Psychoneuroendocrinology 27 (2002) 563–583 www.elsevier.com/locate/psyneuen Molecular genetic approaches to investigate individual variations in behavioral and neuroendocrine stress responses P. Morme `de * , H. Courvoisier, A. Ramos 1 , N. Marissal-Arvy, O. Ousova, C. De ´saute ´s 2 , M. Duclos, F. Chaouloff, M.-P. Moisan Neuroge ´ne ´tique et Stress—Institut Franc ¸ois Magendie de Neurosciences INSERM U471—INRA UR 502—Universite ´ Victor Segalen Bordeaux 2, 33077 Bordeaux, France Received 7 November 2000 Abstract A large response range can be observed in both behavioral and neuroendocrine responses to environmental challenges. This variation can arise from central mechanisms such as those involved in the shaping of general response tendencies (temperaments) or involves only one or the other output system (behavioral vs. endocrine response). The participation of genetic factors in this variability is demonstrated by family and twin studies in humans, the comparison of inbred strains and selection experiments in animals. Those inbred strains diverging for specific traits of stress reactivity are invaluable tools for the study of the molecular bases of this genetic variability. Until recently, it was only possible to study biological differences between contrasting strains, such as neurotransmitter pathways in the brain or hormone recep- tor properties, in order to suggest structural differences in candidate genes. The increase of the power of molecular biology tools allows the systematic screening of significant genes for the search of molecular variants. More recently, it was possible to search for genes without any preliminary functional hypothesis (mRNA differential expression, nucleic acid arrays, QTL search). The approach known as quantitative trait loci (QTL) analysis is based on the associ- * Corresponding author. Tel.: +33-557-573751; fax: +33-557-573752. E-mail address: mormede@bordeaux.inra.fr (P. Morme `de). 1 Present address: Departmento de Biologia Celular, Embriologia e Gene `tica, CCB / Universidade Federal de Santa Catarina, Floriano ´polis, SC - 88.040-900, Brasil. 2 Present address: Partner International, Koumassi, quartier Remblai, Boulevard de Cameroun, Lot 678, llot 53, 04BP430 Abidjan 04, Cote d’Ivoire. 0306-4530/02/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. PII:S0306-4530(01)00093-2