Cocaine And The Rapid Rewiring Of The Brain
Michael Harper for redOrbit.com – Your Universe Online
When mice are introduced to cocaine, the neurons in their brains become rapidly rewired to begin looking for the drug, even it if means not eating. Researchers from California now say this discovery could explain the first steps of addiction in humans.
Armed with a microscope, some mice and a small amount of cocaine, the researchers introduced the animals to the drug and measured the growth of high-level brain circuits inside the mice. Those mice whose brains had been rewired the most began looking for the drug more than the others. The researchers call this a “learning addiction,” meaning the mice’s brains seemingly learned more from their exposure to the drug and therefore went through a very real neurological change. With this information, the researchers hope they can better understand the interaction between drugs and the addict’s brain.
“It’s been observed that long-term drug users show decreased function in the frontal cortex in connection with mundane cues or tasks, and increased function in response to drug-related activity or information,” explained principal investigator Linda Wilbrecht, PhD with the Ernest Gallo Clinic and Research Center at UC San Francisco.
Researchers from the University of California in Berkeley were also a part of the study. Their results are published in the journal Nature Neuroscience.
As the brain learns, it pieces together a network of axons, neurons and synapses to create memory and store new knowledge. Dendritic spines, tiny protrusions from a neuron, work to store the signals sent between neurons and are also closely associated with memory. When given cocaine, the mice produced more of these dendritic cells in the frontal cortex of the brain.
Wilbrecht refers to the frontal cortex as the “steering wheel” of the brain. Therefore when mice are exposed to cocaine, the drug can take over the brain and send it looking for more of the substance. The California researchers used a 2-photon laser scanning microscope to observe the growth of dendritic spines and found an increase in these connections after just two hours of injecting the mice with the drug.
“The number of new, robust spines gained correlated with how much the individual mice learned to prefer the context in which they received the drug,” said Dr. Wilbrecht. This link between increased dendritic spine growth and cocaine has been noted before, but this study is the first time the speed at which these connections are made has been observed. The mice were also injected with a saline solution but did not experience the same levels of dendritic growth.
To begin the study, male mice were placed in what the researchers call a “conditioning box.” Each box contained two compartments decorated in different patterns and textures and were scented with either cinnamon or vanilla. The mice could use a small door in-between compartments to visit the side they preferred. The researchers took note of which side the male mice preferred, set them in this compartment and shut the door.
They were then injected with saline solution with no observable effects. The next day, however, the mice were injected with a dose of cocaine and placed inside the compartment they least favored for fifteen minutes, again with the door closed. The following day the researchers placed the mice back in the conditioning box with the door between compartments open.
“When given a choice, most of the mice preferred to explore the side where they had the cocaine, which indicated that they were looking for more cocaine,” said Dr. Wilbrecht. “Their change in preference for the cocaine side correlated with gains in new persistent spines that appeared on the day they experienced cocaine.”
Though this research explains how a brain can be chemically rewired to seek out more cocaine, it doesn’t present any changes to existing therapy programs to break people of their addictions.