The expression of these behaviors, combined with the challenging transitions that adolescents face (e.g. During this period, adolescent rats (like their human counterparts) show an increased prevalence of behaviors such as risk taking, novelty seeking and peer-directed social behaviors (for reviews see Adriani er al., 2004 Spear, 2000). In the rat, adolescence has been conservatively defined as postnatal days (P) 28 to 42 ( Spear, 2000), although the exact onset and end of adolescence is a gradual one. These across-species commonalities in basic neurochemical and hormonal characteristics of adolescence provide support for the judicious use of animal models of adolescence, particularly under circumstances where such research with human youths would be difficult or unethical. Characterized by the transition from dependence to independence, this ontogenetic phase is associated with numerous conserved neural, behavioral and hormonal features that are evident not only in human adolescents, but in organisms undergoing this transition in other species as well ( Spear, 2000). Ontogenetic alterations are also seen in the expression of specific anxiety disorders and in the efficacy of their treatment with different classes of anxiolytic drugs ( Foa et al., 2005). Within the field of psychology, there has been increasing emphasis on adolescence as a time of notable increases in expression of mental health disorders including schizophrenia, substance abuse and depression (see Kessler et al., 2005 for review). These increases in CORT have been taken as evidence of increased anxiety. They found that adult animals had much greater corticosterone (CORT) response following confinement to open arms than to closed arms in the EPM ( Pellow et al., 1985), with other researchers also demonstrating similar increases in CORT levels following open arm confinement ( Degroot et al., 2004 McCormick et al., 2008). File and colleagues further validated the EPM in terms of the hormonal responses to fearful and anxiety-provoking situations. Moreover, drugs that should not impact anxiety levels, such as haloperidol, have been shown to decrease overall locomotor activity on the maze while not affecting percentage of open arm activity ( Pellow et al., 1985). pentylenetetrazol) have been shown to have the opposite effect, with animals increasing the amount of time spent in the closed arms and avoiding the open arms to a greater extent ( Wada and Fukuda, 1991 Wallis and Lai. diazepam) effectively increase the proportion of time animals spend in the open relative to the closed arms, reflecting decreased anxiety in these animals ( Pellow et al, 1985 Wilson et al., 2004). Pharmacological studies have documented that anxiolytic drugs (e.g. Substantial prior research has focused on validating the EPM as a behavioral assay of anxiety in adult rodents. Since the maze presents a conflict of motivation to explore the novel yet risky open arms against the motivation to remain safe in the enclosed arms, the proportion of time an animal spends in the open versus closed arms is believed to provide an index of that animal’s anxiety level (for reviews see Carobrez and Bertoglio, 2005 Wall and Messier, 2001). This plus-shaped apparatus is elevated from the floor and consists of two arms with walls and two arms that are open platforms. The elevated plus-maze (EPM) is a widely used model for the study of anxiety-like behavior in rodents. Therefore, caution is urged when using the EPM for across-age comparisons of anxiolytic and anxiogenic effects of pharmacological or other manipulations. As a result, observed age differences in anxiety differed as a function of pretest circumstances. In adults, anxiety levels decreased linearly as pretest perturbation increased, whereas adolescents showed comparable levels of anxiety with both the moderate and large perturbations.
2, more varied pretest conditions were examined: testing directly from the home cage testing following 30 min of social isolation in a novel environment or a large saline injection and rehousing 18 h prior to a 30-min period of social isolation in a novelty situation before testing. These pretest manipulations only modestly decreased anxiety levels at both ages. 1, animals removed from their home cage and immediately placed on the EPM were compared to rats tested following 30 min of social isolation, or following 30-min exposure to a novel context. Because of an increasing interest in adolescence, the present experiments examined the impact of pretest manipulations on anxiety levels in the EPM among adolescent and adult Sprague Dawley rats of both sexes. The elevated plus-maze (EPM) is vulnerable to variations in pretest circumstances when testing adult rodents.
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