How to reduce fear in a snail: Take an aspirin, call me in the morning

Aspirin (Acetylsalicylic acid, ASA), one of the widely used non-steroid anti-inflammatory drugs can easily end up in sewage effluents and thus it becomes necessary to investigate the effects of aspirin on behaviour of aquatic organisms. Previous studies in mammals have shown ASA to alter fear and anxiety-like behaviours. In the great pond snail Lymnaea stagnalis, ASA has been shown to block a 'sickness state' induced by lipopolysaccharide injection which upregulates immune and stress-related genes thus altering behavioural responses. In Lymnaea, eliciting physiological stress may enhance memory formation or block its retrieval depending on the stimulus type and intensity. Here we examine whether ASA will alter two forms of associative-learning memory in crayfish predator-experienced Lymnaea when ASA exposure accompanies predator-cue-induced stress during the learning procedure. The two trainings procedures are: 1) operant conditioning of aerial respiration; and 2) a higher form of learning, called configural learning, which here is dependent on evoking a fear response. We show here that ASA alone does not alter homeostatic aerial respiration, feeding behaviour or long-term memory (LTM) formation of operantly conditioned aerial respiration. However, ASA blocked the enhancement of LTM formation normally elicited by training snails in predator cue. ASA also blocked configural learning, which makes use of the fear response elicited by the predator cue. Thus, ASA alters how Lymnaea responds cognitively to predator detection.

DNA Instability in Neurons: Lifespan Clock and Driver of Evolution

In the last ten years, the discovery of neuronal DNA postmitotic instability has changed the theoretical landscape in neuroscience and, more broadly, biology. In 2003, A. M. Olovnikov suggested that neuronal DNA is the "initial substrate of aging". Recent experimental data have significantly increased the likelihood of this hypothesis. How does neuronal DNA accumulate damage and in what genome regions? What factors contribute to this process and how are they associated with aging and lifespan? These questions will be discussed in the review. In the course of Metazoan evolution, the instability of neuronal DNA has been accompanied by searching for the pathways to reduce the biological cost of brain activity. Various processes and activities, such as sleep, evolutionary increase in the number of neurons in the vertebrate brain, adult neurogenesis, distribution of neuronal activity, somatic polyploidy, and RNA editing in cephalopods, can be reconsidered in the light of the trade-off between neuronal plasticity and DNA instability in neurons. This topic is of considerable importance for both fundamental neuroscience and translational medicine.

Agricultural Use of Insecticides Alters Homeostatic Behaviors and Cognitive Ability in Lymnaea stagnalis

Lymnaea stagnalis is an ecologically important, stress-sensitive, freshwater mollusk that is at risk for exposure to insecticides via agricultural practices. We provide insight into the impact insecticides have on L. stagnalis by comparing specific behaviors including feeding, locomotion, shell regeneration, and cognition between snails collected at two different sites: one contaminated by insecticides and one not. We hypothesized that each of the behaviors would be altered in the insecticide-exposed snails and that similar alterations would be induced when control snails were exposed to the contaminated environment. We found no significant differences in locomotion, feeding, and shell regeneration of insecticide-exposed L. stagnalis compared with nonexposed individuals. Significant changes in feeding and shell repair were observed in nonexposed snails inhabiting insecticide-contaminated pond water. Most importantly, snails maintained and trained in insecticide-contaminated pond water did not form configural learning, but this cognitive deficit was reversed when these snails were maintained in insecticide-free pond water. Our findings conclude that insecticides have a primarily negative impact on this higher form of cognition in L. stagnalis. Environ Toxicol Chem 2023;42:2466-2477. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Tracking the path of predator recognition in a predator-naive population of the pond snail

