Scopolamine prevents retrograde memory interference between two different learning tasks

Translationally controlled tumor protein restores impaired memory and altered synaptic protein expression in animal models of dementia

This study describes the effects of translationally controlled tumor protein (TCTP) on mice with memory impairment caused by scopolamine (SCO) administration. Specifically, memory functions and expression levels of hippocampal synaptic proteins in 7- to 12-month-old SCO-treated wild-type (WT-SCO) mice were compared to those of TCTP-overexpressing (TG) and TCTP knocked-down (KD) mice similarly treated with SCO. Passive-avoidance tasks were performed with WT, TG, and KD mice for four weeks after intraperitoneal injection of SCO or saline followed by an acquisition test. After completing behavioral studies, hippocampi of all mice groups were collected and their synaptic protein contents were subjected to Western blotting or immunohistochemical analyses, and compared with those of 5x familial Alzheimer's disease (5xFAD) mice and postmortem AD patients. Results of passive avoidance tests revealed that SCO-induced memory impairment was repaired in TCTP-TG mice, but not in TCTP-KD mice. Hippocampal expression levels of synaptophysin, synapsin-1, and PSD-95 were increased in TCTP-TG mice treated with SCO (TG-SCO) but decreased in TCTP-KD mice treated with SCO (KD-SCO). Decreased levels of TCTP, synaptophysin, and PSD-95 were also found in hippocampi of 5xFAD mice and AD patients. Expression levels of p-CREB/CREB and brain-derived neurotrophic factor (BDNF) in TCTP-TG and TG-SCO mice were similar to or increased compared to those in WT mice, but decreased in TCTP-KD and KD-SCO mice. BDNF immunoreactivity was restored in CA1 regions of hippocampi of TG-SCO mice, but not in KD-SCO mice. These results suggest that TCTP can restore damaged memory in mice possibly through restored synaptic protein expression.

Diazepam induces retrograde facilitation of object recognition and object location memory in male mice

Benzodiazepines are widely prescribed for patients suffering from anxiety and insomnia. Although amnesic effects of benzodiazepines are commonly known as side effects, it has also been reported that these drugs improve memory for information learned before drug intake, a phenomenon called retrograde facilitation. However, the retrograde effects of benzodiazepines on cognitive performances in rodents remain controversial. It should be considered that studies on diazepam-induced retrograde facilitation in humans have been conducted using a recall paradigm focused on short-term memory, whereas these studies in rodents have been conducted using memory tasks that mainly target long-term memory and/or require negative or positive reinforcers. In the current study, we investigated whether diazepam, a benzodiazepine, induces retrograde facilitation for object recognition memory and spatial memory in mice, using a novel object recognition test and an object location test, respectively. These tests are available for short-term memory and do not require any reinforcer. The mice treated with diazepam retained object recognition memory for at least 180 min and spatial memory for at least 150 min. In contrast, vehicle-treated control mice retained object recognition memory for 120 min but not 150 min or longer, and spatial memory for 90 min but not 120 min or longer. These data clearly demonstrated diazepam-induced retrograde facilitation for both object recognition and spatial memories in mice. The present study is expected to contribute to the elucidation of the neural basis of retrograde facilitation.

The Influence of CB2-Receptor Ligands on the Memory-Related Responses in Connection with Cholinergic Pathways in Mice in the Passive Avoidance Test

Background: Dysfunction of the cholinergic system is associated with the development of Alzheimer’s disease (AD). One of the new possible strategies for the pharmacological modulation of memory-related problems typical of AD, is connected with the endocannabinoid system (ECS) and the cannabinoid (CB: CB1 and CB2) receptors. Methods: The aim of the study was to determine the influence of the selective CB2 receptor ligands: agonist (JWH 133) and antagonist (AM 630) on different stages of memory and learning in mice, in the context of their interaction with cholinergic pathways. To assess and understand the memory-related effects in mice we used the passive avoidance (PA) test. Results: We revealed that co-administration of non-effective dose of JWH 133 (0.25 mg) or AM 630 (0.25 mg/kg) with the non-effective dose of cholinergic receptor agonist - nicotine (0.05 mg/kg) enhanced cognition in the PA test in mice; however, an acute injection of JWH 133 (0.25 mg/kg) or AM 630 (0.25 mg/kg) had no influence on memory enhancement induced by the effective dose of nicotine (0.1 mg/kg). Co-administration of JWH 133 (0.25 mg) or AM 630 (0.25 mg/kg) with the effective dose of the cholinergic receptor antagonist scopolamine (1 mg/kg) attenuated the scopolamine-induced memory impairment in the PA test in mice. Conclusion: Our experiments have shown that CB2 receptors participate in the modulation of memory-related responses, especially those in which cholinergic pathways are implicated.

