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Tavares TF, Bueno JLO, Doyère V. Temporal prediction error triggers amygdala-dependent memory updating in appetitive operant conditioning in rats. Front Behav Neurosci 2023; 16:1060587. [PMID: 36703723 PMCID: PMC9873233 DOI: 10.3389/fnbeh.2022.1060587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 12/21/2022] [Indexed: 01/11/2023] Open
Abstract
Reinforcement learning theories postulate that prediction error, i.e., a discrepancy between the actual and expected outcomes, drives reconsolidation and new learning, inducing an updating of the initial memory. Pavlovian studies have shown that prediction error detection is a fundamental mechanism in triggering amygdala-dependent memory updating, where the temporal relationship between stimuli plays a critical role. However, in contrast to the well-established findings in aversive situations (e.g., fear conditioning), only few studies exist on prediction error in appetitive operant conditioning, and even less with regard to the role of temporal parameters. To explore if temporal prediction error in an appetitive operant paradigm could generate an updating and consequent reconsolidation and/or new learning of temporal association, we ran four experiments in adult male rats. Experiment 1 verified whether an unexpected delay in the time of reward's availability (i.e., a negative temporal prediction error) in a single session produces an updating in long-term memory of temporal expectancy in an appetitive operant conditioning. Experiment 2 showed that negative prediction errors, either due to the temporal change or through reward omission, increased in the basolateral amygdala nucleus (BLA) the activation of a protein that is critical for memory formation. Experiment 3 revealed that the presence of a protein synthesis inhibitor (anisomycin) in the BLA during the session when the reward was delayed (Error session) affected the temporal updating. Finally, Experiment 4 showed that anisomycin, when infused immediately after the Error session, interfered with the long-term memory of the temporal updating. Together, our study demonstrated an involvement of BLA after a change in temporal and reward contingencies, and in the resulting updating in long-term memory in appetitive operant conditioning.
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Affiliation(s)
- Tatiane Ferreira Tavares
- Laboratory of Associative Processes, Temporal Control and Memory, Department of Psychology, University of São Paulo, Ribeirão Preto, Brazil,Institut des Neurosciences Paris-Saclay – NeuroPSI CNRS, Université Paris-Saclay, Saclay, France,*Correspondence: Tatiane Ferreira Tavares,
| | - José Lino Oliveira Bueno
- Laboratory of Associative Processes, Temporal Control and Memory, Department of Psychology, University of São Paulo, Ribeirão Preto, Brazil
| | - Valérie Doyère
- Institut des Neurosciences Paris-Saclay – NeuroPSI CNRS, Université Paris-Saclay, Saclay, France,Valérie Doyère,
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2
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Vitrac C, Nallet-Khosrofian L, Iijima M, Rioult-Pedotti MS, Luft A. Endogenous dopamine transmission is crucial for motor skill recovery after stroke. IBRO Neurosci Rep 2022; 13:15-21. [PMID: 35707766 PMCID: PMC9189999 DOI: 10.1016/j.ibneur.2022.05.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Accepted: 05/31/2022] [Indexed: 11/30/2022] Open
Affiliation(s)
- Clément Vitrac
- Vascular Neurology and Rehabilitation, Department of Neurology, University of Zürich, Switzerland
- Correspondence to: Universitätspital Zürich, Vascular Neurology and Rehabilitation, Rämistrasse 100, 8091 Zürich, Switzerland.
