Differences in LTM-forming capability between geographically different strains of Alberta<i>Lymnaea stagnalis</i>are maintained whether they are trained in the lab or in the wild

The pond snail Lymnaea stagnalis can learn conditioned taste aversion and then consolidate it into long-term memory (LTM). A high-voltage electric shock was used as the unconditioned stimulus, where we have previously used KCl. We varied the strength of both the conditioned and unconditioned stimuli to determine whether the so-called Yerkes-Dodson law prevailed. This is an empirical relationship between the state of arousal and LTM formation, showing that there is an optimal level of arousal leading to memory formation. However, too little or too much arousal results in poorer LTM. We found here that the most appropriate stimuli to use in taste aversion training in Lymnaea were a 10 mmol l −1 sucrose solution as the conditioned stimulus and a 3 s electric shock as the unconditioned stimulus.

Section: Electric Shock As the Appropriate Us For Conditioned Taste Amentioning

confidence: 99%

The Yerkes-Dodson law and appropriate stimuli for conditioned taste aversion in Lymnaea

Ito

Yamagishi

Takigami

et al. 2014

“…5A,B). Several control studies have previously shown that CE does not alter non-specific effects of memory, such as behavior in yoked controls and total breathing time (Orr et al, 2009;Orr et al, 2007). The present study shows that 5-AZA effects are specific to enhanced memory and not to memory tested only 72 h later.…”

Section: Introductionmentioning

confidence: 99%

Enhanced memory persistence is blocked by a DNA methyltransferase inhibitor in the snail Lymnaea stagnalis

Lukowiak

Heckler

Bennett

et al. 2014

Lymnaea stagnalis provides an excellent model system for studying memory because these snails have a well-described set of neurons, a single one of which controls expression of long-term memory of operantly conditioned respiratory behavior. We have shown that several different manipulations, including pre-training exposure to serotonin (5-HT) or methamphetamine, submersion of snails after training to prevent memory interference, and exposure to effluent from predatory crayfish (CE), enhance memory persistence. Changes in DNA methylation underlie formation of strong memories in mammals and 5-HT-enhanced long-term facilitation in Aplysia. Here we determined the impact of the DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine (5-AZA; 87 μmol l −1 ), on enhanced memory persistence by all four manipulations. We found that 5-HT (100 μmol l −1 ) enhanced memory persistence, which was blocked by 5-AZA pretreatment. Snails pre-exposed to 3.3 μmol l −1 Meth 4 h prior to training demonstrated memory 72 h later, which was not present in controls. This memory-enhancing effect was blocked by pretreatment with 87 μmol l −1 5-AZA. Similarly, submersion to prevent interference learning as well as training in CE produced memory that was not present in controls, and these effects were blocked by pretreatment with 87 μmol l −1 5-AZA. In contrast, 5-AZA injection did not alter expression of normal (non-enhanced) memory, suggesting that these four stimuli enhance memory persistence by increasing DNA methyltransferase activity, which, in turn, increases expression of memory-enhancing genes and/or inhibits memory suppressor genes. These studies lay important groundwork for delineating gene methylation changes that are common to persistent memory produced by different stimuli.

“…The Dutch strain has been in the laboratory environment since the 1950s and originated from watercourses in a polder near Utrecht in The Netherlands (Orr et al, 2009;Lukowiak et al, 2014). This strain is now used in many universities world-wide.…”

Section: Introductionmentioning

confidence: 99%

“…An exception to this is that certain stressors when experienced by the Dutch snails can cause an enhancement of memory formation (Lukowiak et al, 2014). The smart snail phenotype, in contrast, is one where a single 0.5 h training session is sufficient to cause LTM formation (Orr et al, 2009;Dalesman et al, 2011;Braun et al, 2012;Dalesman and Lukowiak, 2012). With the exception of lab-reared snails in the Forest et al (2016) study that were exposed and trained in CE as juveniles and then tested as adults, all smart snails have come from naturally occurring populations of Lymnaea stagnalis in specific ponds in the UK, Alberta and, as shown here, Saskatchewan.…”

Section: Introductionmentioning

confidence: 99%

Juveniles ofLymnaeasmart snails do not perseverate and have the capacity to form LTM

Shymansky

Protheroe

Hughes

et al. 2016

Previously, it was concluded that the nervous systems of juvenile snails were not capable of mediating long-term memory (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 not only are capable of associative learning but also have the capacity to form LTM following a single 0.5 h 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.