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In addition to protein synthesis, protein degradation or protein cleavage may be necessary for intermediate (ITM) and long-term memory (LTM) to remove molecular constraints, facilitate persistent kinase activity and modulate synaptic plasticity. Calpains, a family of conserved calcium dependent cysteine proteases, modulate synaptic function through protein cleavage. We used the marine mollusk Aplysia californica to investigate the in vivo role of calpains during intermediate and long-term operant memory formation using the learning that food is inedible (LFI) paradigm. A single LFI training session, in which the animal associates a specific netted seaweed with the failure to swallow, generates short (30min), intermediate (4-6h) and long-term (24h) memory. Using the calpain inhibitors calpeptin and MDL-28170, we found that ITM requires calpain activity for induction and consolidation similar to the previously reported requirements for persistent protein kinase C activity in intermediate-term LFI memory. The induction of LTM also required calpain activity. In contrast to ITM, calpain activity was not necessary for the molecular consolidation of LTM. Surprisingly, six hours after LFI training we found that calpain activity was necessary for LTM, although this is a time at which neither persistent PKC activity nor protein synthesis is required for the maintenance of long-term LFI memory. These results demonstrate that calpains function in multiple roles in vivo during associative memory formation., (Copyright © 2016 Elsevier Inc. All rights reserved.)

We investigated the in vivo role of protein degradation during intermediate (ITM) and long-term memory (LTM) in Aplysia using an operant learning paradigm. The proteasome inhibitor MG-132 inhibited the induction and molecular consolidation of LTM with no effect on ITM. Remarkably, maintenance of steady-state protein levels through inhibition of protein synthesis using either anisomycin or rapamycin in conjunction with proteasome inhibition permitted the formation of robust 24 h LTM. Our studies suggest a primary role for proteasomal activity in facilitation of gene transcription for LTM and raise the possibility that synaptic mechanisms are sufficient to sustain 24 h memory., (© 2016 Lyons et al.; Published by Cold Spring Harbor Laboratory Press.)

Study Objectives: Insufficient sleep in individuals appears increasingly common due to the demands of modern work schedules and technology use. Consequently, there is a growing need to understand the interactions between sleep deprivation and memory. The current study determined the effects of acute sleep deprivation on short and long-term associative memory using the marine mollusk Aplysia californica , a relatively simple model system well known for studies of learning and memory., Methods: Aplysia were sleep deprived for 9 hours using context changes and tactile stimulation either prior to or after training for the operant learning paradigm, learning that food is inedible (LFI). The effects of sleep deprivation on short-term (STM) and long-term memory (LTM) were assessed., Results: Acute sleep deprivation prior to LFI training impaired the induction of STM and LTM with persistent effects lasting at least 24 h. Sleep deprivation immediately after training blocked the consolidation of LTM. However, sleep deprivation following the period of molecular consolidation did not affect memory recall. Memory impairments were independent of handling-induced stress, as daytime handled control animals demonstrated no memory deficits. Additional training immediately after sleep deprivation failed to rescue the induction of memory, but additional training alleviated the persistent impairment in memory induction when training occurred 24 h following sleep deprivation., Conclusions: Acute sleep deprivation inhibited the induction and consolidation, but not the recall of memory. These behavioral studies establish Aplysia as an effective model system for studying the interactions between sleep and memory formation., (© 2016 Associated Professional Sleep Societies, LLC.)

The induction, formation and maintenance of memory represent dynamic processes modulated by multiple factors including the circadian clock and sleep. Chronic sleep restriction has become common in modern society due to occupational and social demands. Given the impact of cognitive impairments associated with sleep deprivation, there is a vital need for a simple animal model in which to study the interactions between chronic sleep deprivation and memory. We used the marine mollusk Aplysia californica, with its simple nervous system, nocturnal sleep pattern and well-characterized learning paradigms, to assess the effects of two chronic sleep restriction paradigms on short-term (STM) and long-term (LTM) associative memory. The effects of sleep deprivation on memory were evaluated using the operant learning paradigm, learning that food is inedible, in which the animal associates a specific netted seaweed with failed swallowing attempts. We found that two nights of 6h sleep deprivation occurring during the first or last half of the night inhibited both STM and LTM. Moreover, the impairment in STM persisted for more than 24h. A milder, prolonged sleep deprivation paradigm consisting of 3 consecutive nights of 4h sleep deprivation also blocked STM, but had no effect on LTM. These experiments highlight differences in the sensitivity of STM and LTM to chronic sleep deprivation. Moreover, these results establish Aplysia as a valid model for studying the interactions between chronic sleep deprivation and associative memory paving the way for future studies delineating the mechanisms through which sleep restriction affects memory formation., (Copyright © 2016 Elsevier Inc. All rights reserved.)