Brain reinforcement mechanisms of alcohol. I. Effects on behavior

Author(s): Cruz, C.

Journal/Book: Salud Ment. 1999; 22: Calz Mexico-Xochimilco #101, Mexico City 22 DF, Mexico. Inst Mex Psiquiatria. 46-51.

Abstract: The development of animal models and specialized techniques to study brain function, as well as the studies on behavior, physiology, and neurological effects of alcohol in humans, have increased our knowledge of alcohol abuse, tolerance and physical dependence processes. Alcohol, as other drugs of abuse, exerts its actions through positive and negative reinforcement mechanisms, which are related to a variety of different subjective states, ranging from pleasant sensations to euphoria, or to relaxation effects. Alcohol positive reinforcement mechanisms have been studied in several experimental models. The development of rodent strains selectively bred for different alcohol preferences have been useful to identify some neural substrates and the neurotransmitter systems involved. The reinforcing properties of alcohol may have a role in the biological events which lead to the initial consumption, continuous alcohol intake, abuse of the substance and eventually, to the development of the physical dependence on the drug. These events have been suggested to occur through the activation of specific neural circuits known as brain reward and positive reinforcement mechanisms. The dopaminergic mesolimbic system plays a key role in these mechanisms. The reinforcing effects of alcohol in this neural pathway have been studied by the experimental procedure known as brain stimulation reward (BSR). Alcohol increases the animal's rate of self-stimulation and diminishes the electrical current threshold, thus facilitating the BSR performance. On the other hand, low doses of alcohol stimulate, while high doses reduce motor spontaneous activity. These effects may occur through a common mechanism related to an increased activity of the dopaminergic mesolimbic system. In addition, some studies show that animals self-administer alcohol in specific brain regions, such as the ventral tegmental area, suggesting that they consume alcohol due to the drug's pharmacological effects at the brain level. In conclusion, alcohol acts as a positive reinforcer in the brain, exerting its actions on the same neural substrates as other drugs of abuse.

Note: Article Mendez M, Inst Mexicano Psiquiatria, Div Invest Clin, Dept Endocrinol, Calz Mexico Xochimilco 101, Mexico City 14370, DF, MEXICO

Keyword(s): brain reward mechanisms; positive reinforcement; dopaminergic mesolimbic system; drugs of abuse; alcohol; ETHANOL WITHDRAWAL SEIZURES; PREFERRING P RATS; LOCOMOTOR-ACTIVITY; SELF-STIMULATION; TASTE REACTIVITY; DRUG-DEPENDENCE; REWARD SYSTEMS; MICE; TOLERANCE; MODEL

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