Different stressors uniquely affect the expression of endocannabinoid-metabolizing enzymes in the central ring ganglia of Lymnaea stagnalis

The endocannabinoid system (ECS) plays an important role in neuroprotection, neuroplasticity, energy balance, modulation of stress, and inflammatory responses, acting as a critical link between the brain and the body's peripheral regions, while also offering promising potential for novel therapeutic strategies. Unfortunately, in humans, pharmacological inhibitors of different ECS enzymes have led to mixed results in both preclinical and clinical studies. As the ECS has been highly conserved throughout the eukaryotic lineage, the use of invertebrate model organisms like the pond snail Lymnaea stagnalis may provide a flexible tool to unravel unexplored functions of the ECS at the cellular, synaptic, and behavioral levels. In this study, starting from the available genome and transcriptome of L. stagnalis, we first identified putative transcripts of all ECS enzymes containing an open reading frame. Each predicted protein possessed a high degree of sequence conservation to known orthologues of other invertebrate and vertebrate organisms. Sequences were confirmed by qualitative PCR and sequencing. Then, we investigated the transcriptional effects induced by different stress conditions (i.e., bacterial LPS injection, predator scent, food deprivation, and acute heat shock) on the expression levels of the enzymes of the ECS in Lymnaea's central ring ganglia. Our results suggest that in Lymnaea as in rodents, the ECS is involved in mediating inflammatory and anxiety-like responses, promoting energy balance, and responding to acute stressors. To our knowledge, this study offers the most comprehensive analysis so far of the ECS in an invertebrate model organism.

Sensory input from osphradium is involved in fluoride detection that alters feeding and memory phenotype in Lymnaea stagnalis

Fluoride (F-) exposure in organisms remains a significant concern due to its widespread presence and potential health implications. Investigating its detection and subsequent effects on behaviour in aquatic organisms like Lymnaea stagnalis provides valuable insights. Our study focused on elucidating the sensory pathways involved in F- detection and its impact on feeding and memory formation. We explored two potential detection mechanisms: direct flow across the integument onto neurons; and sensory input to the central nervous system (CNS) via the osphradium-osphradial ganglion-osphradial nerve pathway (snails use this system for olfactory sensation of multiple compounds). Injection of F- into snails did not alter feeding behaviour or central neuronal activity, suggesting that internalization might not be the primary detection mode. In contrast, severing the osphradial nerve abolished F-'s suppressive effects on feeding and memory formation, implicating the osphradial pathway in F- sensing and behavioural changes. This finding supports the idea that osphradial nerve signaling mediates the behavioural effects of F-. Our study underscores the importance of sensory pathways in F- detection and behavioural modulation in L. stagnalis. Understanding these mechanisms could provide critical insights into how organisms respond to and adapt to environmental chemical stressors like F-.

Investigating the interactions between multiple memory stores in the pond snail Lymnaea stagnalis

The pond snail Lymnaea stagnalis exhibits various forms of associative learning including (1) operant conditioning of aerial respiration where snails are trained not to open their pneumostome in a hypoxic pond water environment using a weak tactile stimulus to their pneumostome as they attempt to open it; and (2) a 24 h-lasting taste-specific learned avoidance known as the Garcia effect utilizing a lipopolysaccharide (LPS) injection just after snails eat a novel food substance (carrot). Typically, lab-inbred snails require two 0.5 h training sessions to form long-term memory (LTM) for operant conditioning of aerial respiration. However, some stressors (e.g., heat shock or predator scent) act as memory enhancers and thus a single 0.5 h training session is sufficient to enhance LTM formation lasting at least 24 h. Here, we found that snails forming a food-aversion LTM following Garcia-effect training exhibited enhanced LTM following operant condition of aerial respiration if trained in the presence of the food substance (carrot) they became averse to. Control experiments led us to conclude that carrot becomes a 'sickness' risk signal and acts as a stressor, sufficient to enhance LTM formation for another conditioning procedure.

