Brain Protein Linked to Alcohol-Seeking Behavior

Researchers have linked a protein found in the brain to both alcohol-seeking behavior and the sensitivity to the effects of alcohol intoxication.

Researchers at the University of Washington report the first direct evidence in mice that protein kinase A (PKA) signaling regulates both alcohol-seeking behavior and sensitivity to some of the effects of alcohol intoxication, according to the National Institute on Alcohol Abuse and Alcoholism.

Altered Response

Given a choice between plain water and solutions containing alcohol, mice missing the RIIB subunit of PKA preferred the alcohol solution at its highest strengths. In addition, the gene knockout mice were less sensitive than those with normal PKA to alcohol’s sedative effects.

A protein involved in intracellular communication, PKA is present throughout the brain. PKA phosphorylates numerous intracellular proteins and regulates gene expression, thereby altering the electrical properties of the cell and, potentially, cell function and communication between neurons.

Mice missing RIIB, one of six genes that encode PKA, experience alterations in PKA activity, a condition the researchers believe alters their response to the pharmacologic properties of alcohol.

Regulating Alcohol Consumption

"Earlier research in both laboratory cultures and animals indicated that alcohol consumption influences PKA function," said Enoch Gordis, M.D., Director of NIAAA, which provided primary support for the study.

"What is new about this work is the reverse – that, at least in the animal model, PKA can regulate alcohol consumption and some aspects of alcohol response."

Todd Thiele, Ph.D., Department of Psychology and the Alcohol and Drug Abuse Institute, University of Washington, and his colleagues examined drinking behavior in 12 normal mice and 12 knockout mice with a mutation in the RIIb subunit of PKA.

Whereas no differences were found between the two groups in taste preference for sweet or bitter solutions, mice with the PKA mutation drank nearly twice as much 20-percent alcohol solution as normal mice.

Sedative Effects

The researchers also measured the time needed for intoxicated mice to regain the righting reflex. They injected both groups of mice with alcohol and then placed them on their backs in plastic U-shaped troughs. Knockout mice recovered much faster from the sedative effects of alcohol, regaining their footing after 65 minutes compared with 90 minutes for the normal mice.

"It is likely that the mice with the RIIB mutation drink more ethanol because PKA activity is disrupted in brain regions involved in mediating ethanol reward," said Dr. Thiele. "It is now important to determine in which brain regions the RIIB subunit produces these effects."

Sources:

Thiele, TE, et al. "High Ethanol Consumption and Low Sensitivity to Ethanol-Induced Sedation in Protein Kinase A-Mutant Mice." Journal of Neuroscience May 2000