| | | | - Maiko Iijima
- Vascular Neurology and Rehabilitation, Department of Neurology, University of Zürich, Switzerland
| | - Mengia-Seraina Rioult-Pedotti
- Vascular Neurology and Rehabilitation, Department of Neurology, University of Zürich, Switzerland
- Department of MCB, Brown University, Providence, RI, USA
| | - Andreas Luft
- Center for Neurology and Rehabilitation, Vitznau, Switzerland
- Department of Neurology, University Hospital Zürich, Zürich, Switzerland
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3
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Kam K, Kang M, Eren CY, Pettibone WD, Bowling H, Taveras S, Ly A, Chen RK, Berryman NV, Klann E, Varga AW. Interactions between sleep disruption, motor learning, and p70 S6 kinase 1 signaling. Sleep 2020; 43:zsz244. [PMID: 31608388 PMCID: PMC7315768 DOI: 10.1093/sleep/zsz244] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2018] [Revised: 09/11/2019] [Indexed: 11/14/2022] Open
Abstract
Offline gains in motor performance after initial motor learning likely depend on sleep, but the molecular mechanisms by which this occurs are understudied. Regulation of mRNA translation via p70 S6 kinase 1 (S6K1) signaling represents one potential mechanism, as protein synthesis is thought to be increased during sleep compared to wake and is necessary for several forms of long-term memory. Using phosphorylation of ribosomal protein S6 (RpS6) as a readout of S6K1 activity, we demonstrate that a period of 10 h of acute sleep disruption impairs both S6K1 signaling and offline gains in motor performance on the rotarod in adult wild type C57/Bl6 mice. Rotarod motor learning results in increased abundance of RpS6 in the striatum, and inhibition of S6K1 either indirectly with rapamycin or directly with PF-4708671 diminished the offline improvement in motor performance without affecting the initial acquisition of rotarod motor learning when sleep is normal. In sum, S6K1 activity is required for sleep-dependent offline gains in motor performance and is inhibited following acute sleep disruption, while motor learning increases the abundance of striatal RpS6. Thus, S6K1 signaling represents a plausible mechanism mediating the beneficial effects of sleep on motor performance.
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Affiliation(s)
- Korey Kam
- Mount Sinai Integrative Sleep Center, Division of Pulmonary, Critical Care, and Sleep Medicine, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Mihwa Kang
- Center for Neural Science, New York University, New York, NY
| | - C Yasemin Eren
- Mount Sinai Integrative Sleep Center, Division of Pulmonary, Critical Care, and Sleep Medicine, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Ward D Pettibone
- Mount Sinai Integrative Sleep Center, Division of Pulmonary, Critical Care, and Sleep Medicine, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Heather Bowling
- Center for Neural Science, New York University, New York, NY
| | - Shantal Taveras
- Center for Neural Science, New York University, New York, NY
| | - Annie Ly
- Mount Sinai Integrative Sleep Center, Division of Pulmonary, Critical Care, and Sleep Medicine, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Rebecca K Chen
- Mount Sinai Integrative Sleep Center, Division of Pulmonary, Critical Care, and Sleep Medicine, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Natasha V Berryman
- Mount Sinai Integrative Sleep Center, Division of Pulmonary, Critical Care, and Sleep Medicine, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Eric Klann
- Center for Neural Science, New York University, New York, NY
| | - Andrew W Varga
- Mount Sinai Integrative Sleep Center, Division of Pulmonary, Critical Care, and Sleep Medicine, Icahn School of Medicine at Mount Sinai, New York, NY
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Protein Synthesis Inhibition in the Peri-Infarct Cortex Slows Motor Recovery in Rats. PLoS One 2016; 11:e0157859. [PMID: 27314672 PMCID: PMC4912164 DOI: 10.1371/journal.pone.0157859] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Accepted: 06/06/2016] [Indexed: 12/02/2022] Open
Abstract
Neuroplasticity and reorganization of brain motor networks are thought to enable recovery of motor function after ischemic stroke. Especially in the cortex surrounding the ischemic scar (i.e., peri-infarct cortex), evidence for lasting reorganization has been found at the level of neurons and networks. This reorganization depends on expression of specific genes and subsequent protein synthesis. To test the functional relevance of the peri-infarct cortex for recovery we assessed the effect of protein synthesis inhibition within this region after experimental stroke. Long-Evans rats were trained to perform a skilled-reaching task (SRT) until they reached plateau performance. A photothrombotic stroke was induced in the forelimb representation of the primary motor cortex (M1) contralateral to the trained paw. The SRT was re-trained after stroke while the protein synthesis inhibitor anisomycin (ANI) or saline were injected into the peri-infarct cortex through implanted cannulas. ANI injections reduced protein synthesis within the peri-infarct cortex by 69% and significantly impaired recovery of reaching performance through re-training. Improvement of motor performance within a single training session remained intact, while improvement between training sessions was impaired. ANI injections did not affect infarct size. Thus, protein synthesis inhibition within the peri-infarct cortex impairs recovery of motor deficits after ischemic stroke by interfering with consolidation of motor memory between training sessions but not short-term improvements within one session.