Odour Retrieval Processing in Mice: Cholinergic Modulation of Oscillatory Coupling in Olfactory Bulb-Piriform Networks

BACKGROUND/AIMS

Olfactory dysfunction can provide valuable insight into early pathophysiological processes of brain disorders. Olfactory processing of chemosensory and odour sensitivity relies on segregating salient odours from background odours cues. Odour-evoked fast oscillations in the olfactory bulb (OB) are hypothesized to be an important index of odour quality coding. The present preclinical work aimed at better understanding connectivity associated with odour coding and behavioural odour discrimination.

METHODS

Network oscillations and functional connectivity (FC) were measured in C57BL/6 mice performing the olfactory associative odour learning (OL) test, using multichannel local field potential recordings in key olfactory networks. Cholinergic modulation of odour processing was investigated using the muscarinic antagonist scopolamine.

RESULTS

At the behavioural level, olfactory memory, which refers to the acquisition and recollection of a reference odour by reduced exploration time, was observed in animals that correctly learned the task. Significant decrease in mean investigation and retrieval time of the associated odour-food reward was observed between trials. At the network level, the associated odour during sniffing behaviour was associated with enhanced coherence in the β and γ frequency oscillations across the olfactory pathway, with marked changes observed between the OB and anterior piriform cortex (PC). The enhanced phase-amplitude cross-frequency coupling in the OB and the weak coupling index in the hippocampal CA1 suggests a role of the OB network in olfaction encoding and processing. Scopolamine impaired behavioural and FC underlying recall and retrieval of the associated odour.

CONCLUSION

The results suggest that the acquisition and formation of odour reference memory rely primarily on FC at the OB-PC network and confirm the role of muscarinic receptors in olfactory retrieval processing.

Role of prediction error and the cholinergic system on memory reconsolidation processes in mice

The ability to make predictions based on stored information is a general coding strategy. A prediction error (PE) is a mismatch between expected and current events. Our memories, like ourselves, are subject to change. Thus, an acquired memory can become active and update its content or strength by a labilization-reconsolidation process. Within the reconsolidation framework, PE drives the updating of consolidated memories. In the past our lab has made key progresses showing that a blockade in the central cholinergic system during reconsolidation can cause memory impairment, while reinforcement of cholinergic activity enhances it. In the present work we determined that PE is a necessary condition for memory to reconsolidate in an inhibitory avoidance task using both male and female mice. Depending on the intensity of the unconditioned stimulus (US) used during training, a negative (higher US intensity) or positive (lower US intensity/no US) PE on a retrieval session modified the behavioral response on a subsequent testing session. Furthermore, we demonstrated that the cholinergic system modulates memory reconsolidation only when PE is detected. In this scenario administration of oxotremorine, scopolamine or nicotine after memory reactivation either enhanced or impaired memory reconsolidation in a sex-specific manner.

The Black Box effect: sensory stimulation after learning interferes with the retention of long-term object location memory in rats

