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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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Classical conditioning increases the number of GluA1 receptors in the ‘learning ganglia’(a, b) The top panels in each part show examples of GluA1 immunostaining in sections from the buccal and cerebral ganglia, respectively. The ganglia were dissected at 6 h post-training from Paired, Unpaired and Naïve animals (N=5 in each group). The bottom panels in each part show the signals in the same sections computed to be above a pre-set 8-bit grey-scale threshold value (65) that was the same for all samples (for details see Methods). Asterisks indicate comparable locations of the neuropile in the samples from paired, unpaired and naïve animals. Scale bars represent 100 μm. (c, d) Statistical data obtained by the analysis of all the buccal and cerebral ganglia samples, respectively. The bar diagrams show the % of the area of immunostaining (means±SEM) that exceeds threshold. Asterisk indicates that in both pairs of ganglia this value is significantly greater in the paired group compared against both the unpaired and naïve group. (c, One-way ANOVA: P<0.0003. Tukey’s: Paired versus Unpaired and Paired versus Naïve, P<0.05; Unpaired versus Naïve, P>0.05. d, One-way ANOVA P<0.001. Tukey’s: Paired versus Unpaired and Paired versus Naïve, P<0.05; Unpaired versus Naïve, P>0.05). Very similar statistical results were obtained when we analyzed the differential expression of GluA1 in the paired and unpaired snail ganglia relative to naïve levels (see Methods). This experiment was replicated twice.
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Figure 4: Classical conditioning increases the number of GluA1 receptors in the ‘learning ganglia’(a, b) The top panels in each part show examples of GluA1 immunostaining in sections from the buccal and cerebral ganglia, respectively. The ganglia were dissected at 6 h post-training from Paired, Unpaired and Naïve animals (N=5 in each group). The bottom panels in each part show the signals in the same sections computed to be above a pre-set 8-bit grey-scale threshold value (65) that was the same for all samples (for details see Methods). Asterisks indicate comparable locations of the neuropile in the samples from paired, unpaired and naïve animals. Scale bars represent 100 μm. (c, d) Statistical data obtained by the analysis of all the buccal and cerebral ganglia samples, respectively. The bar diagrams show the % of the area of immunostaining (means±SEM) that exceeds threshold. Asterisk indicates that in both pairs of ganglia this value is significantly greater in the paired group compared against both the unpaired and naïve group. (c, One-way ANOVA: P<0.0003. Tukey’s: Paired versus Unpaired and Paired versus Naïve, P<0.05; Unpaired versus Naïve, P>0.05. d, One-way ANOVA P<0.001. Tukey’s: Paired versus Unpaired and Paired versus Naïve, P<0.05; Unpaired versus Naïve, P>0.05). Very similar statistical results were obtained when we analyzed the differential expression of GluA1 in the paired and unpaired snail ganglia relative to naïve levels (see Methods). This experiment was replicated twice.

Mentions: Importantly, after paired, but not unpaired, training, GluA1 expression was significantly increased in both the neuropile and neuronal cell body region, in both the buccal and cerebral ganglia (Fig. 4). These results confirmed that similar to the mouse hippocampus, paired training results in a significant increase in the number of GluA1 receptors in the neurons of the learning circuitry of the Lymnaea CNS. By contrast, the animals subjected to unpaired training did not show an increase in GluA1 levels in the neurons of the ‘learning ganglia’ at 6 h post-training (Fig. 4); neither did they show an increased response to the CS at 24 h post-training (Fig. 1). Interestingly, in the sections from classically conditioned animals there was also an increased level of GluA1 expression in the buccal commissure (Fig. 4), possibly indicating an increased level of trafficking of GluA1 receptors in the contralaterally projecting axons of motoneurons and interneurons of the feeding network, from the cell body to presynaptic terminals.


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)

Classical conditioning increases the number of GluA1 receptors in the ‘learning ganglia’(a, b) The top panels in each part show examples of GluA1 immunostaining in sections from the buccal and cerebral ganglia, respectively. The ganglia were dissected at 6 h post-training from Paired, Unpaired and Naïve animals (N=5 in each group). The bottom panels in each part show the signals in the same sections computed to be above a pre-set 8-bit grey-scale threshold value (65) that was the same for all samples (for details see Methods). Asterisks indicate comparable locations of the neuropile in the samples from paired, unpaired and naïve animals. Scale bars represent 100 μm. (c, d) Statistical data obtained by the analysis of all the buccal and cerebral ganglia samples, respectively. The bar diagrams show the % of the area of immunostaining (means±SEM) that exceeds threshold. Asterisk indicates that in both pairs of ganglia this value is significantly greater in the paired group compared against both the unpaired and naïve group. (c, One-way ANOVA: P<0.0003. Tukey’s: Paired versus Unpaired and Paired versus Naïve, P<0.05; Unpaired versus Naïve, P>0.05. d, One-way ANOVA P<0.001. Tukey’s: Paired versus Unpaired and Paired versus Naïve, P<0.05; Unpaired versus Naïve, P>0.05). Very similar statistical results were obtained when we analyzed the differential expression of GluA1 in the paired and unpaired snail ganglia relative to naïve levels (see Methods). This experiment was replicated twice.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4048835&req=5

Figure 4: Classical conditioning increases the number of GluA1 receptors in the ‘learning ganglia’(a, b) The top panels in each part show examples of GluA1 immunostaining in sections from the buccal and cerebral ganglia, respectively. The ganglia were dissected at 6 h post-training from Paired, Unpaired and Naïve animals (N=5 in each group). The bottom panels in each part show the signals in the same sections computed to be above a pre-set 8-bit grey-scale threshold value (65) that was the same for all samples (for details see Methods). Asterisks indicate comparable locations of the neuropile in the samples from paired, unpaired and naïve animals. Scale bars represent 100 μm. (c, d) Statistical data obtained by the analysis of all the buccal and cerebral ganglia samples, respectively. The bar diagrams show the % of the area of immunostaining (means±SEM) that exceeds threshold. Asterisk indicates that in both pairs of ganglia this value is significantly greater in the paired group compared against both the unpaired and naïve group. (c, One-way ANOVA: P<0.0003. Tukey’s: Paired versus Unpaired and Paired versus Naïve, P<0.05; Unpaired versus Naïve, P>0.05. d, One-way ANOVA P<0.001. Tukey’s: Paired versus Unpaired and Paired versus Naïve, P<0.05; Unpaired versus Naïve, P>0.05). Very similar statistical results were obtained when we analyzed the differential expression of GluA1 in the paired and unpaired snail ganglia relative to naïve levels (see Methods). This experiment was replicated twice.
Mentions: Importantly, after paired, but not unpaired, training, GluA1 expression was significantly increased in both the neuropile and neuronal cell body region, in both the buccal and cerebral ganglia (Fig. 4). These results confirmed that similar to the mouse hippocampus, paired training results in a significant increase in the number of GluA1 receptors in the neurons of the learning circuitry of the Lymnaea CNS. By contrast, the animals subjected to unpaired training did not show an increase in GluA1 levels in the neurons of the ‘learning ganglia’ at 6 h post-training (Fig. 4); neither did they show an increased response to the CS at 24 h post-training (Fig. 1). Interestingly, in the sections from classically conditioned animals there was also an increased level of GluA1 expression in the buccal commissure (Fig. 4), possibly indicating an increased level of trafficking of GluA1 receptors in the contralaterally projecting axons of motoneurons and interneurons of the feeding network, from the cell body to presynaptic terminals.

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