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The purpose of these experiments was to determine the immediate and delayed effects of stress on anxiety/depressive behavior. For the open field and elevated plus maze experiments male CD1 mice (Charles River) were used (n=6-8 per group; arrived at 7 weeks of age, tested at 9-11 weeks, handled for 5 days prior to testing). The GFAP-tk mice used for the novelty-suppressed feeding test were as described in Snyder, 2011, Nature. Mice were housed 4/cage, kept on a 12 hour light/dark cycle with lights on at 6 am and were tested during the light phase. Testing was performed either directly from the home cage (controls), immediately following 30 min restraint (stress) or following 30 min restraint with a 30 min post-restraint delay interval (stress+delay).
Figure 1: Increased fear/anxiety in the open field immediately following stress. a) The open field was a white plastic box (50cm x 50cm x 50cm) which was divided into outer (o), middle (m), and center (c) regions. Mice were tracked with Ethovision software (Noldus) and latency to approach the center region and time spent in the 3 regions during a 15 min test was calculated. Light intensity was approxmiately 150 lux. b) The presence of an object (~2 cm diameter, 3 cm tall wire metal cylinder containing a marble) in the center of the open field increased time spent in this subregion, and was therefore included in subsequent experiments (i.e. d-h; ****t-test P<0.001 vs. no object). c) The presence of the object did not affect the latency to approach the center of the open field. d) Neither stress condition affected the latency to approach the center of the open field. e) Stress significantly reduced the time spent in the center of the open field but this effect was absent after 30 min (stress+delay group; 1 way ANOVA main effect P=0.001, #Tukey post-test P<0.001 vs. control & P<0.05 vs. stress+delay). f-h) Time spent in the center, middle and outer regions across the test’s 3 x 5 min bins. Compared to controls, stress reduced time spent in the center and middle regions and increased time spent in the outer region (2 way repeated measures ANOVA, main effects of treatment all P<0.01, effect of time and interactions ns; Bonferroni post-test *P<0.05, **P<0.01, ***P<0.001 vs. control). Read the rest of this entry »