Organisms evolve adaptive strategies to adjust to rapidly changing environmental stressors. Predation pressure is one of the strongest selective forces and organisms respond to predatory threats via innate and learned responses. We utilized a natural, experimental set-up, where two lakes Stoney and Margo in Canada containing natural populations of the prey Lymnaea stagnalis differed in the presence and absence of an invasive, predatory Northern crayfish, Faxonius virilis. We exploited the contrast in the predation backgrounds of the snail populations from the two lakes to test, 1) predator recognition in predator-experienced snails is innate, (2) predator-naive snails learn to detect a novel invasive predator, and 3) learning about a novel predator gets transmitted to the successive generations. We quantified predator fear memory formation using a higher-order learning paradigm called configural learning. We found that 1) predator recognition in predator-experienced snails is innate, 2) predator-naive snails learned to recognize the novel predator even after a brief exposure to predator cues highlighting the role of learning in combating invasive predators and the critical time-window during development that accounts for predator recognition, and 3) the learning and predator detection mechanism in predator-naive snails are not transmitted to successive generations. The population variation observed in the predator-detection mechanism may be due to the past and current experience of predators in one population over the other. We find an interesting study system to address how fear learning occurs and prospective future directions to understand the mechanism of innate fear recognition from a learned fear recognition.

Nature versus nurture in heat stress induced learning between inbred and outbred populations of Lymnaea stagnalis

Changing environmental conditions often lead to microevolution of traits that are adaptive under the current selection pressure. Currently, one of the major selection pressures is the rise in temperatures globally that has a severe impact on the behavioral ecology of animals. However, the role of thermal stress on neuronal plasticity and memory formation is not well understood. Thermal tolerance and sensitivity to heat stress show variation across populations of the same species experiencing different thermal regimes. We used two populations of the pond snail Lymnaea stagnalis: one lab-bred W-snails and the other wild Delta snails to test heat shock induced learning and memory formation for the Garcia effect learning paradigm. In Garcia effect, a single pairing of a heat stressor (30 °C for 1h) with a novel taste results in a taste-specific negative hedonic shift lasting 24h as long-term memory (LTM) in lab bred W-snails. In this study we used a repeated heat stress procedure to test for increased or decreased sensitivity to the heat before testing for the Garcia effect. We found that lab-bred W-snails show increased sensitivity to heat stress after repeated heat exposure for 7days, leading to enhanced LTM for Garcia effect with only 15min of heat exposure instead of standard 1h. Surprisingly, the freshly collected wild snails do not show Garcia effect. Additionally, F1 generation of wild snails raised and maintained under laboratory conditions still retain their heat stress tolerance similar to their parents and do not show a Garcia effect under standard learning paradigm or even after repeated heat stressor. Thus, we found a differential effect of heat stress on memory formation in wild and lab bred snails. Most interestingly we also show that local environmental (temperature) conditions for one generation is not enough to alter thermal sensitivity in a wild population of L. stagnalis.

The Evolutionary Relevance of Social Learning and Transmission in Non-Social Arthropods with a Focus on Oviposition-Related Behaviors

Research on social learning has centered around vertebrates, but evidence is accumulating that small-brained, non-social arthropods also learn from others. Social learning can lead to social inheritance when socially acquired behaviors are transmitted to subsequent generations. Using oviposition site selection, a critical behavior for most arthropods, as an example, we first highlight the complementarities between social and classical genetic inheritance. We then discuss the relevance of studying social learning and transmission in non-social arthropods and document known cases in the literature, including examples of social learning from con- and hetero-specifics. We further highlight under which conditions social learning can be adaptive or not. We conclude that non-social arthropods and the study of oviposition behavior offer unparalleled opportunities to unravel the importance of social learning and inheritance for animal evolution.