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Motor Learning Consolidates Arc-Expressing Neuronal Ensembles in Secondary Motor Cortex. Neuron 2015; 86:1385-92. [PMID: 26051420 DOI: 10.1016/j.neuron.2015.05.022] [Citation(s) in RCA: 102] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 11/24/2014] [Accepted: 05/05/2015] [Indexed: 12/23/2022]
Abstract
Motor behaviors recruit task-specific neuronal ensembles in motor cortices, which are consolidated over subsequent learning. However, little is known about the molecules that can identify the participating neurons and predict the outcomes of the consolidation process. Using a mouse rotarod-learning task, we showed that lesion or inactivation of the secondary motor (M2) cortex disrupts learning of skilled movements. We tracked the endogenous promoter activity of the neuronal activity-regulated gene Arc in individual M2 neurons during rotarod learning by in vivo two-photon imaging of a knockin reporter. We found that task training initially recruits Arc-promoter-activated neurons and then consolidates them into a specific ensemble exhibiting persistent reactivation of Arc-promoter. The intensity of a neuron's initial Arc-promoter activation predicts its reactivation probability and neurons with weak initial Arc-promoter activation are dismissed from the ensemble during subsequent training. Our findings demonstrate a task-specific Arc-dependent cellular consolidation process in M2 cortex during motor learning.
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Lesions to primary sensory and posterior parietal cortices impair recovery from hand paresis after stroke. PLoS One 2012; 7:e31275. [PMID: 22363604 PMCID: PMC3282712 DOI: 10.1371/journal.pone.0031275] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2011] [Accepted: 01/05/2012] [Indexed: 01/10/2023] Open
Abstract
Background Neuroanatomical determinants of motor skill recovery after stroke are still poorly understood. Although lesion load onto the corticospinal tract is known to affect recovery, less is known about the effect of lesions to cortical sensorimotor areas. Here, we test the hypothesis that lesions of somatosensory cortices interfere with the capacity to recover motor skills after stroke. Methods Standardized tests of motor skill and somatosensory functions were acquired longitudinally over nine months in 29 patients with stroke to the pre- and postcentral gyrus, including adjacent areas of the frontal, parietal and insular cortices. We derived the recovery trajectories of each patient for five motor subtest using least-squares curve fitting and objective model selection procedures for linear and exponential models. Patients were classified into subgroups based on their motor recovery models. Lesions were mapped onto diffusion weighted imaging scans and normalized into stereotaxic space using cost-function masking. To identify critical neuranatomical regions, voxel-wise subtractions were calculated between subgroup lesion maps. A probabilistic cytoarchitectonic atlas was used to quantify of lesion extent and location. Results Twenty-three patients with moderate to severe initial deficits showed exponential recovery trajectories for motor subtests that relied on precise distal movements. Those that retained a chronic motor deficit had lesions that extended to the center of the somatosensory cortex (area 2) and the intraparietal sulcus (areas hIP1, hIP2). Impaired recovery outcome correlated with lesion extent on this areas and somatosensory performance. The rate of recovery, however, depended on the lesion load onto the primary motor cortex (areas 4a, 4p). Conclusions Our findings support a critical role of uni-and multimodal somatosensory cortices in motor skill recovery. Whereas lesions to these areas influence recovery outcome, lesions to the primary motor cortex affect recovery dynamics. This points to a possible dissociation of neural substrates for different aspects of post-stroke recovery.