Five-minute exposure to a novel appetitive food substance is sufficient time for a microRNA-dependent long-term memory to form

The Garcia effect is a unique form of conditioned taste aversion which requires that a novel food stimulus be followed sometime later by a sickness state associated with the novel food stimulus. The long-lasting associative memory resulting from the Garcia effect ensures that organisms avoid toxic foods in their environment. Considering its ecological relevance, we sought to investigate whether a brief encounter (5 min) with a novel, appetitive food stimulus can cause a persisting long-term memory (LTM) to form that would in turn block the Garcia effect in Lymnaea stagnalis. Furthermore, we wanted to explore whether that persisting LTM could be modified by the alteration of microRNAs via an injection of poly-L-lysine (PLL), an inhibitor of Dicer-mediated microRNA biogenesis. The Garcia effect procedure involved two observations of feeding behavior in carrot separated by a heat stress (30 °C for 1 h). Exposing snails to carrot for 5 min caused a LTM to form and persist for 1 week, effectively preventing the Garcia effect in snails. In contrast, PLL injection following the 5-min carrot exposure impaired LTM formation, allowing the Garcia effect to occur. These results provide more insight into LTM formation and the Garcia effect, an important survival mechanism.

The multifaceted effects of flavonoids on neuroplasticity

There has been a significant increase in the incidence of multiple neurodegenerative and terminal diseases in the human population with life expectancy increasing in the current times. This highlights the urgent need for a more comprehensive understanding of how different aspects of lifestyle, in particular diet, may affect neural functioning and consequently cognitive performance as well as in enhancing overall health. Flavonoids, found in a variety of fruits, vegetables, and derived beverages, provide a new avenue of research that shows a promising influence on different aspects of brain function. However, despite the promising evidence, most bioactive compounds lack strong clinical research efficacy. In the current scoping review, we highlight the effects of Flavonoids on cognition and neural plasticity across vertebrates and invertebrates with special emphasis on the studies conducted in the pond snail, Lymnaea stagnalis, which has emerged to be a functionally dynamic model for studies on learning and memory. In conclusion, we suggest future research directions and discuss the social, cultural, and ethnic dependencies of bioactive compounds that influence how these compounds are used and accepted globally. Bridging the gap between preclinical and clinical studies about the effects of bioactive natural compounds on brain health will surely lead to lifestyle choices such as dietary Flavonoids being used complementarily rather than as replacements to classical drugs bringing about a healthier future.

What are olfaction and gustation, and do all animals have them?

Different animals have distinctive anatomical and physiological properties to their chemical senses that enhance detection and discrimination of relevant chemical cues. Humans and other vertebrates are recognized as having 2 main chemical senses, olfaction and gustation, distinguished from each other by their evolutionarily conserved neuroanatomical organization. This distinction between olfaction and gustation in vertebrates is not based on the medium in which they live because the most ancestral and numerous vertebrates, the fishes, live in an aquatic habitat and thus both olfaction and gustation occur in water and both can be of high sensitivity. The terms olfaction and gustation have also often been applied to the invertebrates, though not based on homology. Consequently, any similarities between olfaction and gustation in the vertebrates and invertebrates have resulted from convergent adaptations or shared constraints during evolution. The untidiness of assigning olfaction and gustation to invertebrates has led some to recommend abandoning the use of these terms and instead unifying them and others into a single category-chemical sense. In our essay, we compare the nature of the chemical senses of diverse animal types and consider their designation as olfaction, oral gustation, extra-oral gustation, or simply chemoreception. Properties that we have found useful in categorizing chemical senses of vertebrates and invertebrates include the nature of peripheral sensory cells, organization of the neuropil in the processing centers, molecular receptor specificity, and function.

Better together: isolation impedes memory formation for configural learning in Lymnaea stagnalis

Social interactions play an important role in learning and memory. There is great variability in the literature regarding the effects of social isolation on cognition. Here, we investigated how memory formation was affected when Lymnaea stagnalis, our model system, were socially isolated at three different time periods: before, during or after the configural learning training procedure. Each group of snails underwent configural learning where we recorded and compared their feeding behaviour before and after the pairing of an appetitive food stimulus with predator kairomones (i.e. the training procedure). We found that isolating snails before the training procedure had no effect on their learning and memory. However, when snails were isolated either during the training procedure or immediately after the training procedure, they no longer formed memory. These data provide further insight into how isolation impacts cognitive functioning in the context of higher-order learning.

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.