The temperature sensitivity of memory formation and persistence is altered by cold acclimation in a pond snail

There are reports on the inability of inbred, laboratory-reared Lymnaea stagnalis to perform feeding and aerial respiration in the cold. It has also been suggested that laboratory-bred snails have an inability to perform aerial respiration in winter months in the laboratory. Here, we used an inbred, laboratory-reared strain of Lymnaea (the S-strain) to demonstrate that the snails are capable of performing those behaviours in a cold (4°C) environment after a 2 day acclimation period. In addition, the inbred snails were able to perform aerial respiration during winter months at room temperature (20°C) in the laboratory. The persistence of long-term memory (LTM) was extended for at least 4 weeks by placing S-strain snails into a 4°C environment following training. Typically, the cold block (CB) procedure (1 h at 4°C) immediately after a training session blocks LTM formation in the S-strain but not in a freshly collected strain. Four weeks at 4°C transformed the S-strain phenotype into one resisting the CB procedure. Thus, with a 4 week cold spell snails gain a resistance to the CB procedure, and that would explain why freshly collected snails are resistant to the procedure. However, we found that F1 progeny of a freshly collected strain reared in the laboratory were resistant to the CB procedure. This suggests that an unknown selection resulted in the S-strain being susceptible to the CB procedure.

A thermal stressor, propranolol and long-term memory formation in freshly collected Lymnaea

A heat stressor (1 h at 30°C) in Lymnaea stagnalis before operant conditioning training of aerial respiration is sufficient to enhance long-term memory (LTM) formation in 'average' cognitive ability, laboratory-reared, inbred snails. However, in freshly collected outbred snails, the same heat stressor blocks LTM formation in 'smart' cognitive phenotype but not in average cognitive phenotype strains. Here, we hypothesize that (1) preventing the stress associated with the heat stressor before training allows LTM to form in the smart phenotype strains; and (2) alleviating the stress before a memory recall session allows a formed LTM to be recalled in the smart phenotype strains. We found that an injection of propranolol, which mitigates the stressor, before snails experience the heat stressor enabled two strains of the smart phenotype snails to form LTM, consistent with our first hypothesis. However, the injection of propranolol before a memory test session did not alleviate a memory recall block in the smart phenotype snails. Thus, our second hypothesis was not supported. Therefore, smart cognitive phenotype snails encountering a heat stressor have an inability to form LTM, but this inability can be overcome by the pre-injection of propranolol.

In the great pond snail (Lymnaea stagnalis), two stressors that individually enhance memory in combination block memory formation

Stress plays an important role in memory formation in the great pond snail (Lymnaea stagnalis (Linnaeus, 1758)). Individual stressors have been shown to enhance or to perturb long-term memory (LTM) formation. However, when snails perceive a combination of two stressors, it is unclear the outcome with regards to LTM formation. Here we first show that when L. stagnalis are exposed individually to either a predator stressor (crayfish effluent (CE), which is a kairomone) or a thermal stressor (30 °C), LTM formation is enhanced. In their natural environment, L. stagnalis may experience temperatures approaching 30 °C and they may encounter crayfish at the same time. How such a combination of stressors alters adaptive behaviour is unknown. Here we show that when these two stressors are combined, LTM formation is blocked. Since boiling CE inactivates the kairomone, we used previously boiled CE that we combined with the thermal stressor and found that LTM formation is again enhanced. These data show that (i) it cannot accurately be predicted how a combination of stressors when combined interact to alter LTM formation and (ii) there is a difference between hot CE and room temperature CE.

Stress before training alters memory retrieval of a non-declarative memory in Lymnaea

Stress alters both memory formation and its retrieval. Here, we show that a combination of stressors before an associative learning event alters memory retrieval of a non-declarative memory in an invertebrate model system. Previously, two combinations of stressors were purported to prevent long-term memory (LTM) formation in 'smart' Lymnaea and this inability to form LTM was considered to be a cost of being smart. Here, we show that is not the case. The specific combinations of stressors used here cause emotional memory formation. Previously, it was shown that propranolol, a synthetic beta-blocker, altered emotional memory in Lymnaea. We show here that when propranolol but not saline is injected into smart snails before they perceive the combination of stressors, these snails form LTM. We then show that the injection of propranolol but not saline before a memory activation session allowed the memory to be recalled. That is, LTM formed but was not retrievable unless propranolol was injected pre-retrieval. Thus, the smart snails formed LTM in the face of the stressors but could not retrieve it.

