Behavioural Brain Research 169 (2006) 57–65 Research report Factor analysis of Forced Swimming test, Sucrose Preference test and Open Field test on enriched, social and isolated reared rats Juan Carlos Brenes S´ aenz a,1 , Odir Rodr´ ıguez Villagra a,1 , Jaime Fornaguera Tr´ ıas a,b,∗ a Neuroscience Research Program, Universidad de Costa Rica, Post-Office Box, San Pedro, ZIP code 2060, Costa Rica b Biochemistry Department, School of Medicine, Universidad de Costa Rica, San Pedro, Costa Rica Received 19 October 2005; received in revised form 2 December 2005; accepted 8 December 2005 Available online 18 January 2006 Abstract Developmental and social factors are known to play a crucial role in the pathogenesis of affective disorders. Although it has been demonstrated that early life aversive experiences can be a risk factor in the development of human depression, most of the investigation in animals that try to model depression do not include postnatal manipulations. Since housing represents a fundamental ethological factor which modifies behavior and brain development, this study aimed to investigate the impact of different social and structural housing conditions on the development of a depressive-like syndrome in the behavioral despair paradigm and an anxiety-like syndrome in the unconditioned anxiety paradigm. The present study uses several multivariate analyses to study the impact of housing conditions in animal models of depression and anxiety. In this study, social isolation was able to reproduce the effects found in other animals models based on stress, suggesting that only 2 months of social isolation are enough to produce effects that can be useful as behavioral model of depression. Moreover, environmental enrichment showed an antidepressive and anxiolytic like effect in animal models of depression and anxiety. This effect, which has not been reported in earlier studies, suggests that stimulation during the first stages of growth might play a “protective” role on behavior and brain development. © 2005 Elsevier B.V. All rights reserved. Keywords: Environmental enrichment; Social isolation; Forced Swimming test; Open Field test; Sucrose Preference test; Factor analysis 1. Introduction The environments in which human infants and children grow are fundamental to determine their progress. Several aversive sit- uations like parental loss, emotional and physical neglect, and abuse have been shown to be associated with the risk of suffering psychological disorders across the life span [47]. Although it has been demonstrated that early life aversive experiences can be a risk factor in the development of human depression [30,41], most of the investigations in animals that try to model depression do not include postnatal manipulations. However, specific manip- ulations of the postnatal social environment in rats can result in chronic developmental changes, such that, when studied in terms of behavior and physiology under basal and laboratory test conditions [47,49], they provide important models of spe- ∗ Corresponding author. Tel.: +506 207 49 03; fax: +506 207 58 27. E-mail address: jfornagu@cariari.ucr.ac.cr (J. Fornaguera Tr´ ıas). 1 Tel.: +506 207 49 03; fax: +506 207 58 27. cific symptoms and associated abnormalities in depression or anxiety [48,49,53]. The association between environment fac- tors and the appearance of abnormal behaviors has motivated the design of devices and techniques for enrichment or impov- erishment of the animals’ environments. Environmental enrichment, that can be achieved using objects and several cage designs to improve the quality of life of the lab- oratory animal [18], have shown that animals that are reared in these conditions, display lower basal activity in an inescapable novel environment relative to animals housed in an impoverished condition [3]. On the other hand, social isolation may have long- term consequences for the animal. It has been demonstrated that when comparing socially isolated rats (SI) with environmentally enriched rats (EE), SI animals generally show higher states of fearfulness, and become more responsive and vulnerable to envi- ronmental changes [14,15,21–23]. Thus, social isolation may be considered as a long-term stressor and environmental impover- ishment [29,49,54,60]. With regard to the latter, in our recent study (unpublished data) we show that chronic exposure of rats to an enriched environment improves behavior using depression 0166-4328/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2005.12.001