Reducing sensory experiences during the period that immediately follows learning improves long-term memory retention in healthy humans, and even preserves memory in patients with amnesia. To date, it is entirely unclear why this is the case, and identifying the neurobiological mechanisms underpinning this effect requires suitable animal models, which are currently lacking. Here, we describe a straightforward experimental procedure in rats that future studies can use to directly address this issue. Using this method, we replicated the central findings on quiet wakefulness obtained in humans: We show that rats that spent 1 h alone in a familiar dark and quiet chamber (the Black Box) after exploring two objects in an open field expressed long-term memory for the object locations 6 h later, while rats that instead directly went back into their home cage with their cage mates did not. We discovered that both visual stimulation and being together with conspecifics contributed to the memory loss in the home cage, as exposing rats either to light or to a cage mate in the Black Box was sufficient to disrupt memory for object locations. Our results suggest that in both rats and humans, everyday sensory experiences that normally follow learning in natural settings can interfere with processes that promote long-term memory retention, thereby causing forgetting in form of retroactive interference. The processes involved in this effect are not sleep-dependent because we prevented sleep in periods of reduced sensory experience. Our findings, which also have implications for research practices, describe a potentially useful method to study the neurobiological mechanisms that might explain why normal sensory processing after learning impairs memory both in healthy humans and in patients suffering from amnesia.

Open field exposure facilitates the expression of a spatial, recognition memory

Novelty seems to reduce the persistence of aversive memories and to modulate frustration responses, yet much less is known on how this treatment affects memories lacking hedonic or emotional content. The present study analyzed how a 5-min exposure to a novel open field modulated the expression of a spatial recognition memory. Experiment 1 indicated that male Wistar rats trained in a T-maze in which one goal arm is blocked exhibit, when tested 2 h later, preference for the novel arm. This recognition memory was impaired by the muscarinic cholinergic antagonist scopolamine. Postraining, but not pretraining, novelty exposure rescued the cognitive impairment induced by scopolamine (Experiment 2 and 3). Pretraining open field exposure alleviated the lack of memory expression, induced by imposing a 6 h delay between training and testing (Experiment 4). The study shows that a very brief exposure to novelty can improve expression of a spatial, recognition memory, a modulation that - in the case of the pretraining novelty exposure -- emerges even in spite of cholinergic blockade. The present results are consistent with research suggesting that novelty exposure can be an effective, non-pharmacological, treatment to modulate memory expression.

Critical role of hippocampal muscarinic acetylcholine receptors on memory reconsolidation in mice

Over the years, experimental and clinical evidence has given support to the idea that acetylcholine (Ach) plays an essential role in mnemonic phenomena. On the other hand, the Hippocampus is already known to have a key role in learning and memory. What is yet unclear is how the Ach receptors may contribute to this brain region role during memory retrieval. The Ach receptors are divided into two broad subtypes: the ionotropic nicotinic acetylcholine receptors and the metabotropic muscarinic acetylcholine receptors. Back in 2010, we demonstrated for the first time the critical role of hippocampal α7 nicotinic acetylcholine receptors in memory reconsolidation process of an inhibitory avoidance response in mice. In the present work, we further investigate the possible implication of hippocampal muscarinic Ach receptors (mAchRs) in this process using a pharmacological approach. By specifically administrating agonists and antagonists of the different mAchRs subtypes in the hippocampus, we found that M1 and M2 but not M3 subtype may be involved in memory reconsolidation processes in mice.

Differential effects of post-training scopolamine on spatial and non-spatial learning tasks in mice

Muscarinic antagonist scopolamine has been extensively used to model amnesia in lab rodents, but most studies have focused on the effects of pre-training scopolamine administration. Here, we examined post-training scopolamine administration in C57BL/6JRj mice. Learning was assessed in three different procedures: odour discrimination in a digging paradigm, visual discrimination in a touchscreen-based setup, and spatial learning in the Morris water maze. Scopolamine administration affected performance in the odour discrimination task. More specifically, scopolamine decreased perseverance, which facilitated reversal learning. Similar results were obtained in the visual discrimination task, but scopolamine did not affect performance in the spatial learning task. It is unlikely that these results can be explained by non-memory-related cognitive effects (e.g., attention), non-cognitive behaviours (e.g., locomotor activity) or peripheral side-effects (e.g., mydriasis). They likely relate to the various neuropharmacological actions of scopolamine.

