Yawning behavior for preclinical drug evaluation.

The use of psychotropic agents is widespread, as is evident from the fact that many patients have been treated with them since their introduction. Concepts of the relationship between the actions of psychotropic drugs and the functions of specific brain systems have particularly progressed through the relatively brief history of psychopharmacology. Furthermore, efforts to provide explanations for drug-induced neurological changes will continue to focus on synaptic transmitters and their mechanisms. New approaches in drug development have been advanced by studies which have permitted the identification of receptor subtypes, undetected by traditional pharmacological approaches, with receptor heterogeneity providing an opportunity for greater pharmacological selectivity. All of these factors must be kept in mind when attempting to develop comprehensive explanations of the effects of drugs.