Norepinephrine Induces PTSD-Like Memory Impairments via Regulation of the β-Adrenoceptor-cAMP/PKA and CaMK II/PKC Systems in the Basolateral Amygdala

Abstract

Glucocorticoids (GCs) can modulate the memory enhancement process during stressful events, and this modulation requires arousal-induced norepinephrine (NE) activation in the basolateral amygdale (BLA). Our previous study found that an intrahippocampal infusion of propranolol dose-dependently induced post-traumatic stress disorder (PTSD)-like memory impairments. To explore the role of the noradrenergic system of the BLA in PTSD-like memory impairment, we injected various doses of NE into the BLA. We found that only a specific quantity of NE (0.3 μg) could induce PTSD-like memory impairments, accompanied by a reduction in phosphorylation of GluR1 at Ser845 and Ser831. Moreover, this phenomenon could be blocked by a protein kinase A (PKA) inhibitor or calcium/calmodulin-dependent protein kinase II (CaMK II) inhibitor. These findings demonstrate that NE could induce PTSD-like memory impairments via regulation of the β-adrenoceptor receptor (β-AR)-3',5'-cyclic monophosphate (cAMP)/PKA and CaMK II/PKC signaling pathways.

Keywords: AMPA; CaMK II/PKC; PTSD; basolateral amygdala; cAMP/PKA; fear conditioning; norepinephrine.

Figure 1

Representative photomicrograph illustrating the location of microinjection into the basolateral amygdale (BLA). The schematic (part A) and actual (part B) results on corresponding section taken from the rat brain atlas of Paxinos and Watson (2007), arrow points to needle tip.

Figure 2

Intra-BLA infusion of norepinephrine (NE) induced a dose-dependent post-traumatic stress disorder (PTSD)-like memory impairments. (A) NE (0.3 μg/0.2 μl) administered into the BLA immediately after fear conditioning impaired retention of contextual fear memory and enhanced retention of cue fear memory. Concurrent infusion of β-adrenoceptor (β-AR) antagonist DL-propranolol (0.5 μg/0.2 μl) blocked this NE-induced memory impairments. Results represent mean ± SEM. **P < 0.01, ^##P < 0.01 compared with vehicle. (B) NE (0.1, 0.3, or 1.0 μg/0.2 μl) administered into the BLA immediately after fear conditioning dose-dependent impaired retention of contextual fear memory. Results represent mean ± SEM. **P < 0.01, ^##P < 0.01 compared with vehicle. (C) NE (0.3 μg/0.2 μl) induced PTSD-like memory impairments, which increased the response to 2 kHz tone but not to white noise. Results represent mean ± SEM. **P < 0.01 vs. 1 kHz cue.

Figure 3

NE induced PTSD-like memory impairments via down-regulation the expression of Ser845 and Ser831 phosphorylation of GluR1. (A) Representative immunoblots showing the effect of the bilateral intra-BLA infusion of NE (0.3 μg/0.2 μl) or propranolol (5 μg/0.2 μl) immediately after fear conditioning induced change in phospho-GluR1 and total GluR1 levels. (B) Representative immunoblots showing the effect of the bilateral intra-BLA infusion of NE with the different doses of NE (0.1, 0.3, or 1.0 μg/0.2 μl) immediately after training induced change in phospho-GluR1 and total GluR1 levels. All results represent mean ± SEM. *P < 0.05, **P < 0.01, vs. vehicle group.

Figure 4

NE induced PTSD-like memory impairments via regulation 3′,5′-cyclic monophosphate (cAMP)/protein kinase A (PKA) and calcium/calmodulin-dependent protein kinase II (CaMK II)/PKC signal pathway. (A) The PKA inhibitor Rp-cAMPS (4.0 μg/0.2 μl) administered into the BLA 10 min before fear conditioning blocked the impairments of retention of contextual (Aa) and cue (Ab) fear memory induced by immediately post-training intra-BLA infusions of NE (0.3 μg/0.2 μl). (B) The CaMKII inhibitor KN-93 (5.0 μg/0.5 μl) administered into the BLA 10 min before fear conditioning also blocked the impairments of retention of contextual (Ba) and cue (Bb) fear memory induced by immediately post-training intra-BLA infusions of NE (0.3 μg/0.2 μl). All results represent mean ± SEM. **P < 0.01 compared with the corresponding vehicle group, ^##P < 0.01 compared with the corresponding saline group.

Figure 5

Inhibition cAMP/PKA or CaMK II/PKC signal pathway can down-regulate the expression of Ser845 and Ser831 phosphorylation of GluR1. Representative immunoblots showing the effect of the bilateral intra-BLA infusion of Rp-cAMPS (4.0 μg/0.2 μl; A) or KN-93 (5.0 μg/0.5 μl; B) 10 min before fear conditioning induced change in phospho-GluR1 and total GluR1 levels. All results represent mean ± SEM. *P < 0.05, **P < 0.01, vs. vehicle group.