LPS-Induced Garcia Effect and Its Pharmacological Regulation Mediated by Acetylsalicylic Acid: Behavioral and Transcriptional Evidence

Lymnaea stagnalis learns and remembers to avoid certain foods when their ingestion is followed by sickness. This rapid, taste-specific, and long-lasting aversion-known as the Garcia effect-can be formed by exposing snails to a novel taste and 1 h later injecting them with lipopolysaccharide (LPS). However, the exposure of snails to acetylsalicylic acid (ASA) for 1 h before the LPS injection, prevents both the LPS-induced sickness state and the Garcia effect. Here, we investigated novel aspects of this unique form of conditioned taste aversion and its pharmacological regulation. We first explored the transcriptional effects in the snails' central nervous system induced by the injection with LPS (25 mg), the exposure to ASA (900 nM), as well as their combined presentation in untrained snails. Then, we investigated the behavioral and molecular mechanisms underlying the LPS-induced Garcia effect and its pharmacological regulation by ASA. LPS injection, both alone and during the Garcia effect procedure, upregulated the expression levels of immune- and stress-related targets. This upregulation was prevented by pre-exposure to ASA. While LPS alone did not affect the expression levels of neuroplasticity genes, its combination with the conditioning procedure resulted in their significant upregulation and memory formation for the Garcia effect.

Remember the poke: microRNAs are required for long-term memory formation following operant conditioning in Lymnaea

MicroRNAs (miRNAs) play an important role in learning and memory formation by controlling the expression of genes through epigenetic processes. Although miRNAs unquestionably play a role in memory, past literature focusing on whether miRNAs play key roles in the consolidation of associative long-term memory in Lymnaea contained confounding variables. Using operant conditioning of aerial respiratory behaviour, we investigated long-term memory (LTM) formation after injection of poly-L-lysine (PLL), an inhibitor of Dicer-mediated miRNA biogenesis, in Lymnaea stagnalis. Homeostatic breathing experiments were also performed to test whether PLL affects breathing. Homeostatic breathing was significantly suppressed 45 min but not 24 h after PLL injection. The operant conditioning procedure involved two 30-min training sessions separated by 1 h to cause LTM. Using this operant conditioning procedure, LTM formation was significantly impaired when snails were injected with PLL 15 min after the second training session. In contrast, when snails were injected with PLL 24 h before the first training session, LTM formation was not impaired. These results are consistent with past literature and highlight an important role for miRNAs in LTM formation.

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.

Fluoride alters feeding in lab-bred pond snails but not in wild snails or their progeny

Increasing concentrations of fluoride in natural bodies of water due to anthropogenic activities can lead to potentially detrimental effects on residing species. Here we investigated the differences in fluoride exposure on feeding behaviour between freshly collected (i.e., wild) and lab-bred Lymnaea stagnalis and if developmental exposure plays a key role in fluoride tolerance. We show that wild snails that reside in naturally fluoridated waters and their fluoride naïve lab-reared progeny have a fluoride tolerance that does not suppress feeding when introduced to a fluoridated food stimulus. These results were also seen in our lab-bred snails who were exposed to artificially fluoridated pond water (at similar concentrations to natural levels) throughout development. However, lab-bred snails that have never been exposed to fluoride, or only exposed during the egg stage demonstrated suppression of feeding in the fluoridated food stimulus condition compared to an unfluoridated food stimulus. Genetic diversity and phenotypic plasticity are suspected to be two key underlying mechanisms for fluoride ion tolerance. These results are critical in understanding how parental and developmental exposure can influence a phenotypic tolerance to a potential chemical pollutant.

Fluoride alters feeding and memory in Lymnaea stagnalis

Fluoride occurs naturally in the terrestrial and aquatic environment and is a major component in tea. Prolonged fluoride exposure alters metabolic activity in several aquatic invertebrates. For the first time, we investigated the effects of fluoride on cognition in the pond snail Lymnaea stagnalis as it is capable of a higher form of associative learning called configural learning. We first showed suppressive effects of black tea and fluoride on feeding (i.e., rasping) behavior. We then investigated how fluoride may alter cognition by introducing fluoride (1.86 mg/L) before, during, after, a day before and a week before the snails underwent the configural learning training procedure. Our results show that any 45-min exposure to fluoride (before, during or after a configural learning training procedure) blocks configural learning memory formation in Lymnaea and these effects are long-lasting. One week after a fluoride exposure, snails are still unable to form a configural learning memory and this result is upheld when the snails are exposed to a lower concentration of fluoride, one which is naturally occurring in ponds that a wild strain of Lymnaea can be found (0.3 mg/L). Thus, fluoride obstructs configural learning memory formation in a fluoride-naïve, inbred strain of Lymnaea.

