Pain
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In a group of 30 subjects suffering from sympathetic reflex dystrophies of the limbs, the sympathetic ganglia of the affected side were blocked with a local anesthetic. Using an original method, we measured the cutaneous pain threshold before the block and at prefixed intervals after the block during a period of 2 days. In all subjects the cutaneous pain threshold showed damped oscillations both in the limb ipsilateral to the block and in the contralateral one. The analysis of these oscillations showed: (a) that the sympathetic control of the cutaneous pain threshold may be exerted through a negative feedback loop (skin-afferent input-CNS-sympathetic output-skin); (b) that the afferent discharge of a limb controls the contralateral sympathetic output through central mechanisms.
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Of 113 patients treated in a 2-year period, for whom complete data were available, 29 who received surgery for pain relief were compared with 84 who did not, both groups receiving psychological treatment and rehabilitation. Using an analysis of covariance to eliminate pre-treatment differences, the surgery patients showed significantly greater reductions on the MMPI Hysteria and Hypomania scales, and on the invalidism scale of a Health Index, and this was associated with a significantly greater reduction of pain. These differences obtained despite a greater increase in activity levels by the non-surgery patients at the time of testing. The results support the hypothesis that the neuroticism associated with chronic pain is the result of it, and may be reversible when the pain is reduced or abolished.
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In the cat, electrical stimulation of the inferior central nucleus of the raphe induces a powerful analgesia. This stimulation totally suppresses the behavioural reactions elicited by strong pinches applied to the tail or to the four limbs; it strongly modifies the threshold of the jaw opening reflex obtained by tooth pulp stimulation and considerably affects the behavioural reactions elicited by continuing such stimulation. ⋯ The analgesia obtained by stimulation of raphe nuclei seems to be sustained by serotoninergic mechanisms and relationships between these are discussed. In preliminary experiments, analgesia induced by CI stimulation has been suppressed by administration of naloxone, a specific opiate antagonist.