Pain, analgesia, and stress: an integrated view.
The different theories on the neuroanatomical substrate of pain have been revised in the frame of new concepts on the intercellular communication in the central nervous system. In fact, it has recently been proposed that two kinds of electrochemical transmission exist in the brain: the first one, called wiring transmission (WT), uses neuronal chains (neuronal plasma membranes and synaptic contacts), whereas the second one, called volume transmission (VT), uses the extracellular fluid as physical substrate. The old concept of a separate system of afferents and central cells that constitute the pain mechanism is no more longer tenable. To reach a better understanding of the psychophysiological basis of pain, we should consider a view where WT and VT cooperate within neuronal systems functionally affected by the pervading modulatory action of endocrine signals.