A flavonoid, quercetin, is capable of enhancing long-term memory formation if encountered at different times in the learning, memory formation, and memory recall continuum

A major extrinsic factor influencing memory and neuro-cognitive performances across taxa is diet. Studies from vertebrates have shown the effects of a flavonoid rich diet on cognitive performance, but the mechanism underlying this action is still poorly understood. A common and abundant flavonoid present in numerous food substances is quercetin (Q). The present study provides the first support for Q-modulated enhancement of cognitive function in an invertebrate model, the pond snail Lymnaea stagnalis, after an operant conditioning procedure. We found that when snails were exposed to Q 3 h before or after a single 0.5 h training session, which typically results in memory lasting ~ 3 h, they formed a long-term memory (LTM) lasting for at least 24 h. Additionally, we assessed the effects of the combined presentation of a single reinforcing stimulus (at 24 h post-training or 24 h before training) and Q-exposure on both LTM formation and reconsolidation. That is, when applied within 3 h of critical periods of memory, Q regulates four different phases: (1) acquisition (i.e., a learning event), (2) consolidation processes after acquisition, (3) memory recall, and (4) memory reconsolidation. In all these phases Q-exposure enhanced LTM persistence.

Transcriptome analysis provides genome annotation and expression profiles in the central nervous system of Lymnaea stagnalis at different ages

BACKGROUND

The pond snail, Lymnaea stagnalis (L. stagnalis), has served as a valuable model organism for neurobiology studies due to its simple and easily accessible central nervous system (CNS). L. stagnalis has been widely used to study neuronal networks and recently gained popularity for study of aging and neurodegenerative diseases. However, previous transcriptome studies of L. stagnalis CNS have been exclusively carried out on adult L. stagnalis only. As part of our ongoing effort studying L. stagnalis neuronal growth and connectivity at various developmental stages, we provide the first age-specific transcriptome analysis and gene annotation of young (3 months), adult (6 months), and old (18 months) L. stagnalis CNS.

RESULTS

Using the above three age cohorts, our study generated 55-69 millions of 150 bp paired-end RNA sequencing reads using the Illumina NovaSeq 6000 platform. Of these reads, ~ 74% were successfully mapped to the reference genome of L. stagnalis. Our reference-based transcriptome assembly predicted 42,478 gene loci, of which 37,661 genes encode coding sequences (CDS) of at least 100 codons. In addition, we provide gene annotations using Blast2GO and functional annotations using Pfam for ~ 95% of these sequences, contributing to the largest number of annotated genes in L. stagnalis CNS so far. Moreover, among 242 previously cloned L. stagnalis genes, we were able to match ~ 87% of them in our transcriptome assembly, indicating a high percentage of gene coverage. The expressional differences for innexins, FMRFamide, and molluscan insulin peptide genes were validated by real-time qPCR. Lastly, our transcriptomic analyses revealed distinct, age-specific gene clusters, differentially expressed genes, and enriched pathways in young, adult, and old CNS. More specifically, our data show significant changes in expression of critical genes involved in transcription factors, metabolisms (e.g. cytochrome P450), extracellular matrix constituent, and signaling receptor and transduction (e.g. receptors for acetylcholine, N-Methyl-D-aspartic acid, and serotonin), as well as stress- and disease-related genes in young compared to either adult or old snails.

CONCLUSIONS

Together, these datasets are the largest and most updated L. stagnalis CNS transcriptomes, which will serve as a resource for future molecular studies and functional annotation of transcripts and genes in L. stagnalis.

What can we teach Lymnaea and what can Lymnaea teach us?

This review describes the advantages of adopting a molluscan complementary model, the freshwater snail Lymnaea stagnalis, to study the neural basis of learning and memory in appetitive and avoidance classical conditioning; as well as operant conditioning of its aerial respiratory and escape behaviour. We firstly explored 'what we can teach Lymnaea' by discussing a variety of sensitive, solid, easily reproducible and simple behavioural tests that have been used to uncover the memory abilities of this model system. Answering this question will allow us to open new frontiers in neuroscience and behavioural research to enhance our understanding of how the nervous system mediates learning and memory. In fact, from a translational perspective, Lymnaea and its nervous system can help to understand the neural transformation pathways from behavioural output to sensory coding in more complex systems like the mammalian brain. Moving on to the second question: 'what can Lymnaea teach us?', it is now known that Lymnaea shares important associative learning characteristics with vertebrates, including stimulus generalization, generalization of extinction and discriminative learning, opening the possibility to use snails as animal models for neuroscience translational research.

