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Enhanced neuronal excitability and rule learning| old_uid | 1440 |
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| title | Enhanced neuronal excitability and rule learning |
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| start_date | 2006/06/19 |
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| schedule | 11h30 |
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| online | no |
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| location_info | bibliothèque de l'EA 3734 |
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| summary | Learning-induced enhancement of neuronal excitability is apparent in piriform (olfactory) cortex neurons pyramidal neurons following olfactory-discrimination learning. This enhanced excitability is manifested in reduced spike frequency adaptation in response to prolonged depolarizing current applications. Neuronal adaptation in these neurons is modulated by the post-burst after-hyperpolarization (AHP), which develops following a burst of action potentials. Indeed, one to three days after learning the amplitude of the post-burst AHP is significantly smaller in neurons from trained rats, compared to neurons from pseudo-trained and naive rats. The AHP’s amplitude returns back to its initial value within days when training is suspended. This recovery is not accompanied by memory loss, but the enhanced ability to acquire new memories rapidly and efficiently (rule learning) is strongly affected.
The cholinergic agonist carbachol reduces the AHP amplitude in neurons from controls, but not in neurons from trained rats. Thus, in the presence of carbachol, the AHP amplitude does not differ between groups. Similar results are obtained by applying the calcium chelator BAPTA via the recording electrode. Moreover, application of the muscarinic blocker, scopolamine, prior to each training session, delays rule learning, but has no effect on further acquisition of odor memory. The PKC inhibitor GF-109203x increases the AHP in neurons from trained rats only, and PKC activator OAG significantly reduces the AHP in neurons from naive and pseudo-trained rats only.
Olfactory learning-induced reduction in AHP is observed also in CA1 hippocampal neurons. AHP reduction occurs in the hippocampus before trained animals’ performance exceeded change level, lasts for three days, and resumes its control value even if training is continued and enhanced learning capability is maintained. One day after rule learning in the olfactory maze, trained rats perform better in the water maze than naïve and olfactory pseudo trained rats.
It is suggested that AHP reduction sets a time window in which pyramidal neurons are more excitable and thus activity-dependent synaptic modifications are more likely to occur. |
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| responsibles | <not specified> |
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