Changes in Gene Expression in the Locus Coeruleus-Amygdala Circuitry in Inhibitory Avoidance PTSD Model

Abstract

The locus coeruleus (LC)-amygdala circuit is implicated in playing a key role in responses to emotionally arousing stimuli and in the manifestation of post-traumatic stress disorder (PTSD). Here, we examined changes in gene expression of a number of important mediators of the LC-amygdala circuitry in the inhibition avoidance model of PTSD. After testing for basal acoustic startle response (ASR), rats were exposed to a severe footshock (1.5 mA for 10 s) in the inhibitory avoidance apparatus. They were given contextual situational reminders every 5 day for 25 days. Controls were treated identically but with the footshock inactivated. Animals were re-tested on second ASR and decapitated 1 h later. The shock group had enhanced hyperarousal and several changes in gene expression compared to controls. In the LC, mRNA levels of norepinephrine (NE) biosynthetic enzymes (TH, DBH), NE transporter (NET), NPY receptors (Y1R, Y2R), and CB1 receptor of endocannabinoid system were elevated. In the basolateral amygdala (BLA), there were marked reductions in gene expression for CB1, and especially Y1R, with rise for corticotropin-releasing hormone (CRH) system (CRH, CRH receptor 1), and no significant changes in the central amygdala. Our results suggest a fast forward mechanism in the LC-amygdala circuitry in the shock group.

Keywords: Cannabinoid receptor; Corticotropin-releasing hormone; Neuropeptide Y; Neuropeptide Y1 and Y2 receptors; Norepinephrine transporter; Tyrosine hydroxylase.

Fig. 1

The scheme of the experimental design. Rats were tested for basal response to acoustic startle (ASR1). On the next day, they received electrical shock in inhibitory avoidance apparatus. They were returned to the apparatus for 1 min 5 more times 5 days apart. On the 26th day, rats were tested again for ASR (ASR2) and sacrificed 1 h later

Fig. 2

Changes in relative mRNA levels of NE, NPY, CRH, and eCB systems in the locus coeruleus in rats subjected to inhibitory avoidance stress with situational reminders. Data are presented as mean ± SEM. n = 10–12 per group. Open bar is control; closed bar is shocked group. *p < 0.05, **p < 0.01 compared to Controls

Fig. 3

Changes in relative mRNA levels of NE, NPY, CRH, and eCB systems in the  a basolateral and b central amygdala in rats subjected to inhibitory avoidance stress with situational reminders. Data are presented as mean ± SEM. n = 10–12 per group. Open bar is control; closed bar is shocked group. *p < 0.05, ***p < 0.001 compared to Controls

Fig. 4

Schematic illustration of proposed feed forward mechanism and changes observed in the study. This scheme is based on Kravets and coauthors (Kravets et al. 2015)