The descending inhibitory pathways. Their role in analgesia, after consideration of specific spinal adrenergic involvement

The four main descending pathways - from the cortex, the diencephalon, the mesencephalon and the pontobulbar structures - are briefly examined with regard to their role as regulatory systems with an overall inhibitory action processing the afferents to the spinal cord. Sketches are given of the possible analgesic properties in the selective gating of C and Ad nociceptive afferences. The involvement of neuronal subpopulations in the spinal cord presenting alpha-2 and alpha-1 receptors, their hypothetic role in certain reactive analgesic processes, and their coactivation are mentioned briefly.