La Revue du praticien
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The placebo induces a significant analgesia on average in 35% patients with some variations according to the studied pathology and the modalities of the therapy. This placebo effect is especially influenced by the expectations and beliefs of the patient, the doctor, the environment and the quality of the doctor-patient relationship. As with a real psychogenic analgesia, this effect could partly result in a release of endogenous opioid substances. By a good relationship with his patient and a treatment corresponding to his expectations and his beliefs, the doctor induces a powerful placebo effect which increases the specific effects of his analgesic treatment.
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During these last years the methods and the indications of analgesic neurosurgery have respectively changed toward greater multiplicity and more selectivity. The conservative methods of neurostimulation have acquired a prominent place in some types of pain from neuropathic origin. ⋯ Intrathecal morphine administration, has been shown to be useful to control some cancer-induced pain. Lastly, the techniques of interrupting the pathways of pain, achieving greater selectivity in their effects, remain the preferred treatment for some types of localised pain having precise mechanisms.
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The description of painful phenomena in humans has to take into account its different components: sensory component (relevant to nociception), affective and emotional components. Nociceptor's (physiology is best understood with electrophysiological and neurochemical methods allowing a clear description of hyperalgesia, with its peripheral and spinal mechanisms. A functional model is partly available to explain allodynia, spontaneous burning pain and lightning pain, the three main consequences following deafferentation. At the thalamo-cortical level, one can describe nociceptive pathways and other pathways or neuronal networks involved in the affective and emotional components of pain.
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The nervous system structures involved in the transmission to the brain of noxious messages are discussed. In the periphery, receptors termed "nociceptors" consist of both fine unmyelinated and myelinated nerve fibres. ⋯ An example of this is the spinoponto-amygdaloid pathway which appears to play a role in the cognitive and affective components of pain. Nowadays numerous strategies are developed for the design of novel analgesics but the major problem for the pharmacologists is the complexity of the nervous system (multiplicity of the receptors, interspecies differences, colocalisations of several transmitters in the same neuron).