Effects of Traumatic Stress Induced in the Juvenile Period on the Expression of Gamma-Aminobutyric Acid Receptor Type A Subunits in Adult Rat Brain

Abstract

Studies have found that early traumatic experience significantly increases the risk of posttraumatic stress disorder (PTSD). Gamma-aminobutyric acid (GABA) deficits were proposed to be implicated in development of PTSD, but the alterations of GABA receptor A (GABA_AR) subunits induced by early traumatic stress have not been fully elucidated. Furthermore, previous studies suggested that exercise could be more effective than medications in reducing severity of anxiety and depression but the mechanism is unclear. This study used inescapable foot-shock to induce PTSD in juvenile rats and examined their emotional changes using open-field test and elevated plus maze, memory changes using Morris water maze, and the expression of GABA_AR subunits (γ2, α2, and α5) in subregions of the brain in the adulthood using western blotting and immunohistochemistry. We aimed to observe the role of GABA_AR subunits changes induced by juvenile trauma in the pathogenesis of subsequent PTSD in adulthood. In addition, we investigated the protective effects of exercise for 6 weeks and benzodiazepine (clonazepam) for 2 weeks. This study found that juvenile traumatic stress induced chronic anxiety and spatial memory loss and reduced expression of GABA_AR subunits in the adult rat brains. Furthermore, exercise led to significant improvement as compared to short-term BZ treatment.

Figure 1

Anxiety-like behaviors and spatial memory performance. (a) Behavioral changes in the open-field test (n = 12, per group): (A) frequency of line crossing, (B) time spent in central squares, (C) rearing times, and (D) grooming numbers. (b) Behavioral results in the elevated plus maze (n = 12, per group): (A) percentage of time in open arm and (B) percentage of open arm entries. (c) Spatial memory performance in the Morris water maze (n = 12, per group): (A) number of crossings in the target area and (B) time spent in the target quadrant. Values were expressed as mean ± SEM. ^∗p < 0.05 and ^∗∗p < 0.01 versus C group; ^#p < 0.05 and ^##p < 0.01 versus T group; ⁺p < 0.05 and ⁺⁺p < 0.01 versus T + D group.

Figure 2

GABA_AR subunits expressions in subregions of brain in western blotting. (a) The expression of γ2 subunit in the PFC, amygdala, and hippocampus. (b) The expression of α2 subunit in the PFC, amygdala, and hippocampus. (c) The expression of α5 subunit in the hippocampus. Values were expressed as mean ± SEM (n = 6, per group). ^∗p < 0.05 and ^∗∗p < 0.01 versus C group; ^##p < 0.01 versus T group; ⁺⁺p < 0.01 versus T + D group.

Figure 3

Representative expression of the GABA_AR subunits in the PFC, CA3, and dentate gyrus (DG) of the hippocampus (×400). The neurons with positive γ2 subunit expression and the results of positive cell counting in the PFC and DG were shown in (A) and (a). The neurons with positive α2 subunit expression and the results of positive cell counting in the PFC and DG were shown in (B) and (b). The neurons with positive α5 subunit expression and the results of positive cell counting in the DG and CA3 subregions of the hippocampus were shown in (C) and (c). Values were expressed as mean ± SEM (n = 6, per group). ^∗∗p < 0.01 versus C group; ^##p < 0.01 versus T group; ⁺⁺p < 0.01 versus T + D group.