Bases biochimiques et neurobiologiques de la psychiatrie

Several decades of research dedicated to the biological basis of mental disorders have resulted in very significant advances in the understanding of brain functions, and have allowed the elaboration of interesting hypothesis regarding the possible pathophysiology of these disorders. This paper succinctly recounts the history of the biochemical discoveries which have led to the understanding of possible biological mechanisms underlying mental disorders. These discoveries concern mainly three systems of neurotransmitters, the serotoninergic, dopaminergic and noradrenergic systems. Today, these hypotheses extend to other biological systems with the observation that most psychotropic drugs have plastic and remodelling effects on neurons. Moreover, brain imaging techniques have allowed the localization of structural and functional abnormalities in the brain of the mentally ill patient. The first section of the paper reviews the hypotheses dealing with the mode of action of psychotropic drugs (antipsychotic agents, antidepressants, mood stabilizers and anxiolytic drugs). In a second section, the major brain structures potentially involved in mental disorders are reviewed (prefrontal cortex, hippocampus, amygdala, thalamus, striatum), with a brief account of their role and of their functional and structural abnormalities as reported in psychiatric patients with in vivo brain imaging and anatomopathological studies. The main arguments supporting the neurodevelopmental hypothesis of mental disorders are also reviewed. It is eventually underlined that the real causes of mental disorders remain almost totally unknown in biological terms, since it appears evident that the clinical expression of mental disorders is largely shifted from the neurobiological abnormalities observed in the brain of patients.