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Cortical plasticity during motor learning and recovery after ischemic stroke. Neural Plast 2011; 2011:871296. [PMID: 22135758 PMCID: PMC3202122 DOI: 10.1155/2011/871296] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 07/18/2011] [Accepted: 08/22/2011] [Indexed: 11/17/2022] Open
Abstract
The motor system has the ability to adapt to environmental constraints and injury to itself. This adaptation is often referred to as a form of plasticity allowing for livelong acquisition of new movements and for recovery after stroke. We are not sure whether learning and recovery work via same or similar neural mechanisms. But, all these processes require widespread changes within the matrix of the brain. Here, basic mechanisms of these adaptations on the level of cortical circuitry and networks are reviewed. We focus on the motor cortices because their role in learning and recovery has been investigated more thoroughly than other brain regions.
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Extinction of appetitive learning is disrupted by cycloheximide and propranolol in the sand maze in rats. Neurobiol Learn Mem 2011; 95:484-90. [PMID: 21371561 DOI: 10.1016/j.nlm.2011.02.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2010] [Revised: 02/11/2011] [Accepted: 02/22/2011] [Indexed: 11/23/2022]
Abstract
The present study investigated whether memory for extinction in an appetitive task (the sand maze) could be attenuated by administration of cycloheximide (protein synthesis inhibitor) or propranolol (β-adrenergic receptor antagonist). Ninety-day-old male Long-Evans rats were trained to retrieve a sweet cereal reinforcer from an open container in the sand maze. One day following this non-spatial training, rats received three extinction trials in which they were placed in the maze with the reinforcer present, but unattainable. Thirty minutes prior to the first extinction trial, rats received an intraperitoneal injection of cycloheximide (1mg/kg), propranolol (25mg/kg), or vehicle (1mg/kg distilled water). Twenty-four hours later, rats were tested in the sand maze with the reinforcer again available. Results from the test trial showed that both cycloheximide and propranolol groups found the reinforcer more quickly than controls. Two weeks later, rats were trained on a spatial version of the sand maze in which they had to search for a buried reinforcer using extramaze cues. Cycloheximide and propranolol groups learned this task significantly faster than the control group, demonstrating the long-lasting effect of cycloheximide and propranolol on the blocking of memory for extinction.
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Peng JY, Li BM. Protein synthesis is essential not only for consolidation but also for maintenance and post-retrieval reconsolidation of acrobatic motor skill in rats. Mol Brain 2009; 2:12. [PMID: 19476636 PMCID: PMC2695814 DOI: 10.1186/1756-6606-2-12] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Accepted: 05/28/2009] [Indexed: 11/25/2022] Open
Abstract
It has been reported that consolidation of motor skill, a type of non-declarative memories, requires protein synthesis, as hippocampus-dependent declarative memory does. However, little is known about the importance of protein synthesis in maintenance and especially post-retrieval reconsolidation of acrobatic motor skill. Here, we show that protein synthesis is essential not only for the consolidation but also for the maintenance and reconsolidation of a rotarod-running skill. Intra-ventricle infusion of the protein synthesis inhibitor anisomycin 0 h but not 2 h post-training caused a severe deficit in the acquisition of the rotarod-running skill. Protein synthesis inhibition (PSI) also caused a deficit in the maintenance of the rotarod-running skill, as well-trained rats demonstrated a deficit in the rotarod-running performance upon treatment with anisomycin. Similarly, PSI impaired the post-retrieval reconsolidation of the rotarod-running skill: well-trained rats treated with anisomycin 0 h but not 0.5, 2 and 4 h after the task performance exhibited amnesia for the running skill later on. Interestingly, rats treated with anisomycin 6 and 12 h post-retrieval exhibited amnesia for the running skill. Thus, protein synthesis is essential not only for the consolidation but also for the maintenance and post-retrieval reconsolidation of rotarod-running acrobatic motor skill.
