Do Limits of Neuronal Plasticity Represent an Opportunity for Mental Diseases, Such as Addiction to Food and Illegal Drugs? Use and Utilities of Serotonin Receptor Knock-Out Mice

Excerpt

The properties of neuronal plasticity are not only studied after brain injury. Adaptive changes also take place in the neurons of genetically modified animals, which provide a rational for genetic studies in humans suffering from mental diseases. Following a brief summary describing the alterations in human serotonin (5-HT, 5-hydrox-ytryptamine) gene receptors found in one of the most complex of mental functions—motivation related to food or illegal drugs intake—we will describe that the only gene deficit, destroying 5-HT receptor, is not enough to produce apparent maladap-tive behavior in rodents. However, when combined with a novel environmental challenge, modified genetic predisposition induces deviant behavior. Locomotion, feeding, and emotion-like state disorders (anxiety-like behavior, depression-like syndrome) are classically underlined by brain deficits and subsequently linked to adaptive neuronal changes. This review gathered evidence to postulate that following genetic alterations, the brain partly “burns” its adaptive resources over time, and lacks a sufficient flexibility to adapt during adulthood. The limits of adaptive changes in neurons in the face of an unexpected environmental context, may therefore represent an “open door” for mental-like disorders to emerge.