生态学中的植物记忆研究

近年来,植物记忆研究为深入理解种群分布格局、群落构建、群落演替等生态学过程提供了新的视角,因此备受生态学家的关注。在介绍生态胁迫记忆、表观遗传记忆、生态记忆、土壤记忆概念的基础上,综述了近几年来相关领域在生态学研究中的最新进展,并提出了植物记忆在生态学研究中值得关注的方向,以期为全面深入的理解生态学过程提供一个新的角度。     

Inception of a false memory by optogenetic manipulation of a hippocampal memory engram

Memories can be easily distorted, and a lack of relevant animal models has largely hindered our understanding of false-memory formation. Here, we first identified a population of cells in the dentate gyrus (DG) of the hippocampus that bear the engrams for a specific context; these cells were naturally activated during the encoding phase of fear conditioning and their artificial reactivation using optogenetics in an unrelated context was sufficient for inducing the fear memory specific to the conditioned context. In a further study, DG or CA1 neurons activated by exposure to a particular context were labelled with channelrhodopsin-2 (ChR2). These neurons were later optically reactivated during fear conditioning in a different context. The DG experimental group showed increased freezing in the original context in which a foot shock was never delivered. The recall of this false memory was context specific, activated similar downstream regions engaged during natural fear-memory recall, and was also capable of driving an active fear response. Together, our data demonstrate that by substituting a natural conditioned stimulus with optogenetically reactivated DG cells that bear contextual memory engrams, it is possible to incept an internally and behaviourally represented false fear memory.     

Molecular pharmacological dissection of short- and long-term memory

1. It has been discussed for over 100 years whether short-term memory (STM) is separate from, or just an early phase of, long-term memory (LTM). The only way to solve this dilemma is to find out at least one treatment that blocks STM while keeping LTM intact for the same task in the same animal.2. The effect of a large number of treatments infused into the hippocampus, amygdala, and entorhinal, posterior parietal or prefrontal cortex on STM and LTM of a one-trial step-down inhibitory avoidance task was studied. The animals were tested at 1.5 h for STM, and again at 24 h for LTM. The treatments were given after training.3. Eleven different treatments blocked STM without affecting LTM. Eighteen treatments affected the two memory types differentially, either blocking or enhancing LTM alone. Thus, STM is separate from, and parallel to the first hours of processing of, LTM of that task.4. The mechanisms of STM are different from those of LTM. The former do not include gene expression or protein synthesis; the latter include a double peak of cAMP-dependent protein kinase activity, accompanied by the phosphorylation of CREB, and both gene expression and protein synthesis.5. Possible cellular and molecular events that do not require mRNA or protein synthesis should account for STM. These might include a hyperactivation of glutamate AMPA receptors, ribosome changes, or the exocytosis of glycoproteins that participate in cell addition.     

Dissociation of rugose‐dependent short‐term memory component from memory consolidation in Drosophila

Extensive investigations show several molecular and neuroanatomical mechanisms underlying short‐lived and long‐lasting memory in Drosophila. At the molecular level, the genetic pathway of memory formation, which was obtained through mutant research, seems to occur sequentially. So far, studies of Drosophila mutants appear to support the idea that mutants defective in short‐term memory (STM) are always associated with long‐term memory (LTM) impairment. At the neuroanatomical level, distinct memory traces are partially independently distributed. However, whether memory phase dissociation also exists at the molecular level remains unclear. Here, we report on molecular separation of STM and consolidated memory through genetic dissection of rugose mutants. Mutants in the rugose gene, which encodes an evolutionarily conserved A‐kinase anchor protein, show immediate memory defects as assayed through aversive olfactory conditioning. Intriguingly, two well‐defined consolidated memory components, anesthesia‐resistant memory and protein synthesis‐dependent LTM, are both normal in spite of the defective immediate memory after 10‐session massed and spaced training. Moreover, rugose genetically interacts with cyclic AMP‐protein kinase A signaling during STM formation. Considering our previous study that AKAP Yu specifically participates in LTM formation, these results suggest that there exists a molecular level of memory phase dissociation with distinct AKAPs in Drosophila.     

Decades-long social memory in bottlenose dolphins

Long-term social memory is important, because it is an ecologically relevant test of cognitive capacity, it helps us understand which social relationships are remembered and it relates two seemingly disparate disciplines: cognition and sociality. For dolphins, long-term memory for conspecifics could help assess social threats as well as potential social or hunting alliances in a very fluid and complex fission–fusion social system, yet we have no idea how long dolphins can remember each other. Through a playback study conducted within a multi-institution dolphin breeding consortium (where animals are moved between different facilities), recognition of unfamiliar versus familiar signature whistles of former tank mates was assessed. This research shows that dolphins have the potential for lifelong memory for each other regardless of relatedness, sex or duration of association. This is, to my knowledge, the first study to show that social recognition can last for at least 20 years in a non-human species and the first large-scale study to address long-term memory in a cetacean. These results, paired with evidence from elephants and humans, provide suggestive evidence that sociality and cognition could be related, as a good memory is necessary in a fluid social system.     

Episodic-like memory: pigeons can report location pecked when unexpectedly asked

Pigeons were tested for their ability to report the location they recently pecked, without prior experience having to do so. They were first pretrained to report the location that they had just pecked. They were then trained on a conditional discrimination to associate yellow and blue samples with vertical and horizontal comparisons, respectively, independent of comparison location. On probe trials in testing, when after choosing a vertical or horizontal line following the yellow or blue sample, the pigeons were ‘asked’ which location they had just pecked, they showed a significant tendency to choose correctly in spite of the fact that location of the correct comparison was incidental to the task. Performing on probe trials is analogous to asking the pigeons an unexpected question about their recent behavior and it is similar to the episodic memory question asked of humans, “What did you have for breakfast this morning?”.     

Vasopressin analogues and spatial short-term memory in rats

The effect of vasopressin analogues on short-term memory was tested in the 12-arm radial maze. After the first 6 choices rats (n=6) were removed from the apparatus and allowed to complete the remaining 6 choices 20 min later. Whereas desgly-NH₂-VP, AVP, dAVP and DAVP (3.0 μ/kg) administered 40 min before or immediately after the first 6 choices did not change the incidence of errors in the second series of choices (2.0 errors under control conditions), similarly applied dDAVP deteriorated the rat's performance almost to the chance level of 3 errors. The significance of short-term memory tests for assessing the mnestic role of peptide hormones is stressed.     

Molecular mechanisms of memory retrieval

Memory retrieval is a fundamental component or stage of memory processing. In fact, retrieval is the only possible measure of memory. The ability to recall past events is a major determinant of survival strategies in all species and is of paramount importance in determining our uniqueness as individuals. Most biological studies of memory using brain lesion and/or gene manipulation techniques cannot distinguish between effects on the molecular mechanisms of the encoding or consolidation of memories and those responsible for their retrieval from storage. Here we examine recent findings indicating the major molecular steps involved in memory retrieval in selected brain regions of the mammalian brain. Together the findings strongly suggest that memory formation and retrieval may share some molecular mechanisms in the hippocampus and that retrieval initiates extinction requiring activation of several signaling cascades and protein synthesis.     

Taste memory formation: role of nucleus accumbens

When a novel taste has been associated with postingestive malaise, animals recognize this taste as aversive. This associative learning is known as conditioned taste aversion. However, when an animal consumes a novel taste and no aversive consequences follow, it becomes recognized as a safe signal, leading to an increase in its consumption in subsequent presentations. In this review, we will discuss the results related to the taste memory formation focusing particularly on the nucleus accumbens (NAcc). The NAcc keeps projections with amygdala, insular cortex, parabrachial nucleus, and nucleus of the solitary tract areas important for taste memory formation. We will review the evidence relating to how the NAcc could be involved in taste memory formation, due to its role in the taste memory trace formation and its role in the association of the conditioned stimulus-unconditioned stimulus, and finally the retrieval of taste memory. In this context, we will review the participation of the cholinergic, dopaminergic, and glutamatergic systems in the NAcc during taste memory formation.     

内源性甲醛异常蓄积与记忆衰退

近期,本实验室报道了内源性甲醛浓度与认知功能损伤程度之间的关系(Neurobiol Aging,2011,32(1):31-41).观察到转基因痴呆小鼠(APP、APP/PS1)及衰老加速型(SAMP8)小鼠脑内甲醛浓度较对照组显著升高.参照痴呆鼠脑内甲醛浓度,实验人员对正常成年小鼠进行注射,导致其视觉空间记忆能力减退.注射甲醛消除剂可以降低老龄大鼠体内甲醛浓度、减少APP痴呆模型小鼠脑内的老年斑,且能观察到记忆功能的改善.临床观察显示,老年痴呆患者尿甲醛浓度与认知功能损伤程度之间呈正相关.甲醛的过量蓄积造成脑慢性损伤,可能是散发性老年记忆衰退的机制之一.     

牛磺酸对学习记忆影响的研究现状

牛磺酸作为一种条件必须氨基酸对学习记忆能力的影响受到越来越多的关注,许多研究证明适量牛磺酸的添加可明显提高大鼠的记忆能力。通过牛磺酸对神经细胞、基因、激素、离子、受体、酶类等的作用,对其影响学习记忆方面的研究现状作出综述。     

Vasopressin analogues and spatial working memory in the 24-arm radial maze

The effect of vasopressin analogues dAVP, dDAVP, and desgly NH₂ dDAVP on working memory was tested in the 24-arm radial maze in twelve 6-month-old and twelve 19-month-old rats. No age dependent effects were found. All three peptides tested (3 μg/kg) tended to improve the performance but only the desgly NH₂ dDAVP significantly decreased the number of errors. A second application of desgly NH₂ dDAVP was ineffective. The specificity of activation of memory mechanisms by desgly NH₂ dDAVP can be questioned.     

Incidental learning and memory for three basic tastes in food

Forty three subjects were invited under the pretence that they would take part in an experiment on hunger feelings. They came without having eaten anything that morning and received a standard breakfast containing orange juice, cream cheese on crackers and yoghurt. These products were later (when subjects returned after scoring hunger feelings during the day) used as targets amidst a set of distractors varied by adding or subtracting different amounts of two basic tastes. Orange juice was varied in sweetness and bitterness, cream cheese in sourness and bitterness and yoghurt in sweetness and sourness. The changes were made comparable by using just noticeable differences, determined in preliminary experiments with other subjects, as units of change. Two measurements of memory were compared, an absolute (indicating which were the targets) and a relative one (indicating whether the targets and distractors were more, less or equally pleasant, sweet, sour, bitter or salty as the item eaten at breakfast). Both methods showed incidental learning, but relative memory was superior. Memory differed between tastes and was partly product dependent. These experiments suggest that taste memory is tuned to detect novel and potentially dangerous stimuli rather than to remember features of earlier experienced stimuli with great precision.     

Learning related interactions among neuronal systems involved in memory processes

Functional neuroimaging techniques using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have provided new insights in our understanding of brain function from the molecular to the systems level. While subtraction strategy based data analyses have revealed the involvement of distributed brain regions in memory processes, covariance analysis based data analysis strategies allow functional interactions between brain regions of a neuronal network to be assessed. The focus of this chapter is to (1) establish the functional topography of episodic and working memory processes in young and old normal volunteers, (2) to assess functional interactions between modules of networks of brain regions by means of covariance based analyses and systems level modelling and (3) to relate neuroimaging data to the underpinning neural networks. Male normal young and old volunteers without neurological or psychiatric illness participated in neuroimaging studies (PET, fMRI) on working and episodic memory. Distributed brain areas are involved in memory processes (episodic and working memory) in young volunteers and show much of an overlap with respect to the network components. Systems level modelling analyses support the hypothesis of bihemispheric, asymmetric networks subserving memory processes and revealed both similarities in general and differences in the interactions between brain regions during episodic encoding and retrieval as well as working memory. Changes in memory function with ageing are evident from studies in old volunteers activating more brain regions compared to young volunteers and revealing more and stronger influences of prefrontal regions. We finally discuss the way in which the systems level models based on PET and fMRI results have implications for the understanding of the underlying neural network functioning of the brain.