Pain
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The effect of single and repetitive electrical stimulation of the dorsal columns on cells in laminae IV and V of the ipsilateral dorsal horn at S1 was examined in spinalized cats. About two-thirds of the cells responded to thermal nociceptive cutaneous stimulation and of these most responded also to low threshold mechanical stimulation. The other one-third of the cells were innervated by mechanoreceptors including type I or Haarscheiben. ⋯ Assuming that the studied interneurons have a pain-mediating function, the results indicate that some cumulative and poststimulatory DCS suppression of pain may be ascribed to spinal mechanisms. The more effective and longer lasting suppression produced by DCS in pain patients would, however, be dependent on other types of interneurons, on suprasegmental loops and/or on effects on pathophysiological mechanisms which may be operative in the chronic pain state. The lack of cumulative inhibition in most of the cells in this study is compatible with the previous observation of a retained perception of acute pain during DCS in man.
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Experimental evidence is reviewed showing that brain and spinal cord serotonergic neurons are involved in nociceptive responses, as well as in the analgesic effects of opiate narcotics. This evidence, based on studies employing pharmacological, surgical, electrophysiological, and dietary manipulations of central nervous system serotonergic neurotransmission, suggests that increases in the activity of brain and spinal cord serotonin neurons are associated with analgesia and enhanced antinociceptive drug potency, whereas decreases in the activities of these neurons correlate with hyperalgesia and diminished analgesic drug potency.
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Comparative Study
Response to cold pressor pain and to acupuncture analgesia in Oriental and Occidental subjects.
On a no treatment trial, a group of 24 oriental subjects rated cold pressor pain as significantly more painful and distressing than did a group of 24 occidental subjects. For half of the Orientals and half of the Occidentals, a second trial was conducted after acupuncture analgesia had been induced. ⋯ As they had on trial 1, Orientals reported significantly more pain and distress in response to ice water on trial 2. It is concluded that: (1) if acupuncture does work better for the Chinese than for other racial groups, the likely cause is a more refined patient selection procedure rather than an inherent difference in response to acupuncture; (2) evidence does not support the stereotyped view of Orientals as stoical in the face of physical pain.
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Pharmacological actions on the nociceptive flexion flexes of the hindlimb were investigated in 14 normal subjects. These reflexes were used as an index of pain and were recorded in the biceps femoris muscle, elicited by electrical stimulation of the ipsilateral sural nerve (RIII,su) and of the skin in the distal receptive field of this nerve (RIII,Cu). The ratio of the threshold of RIII,Cu/RIII,Su was calculated since it gives an indication on the mechanism and the efficacy of the drug. ⋯ In contrast, pethidine provoked a decrease in the RIII,Su threshold and an increase in RIII,Cu threshold, parallel with an increase in pain threshold sensation. The ratio was found to be 190% at the maximal effect. Practical implications of these results, concerning a method for testing the efficacy and mechamisms of an analgesic, are then discussed.
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Clinical Trial Controlled Clinical Trial
On the sensitivity of the tourniquet pain test.
Twenty-four chronic pain patients were given, on each of 4 successive days, oral doses of 60 mg morphine, 60 mg codeine, 600 mg aspirin and placebo, using a double-blind counterbalanced design. Two hours after ingestion, subjective pain estimates and tourniquet pain scores were obtained. ⋯ However, differences in pain estimates were also too small to discriminate among the drugs, and the lack of sensitivity may be a function of pain chronicity. The tourniquet techniques will continue to be useful until there is a purely objective measure of the severity of clinical pain.