Long-term memory of configural learning is enhanced via CREB upregulation by the flavonoid quercetin in Lymnaea stagnalis

Animals respond to acute stressors by modifying their behaviour and physiology. The pond snail Lymnaea stagnalis exhibits configural learning (CL), a form of higher order associative learning. In CL snails develop a landscape of fear when they experience a predatory cue along with a taste of food. This experience results in a suppression of the food response; but the memory only persists for 3 h. Lymnaea has also been found to upregulate heat shock proteins (HSPs) as a result of acute heat stress, which leads to the enhancement of memory formation. A plant flavonoid quercetin blocks the upregulation of HSPs when experienced prior to heat stress. Here, we used this blocking mechanism to test the hypothesis that HSP upregulation plays a critical role in CL. Snails experienced quercetin prior to CL training and surprisingly instead of blocking memory formation it enhanced the memory such that it now persisted for at least 24 h. Quercetin exposure either prior to or after CL enhanced long-term memory (LTM) up to 48 h. We quantified mRNA levels of the transcription factor CREB1 in the Lymnaea central nervous system and found LymCREB1 to be upregulated following quercetin exposure. The enhanced LTM phenotype in L. stagnalis was most pronounced when quercetin was experienced during the consolidation phase. Additionally, quercetin exposure during the memory reconsolidation phase also led to memory enhancement. Thus, we found no support of our original hypothesis but found that quercetin exposure upregulated LymCREB1 leading to LTM formation for CL.

To eat or not to eat: a Garcia effect in pond snails (Lymnaea stagnalis)

Taste aversion learning is universal. In animals, a single presentation of a novel food substance followed hours later by visceral illness causes animals to avoid that taste. This is known as bait-shyness or the Garcia effect. Humans demonstrate this by avoiding a certain food following the development of nausea after ingesting that food ('Sauce Bearnaise effect'). Here, we show that the pond snail Lymnaea stagnalis is capable of the Garcia effect. A single 'pairing' of a novel taste, a carrot slurry followed hours later by a heat shock stressor (HS) is sufficient to suppress feeding response elicited by carrot for at least 24 h. Other food tastes are not suppressed. If snails had previously been exposed to carrot as their food source, the Garcia-like effect does not occur when carrot is 'paired' with the HS. The HS up-regulates two heat shock proteins (HSPs), HSP70 and HSP40. Blocking the up-regulation of the HSPs by a flavonoid, quercetin, before the heat shock, prevented the Garcia effect in the snails. Finally, we found that snails exhibit Garcia effect following a period of food deprivation but the long-term memory (LTM) phenotype can be observed only if the animals are tested in a food satiated state.

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.

Multisensory integration supports configural learning of a home refuge in the whip spider Phrynus marginemaculatus

Whip spiders (Amblypygi) reside in structurally complex habitats and are nocturnally active yet display notable navigational abilities. From the theory that uncertainty in sensory inputs should promote multisensory representations to guide behavior, we hypothesized that their navigation is supported by a multisensory and perhaps configural representation of navigational inputs, an ability documented in a few insects and never reported in arachnids. We trained Phrynus marginemaculatus to recognize a home shelter characterized by both discriminative olfactory and tactile stimuli. In tests, subjects readily discriminated between shelters based on the paired stimuli. However, subjects failed to recognize the shelter in tests with either of the component stimuli alone. This result is consistent with the hypothesis that the terminal phase of their navigational behavior, shelter recognition, can be supported by the integration of multisensory stimuli as an enduring, configural representation. We hypothesize that multisensory learning occurs in the whip spiders' extraordinarily large mushroom bodies, which may functionally resemble the hippocampus of vertebrates.

Epicatechin increases the persistence of long-term memory formed by conditioned taste aversion in Lymnaea

We examined the effects of epicatechin (Epi), a flavonoid abundant in green tea and cocoa, on long-term memory (LTM) formed following conditioned taste aversion (CTA) training in Lymnaeastagnalis In CTA training, the snails learnt to avoid a food that initially they liked (i.e. sucrose). Twenty-four hours after CTA training, 67% of the trained snails showed a significant decrease in the feeding behaviour elicited by sucrose. Placing snails in the Epi solution in CTA training did not alter the percentage of snails exhibiting LTM, but it significantly increased LTM persistence. We also examined changes following Epi exposure in spontaneous activity of the cerebral giant cells (CGCs) that modulate feeding behaviour and are necessary for CTA-LTM. Our data suggest that Epi causes a decrease in CGC activity and increases LTM persistence, possibly via a GABAergic mechanism.

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.

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.