It would not be unfair to question the relevance of our investigations on axons and glia of the medial giant nerve fibers of the crayfish, and in particular, the synthesis, degradation and recycling of NAAG and NAA to mammalian neuron/glia systems.

In our view the functional and pharmacological properties of the crayfish glial cell appear to be a composite of the properties of cells found in mammalian systems including receptors; ion, substrate and neurotransmitter transporters; intracellular transduction pathways; neurotransmitter and ion channel characteristics of Schwann cells, oligodendrocytes, astrocytes and microglia. Table 2 compares some of the properties of mammalian and crayfish glia that illustrate this concept. Because functional axon-glia interactions have been and are continuing to be defined in the crayfish nerve fiber, this model system represents an opportunity to investigate glial and axonal functional properties in an intact, interactive system in which contributions of each cell in the system can be differentiated.

Although it would not be appropriate to assume functional properties of the crayfish glial cell directly reflect the functional properties of a given mammalian glial cell, many

of the fundamental processes appear to be conserved. We believe investigations in definable model systems such as the crayfish medial giant nerve fiber may provide guidance in developing the protocols that elucidate functional properties of the mammalian axon/neuron-glial systems, not unlike studies in mammalian neuron-glia cell culture models that serve a similar purpose. The difference between the crayfish axon-glia preparation and mammalian cell culture is that the former is a "real world" working system in an anatomically and functionally appropriate relationship.

Table 2. A comparison of functional components of mammalian and crayfish axons, neurons and glia with regard to NAAG.



Neurons (perikarya)

Astrocytes/ Microglia

Axons glia


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