Lymnaea stagnalis as model for translational neuroscience research: From pond to bench

The purpose of this review is to illustrate how a reductionistic, but sophisticated, approach based on the use of a simple model system such as the pond snail Lymnaea stagnalis (L. stagnalis), might be useful to address fundamental questions in learning and memory. L. stagnalis, as a model, provides an interesting platform to investigate the dialog between the synapse and the nucleus and vice versa during memory and learning. More importantly, the "molecular actors" of the memory dialogue are well-conserved both across phylogenetic groups and learning paradigms, involving single- or multi-trials, aversion or reward, operant or classical conditioning. At the same time, this model could help to study how, where and when the memory dialog is impaired in stressful conditions and during aging and neurodegeneration in humans and thus offers new insights and targets in order to develop innovative therapies and technology for the treatment of a range of neurological and neurodegenerative disorders.

Shell damage leads to enhanced memory formation in Lymnaea

Ecologically relevant stressors alter the ability of the pond snail, Lymnaea stagnalis, to form long-term memory (LTM). Here, we show that an environmentally relevant stressor, shell damage, has a dramatic effect on the enhancement of LTM formation. Damage in the form of a shell clip 24 h before operant conditioning training resulted in long-term memory (LTM) formation following a single 0.5 h training session (TS). Typically, in these snails, two 0.5 h TSs with a 1 h interval between the sessions are required to cause LTM formation. We show here that even with a 72 h interval between shell clip and training, memory enhancement still occurred. The stress associated with shell clip could be mitigated by an ongoing high-Ca^{2 +} pond water environment, an injection of propranolol and a DNA methylation blocker. However, use of an anaesthetic (MgCl₂) during the clip or intermittent exposure to the high-Ca^{2 +} pond water environment did not mitigate the stress associated with the shell clip. Shell clip was also sufficient to cause juvenile snails, which neither learn nor form memory, to gain the capacity to form LTM. Together, the experiments demonstrate that shell clipping is an environmentally relevant stressor that can cause enhancement of LTM formation.

Strain transformation: Enhancement of invertebrate memory in a new rearing environment

Memory formation is influenced by a variety of factors, including the environmental conditions in which an organism is reared. Here, we studied the memory-forming ability of the lab-bred B-strain of Lymnaea following a change in their rearing environment from Brock University to the University of Calgary. We have previously demonstrated that this move enhances memory-forming ability and here we studied the magnitude of this phenotypic change. Once reared to adulthood at the University of Calgary, the B-strain animals were first tested to determine how many training sessions were required for the formation of long-term memory (LTM) to occur. Following this change in environment, the B-strain transformed into a ‘smart’ lab-bred strain requiring only a single 0.5 h session to form LTM. Next, we tested whether exposure to physiologically relevant stressors would block the formation of LTM in this ‘transformed’ B-strain, as this obstruction has previously been observed in ‘smart’ snails collected from the wild. Interestingly, neither stressor tested in this study perturbed memory formation in this ‘transformed’ lab-bred strain. Additionally, both the ‘smart’ memory phenotype, as well as the increased stress resiliency, were observed in the second generation of ‘transformed’ B-strain at both the juvenile and adult stages. This suggests that a change in rearing environment can contribute to the memory-forming ability of lab-bred Lymnaea.

Configural learning in freshly collected, smart, wild Lymnaea

An inbred laboratory strain (W-strain) of Lymnaea is capable of configural learning (CL). CL a higher form of learning is an association between two stimuli experienced together that is different from the simple sum of their components. In our CL procedure a food substance (carrot, CO) is experienced together with crayfish effluent (CE) (i.e. CO+CE). Following CL, CO now elicits a fear-state rather than increased feeding. We hypothesized that freshly collected wild strains of predator-experiencedLymnaea also possess the ability to form CL; even though they experience crayfish daily in their environment. We therefore subjected freshly collected wild strain Lymnaea to the CL procedure. Following the CL procedure CO became a risk signal and evoked anti-predator behaviours. Thus, CL was demonstrated in wild, freshly collected snails. We believe that CL occurs in the snail's natural environment and is important for their survival.

