were located in the deeper two-thirds of the dorsal horn. (7) These data indicate that chronic pathological conditions related to articular and/or cutaneous diseases strongly modify the responses of dorsal horn neurones, some being at the origin of ascending tracts. This model seems to be a promising approach to study the fundamental mechanisms involved in chronic pain in order to approach these problems in human beings.
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Case Reports
Inhibition of cutaneous nociception by deep musculoskeletal pain. A clinical observation.
A patient is reported in whom deep musculoskeletal pain apparently blocked transmission from nociceptive cutaneous fibers in an adjacent region. When the deep musculoskeletal pain was abolished with local anesthesia, the cutaneous hypalgesia disappeared. Naloxone did not influence the hypalgesia. Possible mechanisms are discussed.