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Vagus Nerve Stimulation Enhances Extinction of Conditioned Fear in Rats and Modulates Arc Protein, CaMKII, and GluN2B-Containing NMDA Receptors in the Basolateral Amygdala

View Article: PubMed Central - PubMed

ABSTRACT

Vagus nerve stimulation (VNS) enhances the consolidation of extinction of conditioned fear. High frequency stimulation of the infralimbic cortex (IL) produces long-term potentiation in the basolateral amygdala (BLA) in rats given VNS-paired extinction training, whereas the same stimulation produces long-term depression in sham-treated rats. The present study investigated the state of synaptic plasticity-associated proteins in the BLA that could be responsible for this shift. Male Sprague-Dawley rats were separated into 4 groups: auditory fear conditioning only (fear-conditioned); fear conditioning + 20 extinction trials (extended-extinction); fear conditioning + 4 extinction trials paired with sham stimulation (sham-extinction); fear conditioning + 4 extinction trials paired with VNS (VNS-extinction). Freezing was significantly reduced in extended-extinction and VNS-extinction rats. Western blots were used to quantify expression and phosphorylation state of synaptic plasticity-associated proteins such as Arc, CaMKII, ERK, PKA, and AMPA and NMDA receptors. Results show significant increases in GluN2B expression and phosphorylated CaMKII in BLA samples from VNS- and extended-extinction rats. Arc expression was significantly reduced in VNS-extinction rats compared to all groups. Administration of the GluN2B antagonist ifenprodil immediately after fear extinction training blocked consolidation of extinction learning. Results indicate a role for BLA CaMKII-induced GluN2B expression and reduced Arc protein in VNS-enhanced extinction.

No MeSH data available.


Increased expression of p-CaMKII and decreased expression of Arc protein in the BLA of animals given VNS during extinction training. (a) Timeline of behavioral protocol. On days 1 and 2 rats were subjected to auditory fear conditioning (AFC) followed by a conditioned fear response test (CFRT) on day 3. On day 4 rats underwent extinction training (EXT) and were sacrificed 45 min later. (b) Rats given VNS during extinction training show higher levels of p-CaMKII compared to rats given sham stimulation (∗p < 0.05). (c, d) No significance difference in expression of CaMKIIα or CaMKIIβ across groups. (e) VNS-treated rats show lower levels of Arc protein expression compared to sham-treated rats (∗p < 0.05). (f) No difference in p-PKA expression across groups.
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fig1: Increased expression of p-CaMKII and decreased expression of Arc protein in the BLA of animals given VNS during extinction training. (a) Timeline of behavioral protocol. On days 1 and 2 rats were subjected to auditory fear conditioning (AFC) followed by a conditioned fear response test (CFRT) on day 3. On day 4 rats underwent extinction training (EXT) and were sacrificed 45 min later. (b) Rats given VNS during extinction training show higher levels of p-CaMKII compared to rats given sham stimulation (∗p < 0.05). (c, d) No significance difference in expression of CaMKIIα or CaMKIIβ across groups. (e) VNS-treated rats show lower levels of Arc protein expression compared to sham-treated rats (∗p < 0.05). (f) No difference in p-PKA expression across groups.

Mentions: We assessed the state of synaptic proteins in the BLA during consolidation of fear extinction. Rats were subjected to auditory fear conditioning followed by extinction training paired with either VNS (VNS-extinction rats) or sham (sham-extinction rats) stimulation, and tissue was collected from the BLA 45 min later (Figure 1(a)). Rats given VNS during extinction training showed a significant increase in phosphorylation of CaMKII at Thr286 compared to sham-extinction rats (Figure 1(b); t(13) = 2.305, p = 0.038); no difference was seen in total levels of CaMKIIα (Figure 1(c); t(6) = 0.231, p = 0.825) or CaMKIIβ (Figure 1(d); t(6) = 0.947, p = 0.380). Administration of VNS during extinction training also leads to a decrease in Arc protein expression in VNS-extinction rats compared to sham-extinction rats (Figure 1(e); t(11) = 2.907, p = 0.014). No difference was seen in phosphorylation of PKA at Thr197 between groups (Figure 1(f); t(6) = 0.881, p = 0.412).