Configural learning: a higher form of learning in Lymnaea

Events typically occur in a specific context and the ability to assign importance to this occurrence plays a significant role in memory formation and recall. When the scent of a crayfish predator (CE) is encountered in Lymnaea strains known to be predator-experienced (e.g. the W-strain), enhancement of memory formation and depression of feeding occurs, which are part of a suite of anti-predator behaviours. We hypothesized that Lymnaea possess a form of higher-order conditioning, namely configural learning. We tested this by simultaneously exposing W-strain Lymnaea to a carrot food-odour (CO) and predator scent (CE). Two hours later we operantly conditioned these snails with a single 0.5h training session in CO to determine whether training in CO results in long-term memory (LTM). In W-strain snails two 0.5h training sessions are required to cause LTM formation. A series of control experiments followed and demonstrated that only the CO+CE snails trained in CO had acquired enhanced memory forming ability. Additionally, following CE+CO pairing, CO no longer elicited an increased feeding response. Hence, snails have the ability to undergo configural learning. Following configural learning, CO becomes risk-signaling and evokes behavioural responses phenotypically similar to those elicited by exposure to CE.

Habitat and social context affect memory phenotype, exploration and covariance among these traits

Individual differences in cognitive ability are predicted to covary with other behavioural traits such as exploration and boldness. Selection within different habitats may act to either enhance or break down covariance among traits; alternatively, changing the environmental context in which traits are assessed may result in plasticity that alters trait covariance. Pond snails, Lymnaea stagnalis, from two laboratory strains (more than 20 generations in captivity) and F1 laboratory reared from six wild populations were tested for long-term memory and exploration traits (speed and thigmotaxis) following maintenance in grouped and isolated conditions to determine if isolation: (i) alters memory and exploration; and (ii) alters covariance between memory and exploration. Populations that demonstrated strong memory formation (longer duration) under grouped conditions demonstrated weaker memory formation and reduced both speed and thigmotaxis following isolation. In wild populations, snails showed no relationship between memory and exploration in grouped conditions; however, following isolation, exploration behaviour was negatively correlated with memory, i.e. slow-explorers showing low levels of thigmotaxis formed stronger memories. Laboratory strains demonstrated no covariance among exploration traits and memory independent of context. Together these data demonstrate that the relationship between cognition and exploration traits can depend on both habitat and context-specific trait plasticity.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.

Comparison of brain monoamine content in three populations of Lymnaea that correlates with taste-aversive learning ability

To find a causal mechanism of learning and memory is a heuristically important topic in neuroscience. In the pond snail Lymnaea stagnalis, the following experimental facts have accrued regarding a classical conditioning procedure known as conditioned taste aversion (CTA): (1) one-day food-deprived Dutch snails have superior CTA memory formation; (2) the one-day food-deprived snails have a low monoamine content (e.g., serotonin, dopamine, octopamine) in their central nervous system (CNS); (3) fed or five-day food-deprived snails have poorer CTA memory and a higher monoamine content; (4) the Dutch snails form better CTA memory than the Canadian TC1 strain; and, (5) the F₁ cross snails between the Dutch and Canadian TC1 strains also form poor CTA memory. Here, in one-day food-deprived snails, we measured the monoamine content in the CNSs of the 3 populations. In most instances, the monoamine content of the Dutch strain was lower than in the other two populations. The F₁ cross snails had the highest monoamine content. A lower monoamine content is correlated with the better CTA memory formation.

