Effects of RU486 in Treatment of Traumatic Stress-Induced Glucocorticoid Dysregulation and Fear-Related Abnormalities: Early versus Late Intervention

Abstract

Central glucocorticoid receptor (GR) activity is enhanced following traumatic events, playing a key role in the stress-related cognitive abnormalities of posttraumatic stress disorder (PTSD). GR antagonists are expected to have potential as pharmacological agents to treat PTSD-related symptoms such as anxiety and fear memory disruption. However, an incubation period is usually required and stress-induced abnormalities do not develop immediately following the trauma; thus, the optimal intervention timing should be considered. Single prolonged stress (SPS) was employed as a rodent PTSD model to examine the effects of early or late (1-7 versus 8-14 days after the SPS) sub-chronic RU486 (a GR antagonist) administration. Behaviorally, fear conditioning and anxiety behavior were assessed using the fear-conditioning test and elevated T-maze (ETM), respectively. Neurochemically, the expressions of GR, FK506-binding proteins 4 and 5 (FKBP4 and FKBP5), and early growth response-1 (Egr-1) were assessed in the hippocampus, medial prefrontal cortex (mPFC), amygdala, and hypothalamus, together with the level of plasma corticosterone. Early RU486 administration could inhibit SPS-induced behavioral abnormalities and glucocorticoid system dysregulation by reversing the SPS-induced fear extinction deficit, and preventing SPS-reduced plasma corticosterone levels and SPS-induced Egr-1 overexpression in the hippocampus. Early RU486 administration following SPS also increased the FKBP5 level in the hippocampus and hypothalamus. Finally, both early and late RU486 administration inhibited the elevated hippocampal FKBP4 level and hypothalamus GR level in the SPS rats. Early intervention with a GR antagonist aids in the correction of traumatic stress-induced fear and anxiety dysregulation.

Keywords: anxiety; fear memory; glucocorticoid receptor; hippocampus; posttraumatic stress disorder; time-dependent effect.

Figure 1

Three-day cue-dependent fear-conditioning test after SPS paradigm and early/late RU486 intervention. The data represent the mean ± SEM. n = 12 for each group. Statistical analysis was employed with a two-way repeated measures ANOVA followed by Bonferroni post hoc testing. ** p < 0.01, *** p < 0.001, CON-Veh/Veh vs. SPS-Veh/Veh; @@@ p < 0.001, SPS-Veh/Veh vs. SPS-RU486/Veh; & p < 0.05, && p < 0.01, SPS-RU486/Veh vs. SPS-Veh/RU486. CS: conditioned stimulus; US: unconditioned stimulus; context 1: the chamber with white house light, fan on and full of 1% acetic acid smell; context 2: the chamber with red house light, fan off and full of 1% ammonia smell. The contexts 1 and 2 were employed in the same operant chamber.

Figure 2

The preferences of the (A) Baseline (B) Avoidance 1 latency (C) Avoidance 2 latency and (D) Escape latency of ETM test after SPS paradigm and early/late RU486 intervention. The data represent the mean ± SEM. n = 12 for each group. Statistical analysis was employed with a one-way ANOVA followed by Bonferroni post hoc testing. * p < 0.05, ** p < 0.01.

Figure 3

The expressions of the (A) GR, (B) FKBP4, (C) FKBP5, and (D) Egr-1 in the hippocampus after SPS paradigm and early/late RU486 intervention. The data represent the mean ± SEM. n = 6 for each group. Statistical analysis was employed with a one-way ANOVA followed by Bonferroni post hoc testing. * p < 0.05; ** p < 0.01; *** p < 0.001.

Figure 4

The expressions of the (A) GR, (B) FKBP4, (C) FKBP5, and (D) Egr-1 in the mPFC after SPS paradigm and early/late RU486 intervention. The data represent the mean ± SEM. n = 6 for each group. Statistical analysis was employed with a one-way ANOVA followed by Bonferroni post hoc testing.

Figure 5

The expressions of the (A) GR, (B) FKBP4, (C) FKBP5, and (D) Egr-1 in the amygdala after SPS paradigm and early/late RU486 intervention. The data represent the mean ± SEM. n = 6 for each group. Statistical analysis was employed with a one-way ANOVA followed by Bonferroni post hoc testing.

Figure 6

(A) The concentration of Plasma corticosterone concentration and the expressions of the (B) GR, (C) FKBP4, (D) FKBP5 in the hippocampus after SPS paradigm and early/late RU486 intervention. The data represent the mean ± SEM. n = 8 in the data of plasma corticosterone level, and n = 6 in the data of western blot for each group. Statistical analysis was employed with a one-way ANOVA followed by Bonferroni post hoc testing. * p < 0.05.

Figure 7

Schematic illustration of the experimental design in the present study.