Researchers have found in a mice study why and how the use of addictive drugs take control of reward signals and influence neural processes associated with learning and memory.
The study could help explain how drug-associated memories, such as the place of drug use, drive and perpetuate the addiction.
It is known that the neurochemical dopamine, a key player in the brain's reward system, is involved in the process of addiction.
Research has indicated that dopamine participates in neural processes associated with learning, such as the strengthening of neuronal connections, called synaptic potentiation.
Evidence has also implicated the hippocampus, a deep-brain structure that is critical for formation of new memories, in the development of drug addiction.
"Although addictive drugs like nicotine have been shown to influence the induction of synaptic potentiation, there has been little or no research in freely moving animals that monitors ongoing induction of synaptic potentiation by a biologically relevant drug dose," explains senior author Dr. John Dani from the Department of Neuroscience at the Baylor College of Medicine in Houston, Texas.
The researchers recorded from the brains of freely moving mice while applying physiologically relevant concentrations of nicotine, the addictive component in tobacco.
The researchers found that nicotine induced synaptic potentiation correlated with the mice learning to prefer a place associated with the nicotine dose.
Importantly, these effects required a local dopamine signal within the hippocampus.
The finding reinforces the view that dopamine enables memory for specific events.
Overall, the results point to some intriguing possibilities about how drug-associated memories might contribute to behaviors associated with addiction.
"An animal's memories or feelings about the environment are updated when the dopamine signal labels a particular event as important, new, and salient. Normally these memories help us to perform successful behaviors, but in our study, those memories were linked to the addictive drug.
When specific environmental events occur, such as the place or people associated with drug use, they are capable of cuing drug-associated memories or feelings that motivate continued drug use or relapse," concluded Dani.
The study has been published in the latest issue of the journal Neuron.