[The brain and the pain: neurotransmitters and neuronal pathways of pain perception and response]

The pain, an unpleasant feeling, induces several central nervous system mechanisms, like sensory-discriminative, motivational-affective activities, behavioral changes and it activates various responses, including antinociceptive actions. Accordingly, signals from the nociceptive neurons in the spinal cord and the sensory trigeminal nucleus ascend in various neuronal pathways and target several brain areas. Here, five ascending pain-conducting neuronal pathways and two spinal reflex routes are briefly summarized. The spinal and supraspinal antinociceptive mechanisms are described in more detail. During the past two decades, endogenous opioids, cannabinoids and their receptors have been discovered, localized and cloned. Five groups of endogenous opiates are known: beta-endorphin, enkephalins, dynorphins, endomorphins, and nociceptin. Two endogenous cannabinoids have already been described in the brain: the anandamide and the 2-arachidonyl-glycerol. The site of their antinociceptive (analgesic) actions in the brain are briefly summarized.