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Alcohol and marihuana have similar effects, although they manipulate completely different sections of the brain: consumption results in euphoria, diminished control of body movements, a fall in body temperature. The interface of both drugs seems to be the cannabis receptor CB1: since 1999 it has been known that mice suffering from chronic alcohol consumption produce an increased number of cannabis derivatives in their bodies; at the same time the number of CB1 receptors in their brains drops. 'We therefore wondered whether a complete loss of the receptor influences the drinking behaviour and physiological effect of alcohol in mice,' explains Professor Andreas Zimmer of the Bonn Institute of Molecular Neurobiology.
The researchers are working with mice which are particularly prone to developing alcohol addiction. In one strain the information for the cannabis receptor had been removed, using gene technology. 'After giving differing amounts of alcohol both varieties of mice showed similar symptoms: the animals' body temperature dropped, their faculties of coordination were impaired, they were more bold,' Professor Zimmer added. After three weeks the animals had largely become accustomed to the drug. Symptoms of intoxication only occurred when they were given substantially higher doses. The situation was quite different in the case of withdrawal symptoms: shortly after the researchers had taken the mice off the drug they noticed an increased tendency to convulsions, restlessness and hyperactivity among the mice which had an intact cannabis receptor – the classic symptoms of alcohol withdrawal in mice. The behaviour of the mice lacking the receptor, by contrast, was completely normal.
Studies of alcoholics who have 'dried out' show that situations involving stress, particularly, may trigger a return to the bottle. In an additional experiment the researchers offered both mice groups 8% alcohol and water as drinks. Five weeks after the beginning of the experiment both groups were consuming roughly the same amount of alcohol daily. Then the researchers placed the mice under stress by passing weak electric current through the bottom of the cage. Although both groups revealed obvious signs of discomfort, with their brain activity changing in a similar way, only the mice with an intact cannabis receptor consumed more alcohol in the 24 hours after the stress situation – on average almost 50 per cent more.
MEDICA.de, Sources: Journal of Neuroscience (Vol. 23(6), 2003), University of Bonn