Cholinergic Mechanisms of Target Oddball Stimuli Detection: The Late "P300-Like" Event-Related Potential in Rats

Event-related potentials (ERPs) and oscillations (EROs) provide powerful tools for studying the brain's synaptic function underlying information processing. The P300 component of ERPs indexing attention and working memory shows abnormal amplitude and latency in neurological and psychiatric diseases that are sensitive to pharmacological agents. In the active auditory oddball discriminant paradigm, behavior and auditory-evoked potentials (AEPs) were simultaneously recorded in awake rats to investigate whether P300-like potentials generated in rats responding to rare target oddball tones are sensitive to subcutaneous modulation of the cholinergic tone by donepezil (1 mg/kg) and scopolamine (0.64 mg/kg). After operant training, rats consistently discriminate rare target auditory stimuli from frequent irrelevant nontarget auditory stimuli by a higher level of correct lever presses (i.e., accuracy) in target trials associated with a food reward. Donepezil attenuated the disruptive effect of scopolamine on the level of accuracy and premature responses in target trials. Larger P300-like peaks with early and late components were revealed in correct rare target stimuli trials as compared to frequent tones. Donepezil enhanced the peak amplitude of the P300-like component to target stimuli and evoked slow theta and gamma oscillations, whereas scopolamine altered the amplitude of the P300-like component and EROs to target stimuli. Pretreatment with donepezil attenuated effects of scopolamine on the peak amplitude of the P300-like component and on EROs. This study provides evidence that AEP P300-like responses can be elicited by rats engaged in attentive and memory processing of target stimuli and outline the relevance of the cholinergic system in stimulus discrimination processing. The findings highlight the sensitivity of this translational index for investigating brain circuits and/or novel pharmacological agents, which modulate cholinergic transmission associated with increased allocation of attentional resources.

Learning Situations in Nursing Education: A Concept Analysis

Background and purpose:

The nursing student requires opportunities to learn within authentic contexts so as to enable safe and competent practice. One strategy to facilitate such learning is the creation of learning situations. A lack of studies on the learning situation in nursing and other health care fields has resulted in insufficient knowledge of the characteristics of the learning situation, its antecedents, and consequences. Nurse educators need to have comprehensive and practical knowledge of the definition and characteristics of the learning situation so as to enable their students to achieve enhanced learning outcomes. The aim of this study was to clarify the concept of the learning situation as it relates to the education of nurses and improve understanding of its characteristics, antecedents, and consequences.

Methods:

The Bonis method of concept analysis, as derived from the Rodgers’ evolutionary method, provided the framework for analysis. Data collection and analysis were undertaken in two phases: “interdisciplinary” and “intra-disciplinary.” The data source was a search of the literature, encompassing nursing and allied health care professions, published from 1975 to 2016.

Results:

No agreement on the conceptual phenomenon was discovered in the international literature. The concept of a learning situation was used generally in two ways and thus classified into the themes of: “formal/informal learning situation” and “biologic/nonbiologic learning situation.” Antecedents to the creation of a learning situation included personal and environmental factors. The characteristics of a learning situation were described in terms of being complex, dynamic, and offering potential and effective learning opportunities. Consequences of the learning situation included enhancement of the students’ learning, professionalization, and socialization into the professional role.

Implication for Practice:

The nurse educator, when considering the application of the concept of a learning situation in their educational planning, must acknowledge that the application of this concept will include the student’s clinical learning experiences. More studies are required to determine factors influencing the creation of a successful learning situation from the perspectives of nurse educators and nursing students, clinical nurses and patients.

Vanillin improves scopolamine‑induced memory impairment through restoration of ID1 expression in the mouse hippocampus

4-Hydroxy-3-methoxybenzaldehyde (vanillin), contained in a number of species of plant, has been reported to display beneficial effects against brain injuries. In the present study, the impact of vanillin on scopolamine‑induced alterations in cognition and the expression of DNA binding protein inhibitor ID‑1 (ID1), one of the inhibitors of DNA binding/differentiation proteins that regulate gene transcription, in the mouse hippocampus. Mice were treated with 1 mg/kg scopolamine with or without 40 mg/kg vanillin once daily for 4 weeks. Scopolamine‑induced cognitive impairment was observed from 1 week and was deemed to be severe 4 weeks following the administration of scopolamine. However, treatment with vanillin in scopolamine‑treated mice markedly attenuated cognitive impairment 4 weeks following treatment with scopolamine. ID1‑immunoreactive cells were revealed in the hippocampus of vehicle‑treated mice, and were hardly detected 4 weeks following treatment with scopolamine. However, treatment with vanillin in scopolamine‑treated mice markedly restored ID1‑immunoreactive cells and expression 4 weeks subsequent to treatment. The results of the present study suggested that vanillin may be beneficial for cognitive impairment, by preventing the reduction of ID1 expression which may be associated with cognitive impairment.