Green tea and cocoa enhance cognition in Lymnaea

A flavonoid, (-)-epicatechi (Epi), enhances long-term memory (LTM) formation in Lymnaea and reverses memory obstruction caused by stress. Many foods contain substantial amounts of Epi, (e.g. green tea and cocoa). In humans eating such foods may directly or indirectly enhance cognition. We directly test whether operant conditioning training Lymnaea in these natural foods result in the same effects as training snails in pure Epi. We found that exposure to products containing high concentrations of Epi (e.g. green tea and cocoa) during training enhanced memory formation and could even reverse a learning and memory deficit brought about by stress. Epi can be photo-inactivated by exposure to ultraviolet light. We found that following photo-inactivation of Epi, memory enhancement did not occur. Photo-inactivation of foods containing Epi (e,g. green tea) blocked their ability to enhance LTM. Our data are thus consistent with the hypothesis that dietary sources of Epi can have positive benefits on cognitive ability and be able to reverse memory aversive states.

Combining Factors That Individually Enhance Memory in Lymnaea

When applied individually, thermal stress (1 hour at 30 °C) and (-)epicatechin (a flavonol found in green tea, e.g.) each enhance long-term memory formation following operant conditioning of Lymnaea aerial respiratory behavior. Snails demonstrate enhanced long-term memory formation when trained in epicatechin-treated pond water or when placed in 30 °C pond water for 1 hour, 1 hour prior to training in pond water. We ask here whether the combined application of epicatechin + thermal stress enhances long-term memory retention length beyond the maximal lengths of the individual factors alone. We report that the applied combination of epicatechin + thermal stress has a synergistic memory-enhancing effect; that is, when the two are applied in combination, memory persists longer than when either is applied alone. We then ask whether quercetin, a heat shock protein blocker, will affect the memory enhancement produced by the combined treatment of thermal stress and epicatechin. We report that quercetin does not decrease the memory enhancement of epicatechin, but it does decrease the memory enhancement by thermal stress; and it also decreases the memory persistence of snails exposed to both treatments in combination.

Two Strains of Lymnaea stagnalis and the Progeny from Their Mating Display Differential Memory-Forming Ability on Associative Learning Tasks

The pond snail Lymnaea stagnalis learns and forms long-term memory (LTM) following both operant conditioning of aerial respiratory behavior and classical conditioning of taste aversive behavior. In the present study, we examined whether there are interstrain differences in the ability to form LTM following these two types of conditioning. A strain of Lymnaea (TC1) collected in Alberta, Canada exhibits superior memory-forming ability following aerial respiratory operant conditioning compared to a laboratory-reared strain of Lymnaea from Netherlands known as the Dutch strain. We asked whether the offspring of the Canadian TC1 and Dutch snails (i.e., filial 1 (F₁) cross snails) would have the superior memory ability and found, rather, that their memory ability was average like the Dutch snails. That is, the Canadian TC1 snails have superior ability for LTM formation following aerial respiratory operant conditioning, but the Dutch and the generated F₁ cross have average ability for memory forming. We next examined the Canadian TC1, Dutch and F₁ cross snails for their ability to learn and form memory following conditioned taste aversion (CTA). All three populations showed similar associative CTA responses. However, both LTM formation and the ratio of good-to-poor performers in the memory retention test were much better in the Dutch snails than the Canadian TC1 and F₁ cross snails. The memory abilities of the Canadian TC1 and F₁ cross snails were average. Our present findings, therefore, suggest that snails of different strains have different memory abilities, and the F₁ cross snails do not inherit the memory ability from the smart strain. To our knowledge, there have been a limited number of studies examining differences in memory ability among invertebrate strains, with the exception of studies using mutant flies.

Juveniles of Lymnaea smart snails do not perseverate and have the capacity to form LTM

Previously, it was concluded that the nervous systems of the juvenile snails were not capable of mediating LTM. However, exposure and training of those juvenile snails in the presence of a predator cue significantly altered their ability to learn and form LTM. In addition, there are some strains of Lymnaea which have been identified as ‘smart’. These snails form LTM significantly better than the lab-bred strain. Here we show that juveniles of two smart snail strains are not only capable of associative learning, but also have the capacity to form LTM following a single 0.5h training session. We also show that freshly collected ‘wild’ ‘average’ juveniles are also not able to form LTM. Thus, the smart snail phenotype in these strains is expressed in juveniles.