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Affiliation(s)
- Ji-Yun Peng
- Institute of Neurobiology and State Key Laboratory of Medical Neurobiology, Institutes of Brain Science, Fudan University, Shanghai 200032, PR China.
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10
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Abstract
Can memories be unlearned, or is unlearning a form of acquiring a new memory that competes with the old, effectively masking it? We considered motor memories that were acquired when people learned to use a novel tool. We trained people to reach with tool A and quantified recall in error-clamp trials, i.e., trials in which the memory was reactivated but error-dependent learning was minimized. We measured both the magnitude of the memory and its resistance to change. With passage of time between acquisition and reactivation (up to 24 h), memory of A slowly declined, but with reactivation remained resistant to change. After learning of tool A, brief exposure to tool B brought performance back to baseline, i.e., apparent extinction. Yet, for up to a few minutes after A+B training, output in error-clamp trials increased from baseline to match those who had trained only in A. This spontaneous recovery and convergence demonstrated that B did not produce any unlearning of A. Rather, it masked A with a new memory that was very fragile. We tracked the memory of B as a function of time and found that within minutes it was transformed from a fragile to a more stable state. Therefore, a sudden performance error in a well-learned motor task does not produce unlearning, but rather installs a competing but fragile memory that with passage of time acquires stability. Learning not only engages processes that adapt at multiple timescales, but once practice ends, the fast states are partially transformed into slower states.
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Molina-Luna K, Hertler B, Buitrago MM, Luft AR. Motor learning transiently changes cortical somatotopy. Neuroimage 2008; 40:1748-54. [DOI: 10.1016/j.neuroimage.2007.11.018] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Revised: 11/05/2007] [Accepted: 11/13/2007] [Indexed: 10/22/2022] Open
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Flint RW, Valentine S, Papandrea D. Reconsolidation of a long-term spatial memory is impaired by cycloheximide when reactivated with a contextual latent learning trial in male and female rats. Neuroscience 2007; 148:833-44. [PMID: 17766047 DOI: 10.1016/j.neuroscience.2007.07.022] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2007] [Revised: 07/06/2007] [Accepted: 07/18/2007] [Indexed: 10/23/2022]
Abstract
Reconsolidation of long-term memory has become a topic of great interest in recent years, and has the potential to provide important information regarding memory processes and the treatment of memory-related disorders. The present study examined the role of systemic protein synthesis inhibition in reconsolidation of a long-term spatial memory reactivated by a contextual latent learning trial in male and female rats. Using the Morris water maze, we demonstrate that: 1) a contextual latent reactivation treatment enhances memory, 2) systemic protein synthesis inhibition selectively impairs test performance when administered in conjunction with a memory reactivation treatment, and 3) that these effects are more pronounced in female rats. These findings indicate a role for protein synthesis in the reconsolidation of a contextually reactivated long-term spatial memory using the water maze, and a potential differential effect of sex in this apparatus. The role of the strength of the memory trace is discussed and the relevance of these findings to theories of reconsolidation and therapeutic treatment of post-traumatic stress disorder is discussed.
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Affiliation(s)
- R W Flint
- Department of Psychology, The College of Saint Rose, 432 Western Avenue, Albany, NY 12203-1490, USA.