Vagus Nerve Stimulation Enhances Extinction of Conditioned Fear in Rats and Modulates Arc Protein, CaMKII, and GluN2B-Containing NMDA Receptors in the Basolateral Amygdala
Increased expression of p-CaMKII and decreased expression of Arc protein in the BLA of animals given VNS during extinction training. (a) Timeline of behavioral protocol. On days 1 and 2 rats were subjected to auditory fear conditioning (AFC) followed by a conditioned fear response test (CFRT) on day 3. On day 4 rats underwent extinction training (EXT) and were sacrificed 45 min later. (b) Rats given VNS during extinction training show higher levels of p-CaMKII compared to rats given sham stimulation (∗p < 0.05). (c, d) No significance difference in expression of CaMKIIα or CaMKIIβ across groups. (e) VNS-treated rats show lower levels of Arc protein expression compared to sham-treated rats (∗p < 0.05). (f) No difference in p-PKA expression across groups.
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Related In: Results  -  Collection

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fig1: Increased expression of p-CaMKII and decreased expression of Arc protein in the BLA of animals given VNS during extinction training. (a) Timeline of behavioral protocol. On days 1 and 2 rats were subjected to auditory fear conditioning (AFC) followed by a conditioned fear response test (CFRT) on day 3. On day 4 rats underwent extinction training (EXT) and were sacrificed 45 min later. (b) Rats given VNS during extinction training show higher levels of p-CaMKII compared to rats given sham stimulation (∗p < 0.05). (c, d) No significance difference in expression of CaMKIIα or CaMKIIβ across groups. (e) VNS-treated rats show lower levels of Arc protein expression compared to sham-treated rats (∗p < 0.05). (f) No difference in p-PKA expression across groups.
Mentions: We assessed the state of synaptic proteins in the BLA during consolidation of fear extinction. Rats were subjected to auditory fear conditioning followed by extinction training paired with either VNS (VNS-extinction rats) or sham (sham-extinction rats) stimulation, and tissue was collected from the BLA 45 min later (Figure 1(a)). Rats given VNS during extinction training showed a significant increase in phosphorylation of CaMKII at Thr286 compared to sham-extinction rats (Figure 1(b); t(13) = 2.305, p = 0.038); no difference was seen in total levels of CaMKIIα (Figure 1(c); t(6) = 0.231, p = 0.825) or CaMKIIβ (Figure 1(d); t(6) = 0.947, p = 0.380). Administration of VNS during extinction training also leads to a decrease in Arc protein expression in VNS-extinction rats compared to sham-extinction rats (Figure 1(e); t(11) = 2.907, p = 0.014). No difference was seen in phosphorylation of PKA at Thr197 between groups (Figure 1(f); t(6) = 0.881, p = 0.412).

View Article: PubMed Central - PubMed

ABSTRACT

Vagus nerve stimulation (VNS) enhances the consolidation of extinction of conditioned fear. High frequency stimulation of the infralimbic cortex (IL) produces long-term potentiation in the basolateral amygdala (BLA) in rats given VNS-paired extinction training, whereas the same stimulation produces long-term depression in sham-treated rats. The present study investigated the state of synaptic plasticity-associated proteins in the BLA that could be responsible for this shift. Male Sprague-Dawley rats were separated into 4 groups: auditory fear conditioning only (fear-conditioned); fear conditioning + 20 extinction trials (extended-extinction); fear conditioning + 4 extinction trials paired with sham stimulation (sham-extinction); fear conditioning + 4 extinction trials paired with VNS (VNS-extinction). Freezing was significantly reduced in extended-extinction and VNS-extinction rats. Western blots were used to quantify expression and phosphorylation state of synaptic plasticity-associated proteins such as Arc, CaMKII, ERK, PKA, and AMPA and NMDA receptors. Results show significant increases in GluN2B expression and phosphorylated CaMKII in BLA samples from VNS- and extended-extinction rats. Arc expression was significantly reduced in VNS-extinction rats compared to all groups. Administration of the GluN2B antagonist ifenprodil immediately after fear extinction training blocked consolidation of extinction learning. Results indicate a role for BLA CaMKII-induced GluN2B expression and reduced Arc protein in VNS-enhanced extinction.

No MeSH data available.