The chemistry of morphine addiction is being studied by Prof. Rabi Simantov of the Department of Molecular Genetics and Virology. Part of this research, recently published in Neurosciences Letters, may shed light on the addictive properties of a wide range of other substances, including alcohol, amphetamines, cocaine and nicotine.
The euphoria accompanying addiction to morphine and various other drugs results from excessive activity on the part of dopamine -- a neurotransmitter that relays impulses between nerve cells in the brain. Ordinarily, dopamine signals are turned off when the neurotransmitter is absorbed by a neuron; any inhibition of this process leads to excessive signaling. Prof. Simantov has now shown that chronic exposure to morphine inhibits dopamine uptake via a previously unrecognized mechanism.
In animal studies, morphine addiction was found to reduce the number of nerve-cell transporters that normally absorb dopamine and turn off its signals.
Prof. Simantov also showed that this reduction of transporters takes place only in the anterior basal forebrain -- the region containing drug "reinforcement and reward pathways." Since these pathways are strongly associated with the brain activity responsible for euphoria and analgesia -- phenomena induced by substances as varied as alcohol, amphetamines, cocaine and nicotine -- the addiction mechanism triggered by morphine is likely to be involved in the brain's response to these substances as well. The findings, therefore, might provide a basis for new strategies aimed at reducing dependency on some or all of these habit-forming drugs.
The study was supported, in part, by the Anti-Drug Authority of Israel, and the Office of the Chief Scientist in the Israeli Ministry of Health. Prof. Simantov holds the André Lwoff Chair of Neurogenetics.