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Luft AR, Buitrago MM. Stages of motor skill learning. Mol Neurobiol 2006; 32:205-16. [PMID: 16385137 DOI: 10.1385/mn:32:3:205] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2005] [Accepted: 04/29/2005] [Indexed: 11/11/2022]
Abstract
Successful learning of a motor skill requires repetitive training. Once the skill is mastered, it can be remembered for a long period of time. The durable memory makes motor skill learning an interesting paradigm for the study of learning and memory mechanisms. To gain better understanding, one scientific approach is to dissect the process into stages and to study these as well as their interactions. This article covers the growing evidence that motor skill learning advances through stages, in which different storage mechanisms predominate. The acquisition phase is characterized by fast (within session) and slow learning (between sessions). For a short period following the initial training sessions, the skill is labile to interference by other skills and by protein synthesis inhibition, indicating that consolidation processes occur during rest periods between training sessions. During training as well as rest periods, activation in different brain regions changes dynamically. Evidence for stages in motor skill learning is provided by experiments using behavioral, electrophysiological, functional imaging, and cellular/molecular methods.
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Affiliation(s)
- Andreas R Luft
- Abteilung Allgemeine Neurologie, Hertie Institut für Klinische Hirnforschung, Universität Tübingen, Germany.
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Oliveira AMM, Abel T, Brindle PK, Wood MA. Differential role for CBP and p300 CREB-binding domain in motor skill learning. Behav Neurosci 2006; 120:724-9. [PMID: 16768624 DOI: 10.1037/0735-7044.120.3.724] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Cyclic adenosine monophosphate response element binding protein (CREB) binding protein (CBP) and E1A binding protein (p300) are highly homologous transcriptional coactivators with histone acetyltransferase activity. Although CBP and p300 have unique functions in vivo during embryogenesis and hematopoiesis, their functions within the nervous system remain poorly understood. The authors demonstrate that these coactivators have differential roles in motor skill learning. Mice with a mutation in the CREB-binding (KIX) domain of CBP exhibited motor learning deficits. However, mice with the analogous mutation in the KIX domain of p300 showed normal motor learning. Further, CREB knock-out mice exhibited a motor learning deficit similar to that of CBP-KIX mutant mice. These results suggest that the CREB-CBP interaction is more limiting or critical than the CREB-p300 interaction for motor skill learning. Thus, CBP and p300 are genetically distinct at the behavioral level.
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Affiliation(s)
- Ana M M Oliveira
- Department of Biology, University of Pennsylvania, Philadelphia, PA, USA
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Bustos SG, Maldonado H, Molina VA. Midazolam disrupts fear memory reconsolidation. Neuroscience 2006; 139:831-42. [PMID: 16542779 DOI: 10.1016/j.neuroscience.2005.12.064] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2005] [Revised: 12/13/2005] [Accepted: 12/22/2005] [Indexed: 10/24/2022]
Abstract
The current research examines the influence of midazolam (MDZ) on memory reconsolidation using a contextual fear paradigm in rats, based on three context-shock training trials (0.7 mA, 3 s). First, we evaluate the effect of MDZ (1 mg/kg, i.p.) injected shortly after the training procedure. Second, we examined the influence of MDZ after a brief exposure (90 s) either in the training context (reactivation procedure) or in a neutral environment (no reactivation procedure) and one day later, freezing behavior was scored when rats were re-exposed to the training environment. Third, we investigate both the effect of MDZ administered at different times following reactivation on fear memory and the persistence of such effect 10 days after reactivation. Finally, we test whether the MDZ effect could be reverted by a single weak training trial (0.2 mA, 3 s) or by the presentation of the same unconditioned stimulus in the absence of the conditioned stimulus as a reminder which proves to induce significant freezing in rats not previously trained. Results show that MDZ interferes with the formation of a contextual fear memory only when administered after the reactivation procedure but not after the training procedure. This interference was effective up to 60 min after reactivation and not at a later time. No spontaneous recovery of freezing behavior was observed 11 days after MDZ injection which was not reverted by a weak training trial and by the unconditioned stimulus alone. All these data support the idea that stimulating GABA A receptor sites via MDZ selectively disrupts the reconsolidation process of a contextual fear memory.
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Affiliation(s)
- S G Bustos
- Departamento de Farmacología, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, 5000 Córdoba, Argentina
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