Neuronal aspects of opiate dependence and tolerance in comparison to central depressants.

Some acute and chronic effects of opiates and of central depressants have been reviewed, in order that a comparison can be made between the actions of these drugs. Special emphasis has been given to opiate-induced changes at the neuronal level, which have been studied either by the direct microelectrophoretic application of drugs to single neurones or by application of drugs to the myenteric plexus/longitudinal muscle preparation of the guinea pig ileum. Available evidence suggests that chronic exposure of nervous tissue to opiates as well as to central depressants causes changes in neuronal excitability, which become apparent upon withdrawal of the drug. Although opiates and central depressants cause similar changes they appear to do so by different mechanisms. Such differences between the mode of action of opiates and central depressants may provide an explanation for the differing chronic effects of these drugs.