Rats that voluntarily use cocaine show a persistent cellular memory in the brain's reward center even after several months of abstinence from the drug, while their involuntary counterparts had no such memory, according to a new study by researchers at the University of California, San Francisco.
The researchers conclude that the pharmacologic effects of cocaine alone are not enough to cause long-lasting cellular memories in the brain's reward circuit. The discovery by neuroscientists at UCSF's Ernest Gallo Clinic and Research Center appears in the July 31 issue of the journal "Neuron."
The study opens a window onto the significance of active choice in using cocaine and extends our understanding that addiction is caused by more than the pharmacological effects of a given drug, according to Antonello Bonci, MD, senior author of the paper, UCSF associate professor of neurology, Howard J. Weinberger Chair in Addiction Research and principal investigator at the Gallo Center.
"We know that environmental cues are significant in many addictions, including tobacco and alcohol, and contribute to relapses," Bonci said. "This study identifies the specific neuronal process involved and helps explain relapse even after rehabilitative therapy or long-term abstinence."
The researchers trained rats to self-administer cocaine, food or sucrose using a lever-pressing procedure. A separate group of rats also received passive researcher-administered cocaine. Neural activity was compared in brain tissue samples from the four groups and with samples from rats that had not experienced any rewards or training.
The study found that rats that learned to self-administer cocaine showed an increase in communication to dopamine neurons, which form the brain's key natural reward and motivational circuit, known as the ventral tegmental area (VTA).
In rats that self-administered cocaine, the increase in neuronal communication call
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University of California - San Francisco