[Fundamental mechanisms of pain]

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. The mechanisms of the integration of nociceptive messages at the level of the dorsal horn of the spinal cord and the systems which modulate these messages (segmental, suprasegmental and supraspinal) have also been extensively studied. In addition to the classical pathways, including the spinothalamic and spinoreticular tracts, the modern neuroanatomical techniques, have revealed the existence of unknown pathways. 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).