Extinction and recovery of an avoidance memory impaired by scopolamine

Pre-training administration of scopolamine (SCP) resembles situations of cholinergic dysfunction, leading to memory impairment of mice trained in an inhibitory avoidance task. We suggest here that SCP does not impair memory formation, but acquisition is affected in a way that reduces the strength of the stored memory, thus making this memory less able to control behavior when tested. Hence, a memory trace is stored, but is poorly expressed during the test. Although weakly expressed, this memory shows extinction during successive tests, and can be strengthened by using a reminder. Our results indicate that memories stored under cholinergic dysfunction conditions seem absent or lost, but are in fact present and experience common memory processes, such as extinction, and could be even recovered by using appropriate protocols.

Open-field exposure facilitates consummatory extinction

During extinction, the organism learns that a conditioned stimulus or a conditioned response is no longer associated with an unconditioned stimulus, and as a consequence, a decrement in the response is presented. The exposure to novel situations (e.g. exploration of a novel open field) has been used widely to modulate (i.e. either enhance or deteriorate) learning and memory. The aim of the present study was to test whether open-field exposure could modulate consummatory extinction. The results indicated that open-field exposure accelerated the extinction response (i.e. experimental animals provided novelty exposure had lower consummatory behavior than control animals) when applied before - but not after - the first extinction trial, or when applied before the second extinction trial. The results suggest that environmental treatments such as novelty exposure provide a valuable, nonpharmacological alternative to potentially modulate extinction processes.

Sesame indicum, a nutritional supplement, elicits antiamnesic effect via cholinergic pathway in scopolamine intoxicated mice

PURPOSE

Present study was undertaken to evaluate the antiamnesic effect of Sesamum indicum (S. indicum) seeds (standardized for sesamin, a lignan, content) in scopolamine, a muscarinic antagonist intoxicated mice.

METHODS

Male Swiss albino mice (18-22 g bw) were pretreated with methanolic extract of sesame seeds (MSSE) (100 and 200 mg/kg/day, p.o) for a period of 14 days. Scopolamine (0.3 mg/kg, i.p.) was injected on day 14, 45 ± 10 min after MSSE administration. Antiamnesic effect of MSSE was evaluated using step-down latency (SDL) on passive avoidance apparatus and transfer latency (TL) on an elevated plus maze. To unravel the mechanism of action, we examined the effects of MSSE on the genes such as acetyl cholinesterase (AChE), muscarinic receptor M1 subtype (mAChRM₁ ), and brain derived neurotrophic factor (BDNF) expression within hippocampus of experimental mice. Further, its effects on bax and bcl-2 were also evaluated. Histopathological examination of hippocampal CA₁ region was performed using cresyl violet staining.

RESULTS

MSSE treatment produced a significant and dose dependent increase in step down latency in passive avoidance test and decrease in transfer latency in elevated plus maze in scopolamine intoxicated injected mice. MSSE down-regulated AChE and mAChRM₁ and up-regulated BDNF mRNA expression. Further, it significantly down-regulated the bax and caspase 3 and up-regulated bcl-2 expression in scopolamine intoxicated mice brains. Mice treated with MSSE showed increased neuronal counts in hippocampal CA₁ region when compared with scopolamine-vehicle treated mice.

CONCLUSION

Sesame seeds have the ability to interact with cholinergic components involved in memory function/restoration and also an interesting candidate to be considered for future cognitive research. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1955-1963, 2016.

PDE5 inhibition improves acquisition processes after learning via a central mechanism

In previous studies, we have shown that phosphodiesterase type 5 inhibitors (PDE5-Is) can improve early consolidation of object memory. These conclusions were based on the timing of drug administration relative to the learning trial (i.e. before or after). However, there are very little pharmacological data available about the pharmacokinetic profile of orally administered PDE5-Is in the rat. Furthermore, there is still debate whether these effects are achieved via central or peripheral mechanisms and if acquisition processes are improved. In the current study, we tested the effects of the PDE5-I vardenafil in a cholinergic-deficit model and compared the effects after intracerebroventricular (ICV) versus oral (PO) administration. We found that PO vardenafil restored a scopolamine-induced memory impairment when dosed within 2 min after the learning trial while ICV vardenafil was able to restore memory when injected within 4 min after learning. Because the test trial was within 10 min after the learning trial, this suggests that these effects on object memory are related to acquisition processes that may still be ongoing in a time window after the learning trial. To further elucidate the extent of this acquisition window, we investigated the pharmacokinetic profile of vardenafil after PO administration where it was detected within 4 min post-dose. Taken together, our data suggest that PDE5 is involved in acquisition processes, which may linger for at least 4-6 min after learning. Further studies are needed to exclude that these effects could also be explained on basis of an effect on early consolidation processes. Additionally, the effectiveness of ICV-administered vardenafil provides further experimental evidence that PDE5-Is improve memory via a central mechanism.

Amnesia of inhibitory avoidance by scopolamine is overcome by previous open-field exposure

The muscarinic cholinergic receptor (MAChR) blockade with scopolamine either extended or restricted to the hippocampus, before or after training in inhibitory avoidance (IA) caused anterograde or retrograde amnesia, respectively, in the rat, because there was no long-term memory (LTM) expression. Adult Wistar rats previously exposed to one or two open-field (OF) sessions of 3 min each (habituated), behaved as control animals after a weak though over-threshold training in IA. However, after OF exposure, IA LTM was formed and expressed in spite of an extensive or restricted to the hippocampus MAChR blockade. It was reported that during and after OF exposure and reexposure there was an increase in both hippocampal and cortical ACh release that would contribute to “prime the substrate,” e.g., by lowering the synaptic threshold for plasticity, leading to LTM consolidation. In the frame of the “synaptic tagging and capture” hypothesis, plasticity-related proteins synthesized during/after the previous OF could facilitate synaptic plasticity for IA in the same structure. However, IA anterograde amnesia by hippocampal protein synthesis inhibition with anisomycin was also prevented by two OF exposures, strongly suggesting that there would be alternative interpretations for the role of protein synthesis in memory formation and that another structure could also be involved in this “OF effect.”

Propranolol reverses open field effects on frustration

Reactivity to a reward is affected by prior experience with different reinforcer values of that reward, a phenomenon known as incentive relativity. Incentive relativity can be studied via the consummatory successive negative contrast (cSNC) paradigm, in which acceptance of 4% sucrose is assessed in animals that had been exposed to 32% sucrose. These downshifted animals usually exhibit significantly less sucrose acceptance than animals that always received the 4% sucrose solution. In previous work, we found that exploration of a novel open field (OF) before the first trial with the downshifted solution attenuated the contrast effect. The goal of the present experiments was to expand the knowledge on the effects of OF exposure on cSNC. We evaluated the effect OF exposure before the second downshift trial and assessed the mediational role of the adrenergic system in the effects of OF during the first and second trial of cSNC. The results indicate that OF applied before the first or second downshift trials exert opposite effects and that the adrenergic system is involved in the acquisition and consolidation of the OF information.

Post-training scopolamine treatment induced maladaptive behavior in open field habituation task in rats

The effects of scopolamine on memory consolidation are controversial and depend on several factors (i.e. site of administration, time of administration and testing, dose, cognitive task, experimental protocol, specie, strain, etc.). Generally, the range dose of systemic administered scopolamine, used in memory consolidation studies, has varied from 0.05 to 50 mg/kg. However, according to the literature, the most frequently used doses of scopolamine efficient on memory consolidation, are 1 and 30 mg/kg, low and high doses, respectively. In open field habituation studies only lower doses of scopolamine were used to test memory consolidation. Therefore, in the present study we compared the effects of low (1 mg/kg) and high (30 mg/kg) scopolamine dose, on the open field habituation task, in male Wistar rats. Scopolamine was administered immediately after the acquisition task and animals were retested 48 h later on. On the retested day, the ambulation and rearing in the open field decreased in the same manner in all tested groups. In saline- and 1 mg/kg scopolamine-treated animals, the time spent in grooming significantly decreased in the habituation task, while the same parameter significantly increased in animals treated with 30 mg/kg of scopolamine. The defecation rate significantly decreased (control group), maintained (1 mg/kg of scopolamine treated animals) or significantly increased (30 mg/kg of scopolamine treated group) on retention test. In conclusion, the present data suggest that post-training scopolamine administration does not affect locomotion neither exploration in the habituation to a novel environment, but increases defecation and grooming, two behaviours associated with fearful and stressful situations.

Chronic scopolamine-injection-induced cognitive deficit on reward-directed instrumental learning in rat is associated with CREB signaling activity in the cerebral cortex and dorsal hippocampus

RATIONALE

Scopolamine, a nonselective muscarinic receptor antagonist, has been used in experimental animal models of dementia. It has been demonstrated to disrupt performances in a battery of behavioral tests. However, no attempt has been made to determine how scopolamine-treated animals would respond to a series of reward-directed instrumental learning (RDIL) tasks.

OBJECTIVES

The present study was designed to investigate the effects of chronic intraperitoneal injection of scopolamine in Wistar rats on RDIL, as well as on the expression of memory-related molecules in the dorsal hippocampus (DH) and cerebral cortex (CCx).

METHODS

The effects of the pretraining injection of scopolamine on the acquisition of instrumental response (experiment 1) were first investigated. Then, the effects of post-training manipulation on the maintenance of instrumental response and the responses to changes in contingency degradation and signal discrimination were assessed (experiment 2). Finally, the expression of cyclic AMP response element-binding protein (CREB), phosphorylated CREB, and brain-derived neurotrophic factor in the DH and CCx were examined using Western blotting and enzyme-linked immunosorbent assay.

RESULTS

The acquisition of instrumental conditioning is more vulnerable than its maintenance. The 3.0-mg/kg dose of scopolamine rendered rats unable to make adaptive changes in facing contingency degradation and correct responses in signal discrimination tasks. Furthermore, CREB signaling was inactivated by pretraining scopolamine treatment in both the DH and CCx. Nevertheless, this pathway was selectively suppressed by post-training treatment only in the CCx during memory reconsolidation.

CONCLUSIONS

The results suggest that scopolamine-induced cognitive deficits on RDIL are related to the distinguishing alteration of CREB signaling in the DH and CCx.

Hippocampal α7-nicotinic cholinergic receptors modulate memory reconsolidation: a potential strategy for recovery from amnesia

When subjects are exposed to new learning experiences, the novel information could be acquired and eventually stored through memory consolidation process. The exposure of mice to a novel experience (a hole-board) after being trained in an inhibitory avoidance apparatus is followed by impaired performance of the avoidance memory in subsequent tests. The same impairing effect is produced when mice are exposed to the novel environment after the reactivation of the avoidance memory. This interfering effect is due to impaired consolidation or reconsolidation of the avoidance memory. The administration of the α7-nicotinic receptor agonist choline (Ch) in the dorsal hippocampus (0.8 μg/hippocampus) immediately after the inhibitory avoidance memory reactivation, allowed memory recovery. This effect of Ch was time-dependent, and retention performance was not affected in drug-treated mice that were not subjected to memory reactivation, suggesting that the effects on performance are not due to non-specific effects of the drug. The effects of Ch also depended on the age of the reactivated memory. Altogether, our results suggest that Ch exerts its effects by modulating memory reconsolidation, and that the memory impairment induced by new learning is a memory expression failure and not a storage deficit. Therefore, reconsolidation, among other functions, might serve to change whether a memory will be expressed in later tests. Summarizing, our results open new avenues about the behavioral significance and the physiological functions of memory reconsolidation, providing new strategies for recovering memories from some types of amnesia.

Tetramethylpyrazine protects against scopolamine-induced memory impairments in rats by reversing the cAMP/PKA/CREB pathway

Tetramethylpyrazine is used in the treatment of many neurological diseases because of its neuroprotective effect. Here, we demonstrate that administration of tetramethylpyrazine effectively reverses memory deficits induced by scopolamine. Moreover, tetramethylpyrazine preserves postsynaptic protein synthesis and restores cAMP/PKA/CREB pathway signaling deficits. Our study not only explores the actions of tetramethylpyrazine on synapses, but also provides novel evidence for the possible therapeutic use of tetramethylpyrazine in dementia.

Possible interaction of cholinergic and GABAergic systems between MS and CA1 upon memory acquisition in rats

The present study explored the possibility that cholinergic and GABAergic systems of medial septum (MS) might influence acquisition of memory by regulation of acetylcholine (Ach) and γ-aminobutyric acid (GABA) receptors function in hippocampus and vice versa. The step-through passive avoidance (PA) task was used. The results showed that pre-training intra-MS/CA1 administration of nonselective muscarinic Ach antagonist, scopolamine (0.5, 1 and 2 μg/rat) and GABA(A) receptor agonist, muscimol (0.01 and 0.02 μg/rat) impaired, while acetylcholinesterase inhibitor, physostigmine (0.5 and 1 μg/rat) and GABA(A) receptor antagonist, bicuculline (0.25 μg/rat) improved memory acquisition. Moreover, intra-CA1/MS administration of a subthreshold dose of muscimol or bicuculline increased and reversed the impairment induced by scopolamine in MS/CA1 respectively (cross injection). Also, the result revealed that, intra-CA1/MS administration subthreshold dose of muscimol reduced improvement of memory induced by physostigmine in the MS/CA1, respectively (cross injection). On the other hand, subthreshold dose of bicuculline in CA1/MS did not alter memory improvement induced by physostigmine in the other site (MS/CA1). In conclusion, both cholinergic and GABAergic systems not only seem to play a role in the modulation of memory in the MS and CA1 but also to have a complex interaction.

The role of metaplasticity mechanisms in regulating memory destabilization and reconsolidation

Memory allows organisms to predict future events based on prior experiences. This requires encoded information to persist once important predictors are extracted, while also being modifiable in response to changes within the environment. Memory reconsolidation may allow stored information to be modified in response to related experience. However, there are many boundary conditions beyond which reconsolidation may not occur. One interpretation of these findings is that the event triggering memory retrieval must contain new information about a familiar stimulus in order to induce reconsolidation. Presently, the mechanisms that affect the likelihood of reconsolidation occurring under these conditions are not well understood. Here we speculate on a number of systems that may play a role in protecting memory from being destabilized during retrieval. We conclude that few memories may enter a state in which they cannot be modified. Rather, metaplasticity mechanisms may serve to alter the specific reactivation cues necessary to destabilize a memory. This might imply that destabilization mechanisms can differ depending on learning conditions.

The prominent role of stimulus processing: cholinergic function and dysfunction in cognition

PURPOSE OF REVIEW

The present review develops a framework from which to understand the role of the cholinergic system in healthy cognition and in cognitive dysfunction. Traditionally, the cholinergic system has been thought to have direct influence on cognitive processes such as working memory and attention. Although the influence of cholinergic function on stimulus processing has been long appreciated, the notion that cholinergic effects on stimulus processing is the mechanism by which acetylcholine influences cognitive processes has only more recently been considered.

RECENT FINDINGS

Literature supporting the hypothesis that cholinergic modulation influences cognitive functions through stimulus processing mechanisms has been growing for over a decade. Recent conceptualizations of the developing literature have argued for a new interpretation to an old and developing literature.

SUMMARY

The argument that cholinergic function modulates cognitive processes by direct effects on basic stimulus processing extends to cognitive dysfunction in neuropathological conditions including dementia and mood disorders. Memory and attention deficits observed in these and other conditions can be understood by evaluating the impact of cholinergic dysfunction on stimulus processing, rather than on the cognitive function in general.