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pT305-CaMKII stabilizes a learning-induced increase in AMPA receptors for ongoing memory consolidation after classical conditioning.

Naskar S, Wan H, Kemenes G - Nat Commun (2014)

Bottom Line: CaMKIINtide treatment significantly reduces the learning-induced elevation of both pT305-CaMKII and GluA1 levels and impairs associative long-term memory.Inhibition of proteasomal activity offsets the deleterious effects of CaMKIINtide on both GluA1 levels and long-term memory.These findings suggest that increased levels of pT305-CaMKII play a role in AMPAR-dependent memory consolidation by reducing proteasomal degradation of GluA1 receptor subunits.

View Article: PubMed Central - PubMed

Affiliation: 1] Sussex Neuroscience, School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK [2].

ABSTRACT
The role of CaMKII in learning-induced activation and trafficking of AMPA receptors (AMPARs) is well established. However, the link between the phosphorylation state of CaMKII and the agonist-triggered proteasomal degradation of AMPARs during memory consolidation remains unknown. Here we describe a novel CaMKII-dependent mechanism by which a learning-induced increase in AMPAR levels is stabilized for consolidation of associative long-term memory. Six hours after classical conditioning the levels of both autophosphorylated pT305-CaMKII and GluA1 type AMPAR subunits are significantly elevated in the ganglia containing the learning circuits of the snail Lymnaea stagnalis. CaMKIINtide treatment significantly reduces the learning-induced elevation of both pT305-CaMKII and GluA1 levels and impairs associative long-term memory. Inhibition of proteasomal activity offsets the deleterious effects of CaMKIINtide on both GluA1 levels and long-term memory. These findings suggest that increased levels of pT305-CaMKII play a role in AMPAR-dependent memory consolidation by reducing proteasomal degradation of GluA1 receptor subunits.

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Training-induced upregulation of GluA1 AMPA receptors during memory consolidation in Lymnaea(a) A representative example of GluA1 immunoblot bands from a paired, an unpaired and a naïve sample, run on the same gel, is shown above the graphs (full-length blot is presented in Supplementary Fig. 7a). Density data obtained from paired (N=8) and unpaired (N=8) samples were normalized to the mean of the density data obtained from naïve samples ran on the same gels (N=8), which provided a baseline level of 1 (dashed line). In the graphs means±SEM are shown. Both paired and unpaired training results in significantly increased GluA1 receptor protein levels in the ‘learning’ ganglia at 6 h post-training (One sample t tests: paired versus naïve baseline, P=0.047; unpaired versus naïve baseline, P=0.048). There is no statistically significant difference between the GluA1 levels in the samples from the paired and unpaired group (two-tailed unpaired t-test: paired versus unpaired group, P=0.71). Asterisks indicate significant (at least P<0.05) differences compared to the naïve baseline. (b) At 24 h post-training, only the paired group (N=19) showed a conditioned response to the CS. Means±SEM of the feeding response to the CS are shown. Naïve animals (N=22) or animals subjected to unpaired training (CS-US interval 1 h, N=20) did not respond to the CS (ANOVA, P=0.0001. Tukey’s: paired vs. unpaired, P<0.05, paired vs. naïve, P<0.05, unpaired vs. naïve, P>0.05). Asterisk indicates significance compared to both unpaired and naïve response levels. These experiments were replicated twice.
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Figure 2: Training-induced upregulation of GluA1 AMPA receptors during memory consolidation in Lymnaea(a) A representative example of GluA1 immunoblot bands from a paired, an unpaired and a naïve sample, run on the same gel, is shown above the graphs (full-length blot is presented in Supplementary Fig. 7a). Density data obtained from paired (N=8) and unpaired (N=8) samples were normalized to the mean of the density data obtained from naïve samples ran on the same gels (N=8), which provided a baseline level of 1 (dashed line). In the graphs means±SEM are shown. Both paired and unpaired training results in significantly increased GluA1 receptor protein levels in the ‘learning’ ganglia at 6 h post-training (One sample t tests: paired versus naïve baseline, P=0.047; unpaired versus naïve baseline, P=0.048). There is no statistically significant difference between the GluA1 levels in the samples from the paired and unpaired group (two-tailed unpaired t-test: paired versus unpaired group, P=0.71). Asterisks indicate significant (at least P<0.05) differences compared to the naïve baseline. (b) At 24 h post-training, only the paired group (N=19) showed a conditioned response to the CS. Means±SEM of the feeding response to the CS are shown. Naïve animals (N=22) or animals subjected to unpaired training (CS-US interval 1 h, N=20) did not respond to the CS (ANOVA, P=0.0001. Tukey’s: paired vs. unpaired, P<0.05, paired vs. naïve, P<0.05, unpaired vs. naïve, P>0.05). Asterisk indicates significance compared to both unpaired and naïve response levels. These experiments were replicated twice.

Mentions: First, we used the western blot method to measure total GluA1 levels in the buccal and cerebral ganglia (interconnected by the cerebro-buccal connective) at 6 h after classical conditioning. The samples for these tests were obtained at 6 h post-training because a previous study demonstrated a significantly increased number of hippocampal neurons expressing GluA1 AMPA receptor subunits at this time point after fear conditioning in mice17. We found that total GluA1 levels were significantly increased at 6 h post conditioning in the samples from the paired as well as the unpaired group of animals compared to the naïve controls (Fig. 2a) but only the paired group showed a conditioned feeding response at 24 h after classical conditioning (Fig. 2b). This initial finding was consistent with the finding in mice that the proportion of GluA1 expressing hippocampal neurons increased after both paired and unpaired training17, indicating a close similarity of the underlying molecular mechanisms in invertebrates and vertebrates.


pT305-CaMKII stabilizes a learning-induced increase in AMPA receptors for ongoing memory consolidation after classical conditioning.

Naskar S, Wan H, Kemenes G - Nat Commun (2014)

Training-induced upregulation of GluA1 AMPA receptors during memory consolidation in Lymnaea(a) A representative example of GluA1 immunoblot bands from a paired, an unpaired and a naïve sample, run on the same gel, is shown above the graphs (full-length blot is presented in Supplementary Fig. 7a). Density data obtained from paired (N=8) and unpaired (N=8) samples were normalized to the mean of the density data obtained from naïve samples ran on the same gels (N=8), which provided a baseline level of 1 (dashed line). In the graphs means±SEM are shown. Both paired and unpaired training results in significantly increased GluA1 receptor protein levels in the ‘learning’ ganglia at 6 h post-training (One sample t tests: paired versus naïve baseline, P=0.047; unpaired versus naïve baseline, P=0.048). There is no statistically significant difference between the GluA1 levels in the samples from the paired and unpaired group (two-tailed unpaired t-test: paired versus unpaired group, P=0.71). Asterisks indicate significant (at least P<0.05) differences compared to the naïve baseline. (b) At 24 h post-training, only the paired group (N=19) showed a conditioned response to the CS. Means±SEM of the feeding response to the CS are shown. Naïve animals (N=22) or animals subjected to unpaired training (CS-US interval 1 h, N=20) did not respond to the CS (ANOVA, P=0.0001. Tukey’s: paired vs. unpaired, P<0.05, paired vs. naïve, P<0.05, unpaired vs. naïve, P>0.05). Asterisk indicates significance compared to both unpaired and naïve response levels. These experiments were replicated twice.
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Related In: Results  -  Collection

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Figure 2: Training-induced upregulation of GluA1 AMPA receptors during memory consolidation in Lymnaea(a) A representative example of GluA1 immunoblot bands from a paired, an unpaired and a naïve sample, run on the same gel, is shown above the graphs (full-length blot is presented in Supplementary Fig. 7a). Density data obtained from paired (N=8) and unpaired (N=8) samples were normalized to the mean of the density data obtained from naïve samples ran on the same gels (N=8), which provided a baseline level of 1 (dashed line). In the graphs means±SEM are shown. Both paired and unpaired training results in significantly increased GluA1 receptor protein levels in the ‘learning’ ganglia at 6 h post-training (One sample t tests: paired versus naïve baseline, P=0.047; unpaired versus naïve baseline, P=0.048). There is no statistically significant difference between the GluA1 levels in the samples from the paired and unpaired group (two-tailed unpaired t-test: paired versus unpaired group, P=0.71). Asterisks indicate significant (at least P<0.05) differences compared to the naïve baseline. (b) At 24 h post-training, only the paired group (N=19) showed a conditioned response to the CS. Means±SEM of the feeding response to the CS are shown. Naïve animals (N=22) or animals subjected to unpaired training (CS-US interval 1 h, N=20) did not respond to the CS (ANOVA, P=0.0001. Tukey’s: paired vs. unpaired, P<0.05, paired vs. naïve, P<0.05, unpaired vs. naïve, P>0.05). Asterisk indicates significance compared to both unpaired and naïve response levels. These experiments were replicated twice.
Mentions: First, we used the western blot method to measure total GluA1 levels in the buccal and cerebral ganglia (interconnected by the cerebro-buccal connective) at 6 h after classical conditioning. The samples for these tests were obtained at 6 h post-training because a previous study demonstrated a significantly increased number of hippocampal neurons expressing GluA1 AMPA receptor subunits at this time point after fear conditioning in mice17. We found that total GluA1 levels were significantly increased at 6 h post conditioning in the samples from the paired as well as the unpaired group of animals compared to the naïve controls (Fig. 2a) but only the paired group showed a conditioned feeding response at 24 h after classical conditioning (Fig. 2b). This initial finding was consistent with the finding in mice that the proportion of GluA1 expressing hippocampal neurons increased after both paired and unpaired training17, indicating a close similarity of the underlying molecular mechanisms in invertebrates and vertebrates.

Bottom Line: CaMKIINtide treatment significantly reduces the learning-induced elevation of both pT305-CaMKII and GluA1 levels and impairs associative long-term memory.Inhibition of proteasomal activity offsets the deleterious effects of CaMKIINtide on both GluA1 levels and long-term memory.These findings suggest that increased levels of pT305-CaMKII play a role in AMPAR-dependent memory consolidation by reducing proteasomal degradation of GluA1 receptor subunits.

View Article: PubMed Central - PubMed

Affiliation: 1] Sussex Neuroscience, School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK [2].

ABSTRACT
The role of CaMKII in learning-induced activation and trafficking of AMPA receptors (AMPARs) is well established. However, the link between the phosphorylation state of CaMKII and the agonist-triggered proteasomal degradation of AMPARs during memory consolidation remains unknown. Here we describe a novel CaMKII-dependent mechanism by which a learning-induced increase in AMPAR levels is stabilized for consolidation of associative long-term memory. Six hours after classical conditioning the levels of both autophosphorylated pT305-CaMKII and GluA1 type AMPAR subunits are significantly elevated in the ganglia containing the learning circuits of the snail Lymnaea stagnalis. CaMKIINtide treatment significantly reduces the learning-induced elevation of both pT305-CaMKII and GluA1 levels and impairs associative long-term memory. Inhibition of proteasomal activity offsets the deleterious effects of CaMKIINtide on both GluA1 levels and long-term memory. These findings suggest that increased levels of pT305-CaMKII play a role in AMPAR-dependent memory consolidation by reducing proteasomal degradation of GluA1 receptor subunits.

Show MeSH
Related in: MedlinePlus