The neural crux of relapse
Exactly how stress acts in the brain to trigger relapse is a complicated sequence that is still not fully understood, but the new study focuses on and elucidates three key players at the crux of the phenomenon in the VTA: GABA-releasing neurons, dopamine-releasing neurons, and the kappa opioid receptors that affect their connections.
Fulfilling natural needs such as hunger or thirst results in a rewarding release of dopamine from the VTA's dopamine neurons, Kauer said. Unfortunately, so does using drugs of abuse.
In normal brain function, GABA applies the brakes on the rewarding dopamine release, slowing it back to a normal level. It achieves this by forging and then strengthening the connections, called synapses, with the dopamine neuron. The strengthening process is called long-term potentiation (LTP).
In the first of their experiments, the team at Brown, including lead author Nicholas Graziane, showed that stress interrupts the LTP process, hindering GABA's ability to slam the brakes on dopamine release.
Previous research implicated kappa opioid receptors as one of many neural entities that could have a role in stress-related relapse. Kauer, Graziane, and co-author Abigail Polter investigated that directly by blocking the receptors in some rats with a treatment of nor-BNI in the VTA and leaving others untreated. Then they subjected the rats to a standardized five-minute stress exercise. After 24 hours they looked at the cells in the VTA and found that LTP was hindered in the untreated rats but still present and underway in the rats whose receptors had been blocked with nor-BNI.
With the role of stress and the receptors in the GABA-dopamine dynamic both confirmed and then mitigated, the question remaine
|Contact: David Orenstein|