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Early life stress has been shown to alter the behavior of the adult animals and modify the effects of various addictive agents (1-4). The objectives of the present experiments were to study the effects of psychological stress in the early stage of life (social isolation, rearing from weaning) on locomotor activity, and to compare the effect of ethanol on this behavior in rats reared with different psychological stress conditions (socially and isolation reared rats).
Methods: Male Wistar rats were obtained from weaning (21 days of age) and housed either alone (isolation rearing) or groups of five rats/cage (social rearing). After four weeks, these rats were placed individually into an open field arena (an animal model of locomotor activity) either without drug pretreatment or following intraperitoneal injection of saline or ethanol (60 and 240 mg/kg) 30 min before a 5 min test.
Results: The results showed that isolation reared rats exhibited hyperlocomotion (as indicated by increasing total zone transitions), had significantly more number of rears than socially reared rats. Both socially and isolation reared rats spent longer time in the outer zone (P<0.05), however, isolation reared rat demonstrated more entries and spent more time in the inner zone than the social reared rats. Pretreatment with ethanol (60 and 240 mg/kg i.p.) had no marked effect on total zone transitions in both socially and isolation reared rats. However, ethanol significantly reduced the number of inner zone entries and time spent in a dose related manner only in isolation reared rats.
Conclusion: These results indicate that psychological stress during the early stage of life alters locomotor activity and modifies the effect of ethanol in the adult rats. This abnormality may reflect alterations of central neurotransmitters such as GABA etc.
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