Supraspinal and spinal monoamine-modified function and the expression of opioid antinociception.

Opioids are highly valuable clinical agents for the treatment of pain which are thought to act both at the spinal and supraspinal level. During the course of their actions, they have complex interactions with monoamine systems. These include 5-hydroxytryptamine (5-HT) and noradrenaline (NA), so this topic is discussed using these two transmitter systems, their locations and receptor sub-types, as prime candidates for modulating nociceptive and antinociceptive processes. Several classes of 5-HT receptors, as well as α(2)-adrenoceptors, appear to be clearly involved in antinociception and the functions of systems carrying these receptors may be modified using psychotropic agents. In particular, some antidepressants may acutely augment opioid antinociception and this property may be exploited to delay the onset of opioid tolerance in the sub-acute situation.