I appreciate the interest expressed by Dr. Ghoneim for my article. I am pleased to have invoked a response from my clinician counterpart vis-à-vis  the need to understand fundamental mechanisms by which anesthetics may affect learning and memory.

To clarify how cultured neurons may be relevant to memory processes, I wish to point out that at both the cellular and the molecular level, most fundamental mechanisms underlying synaptic plasticity are preserved in a vast majority of in vitro  (slices or cultured neurons) preparations. These plastic changes in synaptic activity, in turn, are thought to form the basis for learning and memory in most animals—ranging from worms, snails, and flies to humans. Therefore, it is highly appropriate and useful to take advantage of in vitro  preparations for understanding complex processes such as learning and memory. Regarding the usefulness of the model system for studies on synaptic plasticity and learning and memory, I wish to point out that mine was the first laboratory to have reconstructed the entire respiratory network in cell culture. I demonstrated that the in vivo  reconstructed circuit, comprising behaviorally and functionally well-defined neurons, was sufficient to generate patterned respiratory rhythm in a manner similar to that seen in vivo . Both the Lukowiak (University of Calgary, Calgary, Alberta, Canada) and my laboratory have since demonstrated that the respiratory behavior in Lymnaea  can be operantly conditioned2,,3,,4,,5,,6,,7 to exhibit short-, intermediate-, and long-term memory and have identified the locus for these memory related changes at the level of a single neuron. By selectively removing a single cell in the intact animals, I have subsequently provided direct evidence regarding the storage site for learning and memory-related changes in individual neurons.8,,9,,10,,11,,12,,13,,14,,15 Moreover, using the cell culture model, I have not only defined the mechanisms that regulate synaptic efficacy16,,17 but also identified novel proteins that can modulate synaptic strength via  interactions with the glial cells. Therefore, I believe that the Lymnaea  model is equally well suited for studies in synaptic plasticity and learning and memory—as has been the case in Aplysia .

Notwithstanding these strengths of my model and a clear demonstration in my article that anesthetics do not affect short-term potentiation, I have still been very careful in drawing a generalized conclusion about the actions of sevoflurane on learning and memory. Specifically, I have explicitly stated in my article that “these data should be treated with caution as learning and memory involve a larger population of neurons, often requiring interplay between complex cognitive information processing mechanisms in the brain” (Discussion, first paragraph, page 924).

In the context of unresolved issues of whether anesthetics affect memory, the bottom line is that we still do not have the answer—notwithstanding Dr. Ghoneim's claim that anesthetics have been shown to block learning and memory. I believe that unequivocal evidence in this regard would still require a multidisciplinary approach and concerted efforts by both clinical investigators and basic scientists.

University of Calgary, Calgary, Alberta, Canada. nisyed@ucalgary.ca

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