Impairment of long-term associative memory in aging snails (Lymnaea stagnalis).

Abstract

Age-dependent impairment in learning and memory functions occurs in many animal species, including humans. Although cell death contributes to age-related cognitive impairment in pathological forms of aging, learning and memory deficiencies develop with age even without substantial cell death. The molecular and cellular basis of this biological aging process is not well understood but seems to involve a decline in the aging brain's capacity for experience-dependent plasticity. To aid in resolving this issue, we used a simple snail appetitive classical conditioning paradigm in which the underlying molecular, cellular, and neural network functions can be directly linked to age-associated learning and memory performance (i.e., the Lymnaea stagnalis feeding system). Our results indicate that age does not affect the acquisition of appetitive memory but that retention and/or consolidation of long-term memory become progressively impaired with advancing age. The latter phenomenon correlates with declining electrophysiological excitability in key neurons controlling the feeding behavior. Together, these results present the Lymnaea feeding system as a powerful paradigm for investigations of cellular and molecular foundations of biological aging in the brain.

Linking the why and how of aging; evidence for somatotropic control of long-term memory function in the pond snail Lymnaea stagnalis

“…Animals were bred and raised in the laboratory under constant and strictly controlled ambient conditions, as previously described (Hermann et al, 2007;Watson et al, 2012a) (12 h:12 h light:dark, ambient temperature 18-19°C). To maintain tight control over the snails aquatic environment, the animals were kept in artificial pond water ( pH 7.4-7.6) reconstituted in-house from purified reverse osmosis (RO) water reconditioned to a conductivity of ∼450 µS cm −1 by the addition of Instant Ocean salts (Aquarium Systems, Mentor, OH, USA) at 0.26 g per litre and calcium to a saturating level of ∼60 mg l −1 in the form of calcium carbonate (light powder; EMD analytics, Gibbstown, NJ, USA) to the tanks.…”

“…Appetitive classical conditioning paradigm LTM performance was assessed 10-12 days after surgery using an established single-day, multi-trial appetitive classical conditioning protocol (Hermann et al, 2007(Hermann et al, , 2013Watson et al, 2012b;Beaulieu et al, 2014). Snails were sampled at random and marked for identification purposes with indelible marker.…”

“…Yet much more needs to be learned before we truly understand all its many intricacies and facets, including, for example, the issue of how neurophysiological changes occurring with age relate to the symptoms of behavioural and cognitive decline manifest in many healthy ageing metazoans, including humans. Using the pond snail Lymnaea stagnalis (Linnaeus 1758), we have gathered biochemical, physiological and behavioural evidence that point towards alterations in (membrane) lipid metabolism as a key factor in the declining neuronal excitability and associative long-term memory (LTM) function that characterize ageing in this model system (Hermann et al, 2007(Hermann et al, , 2013Watson et al, 2012a,b). Here, we investigate how experimental interference with one of the key life history budget control systems of L. stagnalis affects LTM function.…”

Evidence for age-dependent mating strategies in the simultaneous hermaphrodite snail,Lymnaea stagnalis(L.)

“…the penis nerve 1 (NP1), is thought to serve as a nervous pathway for male sexual drive (de Boer et al, 1997). To determine output from the prostate gland, extracellular recordings were made from NP1 (see also Hermann et al, 2007). To this end, snails were anesthetized, by submerging them for 5 min in a 20% Listerine solution, and subsequently de-shelled.…”

“…We investigated the significance of age in sex role preferences of the simultaneous hermaphrodite Lymnaea stagnalis (L.). In captivity, Lymnaea lives for about 1.5 to 3 years and matures sexually at an age of 2.5-3.5 months depending on the ambient conditions and feeding regimen (Hermann et al, 2007). Body growth is indeterminate in Lymnaea although it slows down substantial after about 9-11 months of age in ad libitum fed, captive populations (Janse